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User's Guide
9.5
9.6
9.7
42
Secondary Menu
Functions which are used less often are accessed within the secondary
menu. The secondary menu is accessed by pressing "SET" and "EXIT" simul-
taneously and then releasing. The first function in the secondary menu is
the heater power display. (See Figure 7 on page 38.)
Heater Power
The temperature controller controls the temperature of the bath by pulsing
the heater on and off. The total power being applied to the heater is deter-
mined by the duty cycle or the ratio of heater on time to the pulse cycle
time. This value may be estimated by watching the red/green control indi-
cator light or read directly from the digital display. By knowing the amount
of heating the user can tell if the bath 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 bath temperature is.
With good control stability the percent heating power should not fluctuate
more than ±1% 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.
S+E
Access heater power in secondary menu
12 Pct
Heater power in percent
To exit out of the secondary menu press "EXIT". To continue on to the pro-
portional band setting function press "SET".
E
Return to temperature display
Proportional Band
In a proportional controller such as this the heater output power is propor-
tional to the bath 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 bath 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 bath depends on the width of the propor-
tional band. See Figure 8 on page 43. If the band is too wide the bath tem-
perature will deviate excessively from the set-point due to varying external
conditions. This is because the power output changes very little with tem-
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