Auto-zone-control-systems Auto-Zone CV-C Controller Installation Guide (Vers Bedienungsanleitung PDF herunterladen (Seite 38)

Section 2

Auto-Zone CV-C

2-28 Sequence of Operation

PID Operation

PID OperationPID Operation

PID Operation

The Hot & Chilled Water Valves are controlled via a Proportional, Integral, Derivative (

PID ) loop. This method of control provides accurate temperature control with minimal

adjustments to the valve position. The best method of explaining the PID operation is to

show a simplified form of the formulas incorporated into the controller code.

The following abbreviations will be used in the formula:

TimeSP = Integrating Interval

HotSP = Supply Air Temperature Setpoint

Kp = Proportional Constant

Ki = Integral Constant

Kd = Derivative Constant

P = Proportional Error

I = Integral Error

D = Derivative Error

HWValve = Calculated Valve Position

SupplyAir = Current Supply Air Temperature Reading

IF the TIMER has exceeded the TimeSP THEN

Error = HotSP - SupplyAir

P = ( Error x ( Kp / 100 )) x 100

I = ( Error x ( Ki / 10))

D = ( Error - OldError ) x ( Kd / 10 )

HWValve = P + I + D

OldError = Error “ Save current error for next time “

END ROUTINE

The Error is the difference between the Setpoint and the actual Temperature. The P error

uses a limited amount of this error to create a proportional only valve position. For

example, if the Kp was set to 10 then a 10°C temperature error would cause the P error

to set the valve 100% open.

10° Error = ( 10 x ( 10 / 100)) x 100 = 100%

5° Error = ( 5 x ( 10 / 100)) x 100 = 50%

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Auto-zone-control-systems Auto-Zone CV-C Controller Installation Guide (Vers Bedienungsanleitung Seite 38