5–8 On-Off Control
If the alarm output is configured as an alarm function, it basically performs as an on-off control. If you adjust the P band
to PB=0, you can get an additional channel of on-off control with variable hysteresis. Hysteresis, also called differential
or deadband, is measured in degrees. See the figure below for a description of on-off control.
On-off control may create excessive process variation from the set point, even if the hysteresis is set at the minimum
possible value. When using on-off control, the parameters TI, TD, and CYC will have no effect on the system, and both
manual mode and the auto-tune program will be disabled.
5–9 Cooling Control
Cooling control options:
Output
Configurations
Heating Output Cooling Output Adjusted Parameters
On-Off Cooling
(no heating)
None
OUT1
CONA=DIRT
HYST
SV
Proportional Cooling
(no heating)
None
OUT1
CONA=DIRT
PB, TI, TD, CYC, SV
H
On-Off Cooling
OUT1
ALM2
CONA=REVR
A2SF=NONE
A2MD=DVHI (or FSHI)
AHY2, SV (or ASP2)
H
Proportional Cooling
OUT1
ALM2
CONA=REVR
A2SF=COOL
CPB, DB, CCYC, SV
18
SP+HYST/2
SP–HYST/2
SP
Reverse 100%
OUTPUT
PV
Time
Time
Direct 100%
Action
(CONA=REVR)
0%
0%
Action
(CONA=DIRT)
P action
