Cooling coefficient (heating and cooling control), Figure 4.26 — dead band, Figure 4.27 – Rockwell Automation 900-TC32 Digital Temperature Controllers, Series B User Manual
Page 150
Publication 900-UM007D-EN-E - January 2011
4-14
Parameter Adjustments & Application Considerations
Figure 4.26 — Dead Band
Cooling Coefficient (Heating and Cooling Control)
When the heating and cooling control mode and PID control method are
selected, the Cooling Coefficient parameter can be used. If the heating and
cooling functional characteristics of the control target greatly differ, this could
limit satisfactory control performance from being obtained by the same PID
values. To reduce the possibility of this occurring, adjust the proportional band
(P) at the cooling side of the set point using the cooling coefficient to balance
control between the heating and cooling sides. In heating and cooling control
the proportional band, (P) at the heating or cooling side is calculated by the
following formula:
P for control output assigned to heating side = P
P for control output assigned to cooling side = P for control output
assigned to heating side
× cooling coefficient
The cooling coefficient is multiplied by the P for the control output assigned
to the heating side to obtain control with characteristics that differ from those
of the control output assigned to the heating side.
Figure 4.27
Automatic Cooling Coefficient Adjustment
By executing AT during heating/cooling control, the cooling coefficient can
be automatically calculated along with the PID parameters.
Output
Heating side
Dead band:
dead band width = positive
Cooling side
Set point
Output
Heating side
Cooling side
Overlap band:
dead band width = negative
Set point
PV
PV
PV
0
PV
0
Output
Output
P for control output
assigned to heating side
P for control output
assigned to heat-
ing side
×
1.0
P for control output
assigned to cooling side
Set point
P for control output assigned to
heating side
×
0.8
P for control output
assigned to heating side
P for control output
assigned to heat-
ing side
×
1.0
P for control output
assigned to cooling side
P for control output assigned to
heating side
Ч
1.5