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Technical Bulletin—TC-9100 Universal Controller
Loop 2 active
Loop 1 active
ON
PV
= Process Variable
OCMx = Output Control Module
Loops 1 and 2
DIFx
= Differential Loop 1
DIFx
+1
= Differential Loop 2
WSPx
= Working Set Point Loop 1
WSPx
+1
= Working Set Point Loop 2
WSPx
+1
WSPx
OFF
0
100
Output
(OCMx)
Input (PV)
DIFx
ON
DIFx
+1
Figure 11: Heating/Cooling On/Off Controller – Single Output
When a programmable module is configured as Algorithm 4 (Item
PMxTYP, bits 5…1 = 00100), the module works with the next
programmable module (PMx
+1
) as a heating/cooling PI controller with a
single output. The output of the second module (Loop 2) follows the
output of the first module (Loop 1).
Loop 1 must be configured as a heating controller (reverse acting) and its
working set point must always be lower than the working set point of
Loop 2, which must be configured as a cooling controller (direct acting).
The two modules share the process variable of Loop 1. Loop 1 is active
when the process variable is below the working set point of Loop 1, and
Loop 2 is active when the process variable is above the working set point
of Loop 2. The changeover takes place in the center of the control dead-
band between the two loops with a 10% switching differential.
Algorithm 4:
Heating/Cooling
PI Controller –
Single Output
