US3231802A - Indicating controller - Google Patents

Description

Jan. 25, 1966 A. R. MYERS INDICATING CONTROLLER Filed April 25, 1963 INVENTOR. Alva R. Myers mun-Em JOmPZOo rneys or a thermistor. 'other three legs of the Wheatstone bridge.

United States Patent 3,231,802 INDICATING CONTROLLER Alva R. Myers, Mountain View, Calif., assignor to Electronic Processes Corporation, San (Iarlos, Calif., a corporation of California Filed Apr. 25, 1963, Ser. No. 275,641 12 Claims. (Cl. 31829) This invention relates to an indicating controller and more particularly to a controller which can be utilized for maintaining a predetermined set point for any parameter which can be expressed as a voltage or a current.

In Patent No. 2,971,137, there is disclosed a power control circuit. This power control circuit does not include anticipating means for anticipating when the set point is reached. Although anticipating circuits have heretofore been utilized, there is a need for a controller in which the anticipating means is completely isolated from the control means.

In general, it is an object of the present invention to provide an indicating controller in which the control means is completely isolated from the anticipating means.

Another object of the invention is to provide an indicating controller of the above character which can be readily and accurately calibrated.

Another object of the invention is to provide an indicating controller of the above character in which elements in the anticipating means can be changed without affecting the calibration of the control means.

Another object of the invention is to provide an indicating controller of the above character in which a low voltage D.C. servo can be driven from an AC bridge.

Another obiect of the invention is to provide a controller of the above character which is completely isolated from the power source.

Another object of the invention is to provide a controller of the above character which is compact, light in weight and which can be readily manufactured.

Another object of the invention is to provide a controller of the above character in which the set point can be readily adjusted.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment is set forth in detail in conjunction with the accompanying single figure of the drawing which is a schematic circuit diagram of the invention as applied to temperature control.

As shown in the schematic circuit diagram in the drawing, my indicating controller consists of a control bridge B1 and an anticipator bridge B2. Both of the bridges are Wheatstone bridges. The control bridge B1 consists of a sensing element for measuring a particular parameter, as, for example, temperature. The sensing element R1 can be of any suitable type such as a resistor The resistors R2, R3 and R4 form the A push-toset switch S1 has its contacts 1 and 2 connected across one set or pair of opposite terminals 0 and d of the Wheatstone bridge B1 and has its movable contact 3 connected to ground as shown. The other pair of terminals a and b of the bridge B1 is connected to a suitable voltage supply as, for example, a 6.3 volt A.C. supply supplied by the secondary winding 11 of a transformer T2. Three potentiometers P1, P2 and P3 are serially connected across the last named pair of terminals a and b of the control bridge B1. Potentiometers P1 and P3 are used as low and high range calibration potentiometers, respectively, whereas the potentiometer P2 is utilized as a servo position potentiometer as hereinafter described.

The terminal d of the control B1 is connected to the terminal c of the anticipator bridge B2. The anticipator bridge consists of two temperature sensitive resistors such as thermistors TH1 and TH2 which form two legs of the bridge. The other two legs of the bridge are completed by resistors R6 and R8. The pair of terminals a and b of the anticipator bridge B2 are supplied with a suitable voltage supply such as the 6.3 volt A.C. supply from a winding 12 of the transformer T2. The output of the anticipator bridge B2 is connected to a control amplifier A1 by connecting the input of the control amplifier to the terminal a. of the anticipator bridge B2. The output of the control amplifier A1 is coupled to the base of an NPN transistor Q1 through a coupling capacitor C1. A resistor R9 is connected to the "base of the transistor Q1 and serves to keep the transistor Q1 normally turned off until a signal is received from the control amplifier A1. The emitter of transistor Q1 is connected to ground as shown. The collector of the transistor Q1 is connected through a current limiting resistor R10 to one side of the winding of relay RY1. The other side of the winding is connected to one side of a diode D1. The other side of the diode D1 is connected to a suitable voltage supply as, for example, 20 volts, 60 cycle A.C., as hereinafter described. A capacitor C3 is connected across the winding of the relay RY1 to prevent chattering of the contacts of the relay.

As shown in the circuit diagram, the relay RY1 is provided with contacts 16. Stationary contact 1 of the relay is connected to one side of a load or controlled circuit 16 which can be of any desired type as, for example, the resistive load of an oven indicated by the broken line 17. The resistive load 16 is connected to the terminal L2. Terminals L1 and L2 are connected to a suitable power supply as, for example, volts, 50/60 cycle A.C. supply indicated. The terminal L1 is connected to movable contact 2 of the relay RY1. Thus, when the movable contact 2 is moved into engagement with the stationary contact 1, power is supplied to the heating element 16. Stationary contacts 5 and 6 of relay RY1 are connected to ground through suitable indicating means as, for example, incandescent lamps N1 and N2. In addition, stationary contact 5 is also connected to one side of a current limiting resistor R11 and the other side of the current limiting resistor is connected to a heater H1 which is the heater for the thermistor TH1 in the anticipator bridge B2; Likewise, stationary contact 6 of the relay is connected to one side of the current limiting resistor R12. The other side of the current limiting resistor R12 is connected to a heater H2 which is the heater for the thermistor TH2 in the anticipator bridge B2. The other ends of the heaters H1 and H2 are connected by a potentiometer P4. The tap 18 of the potentiometer P4 is connected to ground. The potentiometer P4 is utilized as a reset adjustment and establishes the duty cycle for the relay RY1.

The point 21 connected to the potentiometer P2 of the control bridge B1 is connected to the input of a servo amplifier A2. The output of the servo amplifier is connected to the base of an NPN driver transistor Q2 through a coupling capacitor C2. The transistor Q2 is biased through the resistor R14 connected to the base of the transistor so that it will only conduct when a signal is applied to it by the servo amplifier A2. The emitter of the transistor Q2 is connected to ground as shown. The collector of the transistor Q2 is connected through a current limiting driver protecting resistor R13 to the bases of two PNP \power transistors Q3 and Q4 through isolating diodes D2 and D3. The base of the transistor Q3 is connected to the emitter of the transistor Q3 through the stablilizing resistor R15 and similarly, the base of the transistor Q4 is connected to the collector of the transistor Q4 through a stabilizing resistor R16. The collector of the transistor Q3 is connected to one side of o the current limiting resistor R17. The other side of the curent limitingresistor R17 is connected to one side of a D.-C. servo motor 23. The other side of the servo motor is connected to the collector of the transistor Q4. The collectors of the transistors Q3 and Q4- are also connected to taps 24a and 24b on opposite ends of a winding 24 provided with a center tap: 26 through diodes D4 and. D to provide a suitable voltage to the transistors Q3 and Q4. Isolating diodes D5 and D7 are connected between the diodes D4 and D5 and the emitters of the associated transistors Q3 and Q4 and serve to isolate the emitters from the remainder of the circuitry during certain portions of the cycle of operation.

The primary winding 27 of the transformer T2 is also connected to the taps 24a and 24b of the winding 24. The transformer T1 is provided with a primary winding 28 which has its terminals L3 and L4 connected to a suitable power supply such as 110 volts, 50/ 60 cycle A.-C. indicated in the drawing. One end of the winding 24 is connected to the diode D1 to provide the Volt 60 cycle A.-C. supply indicated. Isolating shields 29 are provided on the transformer T1 to isolate the primary from the secondary; similarly, shields 31 are provided in the transformer T2 to isolate the secondary from the primary. Since both of the transformers T1 and T2 are provided with separate shielding, it can be seen that the output voltage supplied to the windings 11 and 12 are doubly isolated from the power supply connected to the terminals L3 and L4 of the transformer T1.

The servo motor 23 drives an indicator I1 with a pointer 29 as well as the potentiometer P2 as shown by the broken line in the drawing.

Operation of my indicating controller may now be briefly described as follows. Let it be assumed that the indicating controller has been set for a predetermined set point in a manner hereinafter described by the adjustment of potentiometer R3. Also, let it be assumed that it is desired to bring the control circuit or load up to the set point from a point which is considerably below the starting point. Thus, when power is supplied to the load 16, power is also supplied to the heater H1 to cause the thermistor element THZ to rise in resistance value. When the temperature of the sensing element R1 is considerably below the set point there w-il1 be an output from the control bridge to which is added the output of the anticipator bridge. The combined outputs of the two bridges are supplied to the control amplifier A1. Normally, when the sensing element R1 is below the set point temperature, the output of the control bridge B1 will have one phase, whereas if the sensing element R1 senses a temperature which is above the set point temperature, the control bridge B1 will have an output of opposite phase or, in other words, 180 out of phase with the phase when the sensing element is sensing a temperature below the set point temperature. The relay RY1 will be operated when the combined output 'from the bridges B1 and B2 is of one phase and will not be operated when the combined output is of opposite phase. The diode D1 is arranged so that it will only supply the positive half wave of the 60 cycle A.-C. signals which are supplied to it from the transformer T1. The relay RY1 will only be operated when a signal of one phase is supplied to the base of the transistor Q1 to cause current to flow through the transistor to ground to energize the winding of the relay RY1. Thus, the relay is phase sensitive.

When the relay RY1 is energized, its contacts 1 and 2 are closed as are its contacts 4 and 5 to apply power to the load 16 and also to apply heat to the heater H1. Thus, at the time that the load 16 is being supplied with power, heat is being supplied to the heater H1 and the lamp N1 is lit. Heating of the heater will cause the resistance value of the thermistor TH2 to rise in value to cause an unbalance in the anticipator bridge B2 to pro vide an output which is out of phase with the output of the bridge B1. This output is added to the output from the control bridge B1 which causes the relay RY1 to be deenergized before the setpoint is reached.

As soon as the relay RY1 is deenergized, the contacts 4 and 6 are closed to supply heat to the heater H2 which heats the thermistor THZ to increase its resistance value. As this resistance value changes, the output of the anticipator bridge B2 is of the same phase as the output of the control bridge B1 and is added to the output of the control bridge B1 so that again there is a net signal which is supplied to the base of the transistor Q1 so that the relay RY1 is again operated or energized. As soon as the relay RY1 is operated, heat is again supplied to the load 16 and to the heater H1. As the heater H1 heats up, the resistance value of the thermistor TH1 again changes to provide an output from the anticipator bridge out of phase with the output of control bridge B1 which added to the control bridge output causes the relay RY1 to be deenergized again. As soon as the relay RY1 is deenergized, the heater H2 is again energized. This procedure continues until the set point is reached and thereafter serves to maintain the set point with very minor temperature fluctuations. Thus, it can be seen that the anticipator bridge B2 helps the indicating controller to anticipate the set point to thereby reduce or eliminate the initial overshoot and to eliminate any substantial temperature fluctuations when controlling at the set point.

In summarizing this operation, it can be seen that the output from the control bridge will be much greater than the output from the anticipator bridge which has a tendency to cancel the output from the control bridge. However, the closer to null the set point becomes, the lower the output from the control bridge until eventually a point is reached where the outputs of the control bridge and the anticipator bridge equal each other, and since they are out of phase, they will cancel to supply a zero signal to the control amplifier A1. As soon as this occurs, the transistor Q1 stops conducting and the relay RY1 is deenergized causing the relay to return to its normally open position. This causes heating of the heater H2 to heat the thermistor THZ to change the output phase of the anticipator bridge so that it adds to the output of the control bridge and again causes the transistor Q1 to conduct to again energize the relay RY1. This causes heating of the heater H1 and the thermistor TH1 to again change the output and phase of the anticipator bridge. This cycling continues with the period of time between each cycle being less to thereby line out violent temperature fluctuations as the set point is reached and thereafter to control the temperature so that it is always very close to the set point.

As the output from the control bridge B1 changes because of the change in the temperature of the sensing element R1, a signal is supplied from the point 21 to the servo amplifier A2. The output of the servo amplifier A2 is coupled to the base of the driver transistor Q2 through a coupling capacitor C2. The collector output of the transistor Q2 is supplied through resistor R13 to phase sensitive circuitry consisting of the power transistors Q3 and Q4 and the associated diodes D4 and D5 and diodes D6 and D7. Thus, when the tap 24a of the transformer winding 24 connected to the diode D6 is positive in the first half cycle and the base of the transistor Q2 is also positive during the first half cycle, the transistor Q3 will be turned on to supply its signal of one polarity to the servo motor 23 through the resistor R17. Conversely, if the phase is reversed, the transistor Q4 is turned on to supply power in an opposite direction to the servo 23 and also through the diode D4. When Q3 is turned on, the collector supply for the transistor Q3 is obtained through the diode D5, and conversely, when the transistor Q4 is turned on, the collector supply is obtained through the diode D4. Thus, depending upon the signal received from point 21, the servo motor 23 will be driven in one direc tion or the other which will cause the potentiometer P2 to be adjusted by the servo until the signal at 21 has reduced to zero to thus stop operation of the servo motor 23.

The output from the control bridge will be a sine wave of one phase when the sensing element R1 increases in value and will be a sine wave of the opposite phase when the resistance value of the sensing element R1 decreases. In the circuitry shown, the positive half cycle of each of the sine waves is utilized and supplied to the servo amplifier A2. Thus, in other words, in order to operate the servo motor, a positive signal is required. However, it is readily apparent that, if desired, the negative portions of the sine wave can be utilized instead of the postiive portions.

In adjusting the set point, the push-to-set switch S1 is operated to connect contacts 2 and 3 of the switch S1 and to, in effect, ground terminal d of the control bridge.

Then, by varying the control potentiometer R3, the set. point can be raised or lowered because this will cause a' signal to be supplied to the servo amplifier A2 to cause rotation of the servo motor 23 and the indicator I1 to the'desired position. The potentiometers P1 and P3 are calibration potentiometers and are used for determining the' range of the indicator and, in particular, the lower anduppe'r points, respectively, of the range.

' At the time that the set point is being set, the 20 volts A.-C. supplied to the diode D1 are removed and the anticipator bridge balance control R8 is adjusted to provide a Zero output at terminal a of the anticipator bridge B2. As soon as the set point has been adjusted, the diode D1 is again connected to the power supply and the push-to-set switch is opened to close contacts 1 and 3.

I The circuitry hereinbefore described has several particularly novel features. One is the use of a separate anticipator bridge which is completely isolated from the control bridge. By utilization of the separate anticipator bridge, the balance of the control bridge is unaffected by the anticipator bridge. This is even true if elements in the anticipator bridge are changed.

Another substantial advantage of my indicating controller is that it is possible to drive a D.-C. type servo motor from A.'-C. bridges while still utilizing relatively low D.-C. voltages to make possible the use of relatively inexpensive transistors. The transistors Q2, Q3, Q4 and the associated diodes provide an excellent phase discriminator which makes it possible to utilize the D.-C. servo motor. By utilizing a transistor driver, it is possible to eliminate the need for input and output transformers.

It is apparent from the foregoing that I have provided a new and improved indicating controller. Although I have described my indicating controller as being utilized primarily as a temperature controller, it is readily apparent that it can be utilized to control any set point which can be expressed as a voltage or a current. As is well known to those skilled in the art, there are many transducers available for measuring various types of parameters such as wind velocity, stream flow, etc., and which will provide a variable voltage or current output which can be readily used in my indicating controller so that the indicating controller can be utilized for maintaining a predetermined set point.

I claim:

1. In a controller for controlling the reaching of a predetermined set point by a parameter and for maintaining the parameter at a predetermined set point by controlling the application of power to a control circuit, a first bridge including a sensing element for sensing the selected parameter, a second bridge connected to the output of the first bridge, first A.-C. power supply means connected to said first and second bridges, phase sensitive means connected to the combined outputs of said first and second bridge circuits for determining when the combined output of said first and second bridge circuits is of one phase or of an opposite phase, second power supply means, and means controlled by the phase sensitive means and connected to said second power supply means and to said control circuit for applying power from said second power supply means to said control circuit, said second bridge circuit including anticipating elements affected by the operation of said means controlled by said phase sen sitive means.

2. A controller as in claim 1 wherein said anticipating elements in said second bridge circuit are temperature sensitive elements together with means controlled by the means controlled by the phase sensitive means for changing the temperature of said temperature sensitive elements.

3. A controller as in claim 1 wherein said anticipating elements are in the form of temperature sensitive resistive elements together with heater means associated with each of the resistive elements, and means controlled by the means controlled by the phase sensitive means for controlling the application of power to said heating elements.

4. A controller as in claim 1 wherein said first bridge circuit includes a potentiometer, phase sensitive means connected to said potentiometer, third power supply means, a servo motor connected to said potentiometer for adjusting said potentiometer, and means connected to said last named phase sensitive means and to said third :power supply means for driving said servo motor in one direction or an opposite direction dependent upon the phase of the output from the first bridge circuit.

5. A controller as in claim 4 wherein said servo motor is a DC. servo motor and wherein said third power supply is an A.-C. power supply.

6. A controller as in claim 4 together with a common A.-C. supply for said first, second and third power suspplies, said first power supply including a first transformer means connected to the common A.-C. supply, and a second transformer connected to said first transformer, and isolating means mounted in each of the trans-formers.

7. In a controller for controlling the reaching of a predetermined set point by a parameter and for maintaining the parameter at said predetermined set point by controlling the application of power to a control circuit, a first bridge circuit including first and second pairs of terminals and a sensing element for sensing the value of said parameter, a second bridge circuit having first and second pairs of terminals, a first A.-C. power supply, means connecting the A.-C. power supply to said first pairs of terminals of said first and second bridge circuits, means for connecting the second pair of terminals of the first and second bridge circuits in series so that the outputs of the two bridge circuits are summed, said second bridge circuit including at least two anticipating elements located in at least two legs of the second bridge circuit, each of said bridges having an output of one phase when the 'bridge is out of balance in one direction and of the opposite phase when the bridge is out of balance in the opposite direction, phase sensitive means connected to the combined outputs of the first and second bridge circuits, a second power source, means controlled by said phase sensitive means for supplying power from said third power source to said control circuit in accordance with the condition of said phase sensitive means, means for affecting said anticipator elements, means controlled by said means for controlling the application of power from said third source to said control circuit to said means for affecting the anticipator elements in accordance with the condition of the phase sensitive means, and means for indicating the value of the parameter being sensed by the sensing element.

8. A controller as in claim 7 wherein said last named means includes a potentiometer connected across said first pair of terminals of said first bridge circuit, phase sensitive means connected to said potentiometer, a third power source, a servo motor, and means controlled by said phase sensitive means connecting said third power source to said servo motor to drive said servo motor in one direction or the other dependent upon the phase sensed by the last named phase sensitive means.

9. A controller as in claim 8 wherein said phase sensitive means and said means for applying power from said third power source to said servo motor includes a pair of transistors having collector elements connected to opposite sides of said servo motor and wherein said third power source is an A.-C. power source, and diode means for connecting opposite ends of said power supply to said collectors.

10. In a controller for controlling the reaching of a predetermined set point by a parameter and for maintaining the'parameter at said predetermined set point by controlling the application of power to a control circuit, a bridge circuit, said'bridge circuit having first and second pairs of terminals and a sensing element for sensing the value of said parameter, means for supplying an A.-C. voltage to the first pair of terminals of said bridge circuit, phase sensitive means responsive to the output of said bridge circuit,a secondsource of power, means responsive to the phase sensitive means forcausing the application of power to said control circuit in accordance with the condition of said phase sensitive means, said bridge circuit also including a potentiometer connected across said first pair of terminals of said'b'ridge circuit, a servo motor connected to thepotentiometer for'driving the potentiometer, a third" A' .-C. power supply, phase sensitive means connected to the output of said bridge circuit, and means connected to the phase sensitive means and to said third power supply for driving said servo motor, said phase sensitive means including a pair of transistors having collector elements connected to opposite sides of said servo motor, and diode means connected to said collector elements and to opposite sides of said third A.-C. power supply;

11. In a controller for controlling the reaching of a predetermined set point by a parameter and for maintaining the parameter at said predetermined set point by controlling the application of power to a control circuit, a first bridge circuit including first and second pairs of terminals and a sensing element for sensing the value of said parameter, a second bridge circuit having first and second pairs of terminals, and first and second temperature sensitive resistive elements in at least two legs of said second bridge circuit, means for supplying an A.-C. voltage to the first pairs of terminals of said first and second bridge circuits, phase sensitive means, means for combining the outputs of the first and second bridges and connecting the same to the phase sensitive means, a second power supply, control means connected to the phase sensitive means and to the second power supply for controlling the application of power to said control circuit, first and second heating elements for heating the temperature sensitive resistance elements of the second bridge circuit, said control means including means for applying power to said first and second heating elements in accordance with the condition of said phase sensitive means, said first bridge circuit including a potentiometer, a servomotor for driving said potentiometer, a third power supply, phase sensitive means for sensing the output of said first bridge circuit, and means controlled by said last named phase sensitive means for controlling the application of power to said servo motor to control the movement of the servo motor in accordance with the phase of the output ofthe" 12. A controller as in claim 11 together with a com-.-

No references cited.

JOHN F. COUCH, Primary Examiner,

Claims (1)

1. IN A CONTROLLER FOR CONTROLLING THE REACHING OF A PREDETERMINED SET PONT BY A PARAMETER AND FOR MAINTAINING THE PARAMETER AT A PREDETERMINED SET POINT BY CONTROLLING THE APPLICATION OF POWER TO A CONTROL CIRCUIT, A FIRST BRIDGE INCLUDING A SENSING ELEMENT FOR SENSING THE SELECTED PARAMETER, A SECOND BRIDGE CONNECTED TO THE OUTPUT OF THE FIRST BRIDGE, FIRST A.-C. POWER SUPPLY MEANS CONNECTED TO SAID FIRST AND SECOND BRIDGES, PHASE SENSITIVE MEANS CONNECTED TO THE COMBINED OUTPUTS OF SAID FIRST AND SECOND BRIDGE CIRCUITS FOR DETERMINING WHEN THE COMBINED OUTPUT OF SAID FIRST AND SECOND BRIDGE CIRCUITS IS OF ONE PHASE OR OF AN OPPOSITE PHASE, SECOND POWER SUPPLY MEANS, AND MEANS CONTROLLED BY THE PHASE SENSITIVE MEANS AND CONNECTED TO SAID SECOND POWER SUPPLY MEANS AND TO SAID CONTROL CIRCUIT FOR APPLYING POWER FROM SAID SECOND POWER SUPPLY MEANS TO SAID CONTROL CIRCUIT, SAID SECOND BRIDGE CIRCUIT INCLUDING ANTICIPATING ELEMENTS AFFECTED BY THE OPERATION OF SAID MEANS CONTROLLED BY SAID PHASE SENSITIVE MEANS.

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