US2645765A

US2645765A - Abnormal voltage indicating device

Info

Publication number: US2645765A
Application number: US158042A
Authority: US
Inventors: William H Bixby
Original assignee: DONALD R MIDDLETON; STANLEY M HANLEY
Current assignee: DONALD R MIDDLETON; STANLEY M HANLEY
Priority date: 1950-04-25
Filing date: 1950-04-25
Publication date: 1953-07-14
Anticipated expiration: 1970-07-14

Description

y 14, 1953 w. H. BIXBY 2,645,765

ABNORMAL VOLTAGE INDICATING DEVICE Filed April 25', 1950 2 Sheets-Sheet 1 FIG.

menu/amp 19 I INVENTOR w H B/XBY ATTORNEY y 1953 w. H. BIXBY 2,645,765

ABNORMAL VOLTAGE INDICATING DEVICE I Filed April 25, 1950 2 Sheets-Sheet 2 FIG. 2

lNl/ENTOR n. H B/XBY ZJ W ALZ'O RNEY Patented July 14, 1953 2,645,765 ABNORMAL VOLTAGE INDICATING DEVICE William H. Bixby, Detroit, Mich, assignor to Donald R. Middleton and Stanley M. Hanley, doing business as Power Equipment Company, Detroit, Mich., a copartnership Application April 25, 1950, Serial No. 158,042

16 Claims. (Cl. 10- 248) Thi invention relates to relay circuits and more particularly to circuits for controlling the operation of a relay in response to a predetermined change of an alternating supply voltage. The invention may be used, for example, to control the energization of an electromagnetic relay for openin or closing an alarm circuit for indicating a change of voltage of a current supply source with respect to a predetermined normal voltage. Instead of controlling an alarm circuit, the electromagnetic relay may also be employed for protecting apparatusto which current is supplied directly or indirectly from the supply source to prevent damaging the apparatus due to an abnormally high or low voltage of the supply source.

An object of the invention is to provide an improved circuit for changing in a predetermined sense the current in a current path in response to an increase of voltage of a current supply source and also in response to a decrease of voltage of the supply source.

Another object of the invention is to provide a circuit arrangement for changing the current in one current path in a predetermined sense in response to a decrease of voltage of a current supply source below a minimum voltage of a desired voltage range and for changing the current in another current path in said predetermined sense in response to an increase of voltage of said current supply source above a maximum voltage of said voltage range.

In an embodiment of th invention herein shown and described for the purpose of illustration, there are provided a circuitcomprising a thermistor or other resistance device the resistance of which changes in a consistent, non-linear manner with change of current through thede- I voltage. Such an arrangement is disclosed in my United States Patent No. 2,486,250 granted October 25, 1949, Means are provided for adjusting the amplitudes of the pulsating voltages with respect to the amplitude of the supply voltage. The two pulsating voltages are combined with an alternating voltage derived from the source voltage so that the voltage pulses are opposed to successive half cycles, respectively, of the alternating voltage. The amplitudes of the pulsating voltages and the derived alternating voltage are such as to give a resultant voltage which is substantially zero amplitude when the voltage of the source has a predetermined amplitude and which increases in amplitude in response to an increase of the source voltage and also in response to a decrease of the source voltage. The reultant voltage has one polarity when the sourc voltage rises above the predetermined value and the opposite polarity when the'source voltage falls below the predetermined value. This rsultant voltage is rectified and the rectified pulsating voltage is combined with an alternating voltage in the gridcathode circuit of each of a second pair of space current devices so that the pulses of the rectified pulsating voltage are opposed to the half cycles of the alternating voltage in the control gridcathode circuit of each space current device when the anode of the device is positive with respect to its cathode, the anode cathode voltag of each space current tube also being supplied from the alternating-moment source. The energization of an electromagnetic relay connected in the space current circuits of the second pair of space current devices will thus decrease in response to an increase and also in response to a decrease of the voltage of the alternating-current source to cause the armatureof the relay to be released. The release of the relay armature may cause the completion of an energizing circuit for an indicating lamp or othr alarm device, for example.

In a modified embodiment of the invention, two electromagnetic relays are provided, one for changing the 'energization of an indicating or protective device in" response to an increase of the supply source voltage above a maximum voltage ofra selected normal voltage range and the other for changing the energization of an indi eating or protective device in response to a decrease of the supplysource voltage below a minimum value of the normal voltage range. Pulsating voltages are produced as described in the preceding paragraph and the pulsating voltages are combined with an unsymmetrical alternating voltage derived from the source and in "opposed phase with respecttl'iereto in the control electrode-cathode circuit of each of four space current devices. The relationship of the unsymmetrical alternating voltage and the pulsating voltag s in the grid-cathode circuits of one pair ofthese space current devices is such that the space currents of the devices decreases in responce to a decreae of voltage of the source to cause the release of the electromagnetic relay which is energized by said space currents. The relationship of the unsymmetrical alternating voltage and the pulsating voltages in the gridcathode circuits of the remaining pair of space current devices is such that the space currents of the devices decrease in response to an increase of voltage of the source to cause the release of the remaining electromagnetic relay. Preferably each of the unsymmetrical alternating voltages is formed by adding to half cycles of one polarity of a first symmetrical alternating voltage of a certain amplitude, half cycles of a second symmetrical alternating voltage of a smaller amplitude to thereby increase the amplitude of alternate half cycles of the unsymmetrical voltage and by subtracting from half cycles of opposite polarity of the first symmetrical alternating voltage half cycles of the second symmetrical voltage to thereby reduce the amplitude of the remaining half cycles of the unsymmetrical voltage. The amplitude of the smaller amplitude alternating voltage may be varied to control the voltage range of the alternating-current source for which both electromagnetic relays are actuated so that one relay releases its armature to produce an indication when the source voltage rises above the maximum value of said range and so that the other relay releases its armature to produce an indication when the source voltage decreases below the minimum value of said range.

Fig. 1 of the accompanying drawing is a schematic view of an alarm circuit embodying the invention; and

Fig. 2 is a schematic view of a modification of the alarm circuit of Fig. 1.

Referring to Fig. 1 of the drawing, there is provided a transformer having a primary winding It! connected to an alternating-current supply source II and a plurality of secondary windings i2, i3, 54, I5, I3 and I1. Across transformer winding I2 are connected in series a resistor I3 and a thermistor I9 having the operating characteristic that is resistance decreases in response to an increase of alternating current flowing therethrough at such a rate that the voltage across the thermistor decreases. Thermistors are described, for example, in Bell Laboratories A Record, December 1940, page 106 et seq. potentiometer 20 is connected across a portion of transformer winding I3, the variable tap of the potentiometer being connected to the common terminal of resistor I8 and thermistor I9.

There is provided a twin-triode space current tube ZI comprising space

current triodes

22 and 23 each having an anode, a. cathode and a control electrode. The control electrodes of

triodes

22 and 23 are respectively connected through

resistors

24 and 25 to terminals 43 and 44 of transformer winding I3. Space current is supplied to triode 22 from transformer winding I4 through a circuit comprising a resistor 26 and space current is supplied to triode 23 from transformer winding I through a circuit comprising a resistor 21. A common terminal of

resistors

26 and 27 and the cathodes of

triodes

22 and 23 is conductively connected to a common terminal of thermistor I3 and transformer winding I2 to complete the control grid-cathode circuits of

triodes

22 and 23. The transformer taps 43 and 44 are chosen to provide the proper operating biases for

triodes

22 and 23 when the anodes of the respective triodes are positive with respect to the cathodes. The voltage measured from the tap of potentiometer 20 to the point a which is electrically mid-way between the terminal 43 and 44 is substantially equal to the voltage across thermistor I9 when the voltage of source II is at its normal value so that the voltage measured from the tap of potentiometer 23 to terminal 44 is less than the voltage across thermistor I9 and the voltage measured from the tap of potentiometer 20 to terminal 43 is greater than the voltage across thermistor I9. The grid of each triode will thus be negative with respect to its cathode when its anode is positive with respect to the cathode.

There is provided a bridge-type full wave rectifier 30 having a resistor 3I connected across its output terminals. The input circuit of rectifier 30 comprises in series resistors 26 and 2'! and a portion of secondary transformer winding I5. A twin-triode space current tube 32 comprising

triodes

33 and 34 is connected as a full wave rectifier for rectifying current supplied from transformer winding l. and for supplying the rectified current to the winding of an electromagnetic relay 35 having an armature 35, the end terminals of winding I! being connected to the anodes of

triodes

33 and 34, respectively, and a mid-tap of winding ll being connected through relay 35 to the cathode of

triodes

33 and 34. A circuit completed in response to th release of the armature 36 of relay 35 comprises an indicating device such as lamp 3? and a source of energizing current for the lamp such as battery 38.

A potentiometer 49 is connected across secondary transformer winding l8. Resistors M and 42 in series are provided in a current path connecting the variable tap of potentiometer 4!! and a common terminal of winding I6 and potentiometer 46. The control electrode-cathode circuit of triode 33 comprises resistors 45, M and 3I in series and the control electrode-cathode circuit of triode 34 comprises

resistors

45, 42 and 3! in series. Where it is desired to delay the response of relay 35 to sudden fluctuations in voltage, a capacitor 47 may be comiected in a path across the relay winding. To avoid high frequency oscillations in the circuit, a capacitor 48 of very small capacitance is provided in a path connecting the cathode of triode 34 and the common terminal of

resistors

42 and 46.

An increase of the voltage of source II results in a decrease of voltage across thermistor l!) in addition to a voltage increase across the portion of the transformer winding I3 which is in the control electrode-cathode circuits of

triodes

22 and 23. Therefore, during half-cycl periods of the alternating-current source II when triode 22 is conducting space current, an increase of the voltage of source II, for example, results in the control grid of triode 22 becoming relatively more negative with respect to its cathode to cause the current flowing through resistor 26 to decrease. During half cycles of opposite polarity, an increas of voltage of source l I results in the control electrode of triode 23 becoming relatively more positive with respect to its cathode to cause the space current flowing through resistor 27 to increase.

The pulsating voltages across

resistors

26 and 2! are opposed in phase with respect to and have predetermined amplitudes with respect to the alternating voltage from winding I5 in the input circuit of rectifier 30. The opposed pulsating and alternating voltages may have substantially equal amplitudes when the voltage of source II has a certain normal value so that the output voltage of rectifier 30 is equal to zero. Then, if it is desired to bring the output voltage of rectifier 30 to this same value, zero, for a higher voltage of source it is merely required to adjust potentiometer to increase the voltage between its variable tap and point a. of winding 13. The voltage impressed across the input terminals of rectifier 3|] and the voltage across resistor 3| connected to the rectifier output terminals are then each substantially zero. The voltages across resistors 4| and 42 thus make the control grids of

triodes

33 and 34 positive with respect to the cathodes to cause suificient current flow through relay winding 35 to cause the relay to open the energizing circuit for lamp 31.

When the voltage of source rises above the predetermined amplitude, the pulsating voltage across resistor 26 decreases to a value less than the amplitude of the concurrent half-cycle pulses across the portion of winding l5 which is in the input circuit of rectifier 30 and the pulsating voltage across resistor?! increases to a value greater than the amplitude of the concurrent half-cycle pulses across the portion of winding l5. A pulsating voltage is thus impressed upon the input circuit of rectifier 30. When the voltage of source decreases, the pulsating voltage across resistor 26 increases to an amplitude greater than the voltage across the portion of winding l5 and the pulsating voltage across resistor 2'! decreases to an amplitude less than the voltage across the portion of winding I5; -A pulsating voltage of opposite polarity with respect to the pulsating voltage produced when the source voltage rises is thus impressed upon the input or rectifier 30. The rectified'output voltage across resistor 3| has a polarity such as to make the control electrodes of

triodes

33 and 34 relatively more negative with respect to the cathodes to cause the current in relay 35 to decrease. The increase or decrease of the voltage of source H from the predetermined normal value which is required to cause the armature of relay 3B to'release may be varied by adjusting the potentiometer 40 to change the voltages across resistors 4| and 42. An increase of the voltage acros'sfresistors 4| and 42, for example,'will effect a change in operation of the circuit such that a larger increase or decrease of the voltage of source H will be required to effect the release of the arma-j ture of relay 36 to thereby cause the energization of the lamp 31. The armature 36 of relay 35 thus releases to cause the energization of lamp 3? when the line voltage increases above the maximum voltage of a certain desired voltage range and also when the line voltage decreases below the minimum voltage of the voltage range.

The portions of the circuit shown in Fig. 2 which are similar to corresponding portions of Fig. 1 are identified by the same designations. There is provided a twin-triode space current tube 52 having triodes 53 and 54 the anodes of which are connected to the end terminals, respectively, of a secondary transformer winding 50. The mid-tap of transformer winding 'is connected through the Winding of an electromagnetic relay 55 to the cathodes of triodes 53 p and 54, a condenser '51 being connected in a shunt path across the relay Winding. The release of the armature 56 of relay 55 completes an energizing circuit from battery 58 to an indicator lamp 59. There is provided a twin-triode tube 62 having

triodes

63 and 64 the'anodes of which are similarly connected to the end terminals of a secondary transformer winding 5|. The mid-tap of transformer winding 5| is connected through the winding of an electromagnetic relay 65 to the cathodes of

triodes

63 and 64, a condenser 61 being connected across relay winding. The release of the armature 66 of relay 65 completes an energizing circuit from battery 68 to an indicating lamp 69.

A potentiometer H1 is connected across a portion e--c of transformer winding |5. Similar re- .sistors H and T2 are connected in series across a variable portion of potentiometer 10 between the variable tap of the potentiometer and the terminal connected to terminal 0 of the transformer Winding. The common terminal of resistors H and 12 is connected to the cathodes of triodes E3 and 64. The remaining terminal of resistor H is connected through a resistor 84 to the control electrode of triode 53 and the remaining terminal of resistor 12 is connected through a resistor 35 to the control electrode of triode 54. A condenser 86 is provided in a path connecting the cathode of triode 54 and a common terminal of resistor 72 and 85.

A potentiometer 3|), similar-to potentiometer 10, is connected across a portion fd of transformer winding [4. Similar resistors 8| and 82 in series are connected across a variable portion or potentiometer 30 between the variable tap of the potentiometer and the terminal connected to terminal d of transformer winding M. The variable taps of potentiometers l0 and are mechanically connected so that, preferably, the voltage across resistors 7| and 72 is at all times equal to the voltage across resistors BI and 82. The common terminal of resistors BI and 82 is connected to the cathode of triodes 53 and 54. The other terminal of resistor 8| is connected through a resistor 81. to the control grid of triode 53 and the other terminal of resistor 82 is connected through a resistor 88 to the control grid of triode 64. A condenser 89 is provided in a path connecting the cathode of triode 64 and a common terminal of

resistors

82 and 88.

For the purpose of explaining the operation of the circuit, let it be assumed that potentiometers 10 and are set so that the variable taps are at the potentials of points 0 and d, respectively. There will then be zero voltage across resistors H and E2 and across resistors 8! and 32. Let it further be assumed that the setting of potentiometer 29 and the voltage of source aresuch that the voltage between the movable tap of the potentiometer 29 and point a of transformer vinding I3 is equal to the voltage across thermisto'r l9; Under these conditions, during half cycle periods when the anode of triode 53 is positive with respect to its cathode, there will be impressed upon the grid-cathode circuit of triode 53 half cycles of the voltage across the portion ec of transformer winding i5 and, in opposition thereto, the voltage pulses of equal amplitude across resistor 28, the voltage across resistor 2'! being zero during these half-cycle periods. Similarly, during half-cycle periods when the anode of triode 54 is positive with respect to its cathode, there will be impressed upon the gridcathode circuit of triode 54 half cycles of the voltage e-c and, in opposition thereto; the voltage pulses of equal amplitude across resistor 21. The control grids of triodes 53 and 54 will then be at the same potential as the cathodes and suihcient space current will flow through the winding of relay 55 to maintain the relay in the operated condition. A slight increase of voltage of the source i! above the assumed normal value will cause the voltage pulses across resistor 23 to decrease in amplitude and the voltage pulses across resistor 21 to increase in amplitude, thereb making the control grids of triodes 53 and 54 sufficiently negative with respect to the cathodes to cause the current in the winding of relay 55 to be reduced and to cause the relay armature 55 to be released. The resulting energization of lamp produces an indication of the high line voltage condition.

For the conditions stated in the preceding parag p11, when the anode of triode G3 is positive with respect to its cathode, there will be impressed upon the grid-cathode circuit of triode 5 3 hall cycles of the voltage e-c and, in opposition thereto, the voltage pulses of equal amplitude across resistor 26. When the anode of triode is positive with respect to its cathode, there will be impressed upon the grid-cathode circuit of triode 8 2 half cycles of the voltage e-c and, in opposition 'iereto, the voltage pulses of equal an litude across 'esistor 21. The polarities of the component voltage in the gridcathode circuits of triodes E33 and 64, however, are reversed with respect to the polarities of the corresponding vol ages in the grid-cathode circuits of triodes 53 and 54. A slight decrease of the voltage of the source H below the assumed normal value will cause the voltage pulses across resistor 23 to increase in amplitude and the voltage pulses across resistor 22' to decrease in am plitude, thereby making the grids of triodes 63 and i l sufficiently negative with respect to the cathodes to cause the armature of relay 56 to be released. Lamp 69 is thus energized to pro duce an indication of the low voltage condition.

It will be noted that as the taps of potentiometers 88 and are moved by equal amounts toward positions and 6, respectively, for any positions of the taps, the voltage between the common terminal of resistors Bi and 82 and the common terminal of resistors H and 72 will be equal to the difference of the voltage e-c and the voltage across resistor 26 during half-cycle periods when the anodes of

triodes

22, 53 and 63 positive with respect to their cathodes and said voltage will be equal to the difference of the voltage c-c and the voltage across resistor 27 when the anodes of

triodes

23, 54 and 64 are posiave with respect to their cathodes. The grid-cathode voltages of each of triodes 53, 54 63 and is the voltage between the common terminal of resistors 8! and and the common terminal of resistors H and "i2 plus a bias voltage across one or" the resistors ll, l2, 8!, 82, the bias voltage having a polarity such as to make the grid relatively more positive with respect to the cathode when the anode is positive with respect to the cathode. The voltages across resistors ll, l2, :3! and 82 are the added biasing voltages for

triodes

53, 53, 5 2 and 64, respectively, these biasing voltages being equal and adjustable by moving the taps of potentiometers l0 and 80. An increase of these biasing voltages makes necessary a relatively larger decrease of voltage across resistor 25 and a relatively larger increase of voltage across resistor 21 to effect the release of relay An increase of these biasing voltages also makes necessary a relatively larger increase of voltage across resistor 25 and a relatively larger decrease of voltage across resistor 2'! to effect the release of relay 65. In other words, moving the potentiometer taps from (1 toward 1 and from 0 toward e increases the normal voltage range for which relays 55 and 65 remain operated, the relays, respectively being released only when the source voltage goes above and below the maximum and minimum values, respectively, of the normal voltage range.

If for one setting of potentiometers :9, relay 65 should release when the voltage of source H is 98 per cent of a certain predetermined voltage and the release of relay 55 should occur when the voltage of source I! is 102 percent of the predetermined voltage, for example, increasing the bias voltages by readjusting potentiometers I0, 80 could cause the relay 65 to release at 96 per cent of the predetermined voltage and the relay 55 to release at 104 per cent of the predetermined voltage. Thus the setting of potentiometers 10, 80 determines the range between the low voltage indication produced by lamp B9 and the high voltage indication produced by lamp 59 while the setting of potentiometer 20 determines the voltage level of the center point of this range, the two adjustmerits being almost independent of one another as far as their effects are concerned.

What is claimed is: 1 The combination with a source of alternating voltage the amplitude of which may change, of means for deriving from said source a symmetrical alternating voltage substantially proportional to the voltage of said source, means for deriving from said source during periods of one polarity thereof a first pulsating voltage the amplitude of which decreases by a larger amount than the amplitude increase of said derived al ternating voltage in response to an increase of voltage of said source, means for deriving from said source during periods of opposite polarity thereof a second pulsating voltage the amplitude of which increases by a lar er amount than the amplitude increase of said derived alternating voltage in response to an increase of voltage of said source, and means for combining said derived alternating and pulsating voltages with each of said pulsating voltages in phase opposition to said derived alternating voltage to produce a resultant voltage the amplitude of which changes in a predetermined direction when the voltage of said source either increases or decreases.

2. In combination, a space current device having an anode, a cathode and a control electrode, a first circuit connecting said anode and said cathode, means for causing current to flow in said first circuit, an alternating-current supply source the voltage of which may vary, a second 7 circuit connecting the control electrode and cathode of said device, and means for deriving from said supply source and impressing upon said second circuit a voltage for causing the current in said first circuit to change in a predetermined sense in response to a voltage increase of said supply source to a certain relatively high voltage and for causingthe current in said first circuit to change in said predetermined sense in response to a voltage decrease of said supply source to a certain relatively low voltage.

3.. In combination, a space current device havmg an anode, a cathode and a control electrode, an alternating-current supply source the voltage of which mayvary, a space current circuit for said device comprising a first source oI alternating voltage derived from said supply source, means for deriving from said source a second voltage the amplitudeof which increases in response to an increase of said supply voltage above a predetermined voltage and the amplitude of which 9 increases in response to a decrease of said supply voltage below said predetermined voltage and means for impressing said second derived voltage upon a circuit connecting-said control electrode and said cathode for controlling. the amplitude of said space current.

4. In combination, a space current device having an anode, a cathode and a control electrode, an alternating-current supply source the voltage of which may vary, means for supplying current from said source to a space current circuit connecting said anode and said cathode, means for deriving from said source a voltage the amplitude of which increases in response to an increase of said supply voltage above a predetermined voltage and the amplitude of which increases in response to a decrease of said supply voltage-below said predetermined voltage, means for selecting a desired predetermined voltage above and below which said derived voltage increases, and means for impressing said derived voltage upon a circuit connecting said control electrode' and said cathode for controlling the amplitude of said space current.

5. In combination, a space current device having an anode, a cathode and a control electrode, I

means for supplying current from an alternating-current supply source to a space currentcircuit connecting said anode and said cathode, means for deriving from said supply source avoltage the amplitude of Which'increases in response to an increase of said supply voltage from a first voltage to a second voltage and the amplitude of which increases in response to a decrease of said supply voltage from said first voltage to a third voltage, means for adjusting said second and third voltages relative to said first voltage to determine the voltage range of saidsupply source above and below which said derived voltage increases, and means for impressing said derived voltage upon a circuit connecting said control electrode and said cathode for controlling the amplitude of said space current. I

6. A combination in accordance. with claim 5 v in which 'is provided means for adjusting said a first voltage to a second voltage and the amplitude of'which increases inthe opposite sense in response to a decrease of said supply voltage from said first voltage to a third voltage, means to impress said derived voltage upon a circuit connecting the control electrode and cathode of said first device with a polarity to cause. the space current of said first device to decrease when said supply voltage increases from said first voltage to said second voltage, and means to impress said derived voltage upon a circuit connecting the control electrode and cathode of said second device with an opposite polarity to cause the space current of said second device to decrease when said supply voltage decreases from said first voltage to said third voltage.

8. A combination in accordance with claim 7 in which there are provided a first means connected in the space current path of said first device for producing an indication when said suptrode, means for impressing upon the control electrode and cathode of said first device a voltage derived from said source for causing the current supplied to said first current responsive means to be reducedto a predetermined value in response to an increase of said supply voltage to a voltage above a certain normal range, and means for impressing upon the control electrode and cathode of said second device a voltage derived from said source for causing the current supplied to said second current responsive means to be reduced to a predetermined value in response to a decrease of said supply voltage to a voltage below said normal range.

10. The combination with an alternating-current supply source-the voltage of which may change, of means for deriving from said supply source during periods of one polarity thereof afirst pulsating voltage the amplitude of which decreases in response to a voltage increase of said source but at a higher rate, and vice versa, means for deriving from said supply source during periods of opposite polarity thereof a second pulsating voltage the amplitude of which increases in response to a voltage increase of said source but at a higher-rate, and vice versa, a first full wave rectifier, means for combining said pulsating voltages with an alternating voltage derived from said source in the input circuit of said full wave rectifier, said pulsating voltages being in opposition to half cycles of said derived alternating voltage, resistance means having two end terminals and a mid-terminal, means for impressing across said resistance means an alternating voltage of variable amplitude and fixed phase derived from said source, a second full wave rectifier comprising two space current devices each having an anode, a cathode and a control electrode for rectifying current from said alternating-currentsource, means for connecting the mid-terminal of said resistors to the negative output terminal of said first full wave rectifier, means for connecting the cathodes of said space current devices to the positive output terminal of said first full wave rectifier, and means for connecting the end terminals of said resistance means to the control electrodes of said space current devices, respectively, thereby controlling the output current of said second full wave rectifier.

11. A combination in accordance with claim 10 in which there are provided an indicating device for producing an indication in response to abnormally high and abnormally low voltages of said supply source and an electromagnetic relay energized by the rectified output current of said second full Wave rectifier for controlling the energization of said indicating device.

12. The combination with an alternating-current supply source, of a transformer having a primary winding connected to said source and a plurality of secondary windings, a full wave rectifier comprising a first and a second space current device for rectifying current from said source supplied through a first of said secondary windings, each of said space current devices having an anode, a cathode and a control electrode, a first resistor having a terminal connected to a terminal of a second secondary Winding, a first potentiometer connected across said second secondary winding and having a variable tap, means for connecting said variable tap to the control electrode of said first device, means for connecting a terminal of said second secondary winding to the control electrode of said second device, a second resistor having a terminal connected to a second terminal of said first resistor, a third secondary winding having a first terminal connected to a second terminal of said second resistor, a second potentiometer connected across said third secondary winding and having a variable tap, means for mechanically connecting the variable taps of said potentiometers, resistance means connecting the second terminal of said third secondary winding and the variable tap of said second potentiometer, said resistance means having a mid-tap, means for connecting said midtap to the cathodes of said devices, means for supplying current from said supply source to said first resistor to set up across said resistor during half-cycle periods of one polarity of said source a pulsating voltage the amplitude of which decreases in response to a voltage increase of said source and vice versa, and means for supplying current from said supply source to said second resistor during half-cycle periods of opposite polarity of said source a pulsating voltage the amplitude of which increases in response to a voltage increase of said source and vice versa, each of said pulsating voltages being in opposition to the voltage supplied by said second and third secondary windings in the control electrode-cathode circuits of said space current devices.

13. In combination, a transformer having a primary winding connected to an alternating current supply source and a plurality of secondary windings, a thermistor and a first resistor connected in series to a first of said secondary windings, a first potentiometer connected across a portion of a second of said secondary windings, means for connecting the variabletap of said potentiometer toa common terminalof said thermistor and said first resistor, a first and a second space current device each, having. an anode, a

cathode and a control electrode, a second and a third resistor, means for connecting a terminal of each of said second and third resistors to said cathodes and to a common terminal of said thermistor and said first secondary winding, means for connecting said control electrodes to said second secondary winding, a space current circuit for said first space current device, comprising a third of said secondary windingsv and said second resistor, a space current circuit for said second space current device comprising a fourth of said secondary windings andsaid third resistor, a full wave rectifier, having input and output terminals, means for connecting one of said input terminals to a common terminal of said second resistor and. said third. secondary winding, means for connecting the other of said input terminals to said fourth secondary winding, a fourth resistor connected to the output terminals of said rectifier, a third anda fourth space current device each having an anode, a.

cathode and a control electrode, a second potentiometer connected across a fifth of said sec- 1.2 ondary windings, a fifth and a sixth resistor having a common terminal connected to a first terminal of said fourth resistor, means for connect,- ing the other terminal of said fifth resistor to the variable tap of said second potentiometer,

means for connecting the other terminal of said sixth resistor to a common terminal of said second potentiometer and said fifth secondary winding, means for connecting the terminals of said fifth and sixth resistors other than said common terminal to the control electrodes of said third and fourth space current devices, respectively, means for connecting the cathodes of said third and fourth space current devices to the second terminal of said fourth resistor, means for connecting the anodes of said third and fourth devices to the end terminals, respectively, of a sixth of said secondary windings, current responsive means, and means for connecting said current responsive means in a path connecting the oathodes of saidvthird andfourth devices and a midterminal of said sixth winding.

14. In combination, a transformer having a primary winding connected to an alternatingcurrent supply source and a plurality of secondary windings, a thermistor and a. first resistor connected in series to a first of said secondary windings, a first potentiometer connected across a portion of a second of said secondary windings, means for connecting the variable tap of, said potentiometer to the common terminal of said thermistor and said first resistor, six space current devices each having an anode, a cathode and a control electrode, a second and a thirdresistor having a common terminal connected to the oathodes ofa first and a second of saidspace current devices andto a common terminal of. thermistor and said first secondary winding, means for connecting the control electrodes of said first and second devices to said second secondary winding, a space current circuit for said, first device comprising a third of said secondary windings and said second resistor, a space current circuit for said second device comprising a fourth of said secondary windings and'said third resistor, a second' potentiometer connected to a common terminal of said third secondary winding and said second resistor and to another terminal of said third secondary winding, a third potentiometer connected to a'common terminal of said fourth secondary winding and said third resistor and to another terminal of said fourth secondary winding, means for mechanically connecting the variable taps of said second and third potentiometers, a fourth and a fifth resistor having a common terminal connected to the cathodes of a third and a fourth of said space current devices, means for connecting the other terminal of said fourth resistor to the variable tap of said second potentiometer, means for connecting the other terminal of said fifth resistor to the common terminal of said third secondary'winding and said second resistor, a sixth and a seventh resistor having a common terminal connected to the oathodes of a fifth and a sixth of said space. currentv devices, means for connecting the other terminal. of said sixth resistor to the: variable tap of said third potentiometer, means for connecting the other terminal of said seventh resistor to saidv other terminaliof said fourth secondary winding, means for connecting the terminalsof said fourth and fifth resistors other than their. common terminal to the control electrodes of said fifth and sixth space current devices, respectively, means for connectingtheiterminals of said sixth and seventh resistors other than their common terminal to the control electrodes of said third and fourth space current devices, respectively, a first electromagnetic relay having a winding in a current path connecting the cathodes of said third and fourth space current devices and a mid-terminal of a fifth of said secondary windings, means for connecting the end terminals of said fifth winding to the anodes, respectively, of said third and fourth devices, means for connecting the end terminals of a sixth of said transformer windings to the anodes, respectively, of said fifth and sixth space current devices, and a second electromagnetic relay in a current path connecting the cathodes of said fifth and sixth devices and a mid-terminal of said sixth secondary winding.

15. In combination, a current responsive means, means for supplying current from an alternatingcurrent supply source to said current responsive means, and means for decreasing by a predetermined amount the current supplied to said current responsive means in response to a predetermined voltage increase of said supply source above a certain normal voltage and also in response to a predetermined voltage decrease of said supply source below said normal voltage.

16. A combination in accordance with claim 15 in which means are provided for changing said predetermined voltage increase and said predeterined voltage decrease required for decreasing the current supplied to said current responsive means by said predetermined amount.

WILLIAM H. BIXBY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,642,710 Affel Sept. 20, 1927 2,150,265 Conover Mar. 14, 1939 2,197,868 Knowlton Apr. 23, 1940 2,367,509 Knowlton Jan. 16, 1945 2,369,678 McWhirter Feb. 20, 1945 2,377,506 McWhirter, et al. June 5, 1945 2,391,532 Wilmotte Dec. 25, 1945 2,435,572 Bixby I Feb. 10, 1948 2,441,359 Jones May 11, 1948 2,442,786 Somers June 8, 1948 2,470,067 Callender et al. May 10, 1949 2,472,042 Davies May 31, 1949 2,475,356 Meschter July 5, 1949 2,466,250 Bixby II Oct. 25, 1949