Chapter 6 – Frequently Asked Questions
Page 6-2
TestEquity 1007S Temperature Chamber
Why is there water/ice/snow in the chamber?
Any time the ambient air is subjected to temperatures below the dew point, moisture will
condense out of the air. The effect is ice or frost during low temperature operation. When the
chamber is heated above 0°C, the ice or frost will turn into water. To avoid moisture
condensation, make sure the port plugs are inserted at all times. Also, avoid opening the chamber
door while the chamber is operating at temperatures below room ambient. When a low
temperature test is completed, warm the chamber to at least room ambient before opening the
chamber door and before removing your test sample.
My test specification requires convection heat only. Can I turn the circulator motor off?
NO! This will damage the heating and refrigeration systems and void the warranty. You need a
“gravity convection oven” for that kind of test.
How accurate is the chamber?
That’s a loaded question! There is no “chamber accuracy” specification as such. The answer
requires an understanding of several performance parameters.
Control Tolerance – The Temperature Controller uses a thermocouple control sensor, which is
located in the discharge airflow. Control tolerance is a measure of how much the temperature
varies after stabilization at the control sensor. It is a measure of the relative variations, NOT the
absolute accuracy of the readout. The control tolerance specification for this chamber is
±
0.5°C,
or a total of 1°C. For example, the temperature set point may be –25.0°C. The actual temperature
varies between –25.4°C and –24.5°C. This corresponds to –0.4°C and +0.5°C or a total of 0.9°C
of RELATIVE variations. These specifications are for an empty chamber. The addition of a test
sample may affect the control variations. In some instances, the test sample will reduce these
variations.
Uniformity – Also known as Gradients. This is a measure of variations in temperature at
different locations throughout the chamber interior, at the same time, after stabilization. The
uniformity specification for this chamber is
±
0.5°C or a total of 1°C, when measured at least 2"
away from the chamber interior walls. These specifications are for an empty chamber. The
addition of a test sample may affect the temperature uniformity. For example, an energized test
sample will produce a higher temperature near the sample.
Controller Accuracy – This is the ability of the temperature controller to accurately display a
temperature measurement when compared to a standard. The controller display accuracy is
±1.66°C. However, the total measurement accuracy in the chamber includes the thermocouple
sensor wire accuracy. Thermocouple wire accuracy is ±1°C or 0.75% of reading, whichever is
greater. Therefore, total system accuracy over the chamber’s operating range can be as much as
±2.66°C, although the typical accuracy is often better than ±1.0°C.
Can I tilt the chamber to move it?
You should be able to tilt the chamber 45 degrees to move it. After tilting it and moving it into
place, perform the steps as outlined in “How to inspect the refrigeration machinery
compartment” and “How to check the refrigerant charge” before placing the chamber back into
service to make sure that no damage has occurred.
