US2998371A

US2998371A - Control system

Info

Publication number: US2998371A
Application number: US734322A
Authority: US
Inventors: Rolland C Sabins
Original assignee: A K LINDSAY; BRUCE DOHRMANN
Current assignee: A K LINDSAY; BRUCE DOHRMANN
Priority date: 1958-05-09
Filing date: 1958-05-09
Publication date: 1961-08-29
Anticipated expiration: 1978-08-29
Also published as: NL239003A; GB910460A; DE1160707B; US2982714A; NL121792C

Description

R. C. SABINS CONTROL SYSTEM Aug. 29, 1961 2 Sheets-Sheet 1 Filed May 9, 1958 INVENTOR. 20/49/70 C fab/715 ATTORNEYJ' R. C. SABINS CONTROL SYSTEM Aug. 29, 1961 Filed May 9, 1958 2 Sheets-Sheet 2 JNVENTOR. Pol/and C jab/n5 ATTORNE v5 2,998,371 CONTROL SYSTEM Rolland C. Sabins, 522 Catalina Blvd, San Diego, Calif.,

assignor of forty-five percent to Bruce Dohrrnann, San

Francisco, Calif, and ten percent to A. K. Lindsay,

Walnut Creek, Calif.

Filed May 9, 1958, Ser. No. 734,322 11 Claims. (Cl. 204196) This invention relates generally to a control system and method and more particularly to a control system and method for automatically providing cathodic protection for various types of structures, vessels and the like which are normally submerged in water or some solution which acts as an electrolyte.

As is well known, the current requirement to provide satisfactory protection is dependent upon many factors, as for example, the speed of movement of the hull through the water, temperature, and ionic content of the water through which the hull is moving, etc. Attempts to provide automatic control to take care of these variations have heretofore not been completely satisfactory. This, in large part, has been due to the fact that apparatus of this type must function for long periods of time without maintenance because a ship carrying the system may not return to its home port for months and even years. Automatic control is also complicated by the fact that the system must operate over a wide range of impressed currents. It must respond to very small control currents and must provide magnification of a very high order. There is a need for an automatic control system which will be suitable for use on large vessels and which will require very little, if any, maintenance.

In general, it is an object of the present invention to provide an improved control system and method which will automatically control the current impressed on the structure to be protected to maintain the structure at a predetermined polarization.

Another object of the invention is to provide a system of the above character in which the reference cell is periodically rejuvenated to its standard reference level.

Another object of the invention is to provide a system of the above character in which the reference current is utilized for operating a meter movement.

Another object of the invention is to provide a system of the above character in which the meter movement controls the flow of light to a light sensitive cell.

Another object of the invention is to provide a system of the above character in which the output of the light sensitive cell serves to control the means for impressing the current on the structure to be protected.

Another object of the invention is to provide a system of the above character in which the reference cells are provided in banks.

Another object of the invention is to provide a system of the above character wherein a reference cell of the bank is utilized for controlling the monitoring circuit, another is utilized for driving a visual indicating voltmeter and another is utilized for driving a recording type instrument.

Another object of the invention is to provide a system of the above character in which the reference cells are periodically rejuvenated in sequence.

Another object of the invention is to provide a system of the above character in which one reference cell of a plurality of reference cells is always connected to the monitoring circuit.

Another object of the invention is to provide a system of the above character in which the means for impressing current on the structure includes saturable core reactors.

Another object of the invention is to provide a system 2,993,371 Patented Aug. 29, 1961 of the above character in which the saturable core reactors can be paralleled to increase the impressed current flow.

Another object of the invention is to provide a system of the above character which has practically no moving parts and which requires. very little, if any maintenance.

Another object of the invention is to provide a system and method of the above character which utilizes a high order of magnification.

Another object of the invention is to provide a system and method of the above character with wide ranges of impressed current flow.

Another object of the invention is to provide a system of the above character in which the response is almost instantaneous and closely follows the demand.

Additional objects of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

FIGURE 1 is a circuit diagram incorporating the present invention with certain parts illustrated schematically;

FIGURE 2 is a portion of a circuit diagram for a system with a higher power output than that shown in FIGURE 1;

In general, the present invention comprises a control system and method for automatically providing cathodic portection for various types of structures such as the hulls of vessels and barges and like normally immersed or submerged in fresh or salt water or other electrolyte, A current is impressed on the structure to cause the structure to serve as a cathode. A monitoring circuit is provided in which a reference current is generated and this reference current is utilized for controlling the amount of current impressed on the structure to maintain the structure at a relatively constant predetermined polarization to prevent corrosion of the structure.

As shown in FIGURE 1 of the drawing, my control system comprises generally an impressed current power supply 11, monitoring means which includes a reference current supply and control 12 and means 13 for rejuvenating the reference current supply. The impressed current supply 11 is connected between an anode assembly 114 and a structure 16 to be protected which is represented as ground. The anode assembly 14 and the structure 16 are shown submerged or immersed in an electrolyte 17 which, for example, can be sea water. The structure to be protected can be the hull of a ship as shown and the anode assembly 14 can be of any suitable type such as that disclosed in my copending application entitled Electrolytic System, Serial No. 715,440, filed February 14, 1958.

The monitoring means 12 includes one or more reference cells 21 which are utilized for generating a reference current. As shown, the reference cells are also submerged in the electrolyte 17 and are generally mounted relatively close to the structure 16 to be protected. The reference cells can be of any suitable type such as the silver-silver chloride reference half cells well known to those skilled in the art. Such reference half cells have a potential in the electrolyte 17 which differs from the potential of the structure 16 when it is submerged in the electrolyte so that there is a current flow between the reference cells and the structure 16 to be protected. When reference cells of the silver-silver chloride type are utilized, the reference cells have a relatively uniform potential which is approximately 630 millivolts lower than that of a steel hull of a ship, if for example, that is the structure to be cathodically protected.

When the reference cell is connected by a conductor to the hull of the ship, current will flow through the electrolyte 17, from the hull of the ship to the reference half cell. By current flow, I am referring to the flow of electrons from negative to positive or rather a lower negative than the conventional designation of current flow from positive to negative.

As is well known to those skilled in the art, the silversilver chloride reference half cells have a relatively constant potential when immersed in an electrolyte and for that reason the current flow from the hull of the ship to the reference half cells will be dependent upon the polarization level on the hull of the ship or the structure being cathodically protected. When the polarization level of the ship is rising, the current flow between the hull of the ship and the reference half cells will increase, and conversely when the polarization level of the hull of the ship begins to fall, the current flow between the hull of the ship and the reference half cells will decrease.

The reference cells 21, as shown in the drawing, are connected to a timing device 23 for a purpose hereinafter described. As shown, and as hereinafter described, one of the reference half cells is normally connected by a conductor 24 to the positive terminal of a meter 26, the negative terminal of the meter being connected to ground as shown. As pointed out previously, all points designated as ground, are actually connected to the structure 16 to be protected as, for example, the ships ground when the hull of a ship is being protected. The meter 26 is of a suitable type such as a sensitive D.C. millivoltmeter. The meter 26 has a relatively high resistance in the order of 100,000 ohms per volt or more which prevents any appreciable reference current flow. This serves to prevent rapid polarization of the reference half cells which would otherwise occur if there were appreciable reference current flow. The silver-silver chloride reference half cells therefore serve as reliable references and only require depolarization as hereinafter described at periodic intervals.

The reference half cells 21 as shown in the drawing are designated as positive. This has been done because even though the reference cells are actually negative, they are less negative than a steel hull and thus are positive with respect to the steel hull or structure 16. The reference cells have been designated in this manner to facilitate understanding of the direction of current flow.

The meter 26, as shown schematically, includes a needle-like pointer or hand 27 which has a spade-like tip 28. The dial 29 of the meter is provided with a hole 31 which is adapted to be covered by the spade-like tip 28 of the pointer when the meter is indicating a midpoint position as shown in the drawing. A stop 32 is provided on the dial face to prevent the pointer from advancing beyond the midpoint of the dial. Since the meter 26 is connected in series between the reference half cells and the structure to be protected, it is apparent that the meter 26 will register the reference current flow between the structure 16 and the reference half cell 21 to which it is connected.

A suitable light source such as a lamp 34 is positioned on one side of the dial face 29, for example, as shown it is positioned in front of the dial face. The lamp 34 is connected to a suitable source of power such as 110 volts, 60 cycle single phase A.C. as designated by the terminals L1 and L2. As shown, the lamp is connected across the terminals L1 and L2 through a variable series resistor 36. The lamp 34 is preferably of a type with a very long life such as years. The resistor 36 is provided to vary the intensity of the light from the lamp.

Suitable light sensitive means 37 is mounted on the other side of the dial face opposite the opening or hole 31. For example, a polycrystalline photoconductive cell can be utilized. Particularly, a cadmium-selenide photo cell has been found to be especially satisfactory. The light sensitive means 37 is preferably mounted relatively close to the hole 31 and, for example, may be mounted within the meter housing itself if desired.

As shown, the output of the light sensitive means 37 is connected to a power reactor 39 in series with an ammeter 41. The ammeter 41 is of any suitable type such as a very sensitive D.C. microammeter. The power reactor 39 is of the saturable core type with duplex windings wound on a pair of toroidal cores. As shown, the reactor 39 comprises a pair of toroidal cores 42, a DC. saturating winding 43, a pair of A.C. or output windings 44, a DC bias winding 46, and a DC. shorted winding 47.

The shorted winding 47 is provided to prevent breakdown of the insulation within the power reactor 39 and to prevent damage to other components in the circuit hereinafter described. In the event the A.C. power to the A.C. ouput windings 44 should be suddenly interrupted, the sudden collapse of the lines of force in these coils would normally induce several thousand volts into the D.C. windings of the reactor and, therefore, would have a tendency to cause the damage hereinbefore described. However, the shorted coil which has a very low impedance prevents such an occurrence by shorting out the induced current and thereby preventing the build-up of dangerous voltages within the other windings of the reactor.

The bias winding 46 is wound in the opposite direction to that of the main saturating winding 43 and its purpose is to bias the output of the A.C. windings 44 to cut off when saturating current is not applied to the saturating windings. The bias winding 46 is supplied from the A.C. power supply designated by the lines L1 and L2 through a transformer 49 which has its output connected to a pair of suitable rectifiers 51. The rectifiers 51 are connected to one side of the bias winding 46 and the other side of the bias winding is connected to the centertap 52 of the secondary winding of the transformer 49 through a serially connected shunt resistance 53 and a variable resistance 54. An amrneter 56 of a suitable type, such as a DC microammeter, is connected across the shunt resistance 53. The variable resistance 54 is provided to adjust the flow of current in the bias winding 46. As is well known to those skilled in the art, the current How in the bias winding must be carefully adjusted so that the load from the output windings 44 is zero when the input to the DC. saturating winding is at zero.

As shown, one side of the output of the light sensitive means 37 is connected to one side of the DC. saturating winding 43 and the other side of the DC. saturating winding is connected to the center tap 52 of the secondary of the transformer 49. The other side of the output of the light sensitive means is connected to the side of the bias winding 46 which is connected to the rectifiers 51.

The output of the A.C. windings 44 of the reactor 39 is connected across a full wave bridge 59 comprising four rectifiers 61. The center tap 62 between the A.C. windings 44 is connected to the A.C. line L2 by a conductor 63. The other side of the rectifier bridge is connected to the A.C. line L1 by conductor 65.

The output from the full wave bridge 59 is supplied to the power reactor 64. The power reactor 64 comprises a pair of closed C-type cores 66, a pair of DC. saturating windings 67, four A.C. windings 68, a variable resistance 69 and a fixed resistance 71. The power reactor 64 is wound in such a manner that magnetic opposition is provided under all operating conditions and for that reason a bias winding of the type provided in the power reactor 39 is not required. A bias is also not used because the winding arrangement utilized in the power reactor 64 is not of a type which lends itself to the use of a bias winding. The windings and the core material have been chosen so that the output of the A.C. windings 68 is zero or substantially zero when there is no input to the DO. saturating windings 67.

The output of the full wave bridge 59 is connected across the serially connected D.C. saturating windings 67 of the power reactor 64 by

conductors

73 and 74.

An ammeter 76 is connected in a series with the conductor 74 and can be of any suitable type such as a DC. milliammeter.

It will be noted that the resistances 69 and 71 are serially connected across the

conductors

73 and 74 and in parallel with the DC. saturating windings 67. These resistances 69 and 71 have been inserted in the power reactor because it was found that the normal sinusoidal full wave D.C. output from the full wave bridge 59 would not cause proper operation of the DC. saturating windings 67. In fact, it was found that the saturating windings 67 were actually acting as a choke coil because of the back induced by the rapidly fluctuating sinusoidal full wave D.C. By utilizing the resistances 63 and 71 in parallel with the DC. windings, the resistances serve to bypass or cut oif the peaks of the sinusoidal output from the full wave bridge. Thus, the DC. peaks pass through the resistances and not through the DC. saturating windings. The rapid fluctuations of the DC. in the windings 67 and the generation of back are eliminated. it is apparent that capacitors could be utilized for the same purpose of smoothing out the DC. However, resistors have been chosen because they have much longer life. A pi type filter can also be used for such a purpose and can consist of iron core inductance and a pair of dry plate type capacitors.

The output of the power reactor 64 is fed into an A.C.-DC. rectifier section 78. As shown, the four A.C. windings of the power reactor are connected in series opposition and have one end connected to the A.C. or conductor 65 and the other end connected to the primary winding of an isolation transformer 79. The other side of the primary is connected to the line L2 of the A.C.

supply. The secondary of the isolation transformer is connected across a full wave bridge 81 comprising four rectifiers 82. The positive terminal of the output of the full wave bridge 81 is connected to the anode assembly 14 by a conductor 33, and the negative or ground terminal of the bridge is connected to the structure 16 by conductor 84. A DC. ammeter 86 is connected in series with the conductor 63. A DC. voltmeter 87 is connected across the output of the full wave bridge 81.

Operation of that portion of the system hereinbefore described may now be briefly described as follows: Let it be assumed that the millivoltmeter 26 has been adjusted by adjustment of its external resistance (not shown) so that at the desired polarization on the structure 16, the needlelike pointer 27 of the meter is at its midpoint position and the spade-like tip of the needle is covering the hole 31 in the dial face. The spade-like tip 28 in this position prevents the entrance of light rays through the hole 31 and therefore prevents activation of the light sensitive means 37. The pointer 27 in this position is against the needle stop 32 so that at increased polarization levels of the structure 16 above the desired polarization, no light can pass through the opening 31.

Now let it be assumed that the structure 16 has dropped below the desired level of polarization which is required for cathodic protection. When this occurs, the potential difference between the reference cells 21 and the structure 16 decreases, which in turn causes a decrease in the reference current flow in direct proportion to the decrease in the potential difference. The difference in the decrease in the current flow is registered by the meter 26 and the pointer 27 begins to move towards a decreased current position. As soon as the pointer 27 has moved from its midpoint position, the spade-like tip 28 exposes the hole 31 and permits light from the lamp 34 to enter the hole and activate the light sensitive means or cell 37.

Activation of the light sensitive cell 37 reduces its re-- sistance so that it permits substantial current flow in the D.C. saturating windings 43 of the power reactor 39. Current flow is from the center tap 52 through the DC. saturating winding 43, through the resistance of the light sensitive cell 37, through the microammeter 41 and to the positive side of the rectifiers 51.

The flow of current through the DC. winding 43 saturates the toroidal cores 42 to permit flow of A.C. current in the output windings 44, by eliminating the impedance in the output windings 44. The A.C. output from the windings 44 is rectified by the full wave bridge 5? and the DC. from the bridge is supplied to the DC. saturating windings 67 of the power reactor 64. The flow of DC. current in the saturating windings 67 saturates the cores 66 which reduces the impedance in the A.C. windings 68 to permit A.C. to pass through these power windings and to energize the isolation transformer 79. The A.C. output from the isolation transformer is rectified by the main full wave bridge 81 to deliver a positive DC. current to the anode array 14-. The negative terminal of the bridge 81 is connected to the structure 16 to be protected.

The increased potential difference between the structure 16-and the anode assembly 14- will cause increased current to flow from the structure 16 to the anode array by electrochemical exchange through the electrolyte 17. As the current flow increases, the polarization level of the structure 16 will increase. As the polarization of the structure 16 increases, the potential difference between the reference cells 21 and the structure 16 also increases. As this potential difference increases, the reference current flowing from the structure 16 to the reference half cells will also increase causing the millivoltmeter 26 to register an increase. This will continue until the spade-like tip 28 of the pointer 27 again covers the hole 31 in the dial 29.

From the foregoing description, it is apparent that as soon as the polarization level of the structure 16 drops below the predetermined desired level, the spade-like tip 23 will uncover the opening 31 to cause a sequence of operation which will increase the current flow between the structure 16 and the anode 14 until the increase is sufficient to raise the polarization level of the structure 16 to the desired level. Thus, the polarization level of the structure 16 is maintained relatively constant. If there are no changes in the polarization level, the spade-like tip 28 will cover the opening 31 and a relatively constant flow of current will occur between the structure 16 and the anode 14., When there are changes in the polarization level, the response of the system is almost instantaneous'and the polarization is rapidly built up to the desired level.

'As hereinbefore described, my system includes means 12 for continuously monitoring the polarization on the structure being cathodically protected. This monitoring means which has also been referred to as the reference and current supply has been previously described as including reference cells 21. It has been found that these reference half cells do not maintain an absolutely constant level of polarization, but that when they are subjected to various environments and are employed in a cathodeanode couple they gradually become negatively polarized. When this occurs, the reference cells fail to serve the function of a constant reference.

It has however been found that by periodically rejuvenating or depolarizing the reference half cell by reversing the cathode-anode couple arrangement at periodic intervals, the reference half cells are maintained at a relatively constant polarization level so that they can effectively monitor the polarization level of the structure to be protected. To that end, the means 13 has been provided for periodically rejuvenating the reference half cells and consists of a timing device 23, a transformer 91 and a rectifier assembly 32.

The timing device, as shown, consists of four collector rings 93 and a commutator 94. The collector ring 93 and the commutator 94 are mounted on the same shaft and are all driven at the same speed by the motor 96. The collector rings and commutator can be driven at any suitable speed as, for example, six revolutions per hour.

7 The motor 96 is connected to a suitable source of power such as the lines L1 and L2 which as hereinbefore described are connected to an A.C. supply.

As shown in the drawing, each of the reference half cells 21 is connected to one of the collector rings 93 by a brush 97. The brush 97 and the collector rings 93 are preferably formed of materials which have a relatively long life. For example, the collector rings can be made of silver and the brushes 97 can be of the silver-carbon type. The collector rings 93 are connected to a commutator 94. As shown, the commutator 94 is divided into four

segments

94a, 94b, 94c and 94d, each of which is connected to one of the collector rings 93.

Three brushes 98, 99 and 101 are provided which engage the commutator 94. Brush 98 is connected to the conductor 24 which is connected to the meter 26. Brush 99 is connected to the positive side of a rectifier assembly 92 and brush 101 is connected to a suitable recording instrument 103 by a conductor 104.

The rectifier assembly 92 consists of a pair of rectifiers 106 which are connected to the secondary of the transformer 91. A variable resistance 107 is connected between a tap on the secondary of the transformer 91 and ground. The primary of the transformer 91 is connected to a suitable source of AC. power such as the lines L1 and L2 as shown.

Operation of the rejuvenating means 13 may now be briefly described as follows: Let it be assumed that to cathodically protect the structure 16 that it is necessary to maintain the structure 16 at a predetermined polarization level with respect to the reference cells 21, as for example, 1000 millivolts. If such is the case, the resistance 107 of the rectifier assembly 92 is adjusted so that the rectifier assembly 92 will deliver 1000 millivolts on the conductor 13 through the timing device 23.

With the timing device 23, one of the reference cells 21 is always connected to the millivoltmeter 26 by the brush 98. As explained previously, when the reference cells 21 are connected to the structure being protected through the millivoltmeter 26, there is an electron flow from the structure being protected to the reference cells. After a cell has been utilized as a reference cell by being connected to the millivoltmeter 26, it is rejuvenated when it comes in contact with the brush 99. As hereinbefore explained, the brush 99 is connected to the positive side of the rectifier assembly 92. When the reference cell is connected to the positive voltage, the electron flow between the reference cell and the structure 16 being protected is reversed to restore the reference half cell to its original anodic state with respect to the structure being protected. By thus periodically applying a positive voltage to the reference half cells, the reference half cells are maintained in an anodic state and do not have an opportunity to become partially cathodic with respect to the structure being protected, as for example, the steel hull of a ship.

It should be pointed out that a positive voltage is applied to the reference half cell which is equal to the polarization level of the structure to be protected. This is done to prevent an over-voltage from being applied to the millivoltmeter 26. As pointed out previously, the millivoltmeter 26 has a mechanical stop 32 which prevents the indicating needle 27 from passing beyond or past the hole 31.

With the timing device 23 as shown in the drawing, each of the reference cells will be under the rejuvenating influence of the positive voltage from the rectifier assembly 92 for approximately 25% of the total elapsed time. After the rejuvenation is completed, the circuit to the reference half cell is broken and it is not used for approximately 25% of the elapsed time since only three brushes are provided in the timing device 23. During the time in which the reference cell is idle, the reference cell has an opportunity to stabilize itself. After this period of time, the reference cell is again engaged by the brush 98 and is connected to the millivoltmeter 26.

In large installations of my system, it may be desirable to provide means for continuously recording the polarization level of the structure being protected. To this end, I have provided a recorder 103 which is connected to the brush 101. The brush 101 is always in engagement with one of the segments of the commutator 94 and, therefore, provides a continuous signal to the recorder 103. The recorder 103 can be of any suitable type such as those which utilize a moving pen to give a written indication on a continuously moving strip chart.

With the system hereinbefore described, one of the reference half cells 21 is always connected to the millivoltmeter 26 to provide continuous monitoring for the system. However, if it is desired to simplify the system to reduce the cost, or for other reasons, it is possible to use only one reference cell 21 for operation of the millivoltmeter 26. With such a system, the reference half cell could be periodically disconnected from the meter for a sufficient period of time and connected to the positive voltage of the rectifier assembly 92 by a simple timing device to rejuvenate the half cell. After rejuvenation is completed, the reference cell could again be connected to the meter 26. During the short period of time the reference half cell is being rejuvenated, the polarization of the ship would be allowed to decrease. This is not objectionable because of the short period of time required for rejuvenation of the half cell, as for example, one minute out of every hour.

By way of example, one embodiment of my system utilized components having the following designations, values and characteristics.

Diodes:

51 1N1084. 61 1N1092. 82 1N1167and1N1181. 106 1N1084.

Photocell 37 Clairex type CL-3. Transformers 49 110 volts to 25 volts. 91 w 110 volts to 25 volts. 79 1:1 ratio, 1000 watt capacity. Saturable core reactors:

39 Output of 500 milliamperes. -64 1000 watt capacity. Meters:

26 0-300 maximum millivolts adjustable. 41 0-500 microamperes. 56 0-1 milliampere, shunted to obtain desired milliampere range. 76 0-500 microamperes. 87 0100 volts. 86 0-100 amperes. Resistances:

36 Wire wound, ohms. 54 Wire wound, 1000 ohms. 69 Wire wound, 500 ohms. 71 Wire wound, 25 ohms. 107 Wire wound, 1 megohm.

It has been found that a system having the above components has ample capacity to provide complete cathodic protection for a ship feet in length with a steel hull, and having approximately 5000-6000 square feet of wetted surface. With the 1000 watts available from such a system, the ampere voltage ratio is automatically determined by the ratio of the surface of the anode assembly 14 utilized and the wetted surface of the structure to be protected, and the resistivity of the water or electrolyte. Thus, if a 1:1 isolation transformer 79 is utilized and the isolation transformer is driven from a 115 volt, 60 cycle, single phase A.C. supply and the power reactor 64 is being driven at its full 1000 watts output, the DC. voltage on the output read by the meter 87 would be approximately 20 volts and the amperes read by the meter 86 would be approximately 50 amperes, as

suming that the proper amount of anode surface was utilized to obtain the proper anode-cathode ratio, and also assuming that the structure is in water having a relatively high resistance. If the structure were a vessel operating in the equatorial zones in warm water with low resistivity, the DO. voltage might be as low as 10 volts with 100 amperes D.C.

With a system of the above type having an output of 1000 watts, an amplification of two hundred million to one is achieved by only two stages of amplification as represented by the

reactors

39 and 64. The reference cells have an output of approximately 10 microwatts. Only one-half of the output, microwatts, is utilized for driving the meter 26. These 5 microwatts are amplified into the 1000 watts in the output to give the two hundred million to one power amplification.

Since the current flow from the structure being protected such as the hull of a ship to the anodes l4 determines the polarization level of the structure being protected, it is important that a wide range of current flow be obtainable from any satisfactory system. Generally, it is desirable to obtain a 50 to 1 variation in current flow. With my system, it has been found possible to obtain a 100 to 1 variation in the current flow.

I have found by utilizing the light sensitive cell 37, precise control can be obtained on the polarization level of the structure being protected. If the polarization level of the structure being protected should drop only a very slight amount below the desired level, the system immediately determines this condition and responds practically instantaneously to increase the current flow from the impressed current means. The system is instantly cognizant of any changing conditions which may require increased or decreased current flow, as for example, in the case of a vessel which is passing through water which has different resistance characteristics than that previously passed through.

In the event additional power output is required in a system for cathodic protection, my system can be easily modified to make more power available. For example, as shown in FIGURE 2 of the drawing, the output of the power reactor 64 can be utilized for supplying the DC. saturating current for additional reactors. For example, as shown, the output of the reactor 64 can be passed through a full wave bridge 111 consisting of four rectifiers 112 connected in a conventional manner. The output of the bridge 111 is connected to the DC. saturating coils 67 of a pair of power reactors 64 identical to the power reactor hereinbefore described. The power reactors are connected in parallel as shown and have their outputs connected to an A.C.-D.C. rectifier section 1% similar to section 78, but of a larger size.

The remainder of the system would be identical to that shown in FIGURE 1 and for that reason it has not been shown in FIGURE 2.

Thus, it is apparent that any range of power requirements can be obtained with my system with the use of many standardized parts. For example, the system as shown in FIGURE 2, with the power reactor 64 connected in parallel, would have a D0. power output of 42,500 watts which would be controlled by the 5 microwatts output from the reference cells 21. Thus, with such a system, an amplification of eighty-five billion to one can be obtained with three stages of amplification without any sacrifice in the quality of control.

It is apparent from the foregoing that I have provided a completely automatic control system and method for maintaining a desired polarization level on a structure to be cathodically protected. There are no moving parts in the system except for the slowly moving parts in the timing device 23 and in the meter movements which have an extremely long life. Thus, in contrast to other systems, my system has no mechanical relays, contact points, servo mechanisms, variacs or other moving parts which would require extensive and continued maintenance. By utilizing saturable core reactors, magnifications of a high order are obtained by devices which have a relatively long life and require no maintenance. By utilization of the light sensitive means, a particularly precise control is obtained which has an almost instantaneous response and which closely follows the demand on the system. Such performance coupled with the lack of maintenance is particularly important in systems of this type which are often installed in large ships which may not return to their home ports for long periods of time. If this were not the case, a breakdown of the system while the ship was out of port could permit severe damage to occur to the hull of the ship before the system could again be placed in operation.

It is also apparent that in addition to being useful for the cathodic protection of the hulls of ships, barges and other floating vessels my system can be used for cathodically protecting other structures such as underwater foundations, pipelines, storage reservoirs, and the like.

While the form of embodiment herein shown and described constitutes a preferred form, it is to be understood that other forms may be adopted falling within the scope of the claims that follow.

I claim:

1. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte, saturable core reactor amplification means connected to said anode and said structure to impress a current fiow between the anode and the structure to cause the structure to serve as a cathode, and reference means immersed in the electrolyte, the reference means having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected so that there is a reference current flow between the structure and the reference means, a meter having a pointer and an opening adapted to be closed by the pointer, said meter being responsive to the reference current flow between the structure and the reference means, a light source adapted to shine through the opening of said meter and being in a position on one side of said pointer, light sensitive means positioned on the other side of said pointer and being adapted to receive light passing through said opening, said meter being calibrated and said opening in the meter being positioned so that at a predetermined flow of reference cunrent said pointer overlies said opening and prevents the passage of light through said opening, and means connected to said light sensitive means for regulating said means for impressing current flow between the anode and the structure.

2. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte, means connected to said anode and said structure to impress a current flow between the anode and the structure to cause the structure to serve as a cathode, said means including a pair of saturable core reactors, reference means immersed in the electrolyte, the reference means having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected so that there i a reference current flow between the structure and the reference means, and means responsive to the reference current flow between the reference means and said structure to regulate said means for impressing current flow between the anode and the structure to maintain a relatively constant predetermined polarization potential on said structure.

3. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte, means connected to said anode and said structure including a saturable core reactor amplification means to impress a current flow between the anode and the structure to thereby cause the structure to serve as a cathode, reference means disposed in the electrolyte, the reference means having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected so that there is areference current flow between the structure and the reference means, and means responsive to the reference current flow between the reference means and said structure and connected to said means for impressing current flow between the anode and the structure to regulate the means for impressing current flow to maintain a relatively constant predetermined polarization potential on said structure, said last named means including light sensitive means having a relatively high resistance when no light is being received and a relatively low resistance when light is being received.

4. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte, means connected to said anode and said structure including saturable core reactor amplification means to impress a current flow between the anode and the structure to thereby cause the structure to serve as a cathode, reference means disposed in the electrolyte, the reference means having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected so that there is a reference current flow between the structure and the reference means, and means responsive to the reference current flow between the reference means and said structure and connected to said means for impressing current flow between the anode and the structure to regulate the means for impressing current flow to maintain a relatively constant predetermined polarization potential on said structure, said reference means comprising a plurality of reference cells together with means for continuously connecting one of said cells to said means responsive to reference current flow, and means for periodically depolarizing each of said cells when it is not connected to said means responsive to reference current flow.

5. A control system as in claim 2 wherein one of said saturable reactors utilizes a pair of toroidal shaped cores and the other of said reactors utilizes a pair of C-type cores.

6. A control system as in claim 5 wherein the other of said reactors is provided with a DO saturating winding and filtering means in parallel with the saturating winding.

7. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte, means connected to said anode and said structure to impress a current fiow between the anode and the structure to cause the structure to serve as a cathode, a plurality of reference cells, the reference cells having a relatively constant potential in the electrolyte which differs from the potential of said strcture to be cathodically protected so that there is a reference current flow between the structure and each of the reference cells when a circuit is established between each of the reference cells and the structure, a light source, light sensitive means positioned adjacent said light source, means responsive to the reference current flow for interrupting the passage of the light beam from the light source to the light sensitive means, means responsive to said light sensitive means for regulating said means for impressing current flow between the anode and the structure to maintain a relatively constant predetermined polarization potential on said structure, and a timing device for periodically and sequentially connecting said reference cells of said means responsive to reference current flow.

8. A control system as in claim 7 wherein said timing device includes a plurality of slip rings, each of said reference cells being connected to one of said slip rings, a commutator formed of a. plurality of segments, each of said collector rings being connected to one of said segments, and brush means for engaging said segments one at a time to supply reference current to said means responsive to reference current flow, and means for driving said collector rings and said commutator in synchronization.

9. A control system as in claim 8 together with additional brush means spaced from said first named brush means and adapted to engage the segments of said commutator, and a source of positive DC. voltage connected to said additional brush means to depolarize the reference cells as they come into electrical contact with said additional brush means.

10. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte, means connected to said anode and said structure to impress a current flow between the anode and the structure to cause the structure to serve as a cathode, reference means immersed in the electrolyte and connected to the structure, the reference means having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected so that there is a reference current flow between the structure and the reference means through the electrolyte and means responsive to the reference current flow between the reference means and said structure to regulate said means for impressing current flow between the anode and the structure to maintain a relatively constant predetermined polarization potential on the structure, the reference means comprising a plurality of reference cells together with means for continuously connecting one of said cells to said structure and means for periodically depolarizing each of said cells when it is not connected to said means responsive to reference current flow.

11. In a control system for cathodically protecting a structure immersed in an electrolyte, an anode immersed in the electrolyte, means connected to said anode and said structure to impress a current flow between the anode and the structure to cause the structure to serve as a cathode, reference means continuously immersed in the electrolyte and constantly connected to the structure, the reference means having a relatively constant potential in the electrolyte which differs from the potential of said structure to be cathodically protected so that there is a reference current flow between the structure and the reference means through the electrolyte, and means responsive to the reference current flow between the reference means and said structure to regulate said means for impressing current flow between the anode and the structure to maintain a relatively constant predetermined polarization potential on said structure, the reference means comprising a plurality of reference cells, means for sequentially connecting and disconnecting said cells to said structure and means for sequentially depolarizing said cells when not connected to said structure.

References Cited in the file of this patent UNITED STATES PATENTS 2,221,997 Polin NOV. 19, 1940 2,759,887 Miles Aug. 21, 1956 2,765,986 Pompetti et al. Oct. 9, 1956 2,918,420 Sabins Dec. 22, 1959 FOREIGN PATENTS 669,675 Great Britain Apr. 9, 1952 OTHER REFERENCES Anal. Chem, vol. 23, pages 941-944, July 1951, De Ford.

Corrosion, vol. 13, May 1957, pp. 8-74, art. by Werner.

Claims

1. IN A CONTROL SYSTEM FOR CATHODICALLY PROTECTING A STRUCTURE IMMERSED IN AN ELECTROLYTE, AN ANODE IMMERSED IN THE ELECTROLYTE, SATURABLE CORE REACTOR AMPLIFICATION MEANS CONNECTED TO SAID ANODE AND SAID STRUCTURE TO IMPRESS A CURRENT FLOW BETWEEN THE ANODE AND THE STRUCTURE TO CAUSE THE STRUCTURE TO SERVE AS A CATHODE, AND REFERENCE MEANS IMMERSED IN THE ELECTROLYTE, THE REFERENCE MEANS HAVING A RELATIVELY CONSTANT POTENTIAL IN THE ELECTROLYTE WHICH DIFFERS FROM THE POTENTIAL OF SAID STRUCTURE TO BE CATHODICALLY PROTECTED SO THAT THERE IS A REFERENCE CURRENT FLOW BETWEEN THE STRUCTURE AND THE REFERENCE MEANS, A METER HAVING A POINTER AND AN OPENING ADAPTED TO BE CLOSED BY THE POINTER, SAID METER BEING RESPONSIVE TO THE REFERENCE CURRENT FLOW BETWEEN THE STRUCTURE AND THE REFERENCE MEANS, A LIGHT SOURCE ADAPTED TO SHINE THROUGH THE OPENING OF SAID METER AND BEING IN A POSITION ON ONE SIDE OF SAID POINTER, LIGHT SENSITIVE MEANS POSITIONED ON THE OTHER SIDE OF SAID POINTER AND BEING ADAPTED TO RECEIVE LIGHT PASSING THROUGH SAID OPENING, SAID METER BEING CALIBRATED AND SAID OPENING IN THE METER BEING POSITIONED SO THAT AT A PREDETERMINED FLOW OF REFERENCE CURRENT SAID POINTER OVERLIES SAID OPENING AND PREVENTS THE PASSAGE OF LIGHT THROUGH SAID OPENING, AND MEANS CONNECTED TO SAID LIGHT SENSITIVE MEANS FOR REGULATING SAID MEANS FOR IMPRESSING CURRENT FLOW BETWEEN THE ANODE AND THE STRUCTURE.