band the coolingis 100%. Thus as the temperature rises the heater power is re-
duced, which consequentlytends to lower the temperature back down. In this
waythe temperature is maintained at a fairly constant temperature.
The temperature stability of the well and response time depend on the width of
thep roportionalband. See Figure 8 on page 35. If theb and is too widethe well
temperaturewill deviate excessively from the set-point due to varying external
conditions. This is because the poweroutput changes very little with tempera-
ture and the controller cannot respond verywell to changing conditions or
noisein the system. If the proportional band is too narrow the temperature may
swing back and forth because the controller overreactsto temperature varia-
tions. Forbest control stability the proportional band must be set for the opti-
mum width.
The proportionalband width is set at the factory to about 2.0°C. The propor-
tional band width may be altered by the user if he desires to optimize the con-
trol characteristics for a particular application.
The proportionalband width is easily adjusted from the front panel. The width
may be set todiscrete values in degrees C or F depending on the selected units.
The proportional band adjustmentis accessed within the secondary menu.
Press“SET” and “EXIT” to enter the secondary menu and show the heater
power.Then press “SET” to access the proportional band.
S+E Access heater power in secondary menu
-12 Pct Heater power in percent
SAccess proportional band
9105/9107 35
8Controller Operation
Proportional Band too Narrow Proportional Band too Wide
Optimum Proportional Band
Figure8 Welltemperature fluctuation at various proportional band settings