Automatic Chemical Purge (Interval Purge). Vaisala HUMICAP HMT330 SERIES, HMT330

User's Guide _______________________________________________________________________

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.

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