Vaisala HMP155 - Manual (Page 48)

USER'S GUIDE____________________________________________________________________
46 _______________________________________________________________ M210912EN-C
0508-035
Figure 11 Decrease of Sensor Gain
Automatic Chemical Purge (Interval Purge)
When HMP155 leaves the factory the automatic chemical purge takes
place repeatedly with the time intervals set in the factory, if this option is
chosen. You can change the interval in which the purge takes place by
using serial commands. This can be necessary if the measuring
environment contains high concentrations of interfering chemicals. The
automatic chemical purge can also be turned off if necessary.
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.
Manual Chemical Purge
The chemical purge must be performed always before RH calibration
(see section Calibration and Adjustment on page 57) or when there is a
reason to believe that a sensor has become exposed to an interfering
chemical. Manual chemical purge can be activated by turning the power
up purge on temporarily and resetting the probe. After the operation, the
power up purge can be turned off, see PUR command on page 47. Make
sure that the temperature of the sensor has come down to normal
temperature before starting a calibration.