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Industrial Dual-Block Calibrator
Secondary Menu
11
Heater Power
The temperature controller controls the temperature of the well by pulsing the heater on and off. The
total power applied to the heater is determined by the duty cycle or the ratio of heater 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
±
1
%
within 1 minute.
Note
For the Cold Side, negative numbers indicate the well is being cooled. When the display reads,
-100 P, the well is being cooled at maximum power. When the display reads, 0 P, the well is
neither heating nor cooling. When the display reads, 100 P, the well is being heated at
maximum power.
For the hot side, when the display reads, 0 P, maximum cooling is occurring (no heater power is
applied). The power percentage is never negative on the hot side.
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.
100.0C
Well temperature
Push
SET
and
EXIT
Access heater power in secondary menu
SEC
Flashes for secondary menu, then shows the heater power
13.0 P
Heater power in percent
To exit out of the secondary menu
,
push and 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.