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OMG100N1.21
User Calibration Explained:
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User calibration is a means of optimising the performance of the instrument to the current
operating conditions such as ambient temperature and pressure as well as correcting for
instrument drift caused by lamp and filter settling.
In general, the instrument should not require calibration more than once a month, but we
do recommend verifying the instruments operation each day.
User calibration has two operations and each may be performed individually, however for a
complete user calibration both must be completed.
Factory Calibration (Curve 1)
The G100 instruments are 'Factory' calibrated and stable.
Zero Calibration (Curve 2)
This corrects the entire curve for lamp and filter variations caused by aging and user
induced drift due to dirt etc. If done correctly there is often no need to complete a span
calibration. However a poor calibration[A] will result in a span error as shown with the zero
indicating a small error [B] but a significant span error [C].
Note:
The Zero calibration is very sensitive and even 100% instruments will detect in
the 0 to 100ppm range even though they do not display to this resolution. Please
refer to the chart 'Typical Zero Gas Purge Time'.
Span Calibration (Curve 3)
This optimises the instrument at the span calibration concentration [D] for the current
operational conditions and variations in user calibration gasses. It corrects the span point
leaving the zero unadjusted and should be done at the concentration of normal operation.
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Copyright Geotechnical Instruments (UK) Limited
User Calibration
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G100 Range
Curve 1 - Factory
Curve 2 - Zero
Curve 3 - Span
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