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Calibration of analysers


Why is the calibration of gas analysers necessary?

ALL gas analysers require periodical calibration. During the calibration the analyser is exposed to the reference (calibration) gases. A reaction of each sensor to such gas is registered and stored in the analyser's memory.

Electrochemical cells

Electrochemical cells require regular, periodical calibration. Due to the operation principle, their response (electrical signal) significantly changes in time. Those changes are faster when the cells are exposed to gases more often, and when the exposure concentration is higher.

It is necessary to perform analyser's gas calibration proportionally to their usage intensity (the more often the analyser is used the more frequent the calibration should be performed) . Detailed recommendations on how often the analyser should be calibrated can be found in analyer's user manuals.

Optical sensors (NDIR)

NDIR sensors also require periodical calibration. The necessity of calibration is a consequence of changes of light detector and IR-light source electrical response.
Calibration of NDIR sensors is much more complicated than calibration of electrochemical cells, because the calibration curve of NDIR sensor is strongly non-linear and requires several calibration points for its determination. Such calibration must be performed with the help of gas mixer. It is essential for the accuracy of the results performed with NDIR sensors that their calibration with reference gases is performed on regular basis.

Oxygen sensors

madur uses one of three types of oxygen sensors in analysers. They are: electrochemical cell, partial pressure sensor, paramagnetic sensor.
All of them also require periodical calibration, but they do not need reference gases for the process. In case of oxygen sensors, the reference gas is the atmospheric air, where the concentration of oxygen is with high accuracy constant.
Calibration of oxygen sensor is performed automatically by analyser, each time it is being ventilated with air.

 


Calibration and cross-sensitivity to foreign gases

As is known, the most significant disadvantage of electrochemical cells is their nonzero sensitivity to some foreign gases. If the analyser is equipped with a set of sensors, then, during the calibration process, a sensitivity of each sensor to foreign gases is determined.
In a consequence, a properly calibrated analyser is not effected with the cross-sensitivity of sensors to the foreign gases.
During the analyser's usage, the cross-sensitivity can change and a sensitivity to foreign gases can be observed. Gas calibration with reference gases eliminates this sensitivity.

Where the gas calibration can be performed?

Calibration procedures are either implemented in the firmware of our analysers or they can be performed with the help of our service software (available free-of-charge from madur).
Calibrations are carried out by our dealers, and are in offer of many laboratories equipped with suitable stations.
Calibration of analysers equipped with electrochemical cells is simple and can be carried out oneself by anyone that has suitable reference gases.
In case of multipoint calibration of NDIR sensors, along with the reference gases a gas mixer of an appropriate accuracy is required.

We provide necessary software and manuals for the multipoint calibration. However, because of the complexity of such calibration, we encourage to undergo a suitable training in our company.

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