Process Control Instructions
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018 133
MaxHeatTimeInv (Status.2) BOOL Invalid MaxHeatTime value. The instruction uses
the CycleTime value.
MinHeatTimeInv (Status.3) BOOL Invalid MinHeatTime value. The instruction uses
zero.
MaxCoolTimeInv (Status.4) BOOL Invalid MaxCoolTime value. The instruction uses
the CycleTime value.
MinCoolTimeInv (Status.5) BOOL Invalid MinCoolTime value. The instruction uses
zero.
HeatSpanInv (Status.6) BOOL MaxHeatIn = MinHeatIn.
CoolSpanInv (Status.7) BOOL MaxCoolIn = MinCoolIn.
Description
The length of the SRTP pulse is proportional to the PID output. The instruction
parameters accommodate heating and cooling applications.
Using the Internal Cycle Timer
The instruction maintains a free running cycle timer that cycles from zero to the
programmed CycleTime. The internal timer is updated by DeltaT. DeltaT is the
elapsed time since the instruction last executed. This timer determines if the
outputs need to be turned on.
You can change CycleTime at any time. If CycleTime = 0, the internal timer is
cleared and HeatOut and CoolOut are cleared to false.
Calculating Heat and Cool Times
Heat and cool times are calculated every time the instruction is executed.
HeatTime is the amount of time within CycleTime that the heat output is to be
turned on.
If HeatTime < MinHeatTime, set HeatTime = 0.
If HeatTime> MaxHeatTime, limit HeatTime = MaxHeatTime.
HeatTimePercent is the percentage of CycleTime that the HeatOut pulse is true.
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