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PID Control Loops Guy Zebrick. 2HONEYWELL - CONFIDENTIAL File Number Contents Open & Closed Loops Direct and Reverse Acting Proportional Control Integral.

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Presentation on theme: "PID Control Loops Guy Zebrick. 2HONEYWELL - CONFIDENTIAL File Number Contents Open & Closed Loops Direct and Reverse Acting Proportional Control Integral."— Presentation transcript:

1 PID Control Loops Guy Zebrick

2 2HONEYWELL - CONFIDENTIAL File Number Contents Open & Closed Loops Direct and Reverse Acting Proportional Control Integral Control Derivative Control Definitions Loop Tuning

3 3HONEYWELL - CONFIDENTIAL File Number Open Loop Control / Direct Acting Input Control Variable Output Device 0-100% Mathematical Calculation Setpoint Input: Outside Air Temperature Setpoint: 50F Output: Chiller on/off (0-100%) Action: Direct (input output )

4 4HONEYWELL - CONFIDENTIAL File Number Open Loop Control / Reverse Acting Input Control Variable Output Device 0-100% Mathematical Calculation Setpoint Input: Outside Air Temperature Setpoint: 60F Output: Boiler on/off (0-100%) Action: Reverse (input output )

5 5HONEYWELL - CONFIDENTIAL File Number Closed Loop Control Reverse Acting Input Control Variable Output Device 0-100% Mathematical Calculation Setpoint Input: Room Temperature Setpoint: 70F Output: Radiator Valve (0-100%)

6 6HONEYWELL - CONFIDENTIAL File Number PID Control by Mathematical calculation P roportional Output varies in PROPORTION to input error I ntegral Output varies over TIME based on input error D erivative Output varies based RATE of CHANGE of input error P control P + I control P + I + D control (not used in our industry!)

7 7HONEYWELL - CONFIDENTIAL File Number PID closed loop control – driving at speed 0% P 30% PID 40% PI 60% PI 0% PID 40% PID 70% PI 25% PID 40% PI

8 8HONEYWELL - CONFIDENTIAL File Number Definition: (SETPOINT) The desired value of the input variable T1T2T3T4T5T6 Input Value Setpoint Time

9 9HONEYWELL - CONFIDENTIAL File Number Definition: OFFSET (error) The DIFFERENCE between the input variable and the desired setpoint. T1T2T3T4T5T6 Input Value Setpoint Time Offset

10 10HONEYWELL - CONFIDENTIAL File Number Definition: Throttling Range (Proportional Band) Throttling Range (Proportional Band) (10F) 100% 50% 0% 65° 70° 75° Setpoint Controller Output T1T2T3T4T5T6 Amount of Change in INPUT that equals a 0-100% change in OUTPUT

11 11HONEYWELL - CONFIDENTIAL File Number Proportional Control (with Offset Error) T1T2T3T4T5T6 Control Point Setpoint Time Offset 0=100%

12 12HONEYWELL - CONFIDENTIAL File Number Proportional + Integral Control (eliminates offset) T1T2T3T4T5T6 Control Point Setpoint Time Offset 0=100%

13 13HONEYWELL - CONFIDENTIAL File Number Derivative Calculation based on RATE of CHANGE T1T2T3T4T5T6 Control Point Setpoint Time Offset D P + I + D Not used in our industry!

14 14HONEYWELL - CONFIDENTIAL File Number Integral Windup Condition T1T2T3T4T5T6 Control Point Setpoint Time 100% Prevented by Disabling Loop when system is OFF

15 15HONEYWELL - CONFIDENTIAL File Number PID Enhancements Setpoint Reset Setpoint Recovery Ramp Setpoint Demand Limit BUMP Setpoint Select(s) PID Output BIAS PID Output Start Point PID Output Start Ramp PID Output Adjust Delay PID Output Adjust Threshold PID AUXILLARY Output PID Output Sequencer

16 16HONEYWELL - CONFIDENTIAL File Number Definition: PID Output Bias T1T2T3T4T5T6 100% 50% 0% T1T2T3T4T5T6 100% 50% 0% Output = 50% at SetpointOutput = 0% at Setpoint 50% 0%

17 17HONEYWELL - CONFIDENTIAL File Number PID Setpoint RESET Requires RESET sensor (typically outside air) Automatically adjusts setpoint

18 18HONEYWELL - CONFIDENTIAL File Number PID Setpoint Recovery Ramp Degrees/Hr Requires multiple schedule information - Current State (occupied/unoccupied) - Next State (occupied/unoccupied) - Time until next state (minutes) Setpoint UNOCC OCC Time OCC

19 19HONEYWELL - CONFIDENTIAL File Number PID options (not available on ALL PID loops) Output Start Value (%) - Provides starting value for initial control Output Start Ramp (seconds) - limits action during initial startup to prevent overshoot - Output Dead Band (%) Output Adjust Delay & Threshold - Prevents repeated minor adjustment to output - Prevents needless wear & tear on mechanical devices

20 20HONEYWELL - CONFIDENTIAL File Number Definition: Hunting (over-reacting) Proportional Band Throttling Range (2F) 100% 50% 0% 69° 70 ° 71° Setpoint Controller Output T1T2T3T4T5T6 Time

21 21HONEYWELL - CONFIDENTIAL File Number Tuning Hints: PI control for closed-loop applications only. The narrower (smaller) the throttling range, the more precise the control operation. The wider (larger) the throttling range, the more stable the control action. Generally the throttling range required for PI control is greater than what is used for proportional control only. The integral time value is set in seconds. A slow process such as space temperature control requires a long integral time (600 seconds or more), while a fast process such as static pressure control requires a short integral time. An integral time of 0 eliminates the integral function for the control loop.

22 22HONEYWELL - CONFIDENTIAL File Number Typical Values From Engineering Manual Default Space Temperature Control (CV AHU controller)

23 23HONEYWELL - CONFIDENTIAL File Number Field Tuning 1.Integral Time to Zero 2.Throttling Range = ½ Input Sensor Range 3.Adjust Throttling Range to point where about first begins to hunt. 4.Increase Throttling Range 1.5 X 5.Add Integral Time based on system response time (typically 60 – 2500 seconds) 6.Check for Stable Operation

24 24HONEYWELL - CONFIDENTIAL File Number PID POP Quiz Define open loop Define closed loop A cooling loop is (direct/reverse) acting An AHU static pressure control loop is (direct/reverse) acting Define P, I, D Define throttling range Define integral time When do you use Differential control? What adjustment(s) reduce hunting?

25 25HONEYWELL - CONFIDENTIAL File Number Questions?


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