H2O2 concentration reading when not exposed to H2O2 - HPP271

The PEROXCAP sensor used in HPP270 probes consists of 2 humidity sensors that have a minor difference in behavior when the humidity level changes. Because of this difference, the H₂O₂ concentration reading may vary slightly (typically 0 … 3 ppm) when the probe is not exposed to H₂O₂.

If necessary, the variation in low level output can be hidden by enabling the Low H₂O₂ threshold feature (available starting from probe SW version 1.3.6) that forces the output to 0 when the measurement falls below a set level (for example, 3 ppm), and the configured activation delay ends. The output returns to normal operation after the measurement has remained above the set deactivation level (for example, 10 ppm) for a set time. You can configure the Low H₂O₂ threshold activation and deactivation levels and the activation and deactivation delays with Vaisala Insight PC software and Modbus registers.

Activation level

The level below which the Activation delay timer starts (3 ppm in the example).

Activation delay

The activation delay timer starts when the measurement falls below Activation level. When the delay ends, the H₂O₂ output is forced to 0 ppm. Note that the deactivation limits apply also during the activation delay.

Deactivation level

The level above which the Deactivation delay timer starts (10 ppm in the example).

Deactivation delay

The deactivation delay timer starts when the measurement rises above Deactivation level. If the measurement remains above the deactivation level for the duration of the deactivation delay, the output returns to normal operation.

The same deactivation principle applies both before and after the Low H2O2 threshold feature activates. That is, both during and after the Activation delay, normal measurement output is resumed if the measurement rises above the Deactivation level for the duration of the Deactivation delay.