US2610300A - Flow control - Google Patents

Description

Patented Sept. 9, 1952 1 "rm-ow.- common wilsmwiwaunnnoak RidgeLTe'nn 'and'Richiare DJBweraB'rkeley, Calif.,' assignors lto-th'e United States oflAinerica, as represented by the 'UiiitedStaJtes 'Atomic Energy Commission'- nppuwtionnugustv, 1951,:ScrialNoQ'240fl'38 Ouriinvention relates -to mass spectrometers,

v trometer'tubesimplyfand without mocngpaas and more particularly to devicesv-sfor controlling the flow-aoilgases to. a massrspectrometer or other appropriate equipment.

p The mass :spectrometeris an- :appar'atus -.-for sortingions according to their specific, mass. Gases. to be examined are fed: into the. apparatus and are ionized .by ionizing particles, preferably by gbombardment. with.=.ele.ctrons. The. ions-gthus tormed are eiectedointhe form. of a loeamto the main bod-yof .theztube .by (m'eanssofr accelerating potentials: Here-theyare'ordinarilysubjected to the influence of .a magnetic .field causing them .to;- travel in 'arcuate -.paths -whose radiie-are .determined-b-y-the .massesand charges: of. the-respective ions. By focusing- -thexdesireduion .beam on a zcollector-eat one extremity. of the tube, the "ions, are -causedo-lto impinge successively on :the collector and-:are:discharged.v The current thus obtained zaneindex-iofi the ions in. .the selected beam Inithe prior art it has ibween -the practice to provide an ionlsource inclosed ina glass envelope; and .to inclose. the collector. in 2a :separateglass envelope aso that they -.are ospacedeapart from each-other but joined together through-theex- :tremitiesa of an arcuate piece of :flattenedcopper tubing which defines the main body of the :tube through whichzaniionibeam travelszandiin which it is. subjected to a-magnetic-or. electric field. The glassenvelope of the sourceand the collector respectively are .sealedito the copperrtubing.

vOperational efiiciency' and-reliability of operationare [factors which are under constant observation :and xstudywithwa viewtozimprovement. An-el'ement ofopetationahefiiciency andcstability is the charge consumption rate and .thisis .dependent .among other things,,upon .thenvapor flow to the mass spectrometer. "This in turn Ldepends upon the constriction throughv which the gas must ,pass inorder. .to reach .thespectromete'r;

.In the ,prior art vapor flow has been controlled by .ia manually.,operated valve iniaccordance Lwith instrument lreadings but this .requires the rundivided iattentionsof. the operator. who must make conditions. in the operations, of the 'lspectrometen 'Uli'derstich conditions. .it. ,diificultlto. :maintain uniiorm' pressures 'within .the tube .andilito insure ,AQPhcants'have as astill further object of their finvention'the :provision of a 'flow control which" may -he manufactured with precision and in quantity, and iiany number 'of "which can be m adeito give closely reproducibleresults; I v

Applicants: have :as a still "further .objiec't of thieirinvention the provisionp of a f syste'm re-3 s'p'ons'ive "to pressure within at spectrometer'tube for automatically controllingwithe flow 'of'wapor thereto in order to j maintain substantially uniform' pressure therein; Y p

Other objects and "advantages or Zour j inven tion: wil1"appear from the following specification and accompanying drawings, and the'novel'fe'ae tures thereof 'will be particularly pointed out "in the'anne'xed "claims. a v

iInLthe :drawings, Fig.1 is a schematic o'f'a portion of-one form ofmass spectrometer. 'incorporating our improved Iiovv control therein; Fig. 2"is a: schematic -of 5acbnventionalflirani gauge for "controlling the flow through our; improved valve arrangement. Fig. 3 is'a crossse'ctlOIll'Of our improved flow control 'valvegFigfi4 is a detailfof theipistoniof our improved fiOW'CIQIltrol valve; Fig.5;5 is a schematic of the electronic control circuit :for our improved {control valve.

Referring tox'the drawings in detail; I' des'ignates "the main -body of the mass spectrometer through :wmcmne ion bearrrtravels and whichflis preferably made 'of copper; tubing; To 'th'efend of body I is joined a glass envelope 'offanygap; propriate configuration, .ishown symbolically at '2. j fDisposedwithin'theenvelope 2 and mounted "onthe tube "I is-anfion' source '3: The electrical leads (notsh'own) which feed" the'io'nsour'ce and its'various elements come into 'the envelope Zion either side thereof through appropriate reen' trantmeshes' or the like. Sample line 4, "may enter the "side" of the 'enve'lop'ein the usual manner rand may "terminate "within the source ad- 'jfrequent '-adjustments in zresponseflto-chang'ing invention thelprovis'ion or an arr angement rdr C regulating the flow "of a gas to a mass specithroughfiline 4 is controlled by-valve 5jw hich isiiispo'sed therein'l'between the gas source and the spectrometer. h I

Projecting from'th'e wallof tube I isa vacuum outlet extension 6 which leads to j an 'appropriate vacuumpump'fnot shown). A Pirani gauge "1 is provided for *communication with-the "exten-'- sion 6 leading to the vacuum pumpxand 'is connected to control-the operation'ofthe electronic direetiy "and the operation of this *hot wire gauge "is jidased "onfthe principle that the heat --'conduc'- tivity of "a 'gas at-*low-pressure, e.'- g. below 1000 The wire is inclosed in a tube attachedto the vacuum system so that the wire is ex posed to the same vacuum as is in the system. The wire is heated by an electric current flowing through it. Within a certain range, the temperature of the wire, and thus its resistance depends upon the pressure of the gases surrounding the wire. When the pressure is decreased, relatively less heat escapes from the'wire, its temperature rises with consequent increases in resistance, and less current flows therethrough.

. A simplified arrangement of the Pirani tube is illustrated in Fig. 2. It is desirable that the gauge be very sensitive to pressure. In order to be responsive to various slight changes in the resistance of the wire in the Pirani tube for slight changes in pressure, the length of wire is made one of the four resistances of a sensitive Wheatstone bridge. The gauge unit which is attached to the vacuum system, preferably contains allfour resistances 3, H), II and I2. Resistanceslll, II and I2 are preferably sealed in tubes. Wire resistance 9 is in a tube connected'directly to the vacuum system, as indicated at |3 in Fig. 1. Resistances H), II and I2 are at substantially constant pressure and uniform temperature. The resistance of element 9 changes in response to changes in pressure. Slight changes of resistance unbalance the Wheatstone bridge and are reflected in voltage changes at the output l4. Ordinarily they are recorded by ameter in the usual vacuum systems. However, .they serve to control the. power feed tothe flow control valve in this arrangement. Power is fed to the system at the juncture of resistances 9, i2 and I0, I from the usual D. 0. power source through leads 38.

I ,The flow control valve disclosed in detail in Fig. 3, and shown schematically in Fig. ,'1, comprises a variable orifice, the port area of which is controlled by temperature. A sleeve of a substantially non-expansible material, such as Invar, surrounds an inner sleeve 2 I, of some material which is chemically inert to the gases to be metered.

Within the sleeve 2| is placed a piston or cylinder mensions of the control determine the flow range 1 and pressure drop, and they must be accurately determined, probably by trial and error to satisfy a given set of conditions. .a piston length of 2 inches and a diameter of .497 inch, working in a cylinder bored to .500 inch It was estimated that would satisfy the conditions stated. Increasing theclearance between cylinder bore and piston will increase the flow or decrease the pressure drop, while increasing the length willv have the reverse effect.

As shown in Fig. 3, the cylinder 22 has cross slots l5, l6 milled or otherwise formed in each ,end to permit passage of the gas in the event the cylinder becomes'lodge'd against one end of the sleeve 2| or against-a perforated plug 23 which is installed inthe other end of sleeve 2| to hold the cylinder in place. The plug 23 may be silver soldered or otherwise sealed to the sleeve 2 I.

In operation the clearance between the cylinder .22 and the sleeve-2| is regulated by the temperature of the Whole assembly. A convenient means for maintaining the assembly at an elevated temperature is a heating coil 24, wrapped thereabout and may be in the form of a standard Calrod heater. As the temperature of the assembly is raised, the cylinder 22 expands more than the sleeve 2|, because the latter is restricted by the relatively non-expansible sleeve 20 which is preferablyshrunkfit on the sleeve 2|.

Since the sleeve 2| serves the sole purpose of protecting the sleeve 20 from the action of the gases which may pass through the orifice, it is obvious that'the function of the sleeve 2| may be dispensed with in many cases, for example, a simpler and just as, effective arrangement is to make the sleeve 2| out of the relatively nonexpansible material of sleeve 2|) and to omit sleeve 20 entirely. v

A number-of alternative arrangements in the choice of materials and dimensions of the parts will be apparent. For example, it may be desirable to provide a flow control which will cut off the flow on failure of the heating element 24, and will pass the gas only on being heated. This arrangement might also be of general application. Such a device is obtained when the materials of the cylinder 22 and the sleeve 20 are interchanged. It is obvious that if the cylinder 22 is made of Invar and the sleeves 2| and 22 of copper, the gas flow increases with temperature rather than decreases as in the modification first described. In either case, the Invar element may be protected from the action of the gases being metered by a suitable coating of a resistantmetal. The coating may take the form of a machined sleeve, as shown in the drawing, or'it may be a layer electroplated or otherwise formed on the element to be protected. Another useful variation of the invention lies in the use of differentplastics for the mate'- rial from which the cylinder or sleeves are made. Many plastics and ceramics are available which have sufficiently high softening points to be dimensionally stable when formed in stress free masses.

The variable orifice described above is particularly suited for automatic regulation of the gas flow to a mass spectrometer tube such as that shown in Fig. 1. An appropriate power circuit is shown in Fig. 5 wherein the terminals are connected to the signals of a Pirani gauge through leads M of the bridge. The signals, suitably am plified through the tube 3|, activate a gas filled tube 32 such as a thyratron. The thyratron 32 is connected so as to regulate the current'supplied to the resistance or heating coil 24. The source of potential to the anode of the tube 3| may be any standard type of power supply, although a simple arrangement is shown wherein the output of a transformer 33 is rectified by the tube 3| and filtered sufiiciently for the purpose described by the filter circuit comprising inductance 34, capacitance 35, and resistance 36. The thyratron 32 is supplied with alternating current, which may be from the transformer 33, or a separate transformer 'may be used in accordance with well known practices in the art. As shown, the potential applied to the grid of the tube 32 is adjusted by means of a variable autotransformer 31, commonly known as a variac to provide preset control, for the signal voltage supplied. to the tube 32 Will control the current. through the resistance 24. 1 v v In operation, as the Pirani bridge, 9, IO, U, |2 becomes unbalanced due to pressure conditions, the potential changes andcurrent. flows through the circuit including leads I l and the resistance in the input of tube 3|. The signals impressed upon the grid of tube 3| are amplified and impressed upon the input of thyratron 32 where they act to trigger the tube and cause current to flow in the anode circuit thereof including the load resistance 24. The thyratron 32 is so biased as to permit the grid to gain control after firing in response to signals. Pirani unbalance signals could be more easily amplified to a higher level by exciting the Pirani bridge with 60 cycle alternating voltage and using a transformer coupled high gain amplifier.

From the foregoing it will be apparent that gas flowing through feed line 4 enters the mass spectrometer source 3 and is ionized in the usual manner. The ions are pulled out from the source into the tube l by the usual accelerating potentials and in tube l they are acted upon by a magnetic field to cause them to travel in arcuate paths whose radii correspond to their respective masses. The pressure in tube l controls the flow of current through the Pirani gauge 1 and in turn this current controls the operation of the power source or electronic control circuit 8 for changing the current flow through the control valve 5, thereby changing the restriction of the orifice therein and the flow of gas through line 4 to the spectrometer.

Having thus described our invention, we claim:

1. A vapor flow control system of the character described comprising a mass spectrometer, a pressure responsive gauge within the spectrometer responsive to pressure conditions therein for producing signals, a power supply responsive to signals from said gauge for operation, and a flow control valve actuated by said power for. regulating the flow of vapor to said spectrometer.

2. A vapor flow control system of the character described comprising a chamber, means responsive to vapor changes in the chamber for producing electrical signals, a power source operated by said signals, and vapor flow control means responsive to heat energy supplied by said power source for regulating the flow of vapors to said chamber.

3. A vapor flow control system of the character described comprising a mass spectrometer, means responsive to changes in vapor content in said spectrometer for producing electrical signals, and vapor flow control means responsive to heat energy supplied by said power source for regulating the flow of vapors to said spectrometer.

4. A vapor flow control system of the character described comprising a chamber, means responsive to vapor content in communication with said chamber for producing signals, a source of heat energy responsive to said signals and a flow valve actuated by the heat energy from said source for regulating vapor flow to said chamber.

5. A vapor flow control system of the character described comprising a chamber, means responsive to vapor content in said chamber for producing electrical signals, a power supply controlled by said signals, and a flow valve closing in response to heat energy from said power source for regulating the flow of vapors to said chamber.

6. A vapor flow control system of the character described comprising a chamber, means responsive to pressure changes in the chamber for producing signals, a flow control valve responsive to changes in temperature for regulating the flow of vapors to said chamber, and a power source controlled by signals from said pressure responsive means for supplying power to said valve for controlling its temperature and operation.

7. A vapor flow control system of the character described comprising a chamber, a pressure gauge responsive to pressure changes in said chamber for changing its resistance and producing electrical signals, a power supply coupled to said gauge and controlled by signals therefrom, and a flow control valve operated by power supplied from said power supply for regulating the flow of vapors to said chamber.

3. A vapor flow control system of the character described comprising a chamber, an electrical bridge, means for altering the balance of the bridge to produce electrical signals, a power circuit fed by the bridge and responsive to signals therefrom for providing electrical energy, and a valve operated by an electrical heating element and fed by said power circuit for regulating the flow of vapors to said chamber.

9. A vapor flow control system of the character described comprising a chamber, a bridge network, means responsive to changes in vapor content of said chamber for altering the balance of the network to produce signals, means for amplifying said signals, means coupled to and controlled by the operation of said amplifying means for providing electrical power, means fed by said last means for converting electrical power into heat, and a valve operated in response to heat energy from said converting means for regulating the flow of vapors to said chamber.

10. A fluid flow control valve of the character described comprising an outer casing, an inner.

member smaller than the casing and having a difierent coeflicient of heat expansion than said casing disposed therein, and means for applying heat to said casing and said member for altering relative sizes to regulate the flow of fluid through the casing.

11. A flow control valve of the character described comprising a casing having a bore therein for the passage of fluids, an expansible element having a different coefficient of heat expansion than said casing disposed in said bore, and means for applying heat to said casing and said element to alter the relative sizes of the bore and expansible element to regulate the flow of the passage of fluid, a plug smaller than said bore and having a different coeflicient of heat expansion than said sleeve positioned in said bore, and an electrical resistance element disposed about the sleeve for applying heat to said sleeve and said plug for altering their relative sizes and regulating the flow of fluid through the bore.

WILSON W. WALTON. RICHARD C BOWERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,463,318 Schneider et al Mar. 1, 1949 2,564,175 Roper et a1. Aug. 14, 1951

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