CONTROL METHODS (CONTINUED)
Proportional Only (P) Control
Some processes need to maintain a temperature or process value closer to the set point than an on/off control can
provide. Proportional control provides closer control by adjusting the output when the temperature or process value is
within a proportional band. When the value is in the band, the controller adjusts the output based on how close the
process value is to the set point: the closer to set point the lower the output. This is similar to backing off on the gas
pedal of a car as you approach a stop sign. It keeps the temperature or process value from swinging as widely as it
would with a simple on/off control. However, when a system settles down, the temperature or process value tends to
“droop” short of the set point. With proportional control the output current level equals (set point minus process value)
divided by propband. The PID 1 proportional band can be viewed or changed with Propband 1 [Pb1`] (Main Menu).
ALPHA OMEGA INSTRUMENTS CORP. Instruction Manual
Series 800/850 Thermoelectric Cooler Controller Page 48
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