Calibration Handbook
138 Sensepoint XCD
20. When the reading falls below 50% of the calibration gas level the display indicates a countdown (up to
180 seconds dependant on gas type).
21. When the countdown is finished, the calibration procedure is complete.
22. The instrument returns to the ‘Set CAL’ menu. Activate the ‘T’ or ‘S’ switch to select another menu or
select ‘QuIT’ to return to normal monitoring mode.
NOTE
Zero and Span Calibration of Hydrogen Sulfide sensors
Hydrogen Sulfide 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 Sulfide cartridges the following should be taken into account while following the
Span/Zero procedure:
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 confirm 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 confirm the span calibration.
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