6.6
Secondary Menu
Functions that are used less often are accessed within the secondary menu. The
secondary menu is accessed by pressing “SET” and “EXIT” simultaneously
and then releasing. The first function in the secondary menu is the heater power
display. (See Figure 6 on page 24.)
6.7
Heater Power
The temperature controller controls the temperature of the well by pulsing the
heater on and off. The total power being applied to the heater is determined 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 indicator light or read di-
rectly from the digital display. 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 lets the user
know how stable the well temperature is. With good control stability the per-
cent 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 is displayed as a percent-
age of full power.
100.00 C
Well temperature
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 propor-
tional band setting function press “SET”.
6.8
Proportional Band
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 depends on the width of
the proportional band. See Figure
. If the band is too wide the well tempera-
ture deviates excessively from the set-point due to varying external conditions.
This is because the power output changes very little with temperature and the
9116A Furnace
User’s Guide
30
