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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
) =
(
)
I
PV
WSP
100
PB
100
R
TI
60
t 1
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