100.0 P
Heater power
To exit out of the secondary menu press “EXIT”. To continue on to the propor-
tional band setting function press “SET”.
Return to temperature display
7.8
Proportional Band
In a proportional controller such as this the heater output power is proportional
to the process temperature over a limited range of temperatures around the
set-point. This range of temperature is called the proportional band. At the bot-
tom of the proportional band the heater output is 100%. At the top of the pro-
portional band the heater output is 0. Thus as the temperature rises the heater
power is reduced, which consequently tends to lower the temperature back
down. In this way the temperature is maintained at a fairly constant value.
The temperature stability of the system depends on the width of the propor-
tional band. See Figure 6. If the band is too wide the temperature will tend to
deviate excessively from the set-point due to varying external conditions. This
is because the power output changes very little with temperature and the con-
troller cannot respond very well to changing conditions or noise in the system.
If the proportional band is too narrow the temperature may swing back and
forth because the controller overreacts to temperature variations. For best con-
trol stability the proportional band must be set for the optimum width.
The optimum proportional band width depends on several factors including
system heat transfer characteristics and heater-probe positioning. Thus the pro-
portional band width may require adjustment for best stability when any of
these conditions change.
2200 Temperature Controller
User’s Guide
28
Figure 6
Various Proportional Band Settings
