US2265590A

US2265590A - Electric valve control system

Info

Publication number: US2265590A
Application number: US165463A
Authority: US
Inventors: Winograd Harold; Samuel R Durand
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1937-09-24
Filing date: 1937-09-24
Publication date: 1941-12-09
Anticipated expiration: 1958-12-09

Description

Dec. 9, 1941. H. WINOGRAD ETAL ELECTRIC VALVE CONTROL SYSTEM 4 Sheets-Sheet 1 Filed Sept. 24, 19-37 H. WINOGRAD ETAL ELECTRIC';VALVE CONTROL SYSTEM Dec. 9, 1941;

Filed Sept. 24, 1937 4 Sheets-Sheet 2 Dec. 9, 1941. I H. WINOGRADET AL 2,265,590

ELECTRICVALVE CONTROL SYSTEM Filed Spt. 24, 1957 4 Sheets-Sheath Dec. 9, 1941.

I H. WINOGRAD ETAL ELECTRICtZVALVE CONTROL SYSTEM- Filed' Sept. 24, 1937 4 Sheets-Sheet 4 Patented Dec. 9, 1941 Harold Winograd and Samuel R. Durand, Milwaukee, Wis., assignors, to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application September 24, 1937, Serial No. 165,463

8 Claims. 177-311) This invention relates in general to improvements in electric valve control systems and more particularly to a system for observing the value of the voltage drop between the electrodes of an electric valve and for controlling th operation of the valve in response to the value of the voltage drop therein.

Electric valves of several types are known which have the common characteristic of requiring impression of a voltage of material value between the electrodes thereof for producing a flow of current between the electrodes. The voltage appearing at the electrodes, during the flow of current therebetween, also called the voltage drop in the valve, may vary relatively little from no load to full load as in valves of the vapor type or may vary substantially in proportion to the flow of current through the valve as in valves of the high vacuum type. In both of the above types of valves the magnitude of the Voltage drop remains within predetermined limits during normal operation of the valve and any departure of the voltage drop from the normal range of values thereof is an indication of disturbance in the operation of the valve. It is therefore desirable to obtain an indication of the value of the voltage drop andeven to provide means responsive to this value for controlling the operation of the valve.

If the valve is subjected to an alternating voltage and therefore carries intermittent current, the indication is preferably obtained by means of a voltage responsive device connected between the electrodes of the valve through an auxiliary electric valve to render the device responsive to unidirectional voltages only. The same auxiliary valve or another auxiliary valve serially connected therewith is then preferably controlled to limit the period of response of the device to any desired interval.

necessary to limit the response of the measuring device to periods including less than the entire periods of current flow between the electrodes, which periods may however generally extend beyond the end of the periods of current flow. This result is preferably obtained by controlling the conductivity of the auxiliary valve by an alternating voltage obtained from a circuit intervening in the operation of the main valve, or in response to the flow of current between suitably chosen electrodes of another valve associated with the main valve.

It is therefore one of the objects of the present invention to provide a control system for an electric valve responsive to the value of the voltage drop present between two electrodes of the valve during substantially the entire conductive period thereof.

Another object of the present invention is to provide a device responsive to the voltage drop between two electrodes of a valve during a portion of the period of current flow therethrough and unresponsive to the voltage drop between the electrodes during other periods. 7

Another object of the present invention is to provide a device responsive to the voltage drop between two electrodes of a valve during periods comprising less than the entire period of current flow between the electrodes.

Objects and advantages other than those above described will be apparent'from the following description when read in connection with the accompanying drawings, in which:

When the main valve is of the vapor type in which the flow of current is delayed by means of a control electrode, each conductive period of the valve, during which the voltage drop between two electrodes is to be measured, is preceded by a period during which the voltage be- Fig. 1 diagrammatically illustrates one embodiment of the present invention in which an indicating device is connected between two electrodes of the main electric valve through an auxiliary vapor valve controlled from the control transformer of the main valve through a phase shifting circuit;

Fig. 2 diagrammatically illustrates a modified embodiment of the present invention in which the control transformer is connected with the auxiliary vapor valve through a voltage divider;

Fig. 3 diagrammatically illustrates another modified embodiment of the present invention in which the auxiliary vapor valve associated with one main valve is controlled from a current transformer inserted in circuit with another valve forming part of the system; and i Fig. 4 is a diagram illustrating the operation of the embodiments illustrated in Figs. 1 to 3.

Elements performing the same functions in the several embodiments shown are designated therein by the same reference characters; 'It

'but which preferably comprises a plurality of electric valves generally designated by 8. Each valve '8 is provided with electrodes comprising an anode and a cathode connected with circuits 6 and I for the flow of current between the circuits through the valve. The anodes such as 9 of the valves are preferably arranged within a common casing and the cathodes of the valves may then be combined into a single cathode structure I I preferably comprising a pool of mercury. Suitable means (not shown) are provided for bringing cathode II into electron emitting condition and for maintaining the cathode insuch condition as is well known.

The anodes are severally connected with the phase portions'of the secondary winding l2 of a supply transformer I3 having a primarywinding I4 connected with circuit 6. Winding I2 is con nected in star to provide at least one neutral point connected with one of the conductors of circuit 1, and the other conductor of circuit 1 is connected with cathode II. The operation of valves 8 may be controlled by means comprising a switch I6 inserted in the connection between winding I4 and circuit 6. Switch I6 is urged towards the; open position by means of a spring I! and, after being closed manually, may be retained in the closed position by means of a latch I8. The latch may be withdrawn by the action of a trip coil I9 upon connection of the trip coil with a suitable source of electric current.

The operation of valves 8 may be further con: trolled by means of control electrodes such as 2I severally associated with the anodes for controlling the conductivity of the valves. The control electrodes are diagrammatically illustrated in the drawing as grids each arranged in or about the path of the discharge occurring between the associated anodes and cathode II, but it will be understood that other type of control electrodes may be utilized. In particular, the control electrodes may be of the cathode spot igniting type if the valves are provided withindividual mer cury cathodes.

Valves 8 are assumed to be of the discontinuously controllable or vapor type in which each control electroderprevents the flow of cur- The connected with cathode II through circuits each comprising a current limiting resistor 22 and one of the phase portions of a source of alternating current such as the star connected secondary winding 23 of a control transformer 24. The primary winding 26 of transformer 24 is energized'from circuit 6. Winding 23 is connected in star to provide a neutral point which is preferably connected with cathode II through suitable means for impressing a unidirectional voltage (potential difference) component on the control electrodes, such as a direct current generator or a voltage divider 21 connected between the conductors of circuit 1. The tap of the voltage divider is connected with the neutral point of winding 23 and may also be connected with cathode II through a capacitor 28 to render the potential of the tap substantially uniform.

The above described rectifying system is provided with a device for measuring the voltage drop between two electrodes of valves 8 comprising a voltage responsive device such as a milliammeter 29 responsive to the voltage present between the electrodes and with means for limiting the response of the device to periods comprising less than the entire period of current flow between the electrodes considered. The latter result is obtained by the use-of means serially connected with meter 29 for controlling the response of the meter in dependence upon the voltage cycle of circuit 6. 'In the embodiment illustrated in Fig. 1 meter 29 is directly connected with cathode I I and is connected with another one of the electrodes of valves 8, such as anode 9, through a measuring circuit comprising a current limiting resistor 3|, the electrodes of an auxiliary electric valve of any suitable type such as a thermionic valve 32 of the two electrode high vacuum type, another electric valve 33 and a resistor 34. Meter 29 and resistor 34 are bridged by a capacitor 35 to render meter 29 responsive to the peak value of the voltage drop between device comprising a reactor II and a resistor 42,

the secondary winding of a transformer 43 and a current limiting resistor 44. The primary winding of transformer 43 isenergized from circuit 6 and is preferably connected therewiththrough transformer 24 which thus impressesalternating voltages from circuit 6 between control electrode 2I and cathode II and also between control electrode 38 and cathode 37.

For controlling the operation of switch I6 in response to the voltage between anode 9 and cathode II, a portion of resistor 34 is inserted in series with a battery 45 in the control circuit of a third auxiliary thermionic valve 46 of the three electrode high vacuum type. The anode and the cathode of valve 46 are connectedin series withra battery 41 and the coil of a relay 48. Relay 48 is preferably of any type operable to close its contacts at a predetermined time interval after energization of the relay coil. The contacts of relay 48 are connected in series with trip coil I9 and with a source of current such as a battery 49.

The operation of the system. will be considered assuming that circuit 6 is energized at a substantially sinusoidal voltage of predetermined frequency and that rectified current is to be delivered by the systemto a load device (not'shown) connected with circuit 1. It will be understood, however, that the voltage measuring system herein disclosed may also be utilized when valves 8 are used for converting direct current; from circuit 1 into alternating current to. be supplied to circuit 6, or in connection with any other circuit I employing valves.

When it is desired to put valves 8 into operation, the cathode I I is first brought into electron emitting condition by ignition of an auxiliary are maintaining a cathode spot thereon, as is well known. Switch I6 may then be closed and the voltages impressed from circuit 5 on the phase portions of winding I4 induce corresponding voltages in the associated phase portions of winding I2 to bring the anodes of valves 8 sequentially to a positive potential with respect to the potential of cathode H. When an anode has assumed a positive potential, the flow of current therethrough is prevented as long as the associated control electrode remains at a negative potential. At the instant that a positive potential is impressed on this control electrode by the joint action of winding 23 and of voltage divider 21, the flow of current through the anode considered is initiated and continues until the transfer thereof to another anode. The successive anode current impulses thus produced combine at cathode II to form a flow of substantially uniform direct current as is well known in the art.

The sequence of operation of the anodes is illustrated in Fig. 4 in which a sinusoidal curve 5| represents the potential of anode 9 with respect to the potential of the neutral point of winding I2. The potentials of the other anodes are represented by other curves similar to curve 5I and displaced in phase with respect thereto, of which only the positive portions are illustrated to simplify the drawings. Curve 52 representing the output voltage of the rectifying system. consists of a series of consecutive portions of curves differing from. the curves representing the anode potentials by an amount equal to the voltage drop material distortion of the quantities represented a by the curves.

In the course of the voltage cycle, the voltage between anode 9 and cathode I I becomes positive at the moment represented by point A, be-

comes negative at point B, and again becomes positive at point C. During this portion of the cycle, control electrode 2| associated with anode 9 is at a negative potential and prevents the. flow of current through anode 9. At a predetermined moment depending upon the adjustment of voltage divider 21 and represented by point D, control electrode 2| becomes positive and releases the flow of current through anode 9'. The voltage between anode 9 and cathode II accordingly decreases from the value DE to a lower value FG, which is the value of the voltage drop to be measured, and which may be considered as being constant to simplify the explanation of the operation of the system. The flow of current through anode 9 continues up to point 1-! at which the current is transferred from anode 9 to another anode of valves 8.

It has been found, however, that the voltage between an anode and the cathode requires a material time interval to decrease from the value DE to. the value FG. For example, in a large steel tank rectifier in which the voltage drop is normally of the order of magnitude of 25 volts, a, voltage drop higher by approximately 8 volts has been measured within one electrical degree following the release of the flow of. current at point D. If the voltage drop between anode 9 and cathode I I were measured by a device responsive duringthe entire interval DH, the result obtained therewith would be higher than the value FG: tov be measured.

To obviate the foregoing disadvantage, meter 29 is connected in a circuit in which valve 32 permits the flow of current only when anode 9 is at a positive potential and in which valve 33; permits the flow of current only during predetermined time intervals. It will be understood that valve 33, being of the vapor type, is. controlled similarly to valves 8 and becomes conductive only when control electrode 38 is positive with respect to cathode. 31. The latter con dition obtains whenever the alternating potential component impressed on control electrode 38 from transformer 43 and the potential component impressed on the control electrode from battery 39' add up to a positive value.

The phase of the alternating potential component of control electrode 38 may be adjusted by means of resistor 2 to vary the moment of initiation of the conductive period of valve 33. This conductive period may thus be caused. to begin at any point of the cycle following point D. For example, a conductive period FL may be chosen comprising a period FH less than the entire period DH of current flow between anode 9 and cathode II. During period FH the voltage drop in the valve 3 considered remains substantially constant and current flows from the portion of winding I2 associated with anode 9 through resistor 3|, valve 32, valve 33 and capacitor 35 to charge the capacitor to a voltage of value depending on the value of the voltage drop in the valve 8 considered. The voltage of capacitor 35 is thus a measure of the arc drop in the valve and is read on meter 23 which is calibrated by substituting a series of known voltages for the arc drop in valve 8 in the measuring circuit. Resistor 34 is of such high value that the flow of current therethrough does not materially dischargecapacitor 35 between successive intervals FH of successive cycles of the voltage of circuit 6. During interval HL, although the valve 33 is conductive the measuring circuit does not respond to the voltage between anode 9 and cathode II by reason of the unilateral conductivity of

valves

32 and 33. The voltage impressed on the measuring circuit may then be of considerable magnitude, and while the maximum voltage which may be impressed on a valve of the vapor type, such as valve 33, in the non-conductive direction thereof is limited in value, the addition of a suitable high vacuum valve 32 in series there with permits the measuring circuit to withstand any desired voltage. It will be understood that by adjustment of resistor 42' the period of current flow through valve 33 may also be advanced to begin shortly after point D to measure the peak voltage of the voltage drop in valve 8' during interval DE, or even to begin before point D to measure the value of voltage DE. The voltageimpressed on capacitor 35 during the conductive period of valve 33 is then no longer substantially constant but'the capacitor is always charged at the peak value of the voltage impressed thereon and remains charged at that voltage during the remainderof the conductive period of. valve 33 by reason of the unilateral conductivity of

valves

32 and 33.

Regardless of the adjustment of the voltage impressed between control electrode 38 and cath ode 31, valve 33 ceases tocarry current at point H of the reversal of the voltage impressed on the measuring circuit. Valve 33 is thus without current at point L, at which point control electrode 38 again assumes a negative potential to render valve 33 non-conductive up to point F of the following cycle.

During the above described operation, the potential impressed on the control electrode of valve 46 from battery 45 and from resistor 34 is of such sign and magnitude as tomaintain valve 46 substantially non-conductive. If the voltage drop in valves 8 increases beyond a predetermined value, the potential of the grid of valve 46 is rendered more positive by a sufficient amount to cause valve 46 to carry a current capable of actuating: relay 48. If the voltage drop in valves 8 remains above the predetermined value for a sufficient length of time, relay 48 closes the contacts thereof to cause trip coil I9 to receive current from battery 49. The trip coil releases latch I8 and switch I6 opens under the action of spring II to disconnect valves 8 from circuit 6.

Although the measuring circuit is illustrated and described as being connected between anode 9 and cathode II, it will be understood that the circuit may also be connected between any two electrodes of valves 8 to measure the maximum unidirectional voltage therebetween during predetermined periods.

In the embodiment illustrated in Fig. 2 the measuring circuit comprises, in addition to meter 29, valve 33 and resistor 34, a battery 54 and the anode 55 and cathode 56 of a valve 51 of the three electrode high vacuum type. The negative terminal of battery 54 is directly connected with cathode ,II and the control electrode 58 of valve 51' is connected with anode 9 through a resistor 59. Transformer 43 is energized from a polyphase voltage divider 6| connected with the different terminals of winding 23. Switch I6 and the control means therefor, which are omitted from Fig. 2, may beconnected therein in the manner illustrated in Fig. 1 if desired.

In the present embodiment, valve 33 may again be considered as rendered conductive at point F, but in the absence of battery 39, which is omitted to simplify the system, valve 33 remains con-ductive for an interval FM equal to one-half cycle of the voltage of circuit 6. During portion FH of interval FM, control electrode 58 is maintained at the potential of anode 9 and thus causes valve 51 to be conductive to a predetermined extent. Valve 51 carries current supplied thereto from battery 54 which causes a voltage drop proportional thereto in meter 29 and resistor 34 and a substantially constant voltage drop in valve 33. The potential of cathode 56 is thereby raised to approach the potential of anode 55 with the result that the potential of control electrode 58 is lowered relatively to the potential of cathode 56. The relative lowering of the potential of con-' trol electrode 58 causes the conductivity of valve 51 to decrease and a state of equilibrium is reached wherein the conductivity of valve 51 corresponds to the value of the flow of current therethrough. The flow of current through valve 51 is pulsating, being established only during interval FH of each cycle of the voltage of circuit 6, and if the frequency of the pulsation is sufficiently high meter 29 gives a steady indication of a value proportional to the average value of the voltage drop in valve 8 during interval .EH

and also proportional to the length'of interval Voltage divider 6| is preferably utilized when it is desired to rapidly measure the voltage drop through the different valves 8 in succession. Resistor 59 is then successively'connected with the different anodes of valves 8 and voltage divider BI is adjusted to impress a voltage of the proper phase on transformer 43 for each reading. It will be understood that meter 29 and resistor 34 may also be associated witha capacitor 35 of the embodiment illustrated in Fig. 1 to measure the peak value of the voltage drop in the different valves.

. In the embodiment illustrated in Fig. 3, winding I2 is assumed to be connected to provide two neutral points connected with one of the conductors of circuit I through an interphase transformer 82. As is well known, the result of this arrangement is to double the length of the conductive period of each valve 8, and the voltage between anode 9 and cathode II then follows a curve such as curve 63 in Fig. 4. The response of valve 33 to the voltage drop between electrodes 9 and I I is then preferably controlled in response to the flow of current through another electrode of the valves, namely anode I3 operating during interval NP. For this purpose, resistor 44 may be connected with cathode 31 through a double throw switch 64 and through the secondary winding of a current transformer 65 having a primary winding serially connected with anode I 0. The secondary winding is preferably bridged by a resistor 66 to prevent the voltage across the current transformer from reaching an excessive value when switch 64 is opened or when it is closed to make contact with resistor '44 and cathode 31. When the measuring system is not being used, switch 64 may be reversed to short circuit the secondary winding of current transformer 65. The voltage between anode 9 and cathode I I may be impressed on a measuring circuit, similar to that utilized in Fig. 1, through a double throw switch 61. In the present embodiment, however, valve 2 is replaced by a valve of. the four electrode high vacuum type 68 which has been found more advantageous than valve 32. Resistor 3| is connected with the control electrode or grid 69 of valve 63 which is utilized as an anode. The screen grid II of valve 68 is connected with the associated cathode I2 through a source of direct current such as a battery I3. A continuous discharge is thus maintained through valve 68 and the emission of cathode I2 is thus stabilized even when the measuring circuit carries current of such small magnitude as to only sustain an unstable emission at cathode I2. The measuring circuit may also be connected through switch 61 with a calibrating circuit comprising a source of direct current such as a battery I4, a'voltage divider I5, and a voltmeter I6.

To measure the voltage drop between anode9 and cathode I! switches 64 and 61 are moved to the right. The voltage drop is then impressed on the measuring circuit as in the embodiment illustrated in Fig. 1. During operation of valves 8, anode Ill carries current impulses each of duration equal to approximately one-third of the cycle of the voltage of circuit 6 during interval NP of each cycle. The anode current induces in the windings of current transformer 65, a voltage of substantially rectangular wave form which is impressed between control electrode 38 and cathode 3'! in such sense that control :-electrode 38 isthereby maintained at a positive potential with respect to cathode 3-! during interval NP. Valve 33 is accordingly conductive during interval NP and serves to limit the response of meter 29 to the voltage drop present between anode 9 and cathode H during this interval which, like intervals FL and FM above considered, comprises less than the entire period of cur-- rent flow between anode 9 and cathode l I. When the indication of meter 29 has been observed and recorded, switch 61 may be reversed to connect the measuring circuit with voltage divider forming a source of known variable voltage for the circuit. The voltage impressed on the measuring circuit from the voltage divider is adjusted by moving the tap of voltage divider 15 in the one or the other direction until the original indication of meter 29 is restored. The voltage thus impressed on the measuring circuit is measured by means of voltmeter l6 and is equal to the peak value of the voltage drop between anode 9 and cathode II. By this method the value of the voltage drop may be obtained without reference to any calibration curve and without resorting to any computation. It will be understood that the primary winding of current transformer 65 may also be connected in series with anode 9 or with another anode carrying current during interval QN if it is desired to measure the peak value RS of the unidirectional voltage between anode 9 and cathode II.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a control system comprising an electric current supply circuit, an electric current output circuit, one of said circuits being an alternating current circuit, and an electric valve having electrodes connected with said circuits for the flow of current between said circuits through said valve, the combination with indicating means responsive to the voltage between two of said electrodes, of means for controlling the energization of said indicating means, and means for preventing the operation of the said means for controlling the energization of said indicating means during periods of the decay of the voltage between said electrodes comprising means responsive to the voltage of said alternating current circuit.

2. A device for measuring the voltage drop between two electrodes of an electric valve comprising indicating means responsive to the voltage between the electrodes, and means for limiting the response of said indicating means to periods comprising less than the entire intended periods of current flow between said electrodes comprising means for preventing the response of said indicating means during periods of decay of the voltage between said electrodes.

3. In a control system comprising an electric current supply circuit, an electric current output circuit, one of said circuits being an alternating current circuit, and a plurality of electric valves having electrodes connected with said circuits for the flow of current between said circuits through said valves, the combination with indicating means responsive to the volta e between two of said electrodes of one of said valves. of

means responsive to the flow of current through current supply circuit, an electric current output circuit, one of said circuits being an alternating current circuit, and an electric valvehaving electrodes connected with said circuits for the flow of current between said circuits through said valve, the combination withindicating means responsive to the voltage between two of said electrodes, voltage responsive means for controlling the operation of said indicating means, and means for impressing an alternating voltage from said alternating current circuit on said controlling means, of means for limiting the response of said controlling means to periods less than the durations of the said flow of current through said valve comprising means for shifting the phase of said alternating voltage.

5. In a control system comprising an electric current supply circuit, an electric current output circuit, one of said circuits being an alternating current circuit, an electric valve having electrodes connected with said circuits for the flow of current between said circuits through said valve, the combination with an indicating device connected with one of said electrodes, an auxiliary electric valve having electrodes for connecting said indicating device with another one of the first said electrodes, of another auxiliary electric valve serially connected with said indicating device and having a control electrode and a cathode, means for impressing an alternating voltage from said alternating current circuit between said control electrode and said cathode, and means for limiting the duration of the conductivity of the said another auxiliary electric valve to periods less than the durations of the said flow of current through the first said valve comprising means for shifting the phase of said alternating voltage.

6. In a control system comprising an electric current supply circuit, an electric current output circuit, one of said circuits being an alternating current circuit, a plurality of electric valves having electrodes connected with said circuits for the flow of current between said circuits through said valves, the combination with an indicating device connected with one of said electrodes of one of said valves, an auxiliary electric valve having electrodes for connecting said indicating device with another one of the said electrodes of'the said one of said valves, of another auxiliary electric valve serially connected with said indicating device, and means responsive to the flow of current through one of the said electrodes of another one of the first said valves for controlling the conductivity of the second said auxiliary valve.

7. In a control system comprising an electric current supply circuit, an electric current output circuit, one of said circuits being an alternating current circuit, an electric valve having electrodes including a cathode connected with said circuits for the flow of current between said circuits through said valve, and having a control electrode, the combination with an indicating device connected with one of said electrodes, an auxiliary electric valve having electrodes for connecting said indicating device with another one of the first said electrodes, of another auxiliary electric valve serially connected with said indieating device and having a control electrode and v a cathode, and common means for impressing an alternating voltage between the first said control electrode and cathode and between the second said control electrode and cathode, the said cornmon means including means for causing a predetermined tiine delay of the impression of the said voltage between the said second control electrode and cathode after the impression thereof between the first said electrode and cathode.

8. In an electric current converting system comprising an alternating current circuit, a direct current circuit, and electric valve means 10 trodes.

having electrodes connectedwith said circuits for the continual flow of current therebetween," the combination with means responsive to thevoltage between said electrodes, of means for limit-- HAROLD WINOGRAD; SAMUEL R. DURAND.