CA2165847C - Process gas distribution system and method with automatic transducer zero calibration - Google Patents

Abstract

A system including a plurality of gas flow control units in cabinets which are connected to distribute process gas, on demand, to a plurality of utilization locations known as "tool" locations in a semi-conductor manufacturing plant. Transducers are used in the system to measure pressures and other control parameters. Zero calibration of the transducers is provided by automatically subjecting each transducer to a reference computer routine to compute the difference between the standard value and the transducer output, and store the difference as an "offset" to correct the output of the transducer. Thus, re-calibration is performed simply and quickly, at a relatively low labor cost and with relatively little downtime for the system.

Description

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FIEI.D OF THB Ih V15~ . ~ON
This invention relates to process gas distribution systems and methods.
BAC~GROUND O~ THE INV~NTION
Systems and methods presently are used for the automatic or semi-automatic control of process ga~
distribut~on in semi-conductor manufacturing. One such system and method which is highly advantageous iQ shown in U.S.
Patent No.4,949,160 assigned to the assignee of thi~ patent application.
Despite its excellence, further improvements are needed to solve several remaining problems.
Some prior systems provide for remote control at a -~ single computer console of a large number of remote gas flow control units or "cabinets". Each control unit controls the delivery of process gas to one or more locations where the gas is used to make semiconductor devices. These locations are called "tool" locations. Most control units are located relatively far from the tool locations. It is desired to provide communication links between the tool locations and the flow control cabinets and to provide means for monitoring and controlling the units at a central location. The problem is how to do this without excessive cost.
Another problem with prior systems and methods has been caused by the need to re-calibrate transducers in the gas flow control cabinets at periodic intervals. For example, it has been customary to zero-calibrate pressure transducers once every three to six months or so. The process used in the past often has required up to a full day of labor by one worker for each cabinet. This creates relatively high labor costs and shuts the control unit down for a substantial time during which it cannot be used for production.
A further problem has been created by the expansion of the capabilities of each of the gas flow control cabinets so that it can deliver gas to any one or more of several different tool locations upon demand. This has created problems in purging the gas lines of toxic gas for worker safety during local maintenance of the flow control units. If the "flow-through" process is used, where a purge gas such as 21'5~8~

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nitrogen simply is pumped in one direction through the delivery conduit, it must flow through the long conduit from the cabinet to the tool. This is wasteful of expensive gas, and wastes time. Furthermore, sometimes it is not possible to use the flow-through process, in which case maintenance work on the long delivery conduit can be hazardous. The problems, then, are how to achieve safe local purging without incurring excessive c08ts, and how to purge the long delivery conduit when flow-through purging is not ~va$iablo.
A similar problem in purgin ~ ~iconduits~has been~
created by the addition of means for delivering gas selectively from two different supply tanks and switching back and forth between the two tanks.
Each of the gas flow control cabinets has an exhaust lS outlet which is connected to an exhaust duct and from which air and gas from the inside of the cabinet is exhausted at a relatively high flow rate in order to avoid the accumulation of toxic gas in the cabinet due to lea~s, etc. Flow measurement means are provided to measure the flow rate of the exhaust gas. If the flow rate falls below a pre-determined safe level, an alarm is activated so that the low flow condition can be remedied. Usually, each duct and fan is in place in the plant before the cabinet is installed. If the diameter of the duct is not the same as that of the exhaust outlet, the flow rate measurement will be erroneous. A
tedious and expensive firmware program adjustment then is required in order to avoid this source of error. The labor cost and time to do this constitute another problem to be solved.
A further problem in prior gas distribution systems is that sometimes it is necessary to change the association between a tool location and the gas distribution conduits.
For example, it may become necessary to supply a given tool with a different gas or mix of gases, and it may be necessary or expedient to change the connection of different gas distribution conduits to the tool. In the past, this has required re-wiring of the electrical connections so that the tool is correctly connected to the proper control unit or units corresponding to the new gas conduit connections. The ~d ~

inventors have recognized that the re-wiring requirement is costly and time-consuming; it increases equipment down-time and reduces productivity.
OBJECT OF THE INVENTION
In accordance with the foregoing, it is an object of the present invention to provide improvements relating to process gas distribution systems which allow various transducers which convert process gas distribution parameters into electrical signals to be re-calibrated very quicklyand at a relatively low cost.
SUMMARY OF THE INVENTION
In one aspect of the invention there is provided, in or for a process gas distribution control unit handling hazardous gasses having gas conduit means for conducting said process gas from a source towards a utilization location, control means for controlling the flow of said gas through said conduit means, and at least one gas pressure measurement transducer for measuring the pressure of said gas in said conduit means, a system for calibrating said pressure transducer comprising reference means for subjecting said transducer to a known value of pressure, means for measuring an electrical output signal of said transducer, means for comparing said electrical output signal with a known standard signal and developing a difference signal corresponding to the difference between said standard signal and said output signal, memory means for storing data corresponding to said difference signal, and correction means utilizing the stored data to correct the output signal of said transducer.
A further aspect of the invention provides a method of calibrating gas pressure transducers in a process gas distribution system handling hazardous gasses having gas conduit means for conducting process gas, said method comprising the steps of:
a) subjecting each of said transducers to a reference value comprising a known gas pressure;
b) measuring the electrical output signal of said transducer;

t a 7, c) utilizing a pre-programmed digital computer having a memory to compare said measured output signal with a pre-determined electrical signal corresponding to said known pressure and determining the difference between said signals;
d) storing in the memory of said computer data corresponding to said reference; and e) utilizing said stored data to correct subsequent output signals of said transducer.
As still further aspect of the invention provides, in or for a process gas distribution control unit handling hazardous gasses having gas conduit means for conducting process gas from a pressurized container towards a utilization location, support means for supporting at least one pressurized container of process gas and weighing means for weighing said container to determine the amount of gas in said container while said container is connected to said gas conduit means, said weighing means including at least one weight measurement transducer, a system for calibrating said weight measurement transducer comprising means for measuring and electrical output signal of said transducer means for comparing, with a known standard signal, a reference value of said electrical output signal produced when said weighing means is subjected to a reference weight and developing a difference signal corresponding to the difference between the value of said standard signal and said reference value, memory means for storing data corresponding to said difference signal, said correction means utilizing the stored data to correct the output signal of said transducer.
A still further aspect of the invention provides a method of calibrating gas supply detectors in a process gas distribution system handing hazardous gasses having gas conduit means for conducting process gas from a pressurized container towards a utilization location, said detectors comprising weight transducer for weighing a pressurized container of A

process gas to determine the amount of gas in said container while said container is connected to said gas conduit means, said method comprising the steps of:
a) subjecting each of said transducers to a reference weight;
b) measuring the electrical output signal of each of said transducers;
c) utilizing a pre-programmed digital computer with memory to compare said measured output signal with a pre-determined electrical signal corresponding to a reference weight and determined the difference between said signals;
d) storing in said memory of said computer data corresponding to said difference; and e) utilizing said stored data to correct subsequent output signals of said transducer.
Another aspect of the invention provides, in or for a process gas distribution control unit handling hazardous gasses having a gas conduit to conduct said process gas from a source towards a utilization location, a control unit to control the flow of said gas through said conduit, 20 and at least one gas pressure measurement transducer to measure the pressure of said gas in said conduit, a system for calibrating said pressure transducer comprising a reference source to subject said transducer to a known value of pressure, a measuring unit to measure an electrical output signal of said transducer, a comparator to compare said electrical output 25 signal with a known standard signal and to develop a difference signal corresponding to the difference between said standard signal and said output signal, a memory to store data corresponding to said difference signal, and a corrector which uses the stored data to correct the output signal of said transducer.

- 5a - ~ ;t~ , y A final aspect of the invention provides, in or for a process gas distribution control unit handling hazardous gasses having a gas conduit to conduct process gas from a pressurized container towards a utilization location, a support for supporting at least one pressurized container of 5 process gas and a weighing device to weigh said container to determine the amount of gas in said container while said container is connected to said gas conduit, said weighing device including at least one weight measurement transducer, a system for calibrating said weight measurement transducer comprising a measuring unit to measure an electrical output signal of said 10 transducer, a comparator to compare, with a known standard signal, a reference value of said electrical output signal produced when said weighing device is subjected to a reference weight and to develop a difference signal corresponding to the difference between the value of said standard signal and said reference value, a memory to store data 15 corresponding to said difference signal, and a corrector utilizing the stored data to correct the output signal of said transducer.
Disclosed herein is a process gas distribution system and method in which the remote gas control units are connected sequentially to one another and by a single communication cable to a tool interface 20 controller, which also receives signals from various tool locations and communicates them to the respective cabinets.
A supervisory control computer, preferably a simple and relatively inexpensive personal computer, communicates with the tool interface controller to provide monitoring of the operations of the various 25 cabinets and to control the flow of gases to the tools. A separate data processor is provided in each of the cabinets to control its functions independently from the supervisory control computer. Preferably, direct control by use of the data processor in the cabinet will override control from the central supervisory control computer.

-5b -The cost of this system is further minimized by the use of the interface unit to enable communications between the tools and the cabinets, instead of separate cables connected from each tool to each of several cabinets, as in some prior systems. The cable and installation costs thus are 5 reduced significantly.
Zero calibration is provided, advantageously, by automatically subjecting each transducer to a reference standard having a known parameter value. A computer routine is used to compute the difference between the ideal output of the transducer and its actual output. That 10 difference, called an "offset", is stored in computer memory. Later, the offset is used to correct each reading of the transducer. Advantageously, components of the system which are used for other purposes also are used to provide a zero reference for each of the transducers. By this means, re-calibration is performed simply and quickly, at a relatively low labor cost 15 and with relatively little downtime.
The multiple distribution legs of each gas flow control unit, and the delivery conduits to the tools, may be purged by the alternating connection of an evacuation source and a source of purge gas to the distribution legs, with a number of such cycles being selectable, and the 20 duration of each of such cycles being selectable. This provides variable and adjustable cost-saving local purging for the multiple distribution legs, and also provides purging of the delivery conduits to the tools when flow-through purging is not possible, thus providing improved safety.
Purging of toxic gas from conduits from plural selectable gas 25 sources also is provided by purge control means similar to that described above for the distribution legs.
The exhaust duct diameter can be compensated for, if it is different from that of the exhaust outlet from the cabinet, by storing different constants for different outlet duct sizes, and utilizing a computer 30 routine and the stored constants to compute the flow rate. Thus, the - 5c -measurement corrections are made by means of a few simple keystrokes of the gas cabinet controls.
Programmable interface means may be provided for enabling the control of gas delivery through selected gas distribution conduits.
5 Preferably, communications lines from the tool locations are terminated in a centrally located interface unit. Each tool is identified by a number. The responsiveness of each gas delivery leg to gas demand signals from a given tool is stored in programmable memory, and the association between tool signals and gas delivery legs is stored in computer memory means. A
10 change of the associations can be made by relatively simple software procedures for changing the data stored in memory, thus avoiding expensive re-wiring.

2~6~7 Other objects and advantages of the invention will be set forth in or apparent from the following description and drawings.
BRTEF D~8CRIP~ION OF ~F ~RAwING~
Fig. 1 is a schematic diagram of a process gas distribution system constructed in accordance with the present invention;
Fig. 2 is a schematic circuit diagram of connection between the tool interface controller and one o~
the tool locations shown in Fig. 1;
Fig. 3 is a schematic circuit diagram of an alternative embodiment of the 8ystem shown in Fig. l;
Fig. 4 is a schematic circuit diagram of a portion of the system shown in Fig. 1, showing in some detail the electrical components of the tool interface controller and one of the gas flow control cabinets of Fig. l;
Fig. 5 is a side-elevation view partially broken away of one of the gas cabinets shown in Fig. 1, with the side panel removed to show the internal components;
Fig. 6 is a front-elevation view of the cabinets shown in Fig. 5, with the front doors open and part of the components broken away for the sake of clarity. Fig. 6 is also partially schematic in showing the exhaust system in the upper portion of the figure;
Fig. 7 is a front-elevation view of the control and display portion of the gas cabinet shown in Figs. 5 and 6;
Fig. 8 is a schematic gas flow control diagram showing the distribution of gas by means of the gas cabinet of Figs. S and 6;
Figs. 9 and 10 are generalized flow diagrams for the computer programs used for automatic zero calibration of transducers used in the gas flow control units;
Fig. 11 is a flow diagram for a computer program used for zero calibration of a weighing scale used to measure the contents of one of the gas bottles in the cabinet of Figs.
5 and 6;
Fig. 12 is a flow diagram of a computer program used to zero-calibrate the gas pressure transducers in the distribution gas flow legs of the cabinet shown in Figs. 5 and 6;
Fig. 13 is a flow diagram of a computer program used for zero calibration of the transducers in the gas flow lines leading from the gas bottles in the gas cabinet of Figs. 5 and 6;
Fig. 14 is a schematic diagram of a data packet used in communications between the cabinets and the tool interface controller of Fig. 1;Fig. 15 is an enlarged view of the control panel and display shown in Fig. 7; and Figs 16-25 illusatrate displays which appear on the display screen of the supervisory control computer of the system shown in Fig. 1.
GENERAL DESCRIPrION
Fig. 1 shows a process gas distribution system 20 as it is used in a semi-conductor manufacturing plant. The semi-conductors are manufactured using equipment such as diffusion ovens, etc. at various different locations in the plant, each of which is referred to as a "tool" location.
Located in one or more locations remote from the tool locations are a plurality of gas flow control units 22, 24, 26, 28, etc. which are used to store process gases, which often are highly toxic, and to control the distribution of those gases to the various tool locations. Each of the cabinets is "smart"; that is, it contains its own CPU, memory and other digital and analog interface circuitry, together with its own control panel, to enable it to operate alone without a remote computer.
Each cabinet can be operated separately and independently of every other cabinet, and independently of other equipment in the system. The circuitry of each cabinet is described in some detail below, and in the aforementioned U.S. Patent No.
4,989,160.

The control circuitry of each cabinet 22, 24, etc. is connected to the next cabinet by means of a plug-connectable shielded communications cable 30.
Each cable 30 is connected to its neighbor and to the circuitry of one cabinet through a plug receptacle 31, 33, 35, 37, etc. All of the cabinets are connected in the same manner so that the -8- 2 ~ ~ S ~ ~ I
,.. ,.
cabinets are connected together sequentially in "daisy-chain"
fashion. They are connected through a plug receptacle and a communications cable link 40 to a tool interface controller 42.
Tool interface controller 42 is connected by a communications cable 53 to a supervisory control computer 44 which includes a keyboard 46, a disk drive 48, and a vidQo display screen 50, and has a printer 51 connected to it.
Advantageously, the supervisory control computer i~ a relatively inexpensive personal computQr such a~ th~ IBM PS/2, model 80.
Advantageously, the tool interface controller is connected by the shielded cable 40 to the first cabinet 22 ("cabinet 1"), which is then connected in sequence to cabinets 2, 3 and 4 and as many other cabinets as there are in the system, up to 120 units, aQ the system presently is configured. Of course, larger or smaller numbers of cabinets can be incorporated in the system. For this reason, the number of the last cabinet in the sequence is cabinet "nn.
Additional cabinets can be added into the system simply by plugging in a new cabinet to its nearest neighbor, and re-configuring the system in software. Re-wiring is not needed.
The tool interface controller is adapted to sequentially poll each of the cabinets to send and receive messages to and from each of the cabinets so as to enable monitoring of the cabinet operation at the supervisory control computer 44 and control of the functions of the cabinets from that computer. By the use of this polling technique, the necessity of using separate cables from each of the cabinets to the interface controller 42 is avoided, and a significant cost saving is achieved. Furthermore, since only a relatively low baud rate is used in the communications signal transmissions, the cable can be relatively inexpensiv~
shielded cable rather than the more expensive cable which otherwise might be required.
In accordance with one of the advantageous features of the invention, signals are conducted between the controller 42 and the tools on line~ 52, 54, 56, 58 etc. The number of 9 ~5~7 .~
tools which can be connected i~ relatively large -- e.g., up to 120 tools in a system which has been built and successfully tested. Larger numbers are possible.
Turning now to Fig. 2, one of the lines 52 actually is shown to have six separate conductors connected at tho controller end to a terminal blocX 55, and at th~ tool end to a terminal block 57.
When an operator at a tool location desires to start the flow of process gas to the tool, the operator closQs a switch 60 and momentarily closes a gas reset switch 68 to initiate the flow of gas from an appropriate one of the gas cabinets. 24 volts DC is sent from terminal 61 at the tool location to terminal 59 at the controller location over line 76 to enable switches 77 and 78 to operate. Switch 77 closes and lights an indicator lamp 72 at the tool when gas is flowing.
Switch 78 closes to energize an indicator lamp 74 at the tool location to indicate when a purge is in process.
The "ready for gas" and "gas reset" signals sent over terminals 62, 63, 64, 65, and 70 and 71, are delivered by the tool interface controller 42 to the appropriate gas cabinet to cause the opening of various valves to start the gas flow. Nhen the gas flow is to be shut off, the switch 60 is opened, and the controller 42 sends a signal to the gas cabinet and causes it to shut off the gas flow.
ALTERNATIVE TOOL CONMUNlCATION
Fig. 3 shows an alternative arrangement for communication with each of the tool locations. Instead of a separate six-conductor cable connected from each of the tool locations to the controller 42, a single communications cable 80, like the cable 40, is connected to the controller, and a separate tool termination unit 92, 94, 96, 98, etc. is located at each of the tool locations. Each unit 92, 94, etc.
contains its own memory and CPU, such as that provided by a microprocessor, together with programming sufficient to enable it to communicate with the controller 42 in response to polling.
Each of the tool termination units is connected to its neighbor by means of a plug-in connector 39, 41, 43 and -lo- 216~7 ,,,_ 45, etc., through cables 84, 86, 88, 90, etc. and cable section 82 in "daisy-chain" fashion, in the same way that the cabinets 22, 24 etc. are connected together, and all are connected to the interface controller. By this means, a great deal of wiring, labor and materials cost is saved.
Each of the embodiments shown in Figures 1-3 gives considerable savings of installation and wiring cost~, a~ well as further savings of re-wiring costs when the tools are later connected to receive gas from different cabinets. For example, in one typical prior system, if four different gases are delivered to a single tool, each from a separate cabinet, four different cables are used to connect the tool electrically directly to the four cabinets. With the embodiment of Figures 1-2, only one cable from each tool to the TIC is used, and in the Figure 3 embodiment, only one cable is used for all tools.
Further saving are gained by both embodiments in avoiding the cost of re-wiring the tools to the cabinets when the association of a tool with the cabinets is changed.
2 0 CABINET CIRCIJITRY AND CONq~ROL~R D~TAI~8 Fig. 4 is a schematic circuit diagram of the control circuit 300 for a single gas flow control unit or cabinet, and shows some of the details of the controller 42. The controller 42 communicates with the gas cabinets and the 2S supervisory computer 44 through a standard communications board 320.
The controller 42 is the sole connection between the tool locations and the gas flow control cabinets. Therefore, it is important that it be as fail-safe as possible. To this end, a certain amount of redundancy is provided. Instead of one, there are two CPUs; a first CPU 322 and a second CPU 324, each of which has a random-access memory ("RAMn) 323 or 325.
An arbitrator circuit 326 is provided to determine when one of the CPUs is not operating and automatically switch in the other CPU. Alarms 328 are provided to indicate if either or both of the CPUs is inoperative; to indicate if the arbitrator circuit 326 is inoperative; to indicate whether power is not being supplied to the controller; to determine whether the communication link 40 is not operating, etc., all -11- 21~;5~ ~7 ,j"
in order to maximize chances that the terminal controller i8 - operating at substantially all times, or that an alarm will call attention to any problems so they can be corrected quickly. The construction and operation of the arbitrator circuit and its control of the CPUs is conventional and will not be described further herein.
The controller 42 also has several interface terminal units (nITU~) 327, 329, 331, etc, to which the tool cables 52, 54, 56, 58, etc. are connected. The number o~
ITU's used depends on the number of tools in the system. Each tool and its cable is identified by the simple expedient of connecting it to a single terminal in one of the ITUs, and giving each terminal (and thus, each tool) an identifying number. Each ITU comprises a circuit board with six connection terminals, each terminal connected to a specific tool.
The ITU arrangement is modular. The number of ITU
units can be changed easily to accommodate a greater or lesser number of tools in a system.
As it will be described below in greater detail, when the start or stop of gas flow i8 requested by signals from the tool location, the interface controller broadcasts the signals to the gas flow control cabinets, and each cabinet which controls gas conduits connected to the tool recognizes the tool number and starts or stops the flow of gas to the tool.
In the embodiment of the invention shown in Figure 3, each tool is identified by a uniquely coded signal which is transmitted to the tool interface controller 42 periodically, by polling, along with gas flow start and stop signals, and is broadcast to the cabinets.
The cabinet control circuit 300 shown in the upper left-hand portion of figure 4 includes an analog input circuit 302, which receives analog inputs on lines 304 from various transducers and other sources and amplifies those signals and converts them from analog to digital signals. It delivers the digital signals over a bus 318 to a CPU 306 which has a memory 308. The memory 308 contains both volatile RAM storage chips, ~ ~l6sa~

..._ as well as electrically erasable programmable read-only memory ("EEPROM").
The identity of the signal supplied on each analog input line 304 is marked to the left of the line. Those mar~ings are shown in Figs. 6 and 8 to indicate their source.
Also provided in the circuit 300 i~ a digital input/output unit 314 which receivea digital signal~ and transmit~ them over a bus 316 to the CPU 306. The operator panel 138 which i~ shown in figures 7 and 15, and thQ display panels 310 ~lso receive signals over the bus 316 to display the various warning lights and indicators to be described below.
A set of DIP switches 307 is provided to set a code number to uniquely identify the cabinet to the rest of the system.
Further description of this circuitry and its operation will be given below.
CABIN15T CONSTRtJCTION
Figs. 5 and 6, show the construction of one of the cabinets 22. The cabinet 22 includes a rear wall 106, a bottom wall 112, and front doors 108 and 110. Fig. 5 is a left-side elevation view, with the front doors 108 and 110 open and the side-panel of the cabinet removed to show the inside components, with some of the components broken away.
The cabinet 22 includes a control housing 92 with a display panel 94 having a handle 96 for opening it. As it is shown in figure 5, the panel 94 is angled downwardly so as to be readily viewable by an operator standing in front of the unit.
The cabinet 22 has an upwardly-sloping upper wall 98 (Fig. 6) which ends in a centrally-located exhaust outlet conduit 100. Connected to the exhaust outlet is an exhaust duct 102 whose diameter "d" is less than the diameter of the exhaust conduit 100.
An exhaust fan 104, shown in Figure 6 normally is located on the roof of the building in which the gas distribution system is located. It connects with the conduit 102, as indicated at 136, to exhaust air and other gases from the interior of the cabinet 122 to the atmosphere, where they -13- 215~7 can do no harm. Thus, the exhaust fan minimizes danger to operating personnel by removing process gases which might accumulate in the cabinet.
The cabinet 22 also includes a shelf 120 (Fig. 6) s supporting a scale 118 and a cylinder 116 o~ process gas. A
second cylinder 114 of process gas rests on a second scale 107 resting on the floor 112 of the cabinet. The scales 107 and 118 conta~n transducers which convert the weight of the gas bottles into analog signal~ which are among the analog inputs to the control cabinet circuitry shown in Fig. 4, labeled "SCALE A" and "SCALE Bn. The weight of the gas cylinders indicates the amount of gas left in them.
Gas is distributed from either bottle 114 or 116, as needed, so as to ensure an uninterrupted supply of process gas.
Various gas flow lines in the cabinet 22 include sections 126 and 128 which form a "cylinder manifold" 136 (Fig. 8) which conducts gas from the bottle 114 or 116 to a "cross-over" manifold 124 (Figs. 6 and 8) which changes the bottle from which gas i8 supplied.
A gas distribution conduit system, called a "distribution manifold" is shown at 134 (also see Fig. 8). It includes four vertically aligned distribution "legs", which will be described in greater detail below, to distribute gas to 1, 2, 3 or 4 different tool locations simultaneously.
Also shown in Fig. 6 is an inlet 130 through which nitrogen from a "house" supply of nitrogen is supplied to the cabinet. An inlet 132 is provided for bottled nitrogen from a local supply.
At the top of Figure 6, inside the duct 102, a pitot tube transducer 105 is mounted. The transducer 105 is used to measure the velocity of exhaust gas flow through the conduit for purposes of determining whether the exhaust flow is above predetermined safe level. The output of transducer 105 is labeled NEXHAUST" in Figs. 4 and 6, and is one of the analog inputs to the data processing system of the cabinet.
GA8 DI8TRIBUTION 8Y8TI~M IN CABINET8 Fig. 7 is an enlarged view of the front panel 94 of the cabinet 22. Displayed on the panel is an operator panel -14- ~i6~47 .", 138, and schematic diagrams of the distribution manifold 134 and the cylinder manifold 136.
Fig. 8 is a schematic diagram showing the piping and other flow control elements in a single one of the gas flow control cabinets. Figure 8 is an enlarged reproduction of the two diagram~ 134 and 136 which appear on the panel 94 of Figure 7, except that the two diagrams have been ~oined together and modified, ~or the sake of clarity.
The distribution system shown in Figure 8 consists of the three section~ shown in Figures S and 6; the distribution manifold 134, the cylinder manifold 136 and the cross-over manifold 124.
In the diagram heavy lines indicate process gas distribution lines, whereas lighter lines indicate purge gas lines which are used only during purge and maintenance operations.
The cylinder manifold 136 consists of two halves, an "A" section 126 and a "B" section 128. The "A" section on the left side includes equipment for deliverinq process gas from a first source or cylinder A (cylinder 114 in Figs. S and 6), and a right half, which is a mirror image of the left half, for delivering process gas from a second source "B" (cylinder 116 in Fig. 6).
The distribution manifold 134 includes four distribution "legs" 158 and 160, 162 and 164 ("An, "B", "C~
and "D") each of which delivers process gas to a remote tool location 140, 142, 144 or 146, respectively.
The cross-over manifold 124 consists of a pair of valves IIXAn and "XB", which are connected to a common conduit 55 which distributes gas from either source A or source B to any one or any combination of the four distribution legs.
In general, all of the valves shown in Figure 8 are pneumatically operated with the exception of hand-operated valves 157, 159, 161 and 163 shown at the top of Fig. 8.
Circles made with heavy lines are located in Fig. 8 next to various valves and are designated by the letter "G". Green LED's are located behind the transparent or translucent panel material in the circles. When the valve is open, the LED is -15- ~5~7 .....
on. Thus, each of these circles glows green to indicate when the valve next to it is open.
Other heavy circles marked with the letter "Y" glow yellow when a predetermined condition exists. Those in the distribution manifold marked "RFG A", NRFG B" etc. indicate when either leg A, B, C or D (158, 160, 162 or 164) is Ready For Gas; that i5, ready for the delivery of process gas.
In the cylinder manifold 136, yellow indicator circles labeled "Chang~ A~ and "Change B~ indicate when either gas cylinder A or gas cylinder B is empty and should be changed.
The smaller circles formed with lighter lines in Figure 8 are gas pressure transducers.
The delivery of gas from source A to Tool 1, for example, is accomplished by the opening of valves Al, A2 and A7 in the cylinder manifold 136, valve XA in the cross-over manifold 124; and the opening of valves Al, A7 and 157 in the distribution leg 158 in the distribution manifold 134. It should be understood of course, that the delivery line between the end of a distribution leg and the tool to which it is connected can be relatively long; that is, the cabinet 22 often is up to several hundred feet from the tool location.
If process gas is to be delivered to Tool 2, the foregoing procedure is altered by opening valves Bl, B7 and 159 in the distribution manifold. Similarly, process gas will be delivered to Tool 3 by opening valves Cl, C7 and 161, and to Tool 4 by opening valves Dl, D7 and 163 are opened.
If it is desired to deliver process gas to more than one tool at a time, this is accomplished simply by opening the valves in the appropriate delivery legs. Up to four separate tools can be supplied simultaneously by this means.
If it is desired to deliver gas from source B, such as when the quantity remaining in source A is too low, the valve XA in the cross-over manifold 124 is closed and the valve XB in that manifold is opened, and gas is delivered from source B to the line 155 and to all or any combination of the four tools, in the same manner as described above. Then, the A cylinder can be replaced, without interrupting gas flow to the tool.

-16- 21~5847 '"', In each of the process ga~ flow line~ in the cylinder manifold 136, there is a pressure regulator 154.
Similarly, there is a pressure regulator 154 and a filter 156 - in each of the four delivery legs of the distribution manifold 134.
In the lower portion of the cylinder manifold 136 is a purge isolation section 153 containing valves A3 and A4 with a pressure transducer device 119 located between those valves.
Similarly, there is a purge $solation sect~on consisting of two series-connected valvQs B3 and B4 with a pressure transducer 117 in the right half of the cylinder manifold.
Those transducers supply "PURGE A" and "PURGE 8" analog input signals, as indicated in Figs. 4 and 8.
Purge throttling valves 4LA and 4LB are provided to limit the flow of purge gas at certain times, as it will be explained below.
Similarly, each distribution leg in the distribution manifold 134 contains an isolation section consisting of valves 3 and 4 in series (A3 and A4; B3 and B4; etc.), and a transducer 125, 127, 129 or 131 to deliver a "PURGE LEG X"
signal to the controller ("X" being A or B or C or D) to indicate a leak.
There is a flow switch 166 or 168 in each of the cylinder manifold process gas flow lines, and a flow switch 141, 143, 145 or 147 in each of the four distribution legs.
These switches sense gas flow through them at an excessively high rate and send signals to the controller circuitry on the digital I/O unit 314 (Fig. 4) which cause the controller to shut all valves in the conduit in question to stop flow through it, and creates a high-priority alarm.
Other transducers and valve operations will be explained below.
CABINET MENIJ ANI~ PROMPT DI8PLAY8 Referring now to ~igures 7 and 15, the operator control panel 138 contains a number of pushbutton controls 354, an LCD display 352, and a row of alarm lamps 350. The LCD display 352 will display two lines of character, with up to 20 characterS per line.

~__The cabinet 22 is designed to enable the operator to quickly select and initiate functions with only a few push-buttons, and a full keyboard is not needed. It is also designed to be interactive; that is, to lead the operator through the selection process by displaying appropriate "prompts" or instructions. This is accomplished by means of a layered menu.
By pressing the "menu" button (Figure 15), the functions listed in the menu shown in Fig. 16 are displayed, one at a time on the LCD display 352.

These are the highest menu layers. Within each major category shown, there are several sub-menus and/or sub-functions. To select a function, one merely need press the scroll-up button 357 or the scroll-down button 355 (Fig. 15).
15The layered menu also allows protection of certain modes or functions from activation by other than qualified personnel. Each major function category, such as "Automatic"
or "Configuration" functions, is protected by a password.
Only those individuals given the password select functions 20within those modes. "Manual" mode requires two qualified persons, each with his or her own password, to enable operation.
Following are the automatic functions which can be selected if the "Automatic Functions" submenu is selected.
25Purge to Change Cyl Purge to Change Cyl A
Purge to Change Cyl B
Maintenance Purge 30Cylinder Manifold A Maintenance Purge Cylinder Manifold B Maintenance Purge Manifold Leg Purge Function ~I G5 Purge Leg A ~Off) Purge Leg B (Off) Purge Leg C (Off) Purge Leg D (Off) Secure Manifold Leg Secure Leg A
Secure Leg B
Secure Leg C
Secure Leg D
Startup Manifold Leg Start up Leg A
Start up Leg B
Start up Leg C
Start up Leg D
Pump/Purge Distribution Leg Pump/Purge Leg A
Pump/Purge Leg B
Pump/Purge Leg C
Pump/Purge Leg D

~ /G 5 ,~
Distribution Maintenance Pump/Purge Dist r'~ enal1ce P/P A
Dist Maintenance P/P B
Dist M ~ .lenance P/P C
Dist M ~ ~lenance P/P D
Evacuate Delivery Leg Evacuate Leg A ~Off) Evacuate Leg B (Off) Evacuate Leg C (Off) Evacuate Leg D (Off) Clear Purge Isolation Leak Alarm Clear Cylinder A lsolalion Leak Alarm Clear Cylinder B IsGlalion Leak Alarm Clear Leg A Isolation Leak Alarm Clear Leg B Isolalion Leak Alarm Clear Leg C Istl tion Leak Alarm Clear Leg D Isolcllion Leak Alarm When the "Manual Functions" submenu is selected, it is possible to manually operate each 25 of the cylinder valves, distribution manifold valves, and cross-over manifold valves.
When the "Setpoint Functions" submenu is selected, following are the functions which can be selected:
Manifold Alarm Sets Set Cylinder Empty Setpoint Set High Cylinder Pressure Set High Regll'~ted Pressure Set Low Regulated Pressure Set Purge Isolslion Fail Pressure Manifold Purge Definition Set # of Pre Purge Cycles Set # of Post Purge Cycles Set Minimum Purge Pressure Set Maximum Vent Pressure Set Purge Time Set Vent Time Enable Refill Disable Refill Distribution Alarm Setpoints Set High Delivery Pressure Set Low Delivery Pressure Distribution Purge Function Definition Set # of Purges ~/ ~5~Y~

Set Minimum Purge Pressure Set Maximum Vent Pressure Set Purge Time Set Vent Time General Setpoints Set Minimum Exhaust Flow Rate The setpoints can be set by means of software routines described more fully in the above-identified pending patent application.
When the "Configuration Ftns" mode is selected, the following functions can be performed:
Configure Cabinet Cylinder Pressure Range Cylinder Manifold Reg~'sted Pressure Range Cylinder Manifold Purge Pressure Range Cylinder Manifold Vent Pressure Range Distribution Manifold Reg~'stetl Pressure Range Distribution Manifold Vent Pressure Range Cylinder Weight Range Set Delivery Association Select Line Leg A Assn.
Select Line Leg B Assn.
Select Line Leg C Assn.
Select Line Leg D Assn.
Select Exhaust Duct 10 inch Duct 8 inch Duct 6 inch Duct Do Zero Calibration C_~ b ale Cylinder Manifold A
Calibrate Cylinder Manifold B
C_' b ale Distribution Manifold Leg A
C.' ~ale Distribution Manifold Leg B
Calibrate Distribution Manifold Leg C
C.'-br~lle Distribution Manifold Leg D
Calibrate Scale A
Calibrate Scale B
The steps taken by the operator to select the various functions are set forth in the following table:
OPERATION ACTION SYSTEM RESPONSE
Press MENU Displays the first item in the "Main Menu", which is "Automatic Function?"

2165~47 "Push ENTER to select"
~SQe F1g. 15) Pres~ the UP or DOWN buttons The display will scroll 35s or 357 until the through available - desired function displayed. menu items.
The item displayed will b~
selected. Thi8 may bo a function, which would bQgin it- operation, or th- next menu layer.
We'll assume we've selected the next menu layer.
The display will read nB~TER PASSWOR~"
Enter the appropriate The display will show an password. '~' for each character entered. If the password i~ correct, th~ display will show the first item in the selected menu. If incorrect, it will display "INVALID PASSWORD"
Continue stepping through When the function i5 the menu and selecting the selected, by pressing desired function. "ENTER", it will start.
Many o~ the functions have associated interlock conditions. If any of these interlock conditions are present, the menu prompt for the function will not appear on the display. Therefore, the existence ot an interlock condition inhibits activation of the function.
To better understand the function of the interlocks, consider the case of ~Purge To Change Cylinder A~. If no interlock condition exists, the operator can step through the menu selection process and come to a point where the display reads "Purge To Change Cylinder A?" At this point the cylinder A purge cycle can be initiated. However, if a purge isolation leak alarm was active on cylinder manifold A, the display would not read "Purge To Change Cyl A?~. It would skip to the next valid function.
Details of some of the automatic functions now will be discussed.

8~

.",_.
AUTOMATIC PUR~E TO CHANG~ CY~Nn~R ~A OR B) When it is neces~ry to change either the A or the B gas cylinder to replace it with a fresh one, the toxic process gas should first be removed or purged from the gas flow lines in order to protect the workers making the change from being harmed by the toxic gas. Th- process gas is required to be puro, and special precautions are eceF~-ry to insure this purity. Therefor-, the cylinder change must bc accomplished without significantly exposinq the ~low line~ to air or other extraneous gas, in order to prevent contamination.
Either the A section or the B section 128 of the cylinder manifold is purged by alternatingly exhausting the gas from each conduit, and then filling the conduit with a very pure inert purge gas such as nitrogen. This dilutes and replaces almost all of the process gas with harmless nitrogen.
This process is used instead of a flow-through purge, which might require purging the entire flow line from the cylinder through to the tool. Such a process would be extremely wasteful of both process gas and purge gas.
Following are the steps used in purging the cylinder manifold to change a gas cylinder.
First, the number of purge cycles to be used, and the time of each cycle, are pre-selected by qualified personnel in the Setpoint Function mode of operation.
Assuming that it is desired to change cylinder A, valve A8 in the cylinder manifold 136 is opened to supply pressurized nitrogen from the house ~upply inlet 30 to a venturi pump 148 which creates a vacuum in all parts of the conduit which are not isolated from the pump 148 by a closed valve. The venturi pump vents its exhaust to the exhaust system.
Valve A5 (and valve A2 for the first cycle) are opened for a predetermined time, with the valve on the cylinder and valve A7 closed, to evacuate the gas conduit extending from the cylinder to the valve A2.
Th~ control system automatically measures the pressure at point 101 by means of the transducer 109 at the end of this period and checks to ma~e sure that the vacuum is -23- ~658~7 .",.. .
operating properly. Thi~ i8 done by check~ng to see if the pressure signal "CYLA" i~ below a predetermined Maximum Vent Pressure setpoint level (see above) set by the operator in the Setpoint Function mode. Up to three second~ extra, in addition to the pre-set vent time are allowed. If this condition i~ met, the sequencQ continue- to next stQp. If - not, the seguence is ~borted and an alarm mQss~ge i~ displayed on the panel 138.
Next, valves A2 and AS are closed, and ~a1VQ8 A3 and A4 are opened to supply purge nitrogen from a nitrogen cylinder supply for a predetermined purge time. This dilute~
any process gas remaining in the manifold with nitrogen.
During this phase, the pressurQ in the manifold must rise above the Minimum Purge Pressure (see above), which is preset by the operator in the Setpoint ~unctions mods. Up to three extra secQn~ in addition to the user-set purge time are allowed. If this condition is met, the purge function continues and the process i~ repeated for a number of cycles, called "Pre-purge cycles~, dstermined by the operator in the Setpoint Functions mode.
When the prescribed number of Pre-purge Cycles has been completed, the operator should change the process gas cylinder A.
When the bottle change is complete, the operator should push the ENTER button on the panel 138. This will cause the cylinder manifold to perform a series of post-cylinder-change purge cycles. These cycles are identical to those described above for the pre-change purge. The number of Post Purge Cycles can be set independently of the number of pre-change purge cycles, as it is indicated above.
The manifold next will be filled with process gas by opening valves Al and A2, and then performing three short cycles of opening and closing valve A6 to allow process gas to flow into the conduit.
Now valve A8 now will close, turning off the venturi pump.
Finally, a routine is performed to check for a cylinder connection leak. The controller performs this check by reading the cylinder pressure by means of the transducer -24- 21~5~47 123 which produce~ the output signal PT2A, then counting down for two minutes. If, at any point during thi8 two-minute period, the cylinder pres~ure reading drops by over ~ive percent of the initial value, the controller considers this to be a cylinder connection leak. If a leak is detected, an alarm message will be displayQd. Otherwi~e, at the end of th~
two minute period, the function i~ complete.
If it i~ desired to change the B cylind-r, the sam~
procedures Are used a~ tho~- de~cribed for the A cylinder, except the separatQ valve ~y~te~ 128, a~ well ~ venturi pump 150 and venturi valve B8, ~re used instead of the venturi pump and valves on the left side 126 of Figure 8.
CY~TNDE:P~ ~NIFt~Tn ~ T~NAN~R PUR~t (A OR B~
The maintenance of th~ regulator 154 or other functions requiring access to portion~ of the process gas flow line downstream from the regulator 154, use a different purg~
operation, as follows.
Again, as with the purge to change a gas cylinder, the number of pre-maintenance purge cycles and the time of each cycle can be defined by an operator.
First, assuming that maintenance is being performed on the A sidQ 126, valve A8 is opened to create a vacuum.
Valve A5 and A2 are opened for a predetermined time. Next, valves A2 and A5 are closed and purge nitrogen is applied through valves A3 and A4 for a predetermined time to dilute any process gas remaining in the manifold. This cycle is repeated a predetermined number of times to complete the pre-maintenance purge. At this time, the operator can perform any required maintenance. During thi~ period, the purge nitrogen valves A3 and 4LA and valve A2 are left open so that while the maintenance is performed nitrogen flows through the conduit and little or no air enters the conduit to contaminate it.
Valve 4LA throttles the flow o~ nitrogen to a relatively low level, to minimize wasting of nitrogen during this phase of operation.
When the maintenance is complete, the operator pushes the ENTER button on the control panel 138. The control system will perform a series of po~t-maintenance purge cycle~
identical to those just described.

-25- 2i~5~

Next, the cylinder manifold will be filled with process gas. The cylinder valve will open, and, optionally three short cycles of opening and closing the bypass vent valve A6 will occur. When the refill i~ complete, the s controller will close all valves, and the system again i~
ready to deliver process gas.
As with the cylinder change purge, the same ~c~
steps are performed in purging ~ide B of the ~y~tem, except the side B valve~ and venturi pump are used.
~RG~ D~$~rRnTSoN ~ La. ~. C OR Dl The Purge Distribution Line function automatically turns purge nitrogen on and pA s~es it through a distribution leg, and through the line to the tool. The function is performed according to the following sequence. Valve Al (or B1, or C1 or D1) in the distribution manlfold 134 is closed.
A delay of approximately two seconds then occurs.
Next, valves A3, A4 and A7 are opened to allow nitrogen to ~low through the distribution leg to the tool, where it i5 vented. Nitrogen will continue to flow through the leg and line until the complementary function "Leg X Purge off~ is initiated by the operator. "X" is A or B or C or D.
This procedure, often referred to as a "flow-thrbugh" purge, is capable of producing the most thorough purge, but uses substantial quantities of nitrogen and vents the process gas in the whole line leading to the tool, thus wasting the gas.
TINE PUR~E QFF ~A. B, C OR D) In the ~ine Purge Off function, a vacuum is placed on the purge isolation section by closing valves A3 and A4, and nitrogen i~ turned off so it no longer flows. Valve A7 also is closed.
Of course, the same procedure can be used in each of the separate distribution legs.
~EC~R~ HANIFOLD ~ A. B, C OR D) The Secure Manifold leg function disables automatic delivery of gas from the selected distribution manifold leg.
It does 80 by clearing the "Leg Enable" flag found in the cabinet's EEPROM memory. This means that gas will not be delivered until intentionally started by a qualified operator.

2~S5847 Being stored in EEPROM memory, this status i~ not susceptible to being lo~t during power failure.
The Secure Manifold ~eg function performs the following sequence.
L4g valves 1,3,4,6, and 7 are clo~ed The Leg x enable flag i~ cleared in EEPRON. A two ~econd delay occur~. The display will read ~Securing Leg x~
during thi~ period.
8~ n M~Fnr.n ~
The Start Up Manifold Leg function enable~ automatic delivery from the selected manifold leg. It does 80 by setting the "Leg Enable~ flag found in the cabinet's EEP~OM
memory. This means that automatic gas delivery will be enabled until intentionally secured by a qualified operator.
Being stored in EEPROM memory, it is not susceptible to being lost during power failure.
; The function displays the message "Starting up Leg x" while setting the appropriate flaq.
PUMP/PURG~ ~I8TRIBUTION LINR (A. B, C OR D) Referring again to Fig. 8, the purpose of this routine i8 to clear the toxic gas from one or more of the four distribution legs lS8, 160, 162 or 164 (A, B, C or D) of the ~ distribution manifold 134, and the line leading to the tool, when the flow-through process ("Purge Distribution Line") described above is not possible or is impractical.
The process to be described below has the advantage that it purges toxic gas from each distribution leg up to the first shut-off valve (not shown), which usually i~ located at the tool, without opening the line to allow purge gas to escape at the first shut-off valve. This provides purging where it otherwise ~ight not be feasible, thus improving safety. It also confines all purging operations and venting to the vicinity of the cabinet where the most qualified personnel are on duty.
The operation now will be described with reference to distribution leg 158 (leg A) of the distribution manifold 34. However, it should be understood that the same process -27- 2~65~ ~7 . ,_ would be used in clearing each other dlstribution leg 160(B), 162(C) or 164(D), in a separate operation.
At the start of the operation, Valve Al i~ closed to prevent toxic proces~ gas from entering the difitribution leg.
Valves A3, A4 and A6 usually already will be closed. If open, they will be clo~ed. ValvQ A7 may b~ either open or closed ~t the start of the ~rocGduL~, but usually will b~ closed. The hand-operated valv- 157 is open. Valv~- Al, A3, A4, and A6 are closed at thi~ timQ because it i~ desir~d to c108~ thQ8e valves beforQ V8 i- opene~, in order to ~void contamination o~
the gas flow line~ through the vent outlet of the venturi pump.
The venturi valve A8 now opens to admit house nitrogen, supplied through line 130, to th~ venturi pump 152, which evacuates gas from the line 165 and vents the gas safely to exhaust.
Next, the vacuum in the line 165 is applied to the distribution leg at point 153 by opening the valve A6. Valve A3 now is closed, and valve~ A6, A7 and A4 are opened.
The vacuum is thus applied to the delivery leg for a pre-determined vent time, which can be set by a qualified operator during the Setpoint Function mode.
At the end o~ thi~ time period, the control system checks to make surQ that the vacuum is operating properly by detecting the pressure at point 153 by means of the pressure transducer 139 connected to that point (similarly, pressure transducers 137, 135 and 133 are connected to points 151, 159 and 167, respectively, in the other distribution legs). The analog output of the transducer, PT3A, is sent to the control circuit (Fig. 4), where it is measured and compared with pre-set siqnal levels stored in memory. If the pressure is below a pre-set maximum vent pressure, which also can be set by a qualified operator, then the operation continues to th~ next step. If that pressur~ is not below the maximum vQnt pressure, the operation is aborted and an error message is displayed.
In the next step of the operation, valve A6 is closed and valve A3 ia opened. This allows purge nitrogen from ~ cylinder to flow through valves A3 and A4 to the 2:~5~

~unction between valve Al and the regulator 154, and into the evacuated distribution leg and line leading to the tool ~rom valve Al to the first shut off valve, thus filling and diluting any remaining process ga~ in that conduit. The time that nitrogen is thus allowed to flow into the delivery conduit is pre-determined by a qualiflQd operator.
The transducer i39 al~o measurQs the purge pres~ure during this phase Or the operation. The pressure measured at that point must rise above th- pre-determined distribution minimum purge pres~ure. I~ th~ condition i8 met, the cycl-~ust completed will be repeated a pre-determined number of times. The number being another parameter which can be set by a qualified operator. If the pressure does not rise above the minimum purge pressure, the operation is aborted and an error message i8 displayed.
Upon the completion of the pump/purge operation described above, the distribution leg and delivery conduit are cleansed of most of the process gas so that the system can be worked on safely by operatlng personnel.
P~MP/PURG~ DI8TRIB~TION L~ (A,B,C OR D) This operation is used to clear toxic gas from any distribution leg from valve Vl to the hand-operated valve 157, 159, 161 or 163. This is done for the purpose of clearing only that section, instead of the whole line leading to the first shut-off valve, in order to facilitate changing the filter 156 or performing other maintenance in the distribution leg. This operation is exactly the same a~ that described above for the Pump/Purge Distribution Line operation, except that the hand-operated valve 157, 159, 161 or 163 is shut at the start of the procedure, and remains closed 80 that gas is not evacuated from the line extending to the tool. Thus, wasting gas i5 avoided and time is saved in enabling the changing of the filter or performing other maintenance.
After the filter has been changed or other maintenance has been completed, the pump/purge operation i~
repeated in order to clear the distribution leg of any impurities which might have been introduced during the maintenance.

21$~847 FVACUATB QBLIVERY ~.TU~ (A,B,C OR D~
The Evacuate Delivery ~ine function applie~ vacuum to the selected delivery leg and the line leading to the tool by opening valve~ V8 and then V6, with Vl closed. If used in conjunction with the application of purge source on the other end (the tool end) of the delivery line, ~t will clear the line of toxic gas through the cabinet's vent by a Atraight flow-through proce~, but wlth the gas flowlng in a direction opposite to that used in the ~Purge Distribution Line~ procQss described above.
once inltlated, vacuum will continue to be applied until terminated by the operator via the Line Evacuate Off function.
!-TN~ m C~A~ OF~ ~A,B,C, OR D) -15 The Line Evacuate Off function places a vacuum on the purge isolation section (valves 3 and 4); and then turns off vacuum from the distribution leg. Valves 4, 6 and 7 are closed. If no other legs require vacuum, the venturi valve 8 also is closed.
The purge isolation section referred to above consists of valves A3 and A4 in combination. The purge isolation section is provided for the purpose of isolating the purge source from the delivery leg, and accurately indicating any leaks. A vacuum 18 maintained in the conduit between the valves 3 and 4 in order to better detect such a leak.
CL~AR CY~IND~R PURG~ I~OLA~ION ALARM ~A OR B) Referring agaln to the cylinder manifold section 136 of Fig. 8, if a leak should occur in the purge i~olation section, an alarm is set off. A mechanlsm is provided by the controller for automatically evacuating the purge isolation section 153 and clearing the alarm.
In clearing the alarm, valves 3, 5 and 8 are opened, while valves 2,4 and 7 of the cylinder manifold are closed to create a vacuum in the isolation section. After five seconds, the vacuum is removed and valves 3, 5 and 8 are closed. The vacuum existing between valves 3 and 4 has been restored, so as to enable detection of a future leak.

-30- ~1658 1~

DI8TRIB~TION PURGE I~o~ATION AT~M ~TEG8 A,B,C, 0~ D~
The procedure described above for clearing the purge isolation leak alarm for the cylinder manifold al80 i8 used to clear the leak alarm for th~ isolation section~ A3-A4, B3-84, S etc. of the distribution manifold 134. The isolation section pressures are measurQd by tran~ducer~ 125, 127, 129 and 131.
MAN~A~ F~NCTTON8 When the Manual Function modQ o~ operation i~
selected from the main m-nu (see abov~), and when two passwords are usQd by two qualifi~d maintenance person~, any valve can be operated manually. Opening or closing of a particular valve simply requires selection of the proper valve prompt from the screen and entering it with the ENTER button from the control panel 138 (Fig. 15).
In the Manual mode, various setpoint functions can be set by the qualified operators, as follows.
Alarm and warning indications Cylinder Empty High Cylinder PressurQ
High Regulated Pressure (Cylinder Manifold) Low Regulated Pressure (Cylinder Manifold) Purge Isolation ~ail High Delivery Pressure Low Delivery Pressure Minimum Exhaust Purge cycle definitions Manifold Purge definitions # of pre-purges t of post purge~
minimum purge pressure maximum vent pressure purge time vent time Refill On/Off Distribution Purge definitions t of purges minimum purge pressure maximum vent pressure purge time vent time Note that all pressure readings and setpoints are in terms of absolute pressure-psiA. Therefore, the reference pressure for the system is absolute zero pressure, not ~ 1 6~

.~
atmospheric pressure. That is, the reference pressure i8 approximately negative 14.7 psiG, at sea level.
once the desired set points have been reached they can be permanently stored in memory by pressing the ~ l ~K
s button. This stores the set points in the ~PK~II wherQ it will be stored even i~ the cabinQt 108Q8 power. Thus, battery-backed memory i8 not reguired.
Ot course, as it i- well known, EEPROM'- can be ele~ol.ically Qrased ~o that new data can b~ ~tored in them, and they will operate in this manner ~or a rel~tively large number of cycles (e.g. 100 to SO,OOO or more) depending upon the needs determined by the freguency expected for changes of setpoints etc.
8~rP0INr F~NC~TON8 lS Following i8 an explanation of the setpoints which can be selected in thQ ~Setpoint Functions" mode.
cyl~ r Em~ty 8-tpoint The cabinet determines that the process gas cylinder is empty based on either weight or pressure. I~ th~ cabinet is defined as one having a weighing scale, the setting is based on weight. Otherwise, the setting is based on cylinder pressure. In either case, "Cylinder Empty" i8 defined as occurring when the weight or pressure falls below this setting.
~igh Cylin~er Pressur- 8-tpol~t This setpoint i8 used to test a cylinder for over-pressure or another problem such as temperature rise, pressure applied from an inappropriate source, etc. I~ the cylinder pressure should read above this setpoint value, the "High Cylinder Pressure" Alarm will occur. The pressure~ are measured by the transducers 109 and 118 (Fig. 8), which transmit "CYL A" and "CYL B~ analog signal~ to the control circuit (Fig. 4).
~igh Regulate~ Pxo~sure 8~tpoint This setpoint is used to test the pressurQ
downstream from the cylinder regulators 154, and i8 measured by the transducers 121 and 123, which send signal~ "PT2A" and "PT2B" to the control circuit shown in Fig. 4. This will determine "Regulator Creep" in that area. The ~etpoint should 216~847 ,,~ ,~
be set somewhat abovQ the normal operating pre-regulated pressure.
~w R~gulat--d Pr--ssur--~--t~o~nt This setpoint i8 used to test to determine when thQ
regulated pressure measured by transducer 121 or 123 falls below an establiahed minimum prQssure. It is u~ed to en~ure that sufficient gas pressurQ i8 available to the distribution manifold 134 (Figur~ 8). A regulated prQssure rs~ng below this setpoint will result in a ~Low RegulatQd Pressure~ alar~.
~~~ ol~tlo~ t~o~
This setpoint is used as a basis for determining if either valve V3 or V4 in the purge source line has failed. A
pressure reading above this setpoint, when not purging, indicates that gas has leaked from ono direction or the other.
As it has been noted above, at the end of each a purge cycle, a vacuum is created in the section of pipe ; between V3 and V4. The setpoint should be set at a pressure above the vacuum pressure by an amount which would indicate that there is a leak, if that pressure is reached after a certain period of time.
~w Delivery Pr~sure ~etpoint The Low Delivery Pressure setpoint is used to determine when insufficient gas pressure for proper operation is present downstream from the regulator 154 in any distribution leg. This pressure is measured by the transducers 133, 135, 137 and 139. A pressure below this setpoint, when delivering gas, results in a "Low Delivery Pressure" alarm.
~gh Deliver~ Pres~ur~ 8etpoint A "High Delivery Pressure" alarm occurs when the pressure measured by any of transducers 133, 135, 137 and 139 is too high, usually due to regulator creep.
~in~mu~ Eshaust 8~tDoint The Minimum Exhaust setpoint i8 set as the minimum 3S acceptable exhaust gas flow rate through the exhaust duct 102 (Figure 6) for safe cabinet operation. It is interlocked with the most significant cabinet valve and gas delivery operations, to disable those operations under "Low Exhaust"
conditions.

21~47 p--rg~ 8etpoi~t-The computer program steps utilized in the above purge operation~ and setting o~ purge parameters are given in the above-identi~ied pending patent application and will not be repeated here.
CON~Ta~TP~q!~O~ ~NCTTQ~
When the ~Configuration Functions~ mode i~ ~elected, a qualified operator can modi~y or establi~h th- following parameters.
Cylinder pressure transducsr range Cylinder mani~old regulated pressure transducer range Cylinder mani~old purge pressure transducer range Cylinder manifold vent pressure transducer range Distribution mani~old regulated pressure transducer range Distribution manifold vent pressuro transmitter range Cylinder weight range Delivery association for each distribution leq Exhaust duct size zero calibration,for each manifold Zero calibration for each scale Pres~ur- ~ang- 8el-¢tion~
The range of the pressure transducers can be changed to accommodate the USQ of the transducer~ with different gases, or for any other reason.
As an example, the pressure range selection is performed simply by using the arrow keys 355, 357 on the panel 138 (Fig. lS) to change the range until the desired range is displayed (e.g. O to 100 psiA or O to 3000 psiA). Then ENTER
is pressed to select the range. The selection of the range of the voltage of the analog output signal of each transducer (e.g. O to 5 volts or 1 to 5 volts) also can be selected by a similar procedure.
Cylin~er ~oig~t R~nge 8electio~
Cylinder weight range selection is similar to the 3S pressure range selection described above. One additional option will allow the selection of "No Device Present~ for those cabinets not having a scale.
Dol~very A~ociation (~eg A. B. C or D) Each distribution leg o~ each cabinet i~ associated with a specific tool. The tools are wired to the Tool Interface Controller (TIC) 42 ~hown in Figs. 1 and 4 and discussed above. Each tool is assigned a number associated _34_ ~1 658 47 with the position in the TIC to which it is wired. This number, (e.g., 0 through 120), is ~tored in the memory of the cabinet for the leg which i8 connected to deliver gas to the tool. In operation, when the tool (say Tool ~32) requefits gas by closing its contacts connected to the TIC 42, all cablnet legs having a matching ~tored delivery as~ociation (32) will be opened to deliver ga~.
The delivery as~ociation stored in the memory of each cabinet can be changed ~imply by opQrating the up-down keys 355 and 357 and th- ENTER key 3S9 on the panel 138 (Fig.
15), in the manner described above for other configuration selections. Re-wiring of the tool~ i~ not reguired.
8~-~T ~'~8~ DUCT ~T8~
One of the advantageous featurQs of the invention is that it allows the user to adapt the ga~ cabinet to correctly measure the cabinet exhaust ga~ flow rate through the outlet duct 102 (Figs. S and 6) de~pite a difference between the diameter of the outlet duct 100 on the cabinet and the diameter "dH of the duct 102. This can be done by means o~ a few keystrokes on the control panel 138 (Fig. 15), in the manner described above. This allows each gas cabinet to b~
moved to a plant location in which exhaust ducting already is installed, without having to replace the ducting to match that of the cabinet. Moreover, the adaptation is fast and simple.
Referring again to Fig. 6, as noted above, a pitot tube device 134 i~ mounted in the duct 102 to measure the velocity of the gas ~lowing through that conduit. The device 134 includes a transducer which converts the differential pressure measured by the pitot tube device into an electrical signal. This signal is delivered on the "EXHAUST" line (Fig.4) to the analog input circuit 302 which converts the analog input signal into a digital output signal which i8 delivered to the CPU 306. The CPU then computes the flow rate according to the following equation:
Flow = D x ~P
Where: Flow - Exhaust flow in cubic ft./mlnute D=Duct size constant (examples: D=1425 for a 10 inch duct and 1020 for an 8 inch duct) -35_ 216~
", , .
P~Differential Pressure output of pitot tube device, in inches of water Stored in the memory 308 of the control system shown in Fig. 4 are at least three dlfferent duct constants, AS well as the algorithm corresponding to the above equation.
When the operator selects one of the duct SiZQ8 by manipulation of the pnchb~lttons on the control panel 138 (~ig.
15), the selection i~ ~tored in memory, and the ylGy~m of the controller causes each subsequQnt reading from devlcQ 134 to be operated upon according to the algorith~ to glve correct indication of the flow rate through the exhaust duct. $he operator also can sQlect the minimum acceptable flow rate, in the manner described above, in accordance with st~n~Ards that are set up to insure adequate ventilation of the cabinet to protect operating pQrsonnel. If, for some reason, the flow rate should fall below this minlmum level at any time during operation, an alarm is activated to indicate that correction is needed.
Once the exhaust duct size has been selected, that selection i8 retained in EEPROM and is not lost even if the controller suffers a loss of power.
This feature of the invention facilitates and reduces the cost of installation of the gas flow control cabinets at various existing plant locations, regardless of variations of the exhaust duct size. It increases the versatility of the cabinet by increasing the feasibility of moving it to new locations.
Z~RO ~t-'r~P~TIOII
The transducers which are used to measure gas pressure drift over a period of time. Therefore, the transducers must be re-calibrated from time to time in order to restore their accurate operation.
The transducers tend to drift both in the zero readings and in the "span". The "span" is the difference between the electrical output at zero and that at full scale.
Typically, the span drift i8 les~ significant that the drift of the zero point. This is because the pressures which are measured during purge tend to be very close to the zero point of the transducer range. If the transducer zero reading has 2165~ 17 drifted by an amount which is significant compared to the minimum and maximum pressures permitted during purge cycles, the safety verification of the ~ystem is not valid. This can result in either a serious safety problem, or the inability to perform a purge cycle. For these rea~ons, the zero re~n~s usually reguire relatively frequent calibration, wherea- th~
span seldom requirQs calibration.
In th~ past, a~ it has been explained briefly abov , re-calibration of th~ tran~ducer~ ha~ been performed onc~
every threQ to 8iX month~. Thi~ has been donQ manually, and th~ procedure can take four to eight hours per gas cabinet.
A typical large semiconductor fabrication plant may have one hundred to fiv~ or six hundred such gas cabinets. Thus, it is evident that a relatively large amount of labor is required for re-calibration. Thi~ creates a significant operating cost. Furthermore, each of thQ gas cabinet~, and its related semiconductor manufacturing tools, is out of operation for significant period of time, thus reducing the productivity of each gas distribution system, and of thQ entire plant.
In accordance with the present invention, the zero point of each transducer is re-calibrated automatically in a matter of a few minutes or seconds. This is done by thQ
manipulation of the control pushbuttons on the panel 138 shown in Fig. 15.
The basic procedure for zero calibration i8 to first sub~ect the transducer to a known pressure or weight which is at or very near its zero point, and read the electrical output generated by the transducer. Next, th~ difference between the measured value and the ideal value of the transducer is calculated. That difference, called an "offsetn, is stored in non-volatile memory (EEPROM) and then i8 used to compensate all subsequent readings by adding it to or subtracting it from the readings of the transducers during operation.
The computer program used to perform the zero calibration and subsequent operation described above is shown schematically in Figs. 9 and 10 of the drawings.
Fig. 9 shows the zero calibration routine described a~ove, and Fig. 10 describes the use of the offset value stored in the zero calibration routine to ad~ust subsequent 2l6~8~7 ._ analog readings. The last step in the proce~s illustrated in Fig. 10 is to perform other ~caling on the reading. That is, the signal may be amplified or othQrwise modified in magnitude, as i~ nee1e~ by ths control system.
58cal- Z-ro Calibratio~
Fig. 11 i~ a flow chart describ$ng the computer - program routine used to calibrate the zero setting of the scale transducers. The same routine i8 usQd for both the A
scale and the B scale, if two scales are used in the cabinet.
10The progra~ u~e~ a multi-tasking routine. Each of the deci~ion diamonds in the left hand portion of Fig. ll determines whether the ~tep i~ in progress or not. I~ the answer is "yes", the step proceeds until it i5 completed by the delivery of a return signal, at which point the program 15proce~ to fitep 2. The same procedure is followed for each subsequent ~tep in the routine.
In step l, the display on control panel 138 ~Fig.
15) states "Insure scale empty, Press ENTER when okn. This encourage~ the operator to make certain that the scale being 20calibrated has no weight on it. The program then determine~
whether the "ENTER" button has been pressed, within a certain length of time. If the answer i8 yes, step 2 i~ set. If no, the routine return~ to start.
In step 2, the computer compares the reading of the 25scale transducer with what it should be, and calculates and stores a zero offset value in memory (EEPROM).
When ~tep 2 i8 complete, step 3 is performed in which the analog conversion factors for the scale are re-initialized and stored in memory.
30After step 3 is complete, step 4 is performed in which a display "zero calibration complete" is formed on the control panel display. After a delay of three seconds, step 5 is performed in which a "Function Over" display is produced and the function is cleared. Step 1 is set, and the routine 35is ready for the ~tart of another operation.
Zero Calibratlon of Distributio~ ~eg Pr-~sur- Trans~uaer~
Fig. 12 shows the computer program routine used to perform a zero calibration of the pressure transducers in one of the four distribution lega in the distribution manifold 134 -38- 2165~47 , ,, (Fig.8). In Fig. 12, the valves that are open and closed are referred to with a "V" prece~tng the number of the valvQ
rather than the letters "A" or "B~ etc. used in Fig. 8. This is done ~or the rQason that the routine applie~ to any one of the four lQg~ and thus the valve identification is generalized.
In the first step, V8, the venturi valve i~ opened to apply a vacuum to line 16S, and valve~ Vl, V4 and V7 arQ
c106Qd. Vl i~ closQd to ~hut off the ~low o~ procesR ga~. V4 is closed to shut off the flow of nitrogen, and V7 i~ closed to minimize the length Or conduit to be evacuated.
It is a notable feature of thi~ aspect of the invention that, by using absolute pressure values rather than atmospheric pressure values, and by using the vacuum source as a reference pressure source, a calibration reference source i~
provided by the simple e~p~ent of using the vacuum source which already exists for purging the gas flow lines. ~his not only avoids extra equipment costs, but it has the added benefit of preventing the opening of the gas flow lines to atmosphere, which might be required if atmospheric pressurQ
were used aR the reference pressurQ, and thus avoids contaminating the gas lines.
In step 2 shown in Fig. 12 the vent valve V6 is open to evacuate the distribution leg between valves Vl and V7, thereby sub~ecting the transducers in the leg to the vacuum as a reference pressure. While the distribution leg is being evacuated, a message "Releasing Pressure~ is displayed ~or a certain period of time. Then, after a delay of fifteen seconds to insure that the measured pressure has dropped to the relatively constant pressure of -11.7 psiG (~3 psiA) of the venturi pump, the program continues to step 3.
In step 3, the zero offset values are calculated and stored for each of the separate leg pressure transducers, in sequence.
In step 4 the message displayed is "Storing New Values~. Vent valves V6 are closed and, after a wait of two seconds, step 5 is initiated. Steps 5 and 6 correspond, respectively to steps 3 and 4 of Fig. 11, and will not be explained further bere.

-39- ~1 ~5~7 .,~
In step 7, the vacuum valve V8 is turned off, and in step 8 the function is ended and the program returns to step 1 to wait for another operation.
Of coursQ, the same process i~ repeated for each of the other di~tribution legs in the cabinet.
g-ro Cal~ration of th- cyl~n~or M~n~ol~ ~r~ ucer-Fig. 13 i~ a flow chart for the program used to perform a zero calibration ~or the pre~sure transducer~ ln tho cylinder manifold 136 (Fig.8). ThQse include trAn~ c~r~ 121, 123, 109 and 111, 113 and 115, 117 and 119 ~hown in Fig. 8.
A~ in the distribution leg transducer calibration routine, the vacuum pressure produced by the venturi pumps 148 and 150 by opening the venturi valves A8 and B8 are used to provide a reference for the transducer~.
In step 1 of Fig. 13, venturi A8 is opened. After a delay of X seconds (a value which depends on the typo of cabinet) the program proceeds to step 2.
In step 2, the vent valves V5 and V2 are opened.
Valve Vl is closed. A~ter a delay of Y seconds, which also depend~ on the type of cabinet, the program moves to step 3.
In step 3, valves V3 and V6 are opened, thus exposing the transducers to the low reference pressure provided by the venturi pumps. After a delay of about ten seconds, the program proceeA~ to step 4.
The variou~ delay~ in the pres~ure transducer calibration routines are provided in order to allow time for stabilization of the transducer readings, and to insure that atmosphere does not enter and contaminate the process gas manifold.
In step 4, the offsets for the various transducers are calculated and stored. Then, in step 5, the message "Storing New Values" is displayed, and all cylinder manifold valves except venturi valve~ V8 are closed. After a delay of two seconds, the ~o~ am proceed~ to step 6.
In step 6 the analog conversion factors are re-initiali2ed, and the venturiR V8 are closed.
Finally, the program is completed in steps 7 and 8, as in the programs described above.

21~58 ~7 As it can be seen from the foregoing, the automatic calibration of the tran~ducers can be performed in a few minute~ instQad of sevQral hours. Thi~ ~aves a great deal of labor cost~ and down-time for the flow control units. Thu~, 5labor costs are reduced, and productivity of the gas distribution system i8 increased.
99n~nNTcAT~oNs RRT~R~N ~F~ SnnS
~ 8~Ar~ Co~TRort~B~apD CA8 C~T~
10There ar- several types Or mQ~sages which are uaod in communication betweQn th- tool interface controller (TIC) and the ga~ flow control cabinet~. The following is a list of the message types which are sent by the TlC to the cabinets.
1. Polling Messages. The first message type poll~
15the cabinets seguentially at the rate of about four messages per second or less. Communications are at the rate of approximately 9,600 baud. In response to each polling message, one of the cabinets sends a data packet to the TIC.
The data packet will be described in detail below.
202. Broadcast Messages. Once per second, the tool interface controller broadcasts signals to all of the gas flow control cabinets informing them of which tools are requesting that gas flow be ctarted or stopped. The data processor in each gas cabinet i8 programmed to receive these broadcasts on 25the digital input lines and compare the tool numbers with -those it has stored. When it detects a match, it executes the instructions broadcast. Otherwise, it ignores the signals.
Thus, gas distribution legs for which a given tool number has been stored will b~ enabled to start or stop gas flow.
303. Read Setpoint Signals. On command from the supervisory control computer 44, the setpoints for each selected cabinet are read and displayed on the screen of the computer.

4. Read Setpoint Ranges. On command from the 35supervisory controller, the setpoint ranges for the various flow control are read and displayed.

5. Read Configuration. On command from the supervisory control computer, the configuration of each ga~
flow control cabinet is displayed.

-41- ~16~8~7 6. Direct Valve Control Messages. These messages compri~e commands directly from the supervisory control computer to open or close specific valves in specific gas cabinets.

7. Execute Pre-defined Function. On command from the supervisory control computer, sev~ral automatic functions such as purgQ operation~ can be ordorQd and will bQ execut~d by a SpQCif iC one of the flow control cabinQts.

8. GQt Cabinet Di-play Mossages. Upon command from the supervisory cG.. ~lol co~putQr, the display 352 on tho cabinet control panel 138 (Fig. 15) i8 transmitted to the screen of the supervisory control computer for display to the operator there.

9. Message Display. Pursuant to the operation of the supervisory control computer, thQ display 352 on any selected cabinet can be made to display whatever the operator of the supervisory control computer wishes. This featurQ i8 used, for example, when there i~ direct control of valves from the supervisory computer.

10. Alarm Acknowledg~ Messages. The operator at the supervisory control computer can acknowledge any alarm by operation of th~ computer. This i~ secondary to and supplements acknowledqement of the same alarm condition at th~
cabinet itself. Therefore, the control of the individual units and the supervisory control computer both operate to provide this function.
ll. Abort Function Messages. These messages arQ
sent from the supervisory comput~r to abort a function which is in process at one of the flow control cabinet 12. Set-point Messages. On command from the supervisory control computer, setpoints can downloaded from any of the gas flow control cabinets to the supervisor~
control computer for display there.
DATA PAC~ET 8TR~CTUR~
As noted above, the tool interface controller polls the various gas flow control units periodically at the rat~ o~
about four messages per second. In response to a pollinq signal each cabinet send~ back to the TIC a data packet.

-42- 216 S~ar~
._ Fig. 14 ~hows the arrangement of data in each data packet.- Each packet i~ a maxlmum of 120 byte~ in length. The data packet ~tructure i5 as follow~:
1. First i8 the ~tart of text messagQ (nSTX~) to identify the start of a packet.
2. Next is the acknowledge section (~AKn).
3. Next i~ data indicating the type of cabinet which i8 re~ponding. For exampl-, ther- might b~, in a ~ingle ~ystem, four or ~ore different type~ of cabinet~, some h~ving only one di~tribution leg, ~ome having ~our di~tribution leg~, etc.
5. Next is a byte defining the number of analog values which are to follow.
6. Next are the analog values. Three bytes are used for each analog value.
7. Next is a byte giving the numb4r of alarm status byte~ to follow.
8. Next are the alar~ status bytes (e.g. high flow, low flow, etc.).
9. Next is the number of digital input byte~ to follow.
10. Next are the digital inputs.

11. Next i~ general ~tatu~ information, such as which manifold legs currently are ensbled; which Or the two gas source~ A or B currently i~ being used, etc.

12. Next is the list of associated tool numbers for each distribution leg of the flow control units.

13. Next i~ a checksum.

14. Finally, End of text (ETX).
If reconfiguration i8 desired, this can be done in software in a simple manner. For example if the delivery assoclation is to be changed; that is, if the tool number which is to be connected to a particular distribution leg i~
changed, the following procedure i~ followed.
The tool number is entered at the cabinet by the simple procedure described above. This i~ stored in an EEPROM 80 that a battery-backed memory i8 not necessary.
The next data packet now ha~ the new tool number in it and the tool interface controller reads it and stores the -42A- 216~8 g7 number in its random access memory (RAM) 303. The cabinet now responds to the new tool number request during the broadcast of the call~ for delivery of gas to the various tools.
Since the information from each gas cabinet stored in RAM 303 i5 refreshed once every several seconds, the RAM

-42~ 7 ~

also need not be battery-backed, thus further reducing the _ cost and maintenance requirements of the gas distribution system.

As it was noted above, the supervisory control computer is a personal computer, such as an IBM PSt2 Model 80.
It should be noted again that the control that the supervisory control computer provides over each gas cabinet can be overridden by someone operating the controls at the gas cabinet itself. This is done in order to give preference to local control at the site over central control, whenever the controls compete with one another.

The supervisory control computer is programmed so as to provide the following displays on its screen:
Home 8creen The operator can bring up the Home Screen shown inFig.17bypressingthe ~ k ~ ~ r _ ~ i i /

21.6S8~

"~_ The screen shows, in graphic form, the ~tatus of the entire-system. There i~ a ~eparate block (-.g. "970 G6 Roomn) for each gas cabinet~ in th- system. Only one room block i8 shown on th- home screen above, wherea~ u~ually there will be several ~uch rooms in a given system. The block i~ color-coded to indicate the ~tatu~ o~ th- room: Red mean~ one or more cabinet- in th- roo~ ha- an act$v ~high priorlty" alarm.
Yellow mean~ that one or mor- cabin-t- in th- room ha~ an active warning (low priority) alaro condltion. Green indicates that all cabinet~ in the room are in a non-alarm ~tate.
On the home Qcreen, immediately below the room block or block~ i~ an area "Alarm Message~" where all current ~ystem alarm~ are shown. Two column~ of four row~ each are provided in thi~ area. This allow~ for up to eight alarm me~sages to be displayed at one time. Additlonal messages can b~
displayed by u~ing the down and up arrow~ on the computer keyboard to ~croll down and up through the alarm messages.
The highest priority unacknowledged alarm appears in the upper left-hand position. The next highest priority alarm appears below ~t. This pattern continues by filling the first row and then the ~econd row for unacknowledged alarms. Next, the acknowledged alarms follow in the list in the order of descending priority. The alarm text i~ color-coded.
Unacknowledged alarm~ are printed in red text, whereas acknowledged alarms are in white.
Acknowledgement of the alarms can be made by simply pressing the ~plu~ key on the keyboard.

Room LaYout 8creen By pressing the F2 key the operator can bring up the room layout screen shown in Fig. 18, which shows in graphic form, the status of all cabinets in a particular room.
Each cabinet is given a number, and the layout of the cabinets on the screen the same as the cabinets have in the room. The blocks representing the cabinets are color-coded with either red, yellow or green color, following thecode above, to indicate respectively, whether the cabinet has one or more active high-priority alarms; one or more active lower-priority alarms; or no active alarms at all.
8elow the room layout is an area for alarm messages.
Again, all active alarms are displayed in their descending priority, with the highest-priority unacknowledged alarm in the upper left hand position. The representation of a row of keys displayed at the bottom of the screen identifies the function keys that can be used to quickly move from one mode or screen to another.

Automatic Hod- ~creen To select the automatic mode, while in the room layout mode, the operator presses the F2 key and the computer responds with a prompt asking for the desired cabinet number.
When the cabinet number is typed in and the ENTER key is pressed, the system will bring up the screen shown in Fig. 19.

The various sections on the Automatic Mode screen are described below:
Quic~ ~eys - Along the left-hand side of the display is a block listing of the available quick keys. As discussed previously, these keys can be used to quickly move from one mode to another.
C~binet Identifier - On the top left hand side of the display is a label identifying the chosen cabinet number and the type of gas it contains.
Menu/Prompt arQ~ - Below the Cabinet identifier is a block used for menus, and other alphanumeric information, as appr~priate.
Exh~ust Flow B~r Chart - Below the Menu/Prompt area is a display giving the cabinet exhaust flow rate, in both a bar graph and numerically, in C.F.M.
Al~rm Bloc~ - On the bottom left hand side of the display is an alarm block. Up to eight system alarms can be displayed in prioritized order on the screen. These alarms apply to all cabinets, not just the selected cabinet. If more than eight alarms are active, the arrow keys on the computer keyboard can be used to scroll through additional alarms.
Cabinet Manifold Graphic - The right hand side of the display provides a graphic representation of the cabinet manifold status. The lines and valves are color-coded to illustrate gas flow. An open valve and connected line are shown in green, while closed valves and tubing segments are shown in red.
Analog values of operating parameters are displayed at the appropriate positions in the manifold. These readings are primarily pressures measurements and cylinder weights.
The association of the delivery legs with the tools is given above the piping diagram. As an example, in the screen shown, leg ~1 is connected to tool #570, and leg #2 is connected to tool ~314. In the example shown, only two legs are in use, either because that cabinet has only two legs, or because only two of the four legs are in use.
8electing An Automatic Function Selecting an automatic function is a simple process in which the operator follows the prompts in the Menu/Prompt A

-46~

area of the screen. In the Menu/Prompt area is a list of available automatic functions, along with the control function key that will select each. Additional functions may be made available on other pages by pressing the "Page Up" or "Page Down" keys on the keyboard.
To select a function, the operator presses the associated control key combination. For example, on the screen shown, pressing the Ctrl key and the F1 ~ey simultaneously will display a prompt to enter the password.
The password is typed and entered by pressing ENTER. If the correct password is entered, the Purge to Change Cylinder A
function begins, unless an interlock condition exists which prevents operation.
When a function is selected, the supervisory control computer will co D unicate through the TIC to the cabinet. If everything is satisfactory (no interlocks) the function will start. If not, a message indicating that function operation is inhibited will be displayed for a brief period in the Menu/Prompt area.
During function operation, the Menu/Prompt area displays the same messages that are being displayed at the cabinet. During any automatic function, the operator can abort the function by pressing the ESC key on the computer keyboard.
Maintenance Mode The screen shown in Fig. 20 shows the maintenance mode of operation.
This mode can be used to print system readings or to change the main system password. Its display is identical in configuration to the automatic mode display. This mode can be selected simply by selecting the F4 key to bring the screen up.
A

It may not be necessary to enter a particular cabinet identification number, since the maintenance mode display will display the characteristics of the last cabinet number which was previously selected in another mode.
The "Print Gas Readings" function, which is entered by pressing key 5 F1 while in the maintenance mode, allows the operator to select a gas room and to get a printout of the current pressures and weights of cylinders used to supply gas to each tool. The room number is listed, followed by the date and time at the top of the printout.
The printout lists one row of data for each tool that is connected to a 10 cabinet. Each row contains the tool name, tool number, cabinet number, gas type, the active cylinder, and pressure or weight reading. If scales are present, a weight reading is listed; otherwise, a pressure reading is listed.
From the Maintenance Mode Screen, to select the Print Gas Readings function, the operator presses Ctrl and F1 simultaneously. A prompt is displayed15 to enter the room number. When this is done, a message is displayed "Please wait until printing completes" while the document is being printed. After the printing completes, the previous menu appears with selections to Print Gas Readings and to Change Password.
The Change Password function allows the operator to change the 20 main system password. This password is utilized to enter Configuration Mode, Parameter Set Mode, and the Exit to Dos mode. This password does not apply to activating automatic functions; automatic functions have a built-in password that cannot be changed.
From the Maintenance Mode Screen, to select Change Password, the 25 operator presses Ctrl and F2 simultaneously. A prompt is displayed asking for the current password. The current password is typed in and entered by pressing the ENTER key. If an incorrect password is entered, a prompt appears "Try again" andthe operator can enter the password again to continue or the operator can press Enter to return to the menu selections.

r~

-48- ~ 4 ,._ .",~
If the correct password is entered, a prompt is displayed asking for the new password. The new password is typed and entered. Next, a prompt is displayed asking for the new password again. The same new password is typed again and entered. If the second new password matches the first, a message is 5 displayed indicating that the password has been changed. If the second new password does not match the first, a message is displayed indicating that the password has not changed. In either case, the menu returns with the selections displayed for Print Gas Readings and Change Password.
Parameter Set Mode The supervisory control computer allows an operator at a single supervisory station to review and/or modify setpoints in any cabinet in the system. This is accomplished through the Parameter Set Mode.
Cabinet Parameter Set Mode can be selected from any screen. To do so, the operator simply presses the F9 key, and, in response to a prompt, enters the 15 main system password. The system enters the Parameter Set Mode with the graphics display for the most recently-selected cabinet.
Fig. 21 is a reproduction of the Parameter Set screen.
A

f f Most of the information on the screen is of the same type as on previous screens and need not be explained further. Only THE new features will be explained.
All cabinet setpoints are stored in the gas cabinets themselves. In 5 order to view and/or change setpoints, the supervisory control computer must first be used to retrieve these setpoints.
The first screen displayed upon entry into the Parameter Set mode is one which reads "~F1 Remote Setpoints". The operator presses Ctrl and F1 to get a list of available cabinets, and selects the one desired.
Next, the operator presses the appropriate control and function key combination listed next to the cabinet number to command the supervisory control computer to retrieve setpoints from the desired cabinet. The Menu-Prompt area will display a list of cabinet setpoints along with their current values.
ChanginP A Setpoint To change a setpoint, the operator presses the control key and function key associated with the setpoint. The display will project the current value of the setpoint along with the limits of adjustment. The operator types inthe desired setpoint value and presses ENTER. When the new value is entered, it will be transmitted to the cabinet. If the cabinet accepts the setpoint, it sends back an acceptance message, which will be displayed in the Menu/Prompt area, indicating that the new setpoint has been stored. If not, a setpoint change failure message will be displayed.
Configuration Mode The Configuration Mode is provided to allow a qualified operator to configure the supervisory control computer. It allows the following configuration functions to be performed.
Set number of cabinets in the system Enable/Disable alarm printing Set the chemical gas name for each cabinet Enable/Disable cabinets from being selected in any mode Set the tool names that are displayed for each cabinet delivery leg ;,......

Set the tool numbers that are displayed for each delivery leg Configuration Mode can be selected from any supervisory system screen by pressing the F8 key. After entry OL tne password, the ~ystem enters the Configuration mode with the graphics displayed for the most recently selected cabinet.
Fig. 22 shows the top-level Configuration Mode screen.

Following is an explanation of the functions which can be performed in this mode.
~et Number of Cabinets ln this function, the operator sets the number of cabinets that can be accessed by the operator at the supervisory control computer. This number is the total number of cabinets that are available for selection in any mode that requires a cabinet number to be entered.
To select this functlon, the operator presses Ctrl and F1. A prompt appears asking for the number of cabinets.
The number of cabinets is typed in and entered.
Selecting Enable/Di~able Alarm Printing In the Configuration Mode, whenever Ctrl and F2 are pressed, the alarm printing enableldisable selection toggles.
For example, if the current state is disabled, the menu displays "Enable Alarm Printing." Making the selection Ctrl and ~2 enables alarm printing and the display changes to "Disable Alarm Printing. n Configure Cabinet Selection of Configure Cabinet allows the entry or modification of chemical gas names for a cabinet and tool names and tool numbers that are displayed on the manifold graphic associated with the delivery legs. Of course, this should be done to match changes which are made in the gas used or leg/tool connections at the cabinets. Also, a cabinet can be disabled or enabled from operator selection.
A

.~

"_ Selectin~ Configure Cabinet After entering Configuration Mode, to select the Configure Cabinet function, the operator presses Ctrl and F3 simultaneously. A menu of available cabinets appears in the Menu/Prompt area, as in the screen shown in Fig. 23.
Next the cabinet desired is selected. A menu appears with options to update the chemical name for a cabinet, disable cabinet from operator selection, or update tool data.for a cabinet, as in the Configuration Mode Cabinet Definition List screen (Fig. 24).
~p~ate Ga~ Name This selection allows the operator to update the gas name used on various displays for a particular cabinet.
To update a gas name, after selecting Configure Cabinet, the operator presses Ctrl and Fl. A prompt is displayed requesting entry of the gas name. The desired gas name is typed in and entered. The Configure Cabinet menu returns with the new gas name being displayed.
~isable Cabinet This selection toggles between "Disable Cabinet" and "Enable Cabinet." If a cabinet is disabled, it will not be available for selection for any mode in the system except Configuration Mode. The screen will display "Disable Cabinet"
if it is currently enabled.

A

To select Disable Cabinet, after selecting Configure Cabinet, the operator presses Ctrl and F2. Now the cabinet is disabled and the display now is"Enable Cabinet".
Update Tool Data This selection allows the operator to update tool names and tool numbers for each delivery leg of a particular cabinet.
To update tool data, after selecting Configure Cabinet, the operator presses Ctrl and F3 and a new menu will appear displaying tool update selectionsfor each delivery leg. To update the tool data for a delivery leg, the operator presses the associated control and function key combination. For example, he or she presses Ctrl and F3 to update tool data for Leg 3. A menu will appear with selections to Update Tool Name and Update Tool Hex Number.
To Update Tool Name, the operator presses Ctrl and F1 and a prompt will appear asking for the new tool name. The new name is typed in and entered.
The menu will return with the options to Update Tool Name and to Update Tool Hex Number.
To Update Tool Hex Number, the operator presses Ctrl and F2 and a prompt will appear asking for the new tool hex number. The new hex number is typed in and entered.

;~ A

53 ~
.., , .i,_ ~bular ~/o 8creen The Tabular I/O Screen is shown in Fig. 25.
The above screen provides a presentation of all cabinet inputs and outputs found for a particular cabinet. It provides basically the same information that is found in the cabinet graphics. However, there are data that are not displayed elsewhere.
This mode is used primarily for maintenance purposes. It provides maintenance personnel with detailed informa~ion of exactly what the gas cabinet is reading on its in ~ ~e~t t~-r .~=. . ~_ lines. The inputs and outputs are color-coded. For the valve outputs, green indicates that the valve is open, while red indicates that the valve is closed. For the other outputs to the alarm bus, the color green indicates an energized, normal state, whereas red indicates an alarm state. For the inputs, the color green 5 indicates that the input is active while red indicates that the input is not active.
Printing Pressing key F5 will cause the printer of the control computer to print all the information on the current screen.
Exiting to Dos Exiting to Dos terminates the supervisory program and allows the operator to use the computer for other purposes. To exit to Dos from any screen,the operator presses the F10 key and a prompt appears asking for the password.
The main system password is entered, and the supervisor program will terminate, and the computer can be used for other purposes.
CONCLUSION
It can be seen from the foregoing that the present invention amply satisfies the objectives set forth above. It provides a gas flow control system which is capable of both local operation of each gas flow control unit, and central operation from a single personal computer by a single operator. This provides for 20 simultaneous monitoring of the operation of each flow control unit, and of the system in its entirety.
Centralized control is provided with a minimum cost of cabling and wiring.
A highly versatile gas control unit is provided which supplies process 25 gas to any one or all of four different tools at which the gas is utilized.
Furthermore, the gas can be supplied from either of two alternative source tanksso as to minimize down-time and insure a continuous flow of process gas.
The system provides a high degree of operator safety, without the cost usually required in past systems. The cost of purging various flow lines in the 30 control units is simplified and made faster by the provision of local purging ~ h ~
_ techniques in the short sections of the gas distribution legs in the flow control units, rather than purging the entire length of the conduit from the flow control cabinets to the tool locations. This saves gas and time.
Purging of the delivery lines to the tools is made possible, even 5 though flow-though purging is not available, thus improving safety in line maintenance operations.
Automatic selection of exhaust conduit size parameters allows the parameters, by means of a few simple keystrokes, to accommodate the gas flow control unit to be used with a variety of different sizes of exhaust conduits which 10 may be installed in a given plant, thus increasing the versatility of the flow control equipment, as well as decreasing installation costs.
Considerable labor savings are created by the provision of automatic means to re-calibrate the zero readings of various pressure and weight transducers in the system. By utilizing a pressure source already available in the system, 15 hardware costs are minimized. Moreover, the calibration is done without exposing the gas flow conduits to the contaminating atmosphere. The calibrationsare performed quickly and easily by the operation of a few controls.
Changing the wiring connections between the tools and the gas cabinets does not require mechanical re-wiring. Instead, the connections are 20 changed in software, by means of a few keystrokes.
The above description of the invention is intended to be illustrative and not limiting. Various changes or modifications in the embodiments described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention.

, .~ e - A

Claims (28)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In or for a process gas distribution control unit handling hazardous gasses having gas conduit means for conducting said process gas from a source towards a utilization location, control means for controlling the flow of said gas through said conduit means, and at least one gas pressure measurement transducer for measuring the pressure of said gas in said conduit means, a system for calibrating said pressure transducer comprising reference means for subjecting said transducer to a known value of pressure, means for measuring an electrical output signal of said transducer, means for comparing said electrical output signal with a known standard signal and developing a difference signal corresponding to the difference between said standard signal and said output signal, memory means for storing data corresponding to said difference signal, and correction means utilizing the stored data to correct the output signal of said transducer.

2. A device as in claim 1 including a vacuum source, said reference means comprising means for selectively connecting said vacuum source to said transducer.

3. A device as in claim 2 in which said gas conduit means includes gas conduits for distributing said process gas to a plurality of utilization locations, and purge means for selectively connecting said conduits to said vacuum source for purging.

4. A device as in claim 1 which said correction means comprises digital computer means for adding or subtracting from the output of said transducer a signal corresponding to said difference signal to correct the zero reading of said transducer.

5. A device as in claim 2 in which said gas conduit means includes a plurality of process gas distribution conduits and at least one purge gas supply conduit, in which said output of said transducer represents absolute pressure, and means for selectively and alternatingly connecting first said vacuum source and then said purge gas supply conduit to at least one of said process gas distribution conduits.

6. A device as in claim 2 in which said vacuum source comprises a venturi pump with means for admitting pressurized purge gas as the driving gas for said pump, and having a vent.

7. A device as in claim 1 in wihch said memory means comprises non-volatile data storage means.

8. A device as in claim 7 in which said data storage means is an EEPROM.

9. A method of calibrating gas pressure transducers in a process gas distribution system handling hazardous gasses having gas conduit means for conducting process gas, said method comprising the steps of:

a) subjecting each of said transducers to a reference value comprising a known gas pressure;
b) measuring the electrical output signal of said transducer;
c) utilizing a pre-programmed digital computer having a memory to compare said measured output signal with a pre-determined electrical signal corresponding to said known pressure and determining the difference between said signals;
d) storing in the memory of said computer data corresponding to said reference; and e) utilizing said stored data to correct subsequent output signals of said transducer.

10. A method as in claim 9 in which said subjecting step comprises connecting said transducer to a vacuum source, and including the step of selectively connecting said vacuum source to process gas distribution lines to purge them.

11. A method as in claim 10 in which said transducer is adapted to produce output signals representing absolute gas pressure.

12. In or for a process gas distribution control unit handling hazardous gasses having gas conduit means for conducting process gas from a pressurized container towards a utilization location, support means for supporting at least one pressurized container of process gas and weighing means for weighing said container to determine the amount of gas in said container while said container is connected to said gas conduit means, said weighing means including at least one weight measurement transducer, a system for calibrating said weight measurement transducer comprising means for measuring and electrical output signal of said transducer means for comparing, with a known standard signal, a reference value of said electrical output signal produced when said weighing means is subjected to a reference weight and developing a difference signal corresponding to the difference between the value of said standard signal and said reference value, memory means for storing data corresponding to said difference signal, said correction means utilizing the stored data to correct the output signal of said transducer.

13. A device as in claim 12 in which said reference weight is the weight bearing on said transducer when said weighing means is empty.

14. A device as in claim 13 including means for giving a computer prompt display indicating the need to empty said weighing means before calibrating said transducer, and for inhibiting the calibration of said transducer when said prompt display is not responded to by an operator.

15. A method of calibrating gas supply detectors in a process gas distribution system handing hazardous gasses having gas conduit means for conducting process gas from a pressurized container towards a utilization location, said detectors comprising weight transducer for weighing a pressurized container of process gas to determine the amount of gas in said container while said container is connected to said gas conduit means, said method comprising the steps of:
a) subjecting each of said transducers to a reference weight;

b) measuring the electrical output signal of each of said transducers;
c) utilizing a pre-programmed digital computer with memory to compare said measured output signal with a pre-determined electrical signal corresponding to a reference weight and determined the difference between said signals;
d) storing in said memory of said computer data corresponding to said difference; and e) utilizing said stored data to correct subsequent output signals of said transducer.

16. A method as in claim 15 in which the step of subjecting each of said transducers to a reference weight comprises removing the weight of said container from said transducer.

17. A method as in claim 16 including the step of displaying on a computer control display a prompt to ensure that the container has been removed from said transducer before calibrating said transducer, and inhibiting the calibration routine if the operator does not respond to the prompt.

18. In or for a process gas distribution control unit handling hazardous gasses having a gas conduit to conduct said process gas from a source towards a utilization location, a control unit to control the flow of said gas through said conduit, and at least one gas pressure measurement transducer to measure the pressure of said gas in said conduit, a system for calibrating said pressure transducer comprising a reference source to subject said transducer to a known value of pressure, a measuring unit to measure an electrical output signal of said transducer, a comparator to compare said electrical output signal with a known standard signal and to develop a difference signal corresponding to the difference between said standard signal and said output signal, a memory to store data corresponding to said difference signal, and a corrector which uses the stored data to correct the output signal of said transducer.

19. A device as in claim 18 including a vacuum source, said reference source comprising a valve to selectively connect said vacuum source to said transducer.

20. A device as in claim 19 including gas conduits to distribute said process gas to a plurality of utilization locations, and a purge controller to selectively connect said conduits to said vacuum source for purging.

21. A device as in claim 18 in which said corrector comprises a digital computer for adding or subtracting from the output of said transducer a signal corresponding to said difference signal to correct the zero reading of said transducer.

22. A device as in claim 21 including a plurality of process gas distribution conduits and at least one purge gas supply conduit, in which said output of said transducer represents absolute pressure, and a controller to selectively and alternatingly connect first said vacuum source and then said purge gas supply conduit to at least one of said process gas distribution conduits.

23. A device as in claim 21 in which said vacuum source comprises a venturi pump with means for admitting pressurised purge gas as the driving gas for said pump, said pump having a vent to atmosphere.

24. A device as in claim 18 in which said memory comprises a non-volatile data storage device.

25. A device as in claim 21 in which said data storage device is an EEPROM.

26. In or for a process gas distribution control unit handling hazardous gasses having a gas conduit to conduct process gas from a pressurized container towards a utilization location, a support for supporting at least one pressurized container of process gas and a weighing device to weigh said container to determine the amount of gas in said container while said container is connected to said gas conduit, said weighing device including at least one weight measurement transducer, a system for calibrating said weight measurement transducer comprising a measuring unit to measure an electrical output signal of said transducer, a comparator to compare, with a known standard signal, a reference value of said electrical output signal produced when said weighing device is subjected to a reference weight and to develop a difference signal corresponding to the difference between the value of said standard signal and said reference value, a memory to store data corresponding to said difference signal, and a corrector utilizing the stored data to correct the output signal of said transducer.

27. A device as in claim 1 in which said reference weight is the weight bearing on said transducer when said weighing device is empty.

28. A device as in claim 27 including a controller to cause a prompt display indicating the need to empty said weighing means before calibrating said transducer, and to inhibit the calibration of said transducer when said prompt display is not responded to by an operator.