Vaisala HMT330 - Manual (Page 136)

User's Guide _______________________________________________________________________
134 __________________________________________________________________ M210566EN-K
Before starting the chemical purge, note the following:
- The sensor is protected with a PPS grid with stainless steel netting, a
stainless steel sintered filter or with membrane SST filter.
- The sensor temperature must be below 100 °C. At higher temperatures
the chemicals evaporate spontaneously from the sensor and the
chemical purge is not necessary.
- Subzero temperatures slow down the recovery of the sensor after the
chemical purge. The sensor is completely dry after the purge, and in
very cold temperatures it can take more than two hours for it to reach
ambient humidity again.
Automatic Chemical Purge (Interval Purge)
When HMT330 leaves the factory the automatic chemical purge (if
chosen) takes place repeatedly with the time intervals set in the factory.
User can change the interval in which the purge takes place by using
serial commands or with the optional display/keypad. This can be needed
if the measuring environment contains high concentrations of interfering
chemicals. The automatic chemical purge can also be turned off if
necessary.
Manual Chemical Purge
The chemical purge should be performed always before calibration (see
section Calibration and Adjustment on page 155) or when there is a
reason to believe that a sensor has become exposed to an interfering
chemical. Make sure that the temperature of the sensor has come down to
normal temperature before starting a calibration.
Chemical Purge in Power Up
Chemical purge (start-up purge) can be set to start within 10 seconds
from the power-up of the device.