Chemical purge (optional) - HM70

HM70 User Guide

Document code
M210297EN
Revision
G
Language
English (United States)
Product
HM70
Document type
User guide

Chemical purge is an optional feature of the HM70 series humidity probes HMP75B, HMP76B, and HMP77B. In some specific applications the sensor gain may decrease gradually due to an interference caused by some particular chemical present in the ambient. The sensor polymer absorbs the interfering chemical; this reduces the polymer's ability to absorb water molecules and so decreases the sensor sensitivity. In chemical purge the interfering chemical is evaporated by heating the humidity sensor to a temperature of +160 °C (+140 °F) for 2 minutes.

For most applications it is sufficient to perform the chemical purge once a week. For applications where HM70 is subject to high concentrations of chemicals, chemical purge should be performed more frequently, in extreme cases before each measurement.