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Controller Operation
Thermal Electric Device (TED)
Thermal Electric Device (TED)
9.6
The temperature controller controls the temperature of the well by pulsing the TED on
and off. The total power being applied to the TED is determined by the duty cycle or
the ratio of TED on time to the pulse cycle time. By knowing the amount of heating
the user can tell if the calibrator is heating up to the set-point, cooling down, or
controlling at a constant temperature. Monitoring the percent heater power will let the
user know how stable the well temperature is. With good control stability the percent
heating power should not fluctuate more than ±5% within one minute.
The heater power display is accessed in the secondary menu. Press “SET” and “EXIT”
simultaneously and release. The heater power will be displayed as a percentage of full
power.
100.00C
Well temperature
S
+
E
Access heater power in secondary menu
SEC
Flashes
12.0 P
Heater power in percent
To exit out of the secondary menu hold “EXIT”. To continue on to the propor tional
band setting function press “EXIT” momentarily or “SET”.
Proportional Band
9.7
In a proportional controller such as this the heater output power is proportional to the
well 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 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 will deviate
excessively from the set-point due to varying external conditions. This is be cause the
power output changes very little with temperature 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 be cause the controller overreacts to
temperature variations. For best control stabil ity the proportional band must be set for
the optimum width.
