USER'S GUIDE____________________________________________________________________
52 _______________________________________________________________ M210619EN-C
NOTE
The error output value is shown only when there are minor electrical
faults such as a humidity sensor open circuit. When there is a severe
device malfunction, like analog output electronics failure or
microprocessor ROM/RAM failure, the error output value is not
necessarily shown.
Chemical Purge (Optional)
General
In some specific applications the sensor gain may decrease gradually
due to an interference caused by some particular chemical present in
the ambient (see Figure 16 on page 53). The sensor polymer absorbs
the interfering chemical; this reduces the ability of the polymer to
absorb water molecules and so decreases the sensor gain. In chemical
purge heating the humidity sensor to a temperature level of
approxi180 °C for several minutes evaporates the interfering
chemical.
The purge function starts with heating stage, continues with settling
and when the temperature of the sensor is decreased transmitter
returns to normal mode. The whole cycle takes about 8 minutes.
NOTE
Chemical purge function locks the output values for about 8 minutes.
