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In time proportioning control, the proportional band is employed to
smooth out the oscillating characteristic typical of ON/OFF control.
A feature of proportional control is that the system may run at a
slightly different temperature to the set point (Offset), and have a
slower reaction to disturbances. Refer to Figure 5-5.
5.4 PROPORTIONAL BAND
The purpose of the integral time is to automatically correct for
offset errors caused by the introduction of Proportional control. If
incorrectly set, this can cause instability or increase warm up time.
If the Integral Time (constant) is too long, the process will take a
long time to return the temperature to the set point. Conversely, if
the Integral Time is too short, the process temperature oscillates
because the integral action outruns the process. Refer to
Figure 5-6.
Setting too narrow
system oscillates
Setting Ideal Setting too wide slow
warm up and poor control
Setting too short
Ideal Setting Setting too long
Figure 5-5. Proportional Band
5.5 INTEGRAL (RESET) TIME
Figure 5-6. Integral (Reset) Time
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