21
6 Controller Operation
The heater power display is accessed in the secondary menu. Press “SET” and “EXIT” simulta-
neously and release. The heater power is displayed as a percentage of full power.
100.0 C
Well temperature
S+E
Access heater power in secondary menu
SEC
Flashes “
SEC
” for secondary menu and then displays the heater power
12.0P
Heater power in percent
To exit out of the secondary menu press and hold the “EXIT” button. To continue on to the
proportional band setting function press “SET”.
6.9
Proportional Band
In a proportional controller such as this the heater output power is proportional to the well tem-
perature over a limited range of temperatures around the set-point. This range of temperature is
called the proportional band. At the bottom of the proportional band the heater output is 100%.
At the top of the proportional 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 temperature.
The temperature stability of the well and response time depend on the width of the proportional
band. If the band is too wide the well temperature deviates 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 variations. For best control stability the proportional band
must be set for the optimum width.
The proportional band width is set at the factory to about 25.0
°
C. The user may alter the
proportional band width if he desires to optimize the control characteristics for a particular ap-
plication. However, we recommend the proportional band be changed only by knowledgeable
personnel.
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 adjust-
ment can be accessed within the secondary menu. Press “SET” and “EXIT” to enter the second-
ary menu and show the heater power. Then press “SET” to access the proportional band.
S+E
Access heater power in secondary menu
SEC
Flashes
SEC
for secondary menu and then displays the heater power
12.0P
Heater power in percent
S
Access proportional band
PROP
Flashes
PROP
for secondary menu and then displays the proportional band
setting
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