Siemens ULTRAMAT 23 Manual page 162

Application note
9.1 H2S sensor with 'small' measuring range
Sample switchover between raw gas / pure gas
The sensor only functions correctly if the values at the measuring point do not greatly differ
from one another. We cannot recommend switching over between measuring points on the
raw gas side (high H
the difference between the H
measurement.
Pressure influence
Abrupt changes in pressure must be avoided. Although the sensor compensates pressure
variations within approx. 20 seconds, it cannot handle pressure surges which may occur
when switching over between samples.
Flow
The sample gas should flow continuously and at a constant rate, also during an AUTOCAL.
While an AUTOCAL is being carried out, the sample gas flow must be diverted by means of
appropriate valve switching.
Reason: H
accumulation increases as the sample gas pressure increases. This effect can result in
significant delays in the response time.
Gas moisture
The calibration gas must have the same moisture as the sample gas.
If the sensor is used with a very dry gas for a longer period, e.g. when feeding biogas into
the natural gas network, it is necessary to carry out an AUTOCAL with ambient air every 60
minutes. The dew point of the air should be in the range of approx. 9 °C ... 12 °C
(48 °F ... 54 °F). The AUTOCAL purge time should be at least 5 minutes. This prevents
premature drying-out of the sensor.
H influence
2
The internal design of the 5/50 ppm sensor means that it is immune to the influence of H
NH influence
3
Loading of 300 vpm NH
AUTOCAL / zero
An AUTOCAL of the zero point should be carried out every 60 minutes. On the one hand,
this is used to protect the sensor, but it also compensates the influence of temperature
variations during the day.
162
S concentration) and the pure gas side (low H
2
S concentrations of the two gas flows is too large for a reliable
2
S is highly soluble in water and accumulates in the condensate. This
2
results in destruction of the H
3
S concentration), since
2
S sensor within 2 to 3 days.
2
Manual, 3/2016, A5E37100388-003
.
2
ULTRAMAT 23