US3136927A

US3136927A - Current controller

Info

Publication number: US3136927A
Application number: US35203A
Authority: US
Inventors: Marlow Jacob
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1960-06-10
Filing date: 1960-06-10
Publication date: 1964-06-09
Anticipated expiration: 1981-06-09

Description

June 9, 1964 J MARLOW CURRENT CONTROLLER 2 Sheets-Sheet 1 Filed June 10, 1960 United States Patent, M

3,136,927 CURRENT CONTROLLER Jacob Marlow, King of Prussia, Pa., assignor to Robert Shaw ControlsCompany, Richmond, Va., a corporation of Delaware Filed June 10, 1960, Ser. No. 35,203 10 Claims. (Cl. 317-143) The invention presented herein relates to current controllers using magnetic amplifiers and more particularly to such controllers for controlling the operation of current responsive devices in accordance with a predetermined range of variation of a unidirectional signal with compensation for fluctuations in the alternating current supply applied to the magnetic amplifiers.

One object of the invention is to provide such a circui using two self-saturating magnetic amplifiers, each responsive to a varying unidirectional electrical signal with one magnetic amplifier having an output current which is altered to change the mode of operation of a current responsive device when the signal is less than a predetermined amount and the other magnetic amplifier having an output current which is altered to change the mode of operation of a current responsive device when the signal is greater than a predetermined amount.

Another'object of the invention is to provide a circuit using two self-saturating magnetic amplifiers, each having a separate bias compensation winding supplied from an unregulated direct current power supply to prevent changes in the control set-point of each amplifier due to variations in the alternating current supply applied to the magnetic amplifiers.

A further object of the invention is to provide a current controller which canbe easily adjusted to change the range through which the unidirectional signal can vary before theoutput currents of the magnetic amplifiers are alterted to effect the mode of operation of a current responsive device connected in the output circuit of each magnetic amplifier.

An additional object of the invention is to provide a current controller using two self-saturating magnetic amplifiers that are connected for fail-safe operation of the low and high current limits.

Other objects and advantages will become more apparent from a study of the following description and the accompanying drawings in which:

FIG. 1 is a schematic circuit of a magnetic amplifier current controller according to the present invention; and

FIG. 2 is a graph of the transfer characteristics of the magnetic amplifiers shown in FIG. 1 at difierent values of alternating voltage.

Referring now to the drawings and particularly to FIG. 1, two full-wave self-saturatingmagnetic amplifiers 1 and 2 are shown. magnetic amplifiers is obtained from an alternating current supply line 3 via a transformer 4 having a primary winding 5 connected to the alternating current supply line 3 and a secondary winding 6 with a center tap 7 for connection to the magnetic amplifiers.

The magnetic amplifier 1 is provided with two saturable magnetic cores 8 and 9, a main winding wound on core 8 and a main winding 11 wound on core 9 connected in series by a conductor 12. The other end of winding 10 is connected to one end of secondary winding 6 via a rectifier 13, while the other end of winding 11 is connected to the other end of secondary Winding 6 via a rectifier 14. The cathodes of rectifiers 13 and 14 are each connected to the secondary winding 6.

An output circuit is connected between the conductor 12 and the center tap 7. The load circuit includes a resistor 15 connected in series with the winding 16 of a relay. The relay contacts are not shown.

Alternating current for operation of the For descriptive convenience, it will be assumed that the arrowhead portions of the rectifier symbols point in the conductive direction of the rectifiers and that the rectifiers are conductive when the arrowhead portion of the symbol is connected to the positive side of the supply voltage. Thus, during one half of a cycle of the alternating current, the end of secondary winding 6 connected to the rectifier 14 is positive with respect to the other end of the secondary winding as is the center tap 7 so that current flow is from the center tap 7 through the load circuit, the main winding 10, and the rectifier 13 to the secondary winding 6. During the next half cycle of the alternating current,

the end of the secondary winding 6 connected to rectifier 13 is positive with respect to the other end of the secondary winding. The center tap 7 of the secondary winding 6 is then positive with respect to the end of the secondary winding 6 connected to rectifier 14. Current flow is then through the load circuit, main winding 11, and the rectifier 14 to secondary winding 6.

A feedback winding 17 is wound on both cores 8 and 9 and is connected in parallel with resistor 15. The feedback winding 17 is wound'to provide magnetic flux in the cores 8 and 9 in the same direction as the magnetic flux set up by the current fiow through the main windings 10 and 11, thus providing positive feedback to increase the gain of the magnetic amplifier.

Three

other windings

18, 19, and 20, are Wound on the cores 8 and 9 and serve to control the operating point of the amplifiers. Winding 18 is a control or signal winding and is connected in series with the signal winding of magnetic amplifier 2. The ends of the series connected signal windings are connected to terminals 21 and 22 to which a unidirectional signal is applied. The unidirectional signal is applied so that current through the winding 18 produces a magnetic flux which aids the magnetic flux produced in the main windings 10 and 11. Thus, the signal must be connected so that terminal 21, which is connected to winding 18, is positive with respect to terminal 22 for the winding 18 as shown.

Winding 19 is a bias winding and provides a fixed amount of magnetic flux which is in opposition to the magnetic fiux produced by the main windings 10 and 11 for a desired operating point for the magnetic amplifier 1. The winding 19 is supplied with a direct current voltage appearing across the output terminals 23 and 24 of a resistance bridge 25 that is connected in series with a resistor 26 to a constant direct curret voltage supply indicated at 27. The resistance bridge 25 is adjusted so that terminal 24 is positive with respect to terminal 23 so that winding 19 sets up magnetic flux in cores 8 and'9 in opposition to the flux established by the main windings 10 and 11.

Winding 20 is a bias compensation winding and provides a magnetic flux in cores 8 and 9 which is in opposition to the magnetic flux set up by the main windings 10 and 11. Winding 20 is connected in series with a resistor 28 and the combination is connected in parallel with a capacitor 29. An unregulated direct current voltage is developed across capacitor 29 which varies in accordance wtih fluctuations in the alternating current supply since the capacitor 29 has one end connected to the center tap 7 of the secondary winding 6 via conductor 30 while the other end of capacitor 29 is connected to one end of secondary winding 6 via a rectifier 32' and to the other end of secondary winding 6 via a rectifier 32. The cathodes of

rectifiers

32 and 32 are connected to the capacitor 29.

The constant direct current voltage source 27 is obtained through the use of Zener diodes. The series combination of a resistor 31 and Zener diode 32 is connected in parallel with capacitor 29 and a second series combination of a resistor 33 and a Zener diode 34 is connected Patented June 9, 1964 in parallel with Zener diode 32". The output for the constant direct current source 27 appears across the Zener diode 34.

Zener diodes

32 and 34 are connected for reverse current flow and are operated in the low impedance portion of the diodes characteristic curve so that the voltage across diode 32" is relatively constant though the'voltage across capacitor 29 may vary. The voltage across diode 34 is constant since it is supplied by the relatively constant voltage appearing across diode 32". Resistors 31 and 33 serve as current limiting resistors.

Magnetic amplifier 2 has two saturable magnetic cores 35 and 36. A main winding 37 wound on core 35 and a main winding 38 wound on core 36 are connected in series by a conductor 39. The other end of winding 37 is connected via a rectifier 40 to the end of secondary winding 6 to which rectifier 13 is connected. The other end of winding 38 is connected to the other end of secondary winding 6 via a rectifier 41. The cathodes of rectifiers 40 and 41 are each connected to the secondary winding #3.

As was the case with magnetic amplifier 1, the output circuit of magnetic amplifier 2 is connected between the center tap 7 and the conductor 39 connecting the main windings to establish load current paths similar to those described in connection with magnetic amplifier 1.

The load circuit of magnetic amplifier 2 is similar to magnetic amplifier 1 and includes a resistor 42 which is connected in series with winding 43 of a relay. The contacts of the relay are not shown. As in magnetic amplifier 1, positive feedback is provided by a feedback winding 44 connected in parallel with resistor 42 and wound on cores 35 and 36.

A signal winding 45, bias winding 46, and a bias compensation winding 47 are wound on cores 35 and 31: to control the operating point of magnetic amplifier 2. The signal winding 45 is connected in series with signal winding 18 of magnetic amplifier 1 and is energized by a unidirectional signal applied to terminals 21 and 22. However, signal winding 45 is connected to establish magnetic flux in cores 35 and 36 which opposes the magnetic flux set up by the

main windings

37 and 38. As was pre viously mentioned, the signal winding 18 of magnetic amplifier 1 sets up magnetic flux in the same direction as the magnetic flux established by the main windings and 11. The biasing winding 46 is connected to theconstant direct current voltage supply 27 via a series connected resistance network 48 of parallel connected resistors to provide a fixed amount of magnetic flux as determined by the settings of a variable resistor in each branch of the network 48. The magnetic flux established by bias winding 45 aids the magnetic flux set up by the

main windings

37 and 38. This differs from magnetic amplifier 1 in which the bias winding 19 was connected to establish magnetic flux which was in opposition to the magnetic flux established by the main windings 10 and 11.

The bias compensation winding 4-7 is connected in series with a resistor 49 and responds to an unregulated direct current voltage since the combination is connected in parallel with capacitor 29. As was the case with the bias compensation winding of magnetic amplifier 1, bias compensation winding 47 is connected to establish magnetic flux in the cores 35 and 36 of magnetic amplifier 2 which is in opposition to the magnetic flux established by the

main windings

37 and 38.

Operation of the circuit shown in FIG. 1 can be best understood when the transfer characteristics of magnetic amplifier 1 and magnetic amplifier 2 at different voltages of the alternating current power supply are considered. The transfer characteristics are shown in FIG. 2. The transfer characteristic curves for magnetic amplifier 1 are shown on the left and the transfer characteristic curves for magnetic amplifier 2 are shown on the right in FIG; 2. It is desired that the magnetic amplifier 1 be operated on alternating current at 115 volts with the load current at point-A when the unidirectional input signal applied to terminals 21 and 22 is at its lower limit. At point A, the load current is suflicient to operate the relay in the load circuit. The operating point on a transfer characteristic curve is determined by the resultant magnetic force established by

windings

18, 19, and 20, as measured from the zero bias line for the magnetic amplifier.

The amount of magnetizing force set up in the cores 8 and 9 by

windings

18, 19, and 20 corresponding to operating point A on the volt transfer characteristic curve is equal to H H -H where H is the magnetizing force due to the signal applied to the signal winding 18, H is the magnetizing force due to the unregulated direct current power applied to the bias compensating winding 20, and H is the magnetizing force due to the current supplied from the constant direct current source 27 connected to the bias winding 19 via resistance bridge 25. The resultant magnetic force is in opposition to the magnetic force produced by windings 15 and 11.. When the signal applied to the signal winding 18 increases a slight amount, the output current which passes through the relay winding 16 increases greatly to a point above A due to the high gain of the magnetic amplifier 1 causing the relay to remain operated. When the signal applied to the signal winding 18 is decreased from the value corresponding to operating point A, the load current drops rapidly causing the relay in the load circuit to drop out.

So long as the alternating current voltage applied to the transformer 4 remains at 115 volts, the load current will vary properly with respect to variations in the unidirectional signal applied to terminals 21 and 22 to provide the desired operation of the relay connected in the load circuit. It should be understood that the relays in the load circuits of the magnetic amplifiers can be used to control indicating circuits or initiate corrective action to control the excessive variation in the signal applied to terminals 21 and 22.

However, at certain times, the alternating current voltage available will vary causing a change in the transfer characteristic of the magnetic amplifier due to the corresponding variations in the direct current components of the main windings 1t) and 11. Assuming the magnetic force due to

windings

18, 19, and 20 were to remain the same when the supply voltage is increased to 127 volts or decreased to 103 volts, the load current for magnetic amplifier 1 would be at a point A when the voltage supply is reduced to 103 volts and would be at point A when the voltage supply is increased to 127 volts. Operating point A is a considerable amount above the point at which the relay in the load circuit operates and point A is a considerable amount below the point at which the relay in the load circuit operates. It is, therefore, necessary that the resultant magnetic force produced by wind ings 18, 19, and 211 be altered to cause the load current to be at the same level regardless of variations in the alternating current supply voltage for a given signal applied to the signal winding 18. Referring to the transfer characteristic curve corresponding to the alternating current supply voltage of 103 volts, it is readily apparent that the resultant magnetic force due to windings 18, 19, and 21 must be reduced by AH to have the operating point for the lower limit of the unidirectional signal on the same level as point A. Similarly, an increase of AH is needed when the alternating current supply voltage increases to 127 volts. As previously mentioned, the resultant magnetic force due to

windings

18, 19, and 20, with the alternating current supply voltage at 115 volts, is equal to H H H and is opposite to the magnetic force set up by the main windings 10 and 11. The magnetic force H of course, remains the same since the biasing winding 19 is supplied from the constant direct current source 27. The magnetic force H is also fixed since the load current is to be at the same level for a given value of signal applied to the signal winding 18. Therefore, with H and H fixed, H must change to produce the desired resultant magnetic force. Since the bias compensation winding 20 is connected to the unregulated power supply which varies with changes in the alternating supply source, H will increase when the alternating current supply source increases and decrease when the alternating current supply source decreases. By proper selection of the resistor 28 and design of the bias compensating winding 20, the resultant magnetic force due to

windings

18, 19, and 20 will be reduced by an amount equal to AH when the alternating current supply drops to 103 volts so that the operating point on the transfer characteristic curve for 103 volts is at the same level as for the operating point A for the transfer characteristic curve for 115 volts. Similarly, the resultant magnetic force due to

windings

18, 19, and 20 when the alternating supply voltage increases to 127 volts will be increased by AH due to the increase in the magnitude flux produced by winding 20 so that the operating point on the transfer characteristic curve for 127 volts is at the same level as the operating point A for the transfer characteristic curve for 115 volts. Thus, the resultant magnetic force can be written -H (H AH )-{-H when the alternating supply voltage decreases and b1 bc1+ hc1)+ s1 When the alternating supply voltage increases.

Magnetic amplifier 2 is used to control the operation of a relay by the changes in the load current caused by variations in the unidirectional signal applied to the signal winding 45 via terminals 21 and 22. In this case, when the magnetic amplifier 2 is connected to a source of alternating current at 115 volts and the signal applied to winding 45 is at its upper limit, the operating point will be at point B on the transfer characteristic curve for 115 volts and the relay will be operated. The operating point on the transfer characteristic curve for magnetic amplifier 2 is determined by the resultant magnetic force established by

windings

45, 46, and 47 as measured from the zero bias line for magnetic amplifier 2. Thenithe amount of magnetizing force set up in the cores 35 and 36 is equal to -H -H +H where H is the magnetic force due to the signal applied to the signal winding 45, H is the magnetic force due to the unregulated direct current power applied to the bias compensating winding 47, and H is the magnetic force due to the current supplied from the constant direct current source 27 to the bias winding 46 via resistor network 48. The resultant magnetic force due to

windings

45, 46, and 47 aids the magnetic force produced by the

main windings

37 and 38. In magnetic amplifier2, the magnetic forces due to the bias compensating winding 47 and the biasing winding 46 are subtractive and the magnetic force of the signal winding 45 acts in opposition to the magnetic force produced by the

main windings

37 and 38. In magnetic amplifier 1, the magnetic forces produced by the bias winding 19 and the bias compensating winding 20 are additive and the magnetic force produced by the signal winding 18 is in the same direction as the magnetic force produced by the main windings and 11. As a result, when the signal applied to signal winding 45 decreases a slight amount, the output current increases greatly to a point above B causing the relay connected in the load circuit to remain operated. When the signal applied to the winding 45 increases above that required for the load current corresponding to point B, the load current decreases.

Thus, as was the case with magnetic amplifier 1, the load current will vary properly with respect tovariations in the unidirectional signal applied to terminals 21 and 22 to provide the desired operation of the relay connected 7 to respond to the load current of magnetic amplifier 2. Also, as was the case with magnetic amplifier 1, vanations in the alternating current voltage supplied to the transformer 4 will cause the transfer characteristic curve to change so that the operating point on a transfer characthe alternating current supply source decreases.

'teristic curve for 127 volts would be at B" and at B on the transfer characteristic curve for 103 volts, if the resultant magnetic force due to

windings

45, 46, and 47 were to remain the same as they were when the alternating current supply voltage was 115 volts. It is, therefore, necessary that the resultant magnetic force produced by

windings

45, 46, and 47 be altered to cause the load current to be at the same level regardless of variations in the alternating current supply voltage for a given signal applied to the signal winding 45. In the case of the 103 volt transfer characteristic curve, the resultant magnetic force due to

windings

45, 46, and 47 must be increased by AH to have the operating point for the upper limit of the unidirectional signal on the same level as point B. Similarly, a decrease of AH; is needed in the case of the transfer characteristic curve for 127 volts. The bias compensating winding 46 accomplishes this since it is connected to the unregulated direct current power source which varieswith changes in the alternating current voltage supply. The magnetic force due to the bias compensating winding 46 increases with an increase in the alternating current supply source and decreases when Thus, the resultant magnetic force will be a S2+ b2 baba when the alternating supply voltage decreases and will be s2+ b2 bc2l bc2) when the alternating current supply voltage increases.

By proper selection of the resistor 49 and the design of the bias compensating winding 46, AH can be made equal to AH and AH.,, to bring the operating point on the transfer characteristic curves for 103 volts and 127 volts at the same level of output current for the upper limit of the unidirectional signal level as point B on the s transfer characteristic curve for 115 volts.

The transfer characteristic curves shown in FIG. 2 are for a particular current flow through bias winding 19 and a particular current flow through bias winding 46. The current flow through bias winding 19 as determined by the resistance bridge 25 therefore fixes the lower limit for the signal applied to winding 18 which'must be reduced before the load current of magnetic amplifier 1 is reduced to cause the relay in the output circuit to drop out. Similarly, the upper limit for the signal applied to winding 45 which must be exceeded before the load current of magnetic amplifier 2 is reduced to cause the relay in the output circuit to drop out is determined by the cur rent flow through biasing winding 46 as determined by the resistance network 48. The upper and lower limits of variations in the signal applied to terminals 21 and 22 can be readily and independently adjusted, making the I Similarly, the relay winding 43 connected in the load circuit of magnetic amplifier 2 will be carrying a current that is at least equal to the pick-up value of the relay so long as the signal applied to terminals 21 and 22 is below the upper limit as defined by the current flow through the bias winding 46. This provides fail-safe operation since never will both relay windings 16'and 43 be carrying less than their respective pick-up currents unless there is a malfunction in the circuit causing it. This feature thus provides a means for detecting a malfunctioning magnetic amplifier in the controller.

The invention described herein is not limited to the details shown but may assume numerous forms and the scope of the invention is to be defined solely by the following claims.

I claim:

I. A current controller comprising a first and second self-saturating magnetic amplifier, each having a signal winding, biasing Winding and a load circuit including a current responsive device; means for connecting each signal winding to respond, directly to a unidirectional input signal; means including a regulated direct current supply for energizing said biasing winding of said first amplifier to cause current fiow through the current responsive device of said first amplifier to be above a predetermined level as a unidirectional input signal applied directly to the signal winding of said first amplifier increases above the level of said unidirectional signal corresponding to said predetermined level of current fiow of said first amplifier; and means including a regulated direct current supply for energizing said biasing winding of said second amplifier to cause current flow through the current responsive device of said second amplifier to be above a predetermined level as a unidirectional input signal applied directly to the signal winding of said second amplifier 7 decreases above the level of said unidirectional signal corresponding to said predetermined level of current flow of said second amplifier.

2. A current controller comprising a first and second self-saturating magnetic amplifier adapted to be energized from an alternating current supply subject to voltage variations, each amplifier having a signal winding, a biasing Winding and a load circuit including a current responsive device; means for connecting each signal winding to respond directly to a unidirectional input signal; means including a regulated direct current supply for energizing said biasing winding of said first amplifier to bias said first amplifier to cause current flow through the current i responsive device of said first amplifier to be above a predetermined level as a unidirectional input signal applied directly to the signal winding of said first amplifier increases above the level of said unidirectional signal corresonding to said predetermined level of current flow of said first amplifier; means including a regulated direct current supply for energizing said biasing winding of said second amplifier to bias said second amplifier to cause current flow through the current responsive device of said second amplifier to be above a predetermined level as a unidirectional input signal applied directly to the signal winding of said second amplifier decreases above the level of said unidirectional signal corresponding to said predetermined level of current fiow of said second amplifier;

an unregulated direct current voltage supply which varies in accordance with the variations in said alternating current supply; and a winding in each of said first and second amplifiers connected to said unregulated direct current voltage supply to alter the biasing of said amplifiers to prevent the level of load current as determined by said unidirectional signal from changing due to variations in said alternating current supply.

3. A current controller comprising a first and second self-saturating magnetic amplifier, each having a signal winding, a biasing winding and a load circuit including a relay winding; means for connecting each signal windl ing to respond directly to a unidirectional input signal; means including a regulated direct current supply for lated direct current supply for energizing said biasing winding of said second amplifier to bias said second amplifier to cause current flow through said relay winding of said second amplifier to be at least equal to the pickup current for the relay winding of said second amplifier 01 for all values of the unidirectional input signal applied directly to the signal winding of said second amplifier below a predetermined level.

4. A current controller comprising a first and second self-saturating magnetic amplifier adapted to be energized from an alternating current supply subject to voltage variations, each amplifier having a signal winding and a load circuit including a relay winding; means for connecting each signal winding to respond directly to a unidirectional input signal; means including a regulated direct current supply for biasing said first amplifier to cause current flow through the relay winding of said first amplifier to be at least equal to the pick-up current for the relay winding of said amplifier for all values of the unidirectional input signal applied directly to the signal wi'nding of said first amplifier above a predetermined level; means including a regulated direct current supply for biasing said second amplifier to cause current fiow through the relay winding of said second amplifier to be at least equal to the pick-up current for the relay winding of said second amplifier for all values of the unidirectional input signal applied directly to the signal Winding" of said second amplifier below a predetermined second level whereby fail-safe operation of said first and second amplifiers is provided when said unidirectional input signal varies between said level and said second level; an unregulated direct current voltage supply which varies in accordance with the variations in said alternating current supply; and a bias compensation winding in each of said first and second amplifiers connected to said unregulated direct current voltage supply to alter the biasing of said amplifier to prevent the level of load current as determined by said unidirectional signal from changing due to variations in said alternating current supply.

5. A current controller comprising a first and second self-saturating magnetic amplifier, each having a signal winding, abiasing winding and a load circuit including a relay winding; means for connecting each signal winding to respond directly to a unidirectional input signal; a constant direct current voltage source; means connected to said constant direct current voltage source to provide a first adjustable constant direct current voltage output; means connected to said constant direct current voltage source to provide a second adjustable constant direct current voltage output; means connecting said biasing winding of said first amplifier to said first adjustable con stant direct current voltage output for biasing said first amplifier to cause current fiow through the relay winding of said first amplifier to be at least equal to the pickup current for the relay winding of said amplifier for all values of the unidirectional input signal applied directly to the signal winding of said amplifier above a predetermined level; and means connecting said biasing winding of said second amplifier to said second adjustable constant direct current voltage output for biasing said second amplifier to cause current flow through said relay winding to be at least equal to the pick-up current for the relay winding of said amplifier for all values of the unidirectional input signal applied directly to the signal Winding of said second amplifier below a second predetermined level.

6. A current controller comprising a first and second I self-saturating magnetic amplifier adapted to be energized from an alternating current supply subject to voltage variations, each amplifier having a signal winding, :1 mam winding, a biasing Winding and a load circuit including a current responsive device, the load circuit and main increase as a unidirectional input signal applied directly to the signal winding of said second amplifier decreases;

an unregulated direct current supply which varies in ac-' cordance with the variations in said alternating current supply; and a bias compensation winding in each of said first and second amplifiers connected to said unregulated direct current supply to alter the biasing of said amplifiers to prevent the level of load current for said first and second amplifiers as determined by said adjustably energized biasing windings andsaid unidirectional input signal applied to said signal windings from changing due to variations in said alternating current supply as sensed by said main windings.

7. A current controller comprising a first and second self-saturating magnetic amplifier adapted to be energized from an alternating current supply subject to voltage variations, each having a signal Winding connected to respond directly to a unidirectional input signal and a load circuit including a main winding and a relay winding connected to said alternating current supply; a regulated direct current supply; a biasing winding on said first amplifier, means including said regulated direct current supply for adjustably energizing said biasing winding to cause current flow through the relay winding of said first amplifier to be at least equal to the pick-up current for the relay winding of said first amplifier for all values of the unidirectional signal applied to the signal winding of said first amplifier above a predetermined level; and a biasing winding on said second amplifier; means including said regulated direct current supply for adjustably energizing said last-mentioned biasing winding to cause current flow through said relay winding of said second amplifier to be at least equal to the pick-up current for the relay winding of said second amplifier for all values of the unidirectional signal applied to the signal winding of said second amplifier below a second predetermined level whereby failsafe operation of said first and second amplifiers is provided when said unidirectional signal varies between said predetermined level and asid second level; an unregulated direct current supply which varies in accordance with the variations in said alternating current supply; and a winding in each of said first and second amplifiers connected to said unregulated direct current supply to alter the biasing of said amplifiers to prevent the level of load current as determined by said unidirectional signal from changing due to variations in said alternating current supply.

8. A current controller comprising a first and second self-saturating magnetic amplifier adapted to be energized from an alternating current supply subject to voltage variations, each having a signal winding, a main winding, a biasing winding and a load circuit including a current responsive device, the load circuit and main winding for each amplifier connected to said current supply; means.

for connecting each signal Winding to respond directly to a single unidirectional input signal; a constant direct current source energized by said current source; means connected to said constant direct current source to provide a first adjustable constant direct current output; means connected to said constant direct current source to provide a second adjustable constant direct current output; means connecting said biasing winding of said first amplifier to said first adjustable constant direct current output for biasing said first amplifier to cause current fiow through the current responsive device or said first amplifier to increase as said unidirectional input signal increases; and means connecting said biasing winding of said second amplifier to said second adjustable constant direct current output for biasing said second amplifier to cause current flow through the current responsive device of said second amplifier to decrease as said unidirectional input signal decreases; an unregulated direct current sup- 9. A current controller comprising a first and second self-saturating magnetic amplifier adapted to be energized from an alternating current supply subject to voltage variations; a main winding for each amplifier responsive to said'voltage variations; a signal winding for each amplifier connected to respond directly to a single unidirectional input signal; a bias winding for each amplifier with each bias winding adjustably energized from a regulated direct current supply whereby the operating point for each amplifier is selected; a bias compensation winding for each amplifier responsive to said voltage variations;

, said signal winding for said first amplifier and said bias winding for said second amplifier being arranged to add to the magnetic flux established by their respective main windings, while said signal winding for said second amplifier and the bias winding for said first amplifier are arranged to subtractfrom the magnetic flux established by their respective main windings; a bias compensation winding for each amplifier responsive to said voltage variations and arranged to subtract from the magnetic flux established by their respective main windings whereby the operating point for each amplifier is not influenced by said voltage variations.

10. A current controller comprising a first and second self-saturating magnetic amplifier adapted to be energized from an alternating current supply subject to voltage variations; a main winding for each amplifier responsive to said voltage variations; :1 signal Winding for each amplifier connected to respond directly to a single unidirectional input signal; a bias winding for each ampli fier; a regulated direct current source energized by said current supply; means connected to said regulated direct current source providing a first adjustable regulated direct current source; means connected to said regulated direct current source providing a second adjustable regulated direct current source; means connecting the bias winding for said first amplifier to said first adjustable regulated direct current source whereby the operating point for said first amplifier is selected; means connecting the bias winding for said second amplifier to said second adjustable regulated direct current source whereby the operating point for said second amplifier is selected; a bias compensation winding for each amplifier responsive to said voltage variations; said signal winding for said first amplifier and said bias winding for said second amplifier being arranged to add to the magnetic flux established by their respective main windings, While said signal winding for said second amplifier and the bias winding for said first amplifier are arranged to subtract from the magnetic fiuX established by their respective main windings; a bias compensating winding for each amplifier responsive to said voltage variations and arranged to subtract from the magnetic fiux established by their respective main windings whereby the operating point for each amplifier is not influenced by said voltage variations.

References Cited in the file of this patent UNITED STATES PATENTS 2,757,320 Schuh July 31, 1956 2,895,085 Siedband July 14, 1959 FOREIGN PATENTS 1,222,092 France Ian. 18, 1960

Claims

6. A CURRENT CONTROLLER COMPRISING A FIRST AND SECOND SELF-SATURATING MAGNETIC AMPLIFIER ADAPTED TO BE ENERGIZED FROM AN ALTERNATING CURRENT SUPPLY SUBJECT TO VOLTAGE VARIATIONS, EACH AMPLIFIER HAVING A SIGNAL WINDING, A MAIN WINDING, A BIASING WINDING AND A LOAD CIRCUIT INCLUDING A CURRENT RESPONSIVE DEVICE, THE LOAD CIRCUIT AND MAIN WINDING FOR EACH AMPLIFIER CONNECTED TO SAID CURRENT SUPPLY; MEANS INCLUDING A REGULATED DIRECT CURRENT SUPPLY FOR ADJUSTABLY ENERGIZING EACH OF SAID BIASING WINDINGS TO CAUSE CURRENT FLOW THROUGH THE CURRENT RESPONSIVE DEVICE OF SAID FIRST AMPLIFIER TO INCREASE AS A UNIDIRECTIONAL INPUT SIGNAL APPLIED DIRECTLY TO THE SIGNAL WINDING OF SAID FIRST AMPLIFIER INCREASES AND TO CAUSE CURRENT FLOW THROUGH THE CURRENT RESPONSIVE DEVICE OF SAID SECOND AMPLIFIER TO INCREASE AS A UNIDIRECTIONAL INPUT SIGNAL APPLIED DIRECTLY TO THE SIGNAL WINDING OF SAID SECOND AMPLIFIER DECREASES; AN UNREGULATED DIRECT CURRENT SUPPLY WHICH VARIES IN ACCORDANCE WITH THE VARIATIONS IN SAID ALTERNATING CURRENT SUPPLY; AND A BIAS COMPENSATION WINDING IN EACH OF SAID FIRST AND SECOND AMPLIFIERS CONNECTED TO SAID UNREGULATED DIRECT CURRENT SUPPLY TO ALTER THE BIASING OF SAID AMPLIFIERS TO PREVENT THE LEVEL OF LOAD CURRENT FOR SAID FIRST AND SECOND AMPLIFIERS AS DETERMINED BY SAID ADJUSTABLY ENERGIZED BIASING WINDINGS AND SAID UNIDIRECTIONAL INPUT SIGNAL APPLIED TO SAID SIGNAL WINDINGS FROM CHANGING DUE TO VARIATIONS IN SAID ALTERNATING CURRENT SUPPLY AS SENSED BY SAID MAIN WINDINGS.