PROGRAMMING OF IAQRAE
4-12
Relative Humidity Sensor Calibration
Calibrating the Relative Humidity (RH) sensor is different from
calibrating other sensors. The RH sensor requires for less
frequent calibration than other chemical sensors. Under normal
conditions annual calibration may be adequate.
During single sensor calibration, the user needs to supply dry
gas (<10%) to zero the sensor. The user also needs to supply
a span gas of humidity (>90% relative humidity) to calibrate the
RH sensor. This calibration gas can be obtained by bubbling
dry gas from a cylinder or ambient air through pure water (See
Figure 4-1). When the monitor asks “10% RH?” press [Y/+] if
dry gas is being used to zero the RH sensor. Otherwise, press
[N/-] to calibrate the RH sensor to span value.
Figure 4-1
Water bubbler connections for span calibration
During single or multiple sensor calibration, the RH sensor will
be calibrated to the span value defined in Section 4.2.4.
However, it is good practice to perform zero calibration before
span calibration.
Note:
After <10% RH calibration, the user must perform a span
calibration to ensure that the RH sensor is calibrated correctly.
The sensor response does not change much in the ranges 0-
10% and 90-100%. Therefore, any humidity in these ranges
can be used to zero and span, respectively the RH sensor.
