AMI Analyzer Manual •
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• 11
Display option:
Use the span button then up/down arrows provided on the display unit to calibrate the output. Expose the
probe to air or 100% oxygen, and adjust the span up/down arrows until the meter reads the correct value
(20.9% or 100.0%). The voltage output will then be calibrated to 1V full scale.
Be absolutely sure that you are using at least a certified, and preferably a primary standard span gas
supply as the span gas. Alternatively use known fresh air. So called "Manufactured air" or bottled
compressed air often has an oxygen content that is significantly different from its label.
If the calibration is to be performed in software, bear in mind the following points.
1. The most common error is that the user attempts to span the system on an incorrect gas, often
nitrogen. Some limitation must be made therefore in the permissible gain of the system so that this
condition is detected. Typically the gain is allowed to vary no more than 25% between calibrations.
However it is still possible for a calibration to be sufficiently in error that the system cannot be
recalibrated again once it has been messed up. Therefore it must be possible to force a calibration no
matter the apparent error.
2. The calibration routine should detect an excessive drift and delay calibration until the drift has stopped,
or abort the process if no good reading can be obtained. This might happen because of an inadequate
calibration gas flow, due perhaps to an empty cylinder.
3. If the sensor chosen has a time constant of 13 seconds, the calibration routine should allow at least 65
seconds for the reading to stabilize.
4. If the system performs an automatic calibration, some means of alerting the user to calibration failure
must be made.
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