TestEquity 123HS, Operation And Service Manual

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Chapter 7 – Maintenance
Page 7-8 TestEquity 123HS Temperature/Humidity Chamber
How to Verify the Temperature Calibration
! CAUTION: TestEquity does not recommend performing the controller calibration
procedures unless you have verified that the controller is actually out of
calibration.
TestEquity recommends verifying the calibration before attempting to actually perform a
calibration. The state-of-the-art instrumentation used in TestEquity chambers is of the highest
quality and seldom goes out of calibration. If you try to calibrate the instrumentation before
determining that calibration is necessary, you may make it worse if done incorrectly.
Variations in temperature throughout the chamber interior are NOT a measurement of controller
accuracy. These variations, called “gradients”, are a function of the physical design of the
chamber and its airflow, the characteristics of the test sample, and how it is oriented in the
chamber. You cannot “calibrate” to improve gradients. The common practice of measuring
multiple points in the chamber and adjusting the temperature controller’s calibration to correct
for these errors is incorrect! The correct way to adjust what the temperature controller “displays”
compared to what is measured at some point other than the controller’s sensor, is with the
“Calibration Offset” parameter. The F4 or F4T Temperature/Humidity Controller User’s Manual
for details. Calibration verification should be performed with the Calibration Offset set to 0.0
(zero).
Total system accuracy in the chamber includes the controller plus the thermocouple wire
accuracy. Total system accuracy over the chamber’s operating range is typically ±1.55°C, ±1
LSD or a theoretical total of ±2.55°C. The easiest way to verify the instrumentation accuracy is
with an independent calibrated temperature sensor and display. Place the sensor inside the
chamber, near the chamber’s conditioner fan grille. If the readings agree within the specified
limits, then no calibration adjustments are necessary.
For the F4 Controller: If calibration of the controller is necessary, refer to the “F4
Temperature/Humidity Controller User’s Manual”.
For the F4T Controller:
If calibration of the controller is necessary, refer to the “F4T Touch
Screen Controller User’s Guide”.