Page 8 of 16
The ON-OFF control may introduce excessive process oscillation
even if hysteresis is minimized. If ON-OFF control is set (i.e.,
PB=0), TI, TD, CYC1, OFST, CYC2, CPB, and DB will be hidden
and have no function in the system. The auto-tuning and bumpless
transfer functions will be disabled as well.
Heat only P (or PD) control:
Select REVR for OUT1, set TI to
0. OFST is used to adjust the control offset (manual reset).
O1HY
is hidden
if PB is not equal to 0.
OFST function:
OFST is meas-
ured by % with a range of 0–100.0%. In the steady state (i.e.,
process has been stabilized), if the process value is lower than the
set point by a definite value, say 5°C, while 20°C is used for PB,
that is lower by 25%, then increase OFST 25%, and vice-versa.
After adjusting OFST value, the process value will be varied and
eventually coincide with set point.
Refer to section 3-12 “manual tuning” for the adjustment of PB
and TD. Manual reset (adjust OFST) is not practical because the
load may change from time to time and OFST may need to be ad-
justed repeatedly. PID control can avoid this situation.
Heat only PID control:
If REVR is selected for OUT1, PB and
TI should not be zero. Perform auto-tuning for the new process,
or set PB, TI, and TD with historical values. See section 3-11 for
auto-tuning operation. If the control result is still unsatisfactory,
then use manual tuning to improve control. See section 3-12 for
manual tuning. The unit contains a very advanced PID and Fuzzy
Logic algorithm to create a very small overshoot and very quick
response to the process if it is properly tuned.
Control Outputs
, continued…
Heat only ON-OFF control
: Select REVR for OUT1. Set PB
(proportional band) to 0. O1HY is used to adjust dead band for
ON-OFF control. The output 1 hysteresis (O1HY) is enabled
in case PB=0. The heat only on-off control function is shown
in the following diagram:
3.3 & 3.4 Alarm Figures, next page…
Cool only control:
ON-OFF control, P (PD) control, and PID
control can be used for cool control. Set OUT1 to DIRT (direct
action). The other functions for cool only ON-OFF control, cool
only P (PD) control, and cool only PID control are the same as
for heat only control except that the output variable (and action)
for cool control is inverse to heat control.
NOTE:
ON-OFF control may result in excessive overshoot and
undershoot problems in the process. P (or PD) control will result
in a deviation of process value from the set point. It is recom-
mended to use PID control for heat-cool control to produce a stable
and zero offset process value.
Other setup required:
O1TY, CYC1, O2TY, CYC2, O1FT and
O2FT are set in accordance with the types of OUT1 and OUT2
installed. CYC1 and CYC2 are selected according to the output
1 type (O1TY) and output 2 type (O2TY). Generally, select
0.5~2 seconds for CYC1 if SSRD or SSR is used for O1TY;
10~20 seconds if relay is used for O1TY. CYC1 is ignored if a
linear output is used. Similar conditions are applied for CYC2
selection.
You can use the auto-tuning program for the new process or di-
rectly set the appropriate values for PB, TI, and TD according
to historical records for the repeated systems. If the control be-
havior is still inadequate, use manual tuning to improve the con-
trol. See section 3-12 for manual tuning.
