Vaisala HMM100 - Manual (Page 17)

Chapter 2 ___________________________________________________________ Product Overview
VAISALA ________________________________________________________________________ 15
Catalytic VHP Filter
Vaporized hydrogen peroxide (VHP) is a gaseous form of hydrogen
peroxide that is commonly used in decontamination and sterilization of
environmental chambers. Hydrogen peroxide has relatively low
saturation pressure which increases the possibility of saturation when
used in humid conditions. When saturation conditions occur, liquid
hydrogen peroxide will form on surfaces in the decontaminated space.
Vaisala HUMICAP® sensor is compatible with direct VHP exposure
even at high concentrations and hundreds of VHP cycles up to saturation.
The long term performance is very good at concentrations higher than
typically used for sterilization. However, for the applications where full
saturation is possible, Vaisala recommends using the catalytic VHP filter
to protect the sensor and extend the calibration interval.
The catalytic filter is based on a generally known method where the H
2
O
2
is split to H
2
O and O
2
. This reaction is produced by the catalyst layer that
has been applied to the filter. As the filter prevents the VHP from
reaching the humidity sensor, the sensor responds to humidity only. The
catalytic filter affects the reading approximately +1 %RH at 300 pmm
VHP, or +3 %RH at 900 ppm VHP (at 23 °C / 73.4 °F).