Argweld purge monitor's sensor failure

[Yuri B.]

Hello.
I have seen two or three Argweld purge monitors MKIII which would not want get calibrated - they show values from some minus 5 to plus 5 but never 20.9 (the usual oxygen %). Evidently, faulty sensors, but what made them out of order? Hot gas got on them? (They were used during welding of stainless pipes).

[Brian_UK]

Any of the following happened or done/not done? (From tech docs.
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(MkIII) The benefit of this is the 18 - 36 months life of the new sensor.

Sensor life is reduced by continuous exposure to high levels of oxygen.

Life will be greater if the monitor is used frequently, that is, in measuring weld purging by removing oxygen from the system.

If the monitor is unused for long periods, sensor life can be increased by sealing the sensor or storing the instrument in an argon filled plastic bag or container.
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[Yuri B.]

Thank you! I have passed this info to the person whom those tools belong.