7102
User’s Guide
26
Secondary Menu
Access less-used functions with the secondary menu. To access the secondary menu, push SET and
EXIT simultaneously, then release. The first function in the secondary menu is the heater power
display. (See Figure 6.)
Thermal Electric Device (TED)
The temperature controller controls the temperature of the well by pulsing the TED on and off. The total
power 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. Monitor the percent heater power to know how
stable the well temperature is. With good control stability the percent heating power should not
fluctuate more than ±5 % within 1 minute.
Access the heater power display in the secondary menu. Push SET and EXIT simultaneously and
release. Heater power shows as a percentage of full power.
100.00C Well temperature
Push SET and EXIT 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 to the proportional band setting function,
push EXIT momentarily or SET.
Proportional Band
In a proportional controller such as this, 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 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, heater power is reduced,
which consequently tends to lower the temperature. In this way, the temperature is maintained at a
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 temperature and the
controller cannot respond 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 5.0 °C. The proportional band width can be
altered if the user desires to optimize the control characteristics for a particular application.
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