Watlow Series PD - Manual (Page 137)

W a t l o w S e r i e s P D ■ 1 3 5 ■ C h a p t e r 1 0 F e a t u r e s
Dead Band
In heat/cool PID applications, a dead band above and
below the set point can save energy and equipment wear
by maintaining process temperature within acceptable
ranges. Shifting the effective cooling set point and heating
set point keeps the two systems from fighting each other.
Proportional action ceases when the process value is
within the dead band. Integral action continues to bring
the process temperature to the set point. When the dead
band value is zero, the heating element activates when
the temperature drops below the set point, and the cool-
ing element switches on when the temperature exceeds
the set point.
To view or change the Dead Band, go to Device Con-
figuration > Control Loops > Loop 1 or 2 > Loop
Settings > PID Parameters > PID Set #1 Dead Band
Heat (Indirect) or PID Set #1 Dead Band Cool (Di-
rect). Enter a value for Dead Band and click the Submit
button to send the new value.
Independent Heat and Cool PID
In an application with one output assigned to heating
and another assigned to cooling, each will have a separate
set of PID parameters and separate dead bands. The heat-
ing parameters take effect when the process temperature
is lower than the set point and the cooling parameters
take effect when the process temperature is higher than
the set point.
To view or change the PID Parameter values, go to De-
vice Configuration > Control Loops > Loop 1 or 2 >
Loop Settings > PID Parameters. Enter values for Pro-
portional Band, Integral, Derivative and Dead Band and
click the Submit button to send the new values.
Multiple PID Sets
The Series PD supports up to five heat/cool PID sets.
This feature is extremely valuable if the characteristics
of your thermal system vary over its operating range. All
PID sets can be auto tuned or manually tuned. The Se-
ries PD can be programmed to operate using any of the
five PID sets based on crossover points of the set point or
process value.
When the process or set point value crosses the
crossover point, the PID set designated for that region of
the operating range is used to control the percent power
being supplied to the load.
There is a -1° hysteresis for each crossover. A rising
temperature will change PID sets at the crossover value.
A falling temperature will change PID sets at the
crossover value -1°.
To view or change the the PID values or crossover set
points, go to Device Configuration > Control Loops >
Loop 1 or 2 > Loop Settings > Multiple PID Sets >
PID Set No. 1, 2, 3, 4 or 5. Enter PID values and a
crossover set point for each PID set and click the Submit
button to send the new values.
Example:
Operating Range PID Set 5
Operating Range PID Set 4
Operating Range PID Set 3
Operating Range PID Set 2
Operating Range PID Set 1
PID Crossover SP
4 to 5 @ 1250 F
PID Crossover SP
3 to 4 @ 1,000 F
PID Crossover SP
2 to 3 @ 600 F
PID Crossover SP
1 to 2 @ 300 F
Time
Te
mperature
Set Point
Heating Side Proportional Band
Heating Side Dead Band
Cooling Side Dead Band
Cooling Side Proportional Band
Time
Te
mperature
Heating Set Point
Heating Proportional Band
Cooling Dead Band
Cooling Set Point
Cooling Proportional Band