Fluke 9107 - Manual (Page 40)

band the cooling is 100%. Thus as the temperature rises the heater power is re-
duced, which consequently tends to lower the temperature back down. In this
way the temperature is maintained at a fairly constant temperature.
The temperature stability of the well and response time depend on the width of
the proportional band. See Figure 8 on page 35. If the band is too wide the well
temperature will deviate excessively from the set-point due to varying external
conditions. This is because the power output changes very little with tempera-
ture and the controller 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 varia-
tions. For best control stability the proportional band must be set for the opti-
mum width.
The proportional band 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 proportional band width is easily adjusted from the front panel. The width
may be set to discrete values in degrees C or F depending on the selected units.
The proportional band adjustment is 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
S
Access proportional band
9105/9107 35
8 Controller Operation
Proportional Band too Narrow Proportional Band too Wide
Optimum Proportional Band
Figure 8 Well temperature fluctuation at various proportional band settings