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7102
User's Guide
9-6
9.4.4 Switch Test Example
This section describes a possible application for the temperature hold feature
and how the instrument is set up and operated.
Suppose you have a thermal switch which is supposed to open at about 75 °C
and close at about 50 °C and you want to test the switch to see how accurate
and repeatable it is. You can use the temperature hold feature and the scan
function to test the switch. Measurements can be made by observing the display
or, preferably, by collecting data using a computer connected to the RS-232 port.
To set up the test do the following steps.
1. Connect the switch wires to the terminals on the back of the Micro-Bath and
place the switch in the well.
2. Enable set-point scanning by setting the scan to “ON” in the primary menu
(see Section 9.3.1).
3. Set the scan rate to a low value, say 1.0 °C/min. (see Section 9.3.2). If the
scan rate is too high you may lose accuracy because of transient temperature
gradients. If the scan rate is too low the duration of the test may be longer
than is necessary. You may need to experiment to find the best scan rate.
4. Set the first program set-point to a value above the expected upper switch
temperature, say 90 °C.
5. Set the second program set-point to a value below the expected lower switch
temperature, say 40 °C, in the program menu.
6. Collect data on a computer connected to the RS-232 port. Refer to Section
9.8.2, Serial Interface Parameters, for instructions on configuring the RS-232
communications interface.
9.5 Secondary Menu
Functions which 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 7 on page 32.)
9.6 Thermal Electric Device (TED)
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.
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