PID CONTROLLER FOR HEATING, VENTILATING AND AIR CONDITIONING SYSTEMS

• US 3,834,617 A
• Filed: 05/14/1973
• Issued: 09/10/1974
• Est. Priority Date: 05/14/1973
• Status: Expired due to Term

• Current Assignee: Milos Dyntar
• Original Assignee: Milos Dyntar
• Inventors: Dyntar, Milos
• Primary Examiner(s): Wayner, William E.
• Application Number:
  US05/359,919
• Time in Patent Office: 484 Days
• Field of Search: 236/1C,78,46 165/26 251/129
• US Class Current: 236/1.00C
• CPC Class Codes: G05D 23/1919 characterised by the type of controller

Abstract

A heating and/or air conditioning system including a novel controller of the PID type. A proportional integrator (PI) circuit is arranged to receive the output signal from a differentiator (D) circuit which has been delayed and inverted in a summing circuit together with an input control signal to thereby provide a PID controller having a negative delayed D influence. Such controllers are sometimes referred to as a PIminus-D controller. The circuit employs operational amplifiers and the time delay provided by the differentiator circuit is 7 minutes as compared with the time constant of approximately 2 minutes for the integrator and the PI portion of the circuit. The PID controller as disclosed operates through a broad range of frequencies between about 20 seconds and 50 minutes to produce a substantially optimum regulation of the fuel or heat exchanging medium control valve without the need for a separate field adjustment by the installation mechanic.

Claims

1. Apparatus for controlling the temperature in an enclosed region through regulation of heat exchanger media by actuation of a valve which determines a flow rate comprising:

means for generating a first electrical signal corresponding to the temperature in said region;

means for generating a second electrical signal corresponding to the desired temperature for said region; and

circuit means for controlling said valve including;

a first summing amplifier for generating a first control signal proportional to the difference between said first and second electrical signal voltages;

a delay circuit including amplifier means for producing an amplified output signal with a first time delay, and circuit means for connecting said delay circuit to receive said first control signal;

a second summing amplifier for generating a second control signal connected to receive said first control signal and said delay circuit output signal; and

means including parallel branch circuits for generating an output signal to control said valve and connected to receive said second control signal, an integrating circuit in one of the branch circuits having a second time delay that is shorter than said first time delay, and an amplifier circuit in the other branch circuit.

2. Apparatus of claim 1 wherein the delay circuit includes a third summing amplifier having a predetermined gain Alpha with two input signal channels and one output signal channel, a delay circuit having a time delay connected to said output signal channel, a fourth summing amplifier having two input signal channels one of which is connected to said output signal channel and the other connected to the output of said delay circuit, a feedback circuit including an amplifier circuit having a predetermined gain Beta connected to receive the output signal from said fourth summing amplifier circuit and to have its output signal supplied to one of the signal channels in said third summing amplifier;

wherein the first control signal is applied to the other signal channel in said third summing amplifier; and

wherein the output signal from the fourth summing amplifier circuit is connected as one input to said second summing amplifier.

3. Apparatus of claim 2, characterized by the first time delay being substantially equal to the product of the time delay and said delay circuit and (1 + Alpha Beta ).

4. Apparatus of claim 3 wherein the time delay of said delay circuit is approximately 1 minute;

Alpha is approximately 25; and

Beta is approximately 0.24.

5. Apparatus of claim 4 wherein said second time delay of said integrating circuit is approximately 2 minutes.

6. Apparatus of claim 1 wherein the first time delay is between about 5 and 10 minutes and the second time delay of said integrating circuit is at least 1 minute.

7. Apparatus of claim 2 wherein the polarity of the signal output from said delay circuit is opposite from the polarity of the output signal from said third summing amplifier when applied to said fourth summing amplifier and the polarity of the signal from said feedback circuit is opposite from the polarity of the first control signal when applied to said third summing amplifier.

8. Apparatus of claim 7 wherein the polarity of the second control signal is the same as the polarity of the first control signal when applied to said second summing amplifier.

9. Apparatus of claim 8 wherein the first time delay is substantially equal to the product of the time delay of said delay circuit and (1+ Alpha Beta );

the time delay of said delay circuit is approximately one minute;

Alpha is approximately 25;

Beta is approximately 0.24; and

the second time delay of said integrating circuit is approximately 2 minutes.

10. A proportional integrator and differentiator control element adapted for regulating a valve controlling the influence of a heating or cooling member in a heating, ventilating or air conditioning system in response to a differential signal voltage proportional to the difference between a predetermined desired temperature and a measured temperature, said control element comprising:

a differentiator circuit having a differential time constant (rate time) TD, said differentiator circuit including;

a first input summing amplifier circuit having two input signal channels, an amplification factor Alpha and output terminals with the differential signal voltage connected to one of said input signal channels;

means applying the differential signal voltage to one of said input signal channels;

a second summing amplifier circuit having two input signal channels and output terminals;

a delay circuit having a time constant Td;

first circuit means for connecting the output terminals of said first input summing amplifier circuit to one of the signal channels of said second summing amplifier circuit;

second circuit means for connecting the output terminals from said first input summing amplifier circuit to the input of said delay circuit;

third circuit means for connecting the output signal from said delay circuit to the other signal channel of said second summing amplifier circuit; and

a first amplifier circuit having an amplification factor Beta and connected to have the output signal from said second summing amplifier as its input signal and connected to have its output signal applied to the other input signal channel of said first input summing amplifier circuit; and

a proportional integrating circuit including;

a third summing amplifier circuit having two input signal channels and a amplification factor k and output terminals with the differential signal voltage connected to one of said input signal channels and the output signal from said second summing amplifier connected to said other input signal channel;

a pair of branch circuits including a proportional amplifier circuit in one branch circuit and an integrator having an integral action time TN in the other branch circuit;

means connecting the output signal from said third summing amplifier circuit to the input of said parallel branch circuits; and

an output summing amplifier circuit connected to receive and combine the output signals from said parallel branch circuits and having output terminals adapted for connection to said control valve.

11. The control element of claim 10 wherein the differential circuit time constant TD is between about five and ten minutes and larger than the integral action time TN which is at least about one minute, and the signal from the differential circuit has a polarity so as to provide a control element having a proportional integrator function with a minus differentiator behavior to thereby provide a control element adapted for use without field adjustment with heating and air conditioning systems having a wide range of system time constants.

12. The control element of claim 11 characterized by the differential time constant (time rate) TD being substantially equal to the product of the delay circuit time constant Td and (1 + Alpha Beta ).

13. The control element of claim 10 wherein the polarity of the output signal from said delay circuit is opposite from the polarity of the output signal from said first summing amplifier circuit when applied to said second summing amplifier circuit, and the polarity of the output signal from said first amplifier circuit is opposite from the polarity of the differential signal voltage applied when applied to said first summing circuit.

14. The control element of claim 13 wherein the polarity of the differential signal voltage is the same as the polarity of the output signal from said second summing amplifier when applied to the input signal channels of said third summing amplifier.

15. A method for controlling the temperature in an enclosed region through regulation of heat exchanger media by actuation of a valve which determines flow rate comprising:

generating a first electrical signal corresonding to the temperature detected in said region;

generating a second electrical signal corresponding to the desired temperature for said region;

amplifying the sum of said first control signal and a feedback signal by amount Alpha , applying the amplified signal to a first delay circuit which produces a delay on the order of a minute, substituting the delayed signal from said amplified first control signal to provide a minus D signal, and amplifying said minus D signal by an amount Beta to produce said feedback signal whereby the minus D signal has an effective delay at least five times greater than the delay provided by said first delay circuit;

summing said first control signal and said minus D signal and amplifying said summed signals by an amount k to provide a second control signal;

delaying said second control signal in one of two parallel branch circuits by an amount greater than the delay provided by said first delay circuit but less than the effective delay of said minus D signal; and

summing said second control signal with the delayed second control signal to produce an output signal voltage for actuating said valve.

16. The method of claim 15 wherein Alpha is about 25;

Beta is about 0.24;

k is about 2.5;

the delay of said minus D signal is between about 5 and 10 minutes; and

the delay of said second control signal is at least 1 minute.

17. A method for producing a control voltage signal for regulating a valve which influences the control of a heating or cooling member in an air conditioning system in response to a differential signal voltage proportional to the difference between a predetermined desired temperature and a measured temperature comprising:

providing two signal channels for said differential signal voltage and combining the output signals in a summing amplifier circuit so that the output signal from one signaL channel is subtracted from the output signal from the other signal channel;

amplifying and delaying for a period of several minutes said differential signal voltage in one of said signal channels;

feeding the summing amplifier circuit output signal into two parallel branch circuits;

delaying said output signal in one of said parallel circuits by an amount less than the delay of the signal voltage in said one signal channel; and

summing the output signals from said two parallel branch circuits to produce said control voltage signal.

18. The method as defined in claim 17 wherein said delayed signal is provided by amplifying a combined signal including the differential signal voltage and a feedback signal voltage;

delaying the amplified combined signal for a period of about 1 minute;

subtracting the delayed signal from the amplified combined signal; and

amplifying by an amount Beta the resulting signal produced to provide said feedback signal voltage.

19. The method as defined in claim 18 wherein the feedback signal voltage amplification Beta is less than unity and the feedback signal voltage is subtracted from said differential signal voltage before being amplified, and the amplification factor for said combined signal is about 25.