Tempco tec-220, Instruction Manual, Page: 16 / 36

12
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
when PB=0. The heat only on-off control function is shown in the
following diagram:
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 hid-
den and have no function in the system. The auto-tuning and
bumpless transfer function will be disabled as well.
Heat only P (or PD) control: Select H.TPC or H.L I N for OUT1
and set TI1 and TI2 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 measured in % with a range of 0–
100.0%.
In a steady state (i.e. process has stabilized at a temperature), if
the process value is lower than the set point by a constant value
(we’ll say 5°C) while the PB setting is set for 20°C, we can say
the temperature is lower than the setpoint by 25% of the PB set-
ting. This can be corrected by increasing the OFST setting to
25%. After adjusting the OFST value, the process value will
eventually coincide with set point.
Note that using the P control (TI set to 0), disables auto-tuning.
Refer to Section 3-12 “manual tuning” for the adjustment of P
and PD. Manual reset (adjust OFST) is sometimes not practical
since 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 unsatisfactory,
then use manual tuning to improve control. See section 3-12 for
manual tuning. The unit contains an advanced PID and Fuzzy
algorithm to create a small overshoot and very quick response to
the process if it is properly tuned.
Control Outputs,
continued…
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 sta-
ble 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 sec-
onds if relay is used for O1TY and CYC1 is ignored if linear out-
put is used. Similar conditions are applied for CYC2 selection.
You can use the auto-tuning program for the new process or
directly set the appropriate values for PB, TI, and TD according
to historical records for duplicate systems. If the control behavior
is still inadequate, then use manual tuning to improve the control.
See section 3-12 for manual tuning.
CPB (Cooling Proportional Band) Programming: The cooling
proportional band is measured by % of PB with a range of
50-300. Initially set 100% for CPB and examine the cooling
effect. If the cooling action should be enhanced, then decrease
CPB, if the cooling action is too strong, then increase CPB. The
value of CPB is related to PB and its value remains unchanged
throughout the auto-tuning procedures.
Adjustment of CPB is related to the cooling medium used. If air
is used as the cooling medium, initially set CPB to 100%, then
adjust as necessary. If oil is used as the cooling medium, initially
set CPB to 125%, then adjust as necessary. If water is used as the
cooling medium, initially set CPB to 250%, then adjust as necessary.
DB (Heating-Cooling Dead Band) programming: The adjust-
ment of DB is dependent on the system requirements. If a more
positive value of DB (greater dead band) is used, an unwanted
cooling action can be avoided but an excessive overshoot over the
set point will occur. If a more negative value of DB (greater over-
lap) is used, an excessive overshoot over the set point can be min-
imized, but an unwanted cooling action will occur. It is adjustable
in the range -36.0% to 36.0% of PB. A negative DB value shows
an overlap area over which both outputs are active. A positive DB
value shows a dead band area over which neither output is active.
Output 2 ON-OFF control (alarm function): Output 2 can also
be configured with an alarm function. There are six kinds of
alarm functions that can be selected for output 2. These are:
DE.HI (deviation high alarm), DE.LO (deviation low alarm),
DB.HI (deviation band out of band alarm), DB.LO (deviation
band in band alarm), PV.HI (process high alarm), and PV.LO
(process low alarm). Refer to figure 3.3 and figure 3.4 for
descriptions of the deviation alarm and the process alarm.