US2911547A - Signal voltage responsive control system - Google Patents

Description

Nov. 3, 1959 F. A. MANNERS SIGNAL VOLTAGE RESPONSIVE CONTROL SYSTEM Filed March 24. 1958 3 Sheets-Sheet l .PZUNNDU 3x20 SIG NAL VOLTAGE INVENTOR. fiPAN/e AM/v MAMA/[ks Nov. 3, 1959 F. A. MANNERS 2,911,547

' SIGNAL VOLTAGE RESPONSIVE CONTROL SYSTEM Filed. March 24. 1958 s Sheets-Sheet 2 ill 2 I INVENTOR.

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Nov. 3, 1959 F. A. MANNERS 2,911,547

SIGNAL VOLTAGE RESPONSIVE CONTROL SYSTEM Filed March 24, 1958 3 Sheets-Sheet 3 2 \U N m 3 U .J 2 L In v l 5 SIGNAL VOLTAGE Snnentor FeA NK ALA/v MAMA/5P5 M (Ittonlegs- SIGNAL VOLTAGE RESPONSIVE CONTROL SYSTEM Frank I A, Manners, Cleveland, Ohio, assignor to Square D Company, Detroit, Mich a corporation of Michigan 7 Application March 24, 1958, Serial No. 724,222 10 Claims. (Cl. 307-149) This invention relates to an electrical control system responsive to a variable signalvoltage, and more particularly to a signal voltage responsive control system in which the. rate of-change of signalcurrent with signal voltage is caused to be greatly different for different ranges of. variation in the signal voltage.

In control systems that are responsive to a changing signal voltage when the signal volta'gereaches a predetermined-relatively low value or zero, the signal current during a portion of the operating cycle can become excessive because theratio of signal voltage to signal current does not vary greatly. Since response to the signal voltage is not required during the portion of the cycle when the signal voltage is large, any signal current in excess of a predetermined value would notbe'needed, andthe signal current during that portion of the cycle could either 'remain. constant or.bechangedbut slightly, thus eliminating thedeleterious effects ofexcessive currents. When the signal; voltage is within the low. or operating range, however, the signal current mustvaryin a known relationship with. the signalvoltage, and small changes in the signal voltage must be accompanied by material changes in the signal current to provide adequate sensitivity. In accordance with this invention, a novel circuit arrangement is provided which permi'tsthe signal current to vary directly and; material with the signal voltage when the sigmagnitude is cause'dto flow through the rectifierj in its conducting direction from a separate source of unidirectional voltage, so that, when the signal current, in blocking rectifier portion of the circuit less than. the bias current, the signal current is determined solely by the magnitude of the signal voltage and the impedance of the signal circuit and, when the signal current in the blocking rectifier portion of the circuit is greater than the bias current, the signal cur rent is determined by the combined effects of the magnitude of the signal voltage, the impedance of the signal circuit the resistance of the bias circuit, and the magnitude of thebias voltage,

It is a further object of this invention to impress a predetermined voltage in the conducting direction across a rectifierto control the magnitudeof the current flowing froma signal Voltage source through an electroresponsive means connected in series with the rectifier, the rectifier being connected to oppose flow of current through it from the source of signal, voltage.

Other objects and advantages will become apparent from the following description whereinreference is, made to the. drawings, in. which:

Fig. 1 is awiring diagram of a control system illustrate ing the invention;

Fig. 2- is a graph showing the. relationship between the signal current and signal voltagein the control system of Fig. 1;.

'Fig; 3 is a wiring diagram showing the invention. applied in a followup control system for an electric motor;

Pig. 4 is a wiring diagram of a control system illustrating a modification of the invention; and

range but. which limits the signal currentand maintains it relatively constant, regardless of voltage changes, when the signal voltage. is relatively large and outside of the low. or operating. range.

It is an object. of this invention. to provide an improved control system responsive to a variable signal. voltage.

Anotherobject is to providefa. control system responsive to.v a. variable. signal voltage in which the signal current flowing from the. source of signal. voltage is. caused to be disproportionately. small at high values of signal voltage.

Another object is to provide. a control system res'pon sive to a variable signal; voltage in which the current flowing from the source of signal voltage is. limited. to safevalues when the signal voltage is relatively. large and beyond, the operating. range, but which permits the signal current to,vary' materially with variations in the signal voltage when the. signal voltage is relatively small and Within the operating. range.

A control system. utilizing this invention comprises an electroresponsivejmeans connected across a. source. of variable. signal voltage. The electroresponsive means is of the type which responds at a. predetermined. low value of current to perform a control function. If the signal voltage is alternating or otherwise of variable polarity, a full-wave. rectifier is. used. to cause.the.signal current in a portion, of-th e. circuit tobeunidirectional; In accordance withthevpresent invention, a blocking rectifier is interposed! injsaid; portion. of the circuit and is so poled with respect to the polarity of the signal; voltage impressed on it thatcurrent from. the signal .voltagesourcecannot flow through it. In addition, a bias current of predetermined Fig. 5. is a graph showingthe relationship between the rectifier control current and signal voltage in the control system of Fig. 4.

Referring to Fig. l, a source 10. of variable signal voltage is shown as a potentiometer resistor 11 connected across a. source of substantially constant unidirectional voltage at the polarities indicated and. having taps llaand 11b. One, or both. of the taps 11a and 11b are movable along. the resistor 11 so that, selectively, the taps, may be at the same potential, the. tap 11a may be more positive than the tapllb, and the tap 11b may be. more positivethan the tap. 11a. A control system to be. sup;

plied from the taps 11a and 11b includes suitable electroresponsive means 14, 15, and 16 having respective control coils 14w, 15w, and 16w connected in series with each other across the taps 11a and 11b. The means 14, 15, and 16 may be magnetic amplifiers, electromagnetic re.- lays, or other suitable means as will become apparent. The. electroresponsive. means 141and15 are preferably polarity responsive, and the electroresponsive means 16 is preferably rendered insensitive to the relative polarity of the taps 11a and 11b byinterposing a rectifier bridge 18 between the coil 16w and the resistor 11 P or example, the means 14 may be operative whenever the tap 11a is more positive than the tap 11b and inoperative at all other times; the means 15 may be operative whenever the tap 11b is more positive than the tap 11a and inoperative at all other times, and the means 16. may be inoperative as long as the current in its coil 16w is above a predetermined value and' operative when the current isbelow that value.--.The coils 14w and 15w are connected in series with each other between the tap 11a andthe rectifier bridge 18. The electroresponsive means 16 is connected across the rectifier bridge 18 which is so poled that current flow through the coil 16w is always in the same direction irrespective of the relative polarity of the taps 11a and 1112. An adjustable resistor 19 is connected between the coil I 16w and the rectifier 18. Y 1

In accordance with this invention, a blocking rectifier 20 is interposed in the circuit between the coil 16w and the rectifier bridge 18 and is so poled with respect to the Patented NOV- a polarity of the rectifier bridge 18 that current flowing from the rectifier bridge 18 cannot flow through the rectifier 20. The rectifier 20 carries a bias current in its low impedance or conducting direction which is supplied from a source of unidirectional voltage such as a battery 21 and which is controlled in magnitude by an adjustable resistor 22 interposed in the circuit between the battery 21 and the rectifier 20.

The rectifier 20 and the individual rectifiers of the rectifier bridge 18 are shown as metallic disc rectifiers employing some semi-conductive material such as selenium, copper-oxide, or germanium, but may be of any suitable type such as thermionic discharge tubes or the like.

In the operation of Fig. 1, therelationships of the current in the various parts of the circuit is given by the equation where I is the current flowing through rectifier 20, I is the bias current from the source 21, and I is the signal current from the source 10. When the signal voltage between the taps 11a and 11b is'large enough to cause the signal current flowing from the source through the coils 14w, w, and 16w to be larger than the bias current flowing from the battery 21 through the rectifier 20, the value of the signal current, neglecting any voltage drop at the rectifier bridge 18, depends upon the voltage at the taps 11a and 11b, the resistance of the coils 14w, 15w, and 16w and or the resistor 19, the voltage of the source 21, and the resistance of the resistor 22. The

signal current under these conditions is given by the equation ESIiIEB RB+RS (1) in which I is the signal current in amperes, E is the voltage at the taps 11a and 11b, E is the voltage of the battery 21, R is the resistance of the resistor 22 in ohms, and R is the total resistance in ohms of the coils 14w, 15w, 16w and the resistor 19. Also since I is larger than 1 I is mathematically negative, but, because of rectifier 20, is zero.

When the voltage between taps 11a and 11b is small enough to cause the signal current flowing from the source 10 through the coils 14w, 15w, and 16w to be less than the bias current flowing from the battery 21 through the rectifier 20, the rectifier 20 acts as a short-circuit, insofar as the magnitude of the signal current is concerned, and the signal current then depends upon the voltage at the taps 11a and 11b and the resistance of the coils 14w, 15w, and 16w and the resistor 19, and is independent of the voltage of the battery 21 and the resistance of the resistor 22.

The signal current under these conditions is given by the equation Also since I is smaller than I I is mathematically positive and flows through rectifier 20.

By examination of Equations 1 and 2, itcan be seen that by proper selection of resistance and voltage values, a desirable relationship between the signal voltage and the signal current such as shown by a curve 23 of Fig. 2 can be obtained. When the signal voltage at the source 10 is relatively large so that the signal current exceeds the bias current in the rectifier 20 and Equation 1 applies, the signal current changes relatively little with changes in the signal voltage, as shown by the portion A of the curve. Below a predetermined low value of signal voltage, however, such as the value B, Equation 2 applies, and the signal current changes materially with changes in the signal voltage as shown by the portion C of the curve 23. If the rectifier 20 and the battery 21 were not in the system of Fig. 1, the signal current would vary as shown by the portion C and the broken line curve 24 and would reach excessive values at high values of signal voltage.

It is thus seen that Fig. 1 illustrates a control system in which a signal current flowing in the system from a source of signal voltage is limited to a safe value when the signal voltage is relatively large and beyond the operating range, and in which the signal current changes materially with changes in the signal voltage when the signal voltage is relatively small and within the operating range. It is apparent that, within the scope of this invention, the signal voltage impressed on the rectifier 18 could be omitted if the signal voltage were unidirectional and of constant polarity. 7

Referring now to Fig. 3, wherein the invention of Fig. l is illustrated as applied in a follow-up control system for an electric motor, a tap changing device 25 for a potentiometer resistor 26 has circumferentially spaced contacts 25a through 25] radially spaced from a contact ring 28, the ring and contacts being selectively bridged as an arm 29 rotates. The arm 26 is driven by a direct current motor 30 having an armature winding 30a and a shunt field winding 30 and arranged to bereversibly connected to a suitable voltage source 31 through 'an adjustable resistor 32 by selective operation of double-pole electromagnetic forward and reverse contactors 34 and 35. Slow down of the motor 30 prior to stopping is effected by an armature shunt resistor 36 arranged to be connected across the armature 30a by an electromagnetic slow-down contactor 38.

The potentiometer resistor 26 is connected in series with an adjustable resistor 39 and an ofi-on switch 40 across the direct current terminals of a full wave recti fier 41 supplied through an adjustable resistor 42 from a transformer 44 connected acrossalternating current supply lines 45. The resistor 26 has equally spaced taps connected respectively to the contact segments 26a through 26 Other numbers of taps and contact segments may, of course, be used. The voltage across the resistor 26 can be selected by adjustment of the resistors 39 and 42. I y

A suitable selector device 46 has a plurality of circumferentially spaced contact segments 46a through 46 radially spaced from a contact ring 48, the ring and contacts being selectively bridged as an arm 49 rotates. The arm 49 may be turned manually or by other suitable means as is known in the art. Suitable means areprovided forselectively and adjustably connecting the contact segments 46a through 46j to the taps on the. resistor 26. As shown, this means comprises a plurality of plug and flexible cord sets 50, but other circuit selecting means may be used if desired. As will become apparent, the arm 49 may be positioned on a selected one of the contact segments 46a through 46 thereby to cause the motor to drive the arm 29 to a balance segment, that is, to the one of the segments 25a through 25 to which the selected one of thecontacts 46a through 46 is connected by the cordsets 50.

The operation of the motor 30 for driving the arm 26 to a balance segment selected by adjustment of the arm 49 is controlled by a plurality of magnetic amplifiers 54, 55, and 56 having respective bias windings 54b, 55b, and 56b, pairs of main or reactance windings 54m, 55m, and 56m, and control windings 54c, 55c, and 56c. Each pair of the main windings 54m, 55m, and 56m is connected in a bridge network with associated blocking rectifie'r's 58 in a well-known manner across a transformer 59 supplied from the supply lines 45.

A full-wave rectifier 60 connected across the transformer 59 supplies direct current to the bias windings 54b and 55b through a common adjusting resistor 61, and a fullwave rectifier 62, also connected across. the transformer 59, supplies direct current to the bias winding 56b through an adjusting resistor 64.

The output of the amplifier 54 is supplied through conductors 65 to an operating winding 34w of the forward contactor 34, the output of the amplifier 55 is supplied through conductors 66 to an operating winding 35w of the reverse contactor 35, and-the output of the amplifier 56 supplied through conductors 6 8 to an operating winding 38w of the slowdown contactor 38.

Since the contact segments 25a through 25f are permanently connected to respective taps on the resistor 26, selective connection of the contact segments 46a through 46 to taps on the resistor 26 ,by means of the cord sets 50 causes the potential between the rings 28 and 48 to depend upon the relative turned positions of the arms 29 and 4 9. For example, in the position of the arms shown,

the ring 48 is connected through the segment 46a to the tap on the resistor 26 to which the ring 28 is connected through the contact segment 25a. Hence the voltage between the rings 28 and 48 is zero. If thearm 49 is moved to engage the segment 46b, for example, the voltage difference between the rings 28 and 48 is equal to the voltage between the contact segments 46b and 25a and the ring 28 is positive with respect to the ring 48. Since the contact segments46b and 250 are connected to widely dist placed points along the resistor 26, this voltage is relatively large. If the arm 49 had been moved instead to engage the contact segment 46c the voltage between the rings 28 and 48 would have been relatively low and the ring 28 would be negative with respect to the ring48.

The connection of the control coils 54c, 55c, and 560 now to be described shows how the signal voltage be tween the rings 28 and 48 is used to determine the direction of rotation of the motor 30, its speed of rotation, and the amount of its rotation before it stops automatically when the arm 29 reaches a balance segment. It should be noted that the initial value of the signal voltage, when a relatively long movement of the motor 30 is called for, is relatively large whereas the signal voltage is relatively small when a short movement is called for. To provide the required sensitivity in the control system, it is necessary to limit the current that can flow when the large signal voltage is present. The invention illustrated by Fig. 1 is incorporated in the follow-up system of Fig. 3 for this purpose.

A connection extends from one terminal of a rectifier bridge 69 through the control windings 55c and 540 and a conductor 70 to the ring 28. The opposite terminal of the bridge 69 is connected to the ring 48 through a conductor 71. The remaining two terminals of the rectifier 69 are interconnected through an adjustable resistor 72, the control winding 56c, and a blocking rectifier 74 so poled as to prevent the flow of current therethrough from the rectifier 69. A bias current is passed through the rectifier 74 in its conducting direction from a full-wave rectifier 75 supplied from a transformer 76 connected to the supply lines 45. An adjustable resistor 78 controls the amount of bias current that can flow from the rectifier 75 through the rectifier 74.

With no current in the control windings 54c, 55c, and 560, the amplifiers 54 and 55 are biased into their cut-oft" regions by their respective bias windings 54b and 55b and the amplifier 56 is biased to its conducting region by its bias winding 56b. Consequently, at balance, the winding 38w is energized and the contactor 38 is closed whereas the windings 34w and35w are deenergized and the contactors 34 and 35 are open.

When the ring 28 is positive with respect to the ring 48, current flows through the control winding 540 from left to right and biases the amplifier 54 further into its cut-ofi? region so that the winding 34w remains deenergized. Current flowing through the control windings 55c from left to right, however, drives the amplifier 55 into its conducting region and the winding 35w of the contactor 35 is accordingly energized to cause the motor 30 to operate in the reverse direction moving the arm 29 counterclockwise towards the balance contact segment. If the current flowing in the control winding 56c is above a predeter- I equal to the drop between three or mined low value, the amplifier 56, is driven into its nonconducting region and the conductor 38 opensv topennit the motor to accelerate to maximum speed. As the. arm 29 moves counter-clockwise, the voltage, between, the rings 28 and 48 gradually deereases andfthe current in the 'winding56c becomesless. At a predeterminedvalue of current in the winding 560, the amplifier 56. aga' be.- comes conducting and causes energization of the winding 38w and consequent closureof, the conductor 38 This slows down the'mot or. 30 which continues, to at a slow speed until the arm 29 reaehes the balance segment, that is, the segment to which the ring 48 is connected de? pending upon the turned position of the arm 49. When the balance segment isreached, the'vo ltage between the conductors and 71 becomes zero. and the amplifier 55 becomes non-conducting to cause opening-of thecontaetor 35 and the motor 30 stops.

If the arm 49 is so positionedas tocause the ring28 to be negative with respect to thering 48, current flows through the control winding 550 from right to left and biases the amplifier 55 further into its cut-oflf region so that the contactor 35w remains deenergized. Current flowing through the controlwinding 540 from rightto left, however, drives the amplifier54 into it s conducting region and the winding 34w of the contactor 34 is cordingly energized to cause the motor 30 to operate. in the forward direction moving the arm 29 clockwise toward the balance segment. When the balance segment is approached by the arm 29, the motor 30 slows down as described for reverseoperation and the motonSll; stops when the arm reaches the balance segment. I

When the motor 30 first starts to operate, the signal voltage at the conductors 70 and 71, if a long movement of the arm 29 is called for,.is so largeas tocausethe current in the winding 56c to be greater than the biascurrent flowing through the rectifier 74. The ratioof the current in, the winding 560 to the voltage between the rings and 48 at this time depends upon the resistance oi the re: sister 78 and the output voltage of the rectifier 75., When the arm 29 nears the balance segment, the signal voltage has decreased to a value below the valueBgofFig. 2. and the signal current in the winding 560 is less than the bias currentflowing through the rectifier 74. Since there is a net forward current flowing through the rectifier 74, the ratio of the current in the winding 560 to the signal voltage is now independent of theyoltage of the rectifier and depends only upon the value of the signal voltage and the resistance of the windings 54c, 55c, 56c, and of the resistor 72. i

The voltage between adjacent taps on the resistor 26 is adequate to drive the amplifiers 54 and 55 into their I conducting regions, and for most applications, a voltage four taps on the resistor 26 should be adequate to drive the amplifier 56 into the non-conducting region.

When the control system in accordance with this invention is applied to an automatic pre-set screwdown controller such as described in Schurr Patent No. 2,564,-

284, it is possible to use a rheostat having as many as forty segments with eight volts between its taps and still use magnetic amplifiers of reasonable size and sensitivity to a change of eight volts as the arm nears or reaches the balance segment.

It is sometimes desirable to use the current flowing through the rectifier for control.

The control system, when arranged to respond to a variable signal voltage in which control current flows throughan electroresponsive means is in a predetermined relationship to the signal voltage and is limited to safe values when a signal voltage is relatively large and beyond the operating range but which permits the control current to vary materially with variations in the signal voltage when the signal voltage is relatively small and within the operating range, is illustrated in Fig. 4.

In Fig. 5, the parts corresponding to those shown in Fig. l are designated by primed corresponding numerals.

This embodiment is similar to that of Fig. l in all re spects except that the negative side of the source of energy 21' is connected between the adjustable resistor 19' and the electroresponsive means 16 Whereas, in Fig. 1, the negative side of the battery 21 is connected between the rectifier 20 and the electroresponsive means 161 1 In the circuit in Fig. 4, the current flowing through the electroresponsive means 16" is the current I which also flows through the rectifier 20 whereas, in Fig. 1, the current flowing through the electroresponsive means 16Iis the signal current I By" examination of the Equations a, l, and 2, it can be seen that by proper selection of resistance and voltage values, a desirable relationship, such as shown by a curve 25 of Fig. 5, can be obtained, between the signal voltage and the current I When the signal voltage at the source 10' is relatively large so that the current I exceeds the bias current 1 the current I in the electroresponsive means 16' and the rectifier 20 is zero. The current I reaches zero at the instant the signal currentl equals the bias current 1 It is to be noted that after this transition point is reached, i.e. after I has been increased to equal 1 the'current 1;; remains zero regardless of any further increase in the signal voltage. As further illustrated in Fig. 5, when the signal voltage is below its value at the transition point B, the signal current I is less than the bias current 1 and the current I flowing through the electroresponsive means 16 and the rectifier 20 is in direct relationship to the signal voltage.

Referring'again to Fig. 4, it is apparent that this relationship of rectifier current I to signal voltage can be used to control the electroresponsive means 16 and that the current through the electroresponsive means 16' ranges from zero to a maximum reached when the signal voltage is zero.

This application is a continuation in part of my copending application Serial No. 660,122, filed May 20, 1957, and entitled Signal Voltage Responsive Control System.

. Having thus described my invention, I claim:

1.-In an electrical system, an electroresponsive device operable by flow of current therethrough, a source of signal voltage of magnitude variable within a predetermined range, circuit means connecting said electroresponsive device in circuit with said source of signal voltage for effecting operation of the device in relation to ,thesignal voltage, said circuit means including at least a circuit portion carrying a unidirectional current which is derived from said signal voltage, a rectifier interposed in said portion of said circuit and-so poled as to'prevent flow of said unidirectional current through the rectifier, a source of unidirectional bias voltage of predetermined magnitude, and means connecting said source of unidirectional bias voltage across said rectifier at a polarity to urge bias current to flow through the rectifier in its conducting direction thereby to control the magnitude of the current flowing through the electroresponsive device.

2. The system according to claim 1 characterized in that said signal voltage is non-cyclic and of alternate polarity.

3. The system according to claim 1 characterized in that said signal voltage is unidirectional.

4. The system according to claim 1 wherein said device is capable of withstanding a-. predetermined maximum current and said bias voltagelirnits the current ilow through said device to a value less than said maximum current.

5. The system according to claim 1 wherein said device is connected in said circuit portion carrying a unidirectional current.

6. The system according to claim 1 wherein said cir cuit means includes a signal current circuit portion carrying a signal current from the source of signal voltage and wherein said device is connected in said signal current portion. a

7. The system according to claim 1 wherein said device is connected in series with said rectifier.

8. The system according to claim 1 wherein said device is connected in series with said rectifier and wherein the bias voltage source is connected in series with the electroresponsive device. i

9. The system according to claim 1 wherein said device is connected in series with said rectifier and wherein the bias voltage source is connected in parallel with the electroresponsive device.

10. The system according to claim 1 wherein said source of signal voltage is capable of producing a signal current which increases as the signal voltage increases, and wherein said rectifier, source of unidirectional bias voltage, and means cooperatively allow the signal current to increase as the signal voltage increases when the bias current exceeds theunidirectional current, and further cooperatively restrain the signal current from increasing as the signal voltage increases when the unidirectional current exceeds the bias current.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,911,547 November 3, 1959 Frank A. Manners It is hereb$ certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 40, for "material" read materially column 4, line 13, after "could be" insert a cyclic alternating voltage instead of a non-cyclic voltage of reversible polarity and that the rectifier 18 could be column', line 67, for "flows" read flowing column 7, line 1, for the numeral "5" read 4 Signed and sealed this 19th day of July 1960.

(SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,911,547 November 3, 1959 Frank A. Manners It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 40, for "material" read materially column 4, line 13, after "could be" insert a cyclic alternating voltage instead of a non-cyclic voltage of reversible polarity, and that the rectifier 18 could be column6, line 67, for "flows" read flowing column 7, line 1, for the numeral "5" read 4 Signed and sealed this 19th day of July 1960.

(SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Attesting Officer Commissioner of Patents

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