TestEquity 123H, Operation And Service Manual

Page: 57 / 77

Chapter 8 – Maintenance
TestEquity 123H Temperature/Humidity Chamber Page 8-7
How to Verify the Temperature Calibration
TestEquity recommends verifying the temperature 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 is NOT a measurement of 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 correct way to adjust what the F4 Controller “displays”
compared to what is measured at some point other than the controller’s sensor, is with the
“Calibration Offset” parameter. See page 6.2 of the “Series F4 User’s Manual” for details.
Calibration verification should be performed with the Calibration Offset set to 0.0 (zero).
The F4 Controller accuracy is specified ±1.55°C (above
– 50°C) and ±1.66°C (below – 50°C).
Total system accuracy in the chamber includes the controller plus the thermocouple wire
accuracy of ±1.0°C. Total system accuracy over the chamber’s operating range is can be as much
as ±2.66°C, although it is typically better than ±1.0°C.
The easiest way to verify the instrumentation accuracy is with an independent calibrated
temperature sensor and display. Place the sensor near the chamber’s sensors, which are located
towards the right side of the conditioner fan grille. If the readings agree within the specified
limits above, then no calibration adjustments are necessary.
If calibration of the F4 Controller is necessary, refer to page 9.2 of the “Series F4 User’s
Manual” and follow the instructions for “Thermocouple Input Procedure” for Input 1.
How to Verify the Humidity Calibration
TestEquity recommends verifying the humidity calibration before attempting to actually perform
a calibration. If you try to calibrate the instrumentation before determining that calibration is
necessary, you may make it worse if done incorrectly.
A Vaisala HMM100 capacitive-type sensor is used to measure humidity. The HMM100 output is
configured for 0-100%RH = 0-20 mA. The HMM100 sensor specifications are:
Sensor accuracy at
– 20°C to +40°C* Sensor accuracy at – 40°C to – 20°C, +40°C to +175°C*
±2%RH (0 to 90 %RH
±3%RH (90 to 100%RH) ±2.5%RH (0 to 90 %RH
±3.5%RH (90 to 100%RH)
*Note: Chamber controlled humidity range is 10°C to 85°C
The easiest way to verify the instrumentation accuracy is with an independent calibrated
humidity sensor and display. Place the sensor near the chamber’s humidity sensor, which is
located towards the right side of the conditioner fan grille. If the readings on the F4 Controller
agree within the specified limits above, then no calibration adjustments are necessary.