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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.
Control Outputs
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:
OFST function:
OFST is measured 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
adjusted 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 unsatisfac-
tory, 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.
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.
Note:
When the ramp function is used, the lower display will show
the current ramping value. The ramping value is an artificially de-
termined setpoint created and updated by the control to match the
ramp rate set by the user. However, it will revert to show the set
point value as soon as the up or down key is touched for adjust-
ment. The ramping value is initiated to process value either on
power-up or when RR and/or the set point are changed. Setting
RR to zero means no ramp function.
Ramp
The ramping function is performed during power up as well as any
time the set point is changed. If MINR or HRR is chosen for
RAMP, the unit will perform the ramping function. The ramp rate
is programmed by adjusting RR. The ramping function is disabled
as soon as failure mode, manual control mode, auto-tuning mode
or calibration mode is entered.
Example without dwell timer
Select MINR for RAMP, select °C for UNIT, select 1-DP for DP,
set RR=10.0. SV is set to 200°C initially, and changed to 100°C
30 minutes after power-up. The starting temperature is 30°C. After
power-up, the process runs like the curve shown below:
Figure 3.5 RAMP Function
Содержание PCM10001
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