Chapter 9 – Maintenance
Page 78
TestEquity 101H Temperature/Humidity Chamber
How to Verify the Humidity Calibration
TestEquity recommends verifying the humidity calibration before attempting to perform any
adjustments. 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/F4T
Controller agree within the specified limits above, then no calibration adjustments are necessary.
TestEquity recommends the Vaisala HM70 Handheld Humidity/Temperature Meter with the
HMP77B Probe for verifying the humidity sensor calibration at all humidity conditions that the
chamber can achieve.
If adjustment of the F4T Temperature Controller is necessary, refer to the section for “F4T
Controller Calibration”
Humidity Sensor Calibration and Maintenance
TestEquity highly recommends the Vaisala HM70 Handheld Humidity/Temperature Meter with
the HMP77B Probe (combination package HM70F4E1A0DB) for calibrating the humidity
sensor at all humidity conditions that the chamber is capable of achieving. Most other products
on the market are not adequate for this purpose. Alternatively, the humidity sensor can be
calibration with Vaisala HMK15 Humidity Calibrator which uses saturated salt solutions for
11%RH and 75%RH. These items are available from Vaisala Inc. (www.vaisala.com).
The Vaisala HMM100 sensor is calibrated per the procedure in the Vaisala HMM100 User’s
Guide, which can be downloaded from
www.testequity.com/manuals
.
The humidity sensor element (Vaisala HUMIKAP 180R) is replaceable. The end of the sensor
probe has a stainless steel sintered filter (Vaisala HM47280SP), which can be removed by
unscrewing it. Handle the sensor by its outer plastic support. DO NOT TOUCH THE SENSOR
PLATE.
