60
reactive the output becomes. A proportional band too small, however,
can lead to over-responsiveness leading to process oscillation.
A proportional band which is correct in width approaches main setpoint
as fast as possible while minimizing overshoot. If a faster approach to
setpoint is desired and process overshoot is not a problem, a smaller or
narrower proportional band may be used. This would establish an over-
damped system or one where the output would change greatly, propor-
tional to the error. If process overshoot cannot be tolerated and the
approach to setpoint does not have to be quick, a larger or wider pro-
portional band may be used. This would establish an under-damped
system or one where the output would change little, proportional to the
error.
To Calculate Proportional Band:
Proportional Band
Proportional Band
(as a percentage)
= ____________________
X 100%
Input Range
Example:
30
°
C
3%
= __________
X 100%
100
°
C
Proportional Band
(as a percentage)
Proportional Band Range = ____________________
X 1000
°
C
100%
Example:
3%
30°C
= __________
X 1000°C
100%
