5. Operation
5.1 Probe Start-Up
When powered on, the probe starts up within 2 seconds and the digital/analog outputs are
activated. The probe performs a start-up purge, which takes approximately 4 minutes. During
the purge, hydrogen peroxide, relative humidity, and relative saturation measurements are not
available. If the probe is in analog mode, analog outputs are in the error state (default: 3.6 mA)
during the purge.
Measurements from the outputs (digital and analog) will reach specified accuracy after a 8½-
minute warm-up period. For this reason, you should design your system so that it does not rely
on measurements from the probe during this time.
More Information
‣
Behavior at Exposure to H2O2 (page 25)
5.2 Behavior at Exposure to H
2
O
2
When there is H
2
O
2
in the probe's environment, the probe must
always be powered on. When powered on, the PEROXCAP sensor is heated,
which permits using the probe in condensing H
2
O
2
conditions, maintains
measurement performance, and lengthens the probe's lifetime. When the probe
is powered off, exposure to H
2
O
2
condensation can break the PEROXCAP sensor
within a day, and the sensor will not recover.
CAUTION!
When the bio-decontamination process starts and the probe is exposed to H
2
O
2
, the probe's
H
2
O
2
concentration reading changes to > 0 ppm after approximately 20 ... 30 seconds. This
time is included in the response time of the probe.
5.3 H
2
O
2
Concentration Reading When Not
Exposed to H
2
O
2
The PEROXCAP sensor consists of two humidity sensors that have a minor difference in
behavior when the humidity level changes. Because of this difference, the H
2
O
2
concentration
reading may vary slightly (typically 0 … 3 ppm) when the probe is not exposed to H
2
O
2
. This
variation is normal and does not require any actions. If needed, you can hide the variation by
setting a low clipping limit with the Vaisala Insight software, Modbus configuration register
030C
hex
, or an Indigo 200 transmitter. For example, if you set the low clipping limit to 3 ppm,
any reading < 3 ppm is clipped to show 0 ppm.
Chapter 5 – Operation
25