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Heat PID+Cool PID: set OUT1=REVR, OUT2=COOL, CPB=100, DB=-4.0, PB1=0,
TI1=0, TD1=0, and set appropriate values for O1TY, CYC1, O2TY, and CYC2.
CPB Programming
The cooling proportional band is measured by % of PB with range 1~255. Initially set
100% for CPB and examine the cooling effect. If cooling action should be enhanced then decrease
CPB .If cooling action is too strong then increase CPB. The value of CPB is related to PB and its
value remains unchanged throughout the self-tuning and auto-tuning procedures.
Adjustment of CPB is related to the cooling media used. For air is used as cooling media,
adjust CPB at 100(%). For oil is used as cooling media, adjust CPB at 125(%). For water is used as
cooling media, adjust CPB at 250(%)
DB Programming
Adjustment of DB is dependent on the system requirements. If 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 more negative value of DB (greater overlap) is used, an
excessive overshoot over the set point can be minimized but an unwanted cooling action will occur.
It is adjustable in the range -36.0% to 36.0 % of PB1 (or PB2 if PB2 is selected). 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
4.3.1.1.4.4 Heater Break Alarm
A current transformer CT94-1 should be installed to detect the heater current if a heater
break alarm is required. The CT signal is sent to input 2, and the PV2 will indicate the heater
current in 0.1 Amp. Resolution. The range of current transformer is 0 to 50.0 Amps.
Example
A furnace uses two 2KW heaters connected in parallel to warm up the process. The line
voltage is 220V and the rating current for each heater is 9.09A. If we want to detect any one
heater break, set A1SP=13.0A, A1HY=0.1 A1FN=PV2.L, A1MD=NORM, then
Figure 4-30. Heater Break Alarm
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