8.2.2 Zeroing and span calibration of Hydrogen Sulde sensors
Hydrogen Sulde sensors can be affected by extreme humidity changes. A sudden increase in ambient
humidity can result in a short-term positive drift in the instrument’s reading. A sudden decrease in ambient
humidity can result in a short-term negative drift in the instrument’s reading. These are most likely to
be noticed during calibration with dry or cylinder gas.
When calibrating Hydrogen Sulde cartridges the following should be taken into account while following
the procedure in 8.2.1:
1. To zero the sensor, use a compressed air cylinder of 20.9%Vol oxygen (not Nitrogen). Do not use
background air.
2. Apply the gas to the sensor for three minutes before using ‘’ to conrm the zero calibration.
3. If a span calibration is to be performed, the span calibration gas should be applied to the sensor
immediately after the zeroing procedure. Do not allow the sensor to return to ambient air conditions
between steps 2 and 3.
4. Apply the span gas for two minutes before using ‘’ to conrm the span calibration.
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