Sensor purge - HPP271 - HPP272

HPP271 and HPP272 Quick Guide

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User guide

Sensor purge is a 4-minute process where the sensors are heated to remove possible contamination. The purge is essential for the long-term performance and accuracy of the probe in demanding H2O2 environments. During the purge, H2O2 and H2O measurements are not available.

The purge is automatically performed:
  • At probe start-up.
  • After an RH for H2O2 adjustment is made.
  • At intervals (default 24 hours, configurable between 1 hour ... 1 week using Vaisala Insight software, Modbus, or Indigo transmitters). Purge is postponed by 30 minutes if H2O2 is present or ambient humidity is not steady.
If required, you can also enable purge during H2O2 exposure with the Insight PC software or an Indigo transmitter.

Purge is recommended at least every 24 hours of powered-on time, even if the probe has not been continuously exposed to H2O2.

Optional: if needed, you can also trigger a purge at any time with Vaisala Insight software, Modbus (in digital mode) or pin #5 on the M12 connector (in analog mode).

For more information on the sensor purge, see HPP271 User Guide in English M211888EN and HPP272 User Guide in English M211972EN available at

Optional: Manually triggered purge in analog mode

To trigger a purge in analog mode, disconnect pin #5 from ground for a minimum of 50 ms, and then reconnect the pin to ground.

In analog mode, pin #5 in the probe's M12 connector is connected to ground. Do not connect pin #5 to ground permanently, but instead, use a relay or similar to control the pin.
Figure 1. Example wiring in analog mode to enable manual purge triggering