Metasys TC-9100 Series - Direct-Acting (Cooling) PI Controller; Reverse-Acting (Heating) PI Controller

26 Technical Bulletin—TC-9100 Universal Controller
The following equations define the operation of the PI controller:
Proportional Term (P
t
) =
()
PV WSP
100
PB
100
R
t
−××
Integral Term (I
t
) =
()
IPVWSP
100
PB
100
R
TI
60
t1 t−
+− ×××
Controller Output (OCM
t
) = P
t
+ I
t
where
OCM
t
,
P
t
, I
t
, and PV
t
are values at the current time t,
I
t-1
is the value one second earlier than the current time,
R = (HRIn - LRIn) when PV is connected to AIn (n=1-4),
or R = 100 when PV is connected to OCMn.
The output of the PI controller may be limited between high and low limit
values.
Low Limit (LOL)
High Limit (HIL)
OCM = Output Control Module
PB = Proportional Band
WSP = Working Set Point
PV = Process Variable
WSP
0
100
Output
(OCM)
Input (PV)
PB
Figure 9: Reverse-acting (Heating) PI Controller
Low Limit (LOL)
High Limit (HIL)
WSP
0
100
Output
(OCM)
Input (PV)
PB
Figure 10: Direct-acting (Cooling) PI Controller