CONTROL METHODS (CONTINUED)
Proportional plus Integral (PI) Control
The droop caused by proportional control can be corrected by adding integral (reset) control to the system. When the
system has settled down the integral (reset) value is tuned to bring the temperature or process value closer to the set
point. Integral (reset) determines the speed of the correction. However, this may increase the overshoot that occurs at
startup or when the set point is changed. Too much integral (reset) action will make the system unstable. Integral
(reset) is cleared when the process value is outside of the proportional band. Reset is measured in repeats per minute.
A low reset value causes a slow integrating action. Integral is measured in minutes per repeat (the inverse of reset). A
low integral value causes a fast integrating action. View or change the Output 1 integral or reset value with Integral 1
[It1`] or Reset 1 [rE1`] (PID 1 Menu). Integral appears if Units Type [Unit] (Global Menu) is set to [``S1].
Reset appears if [Unit] is set to
[``US]. Integral Value Equivalent Reset Value 1 minute 1 repeat per minute 2
minutes 0.5 repeats per minute 3 minutes 0.33 repeats per minute 4 minutes 0.25 repeats per Minute.
ALPHA OMEGA INSTRUMENTS CORP. Instruction Manual
Series 800/850 Thermoelectric Cooler Controller Page 49
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