Drift is an undesirable but inevitable quality for any instrument. Long-term drift is attributable to many factors including normal degradation from age. A general rule of thumb is that the long term drift, from all sources combined, leave the instrument reading within reason for a period of five (5) years, to reduce the need for O/M activities and constant maintenance of the device, leaving it to serve instead of being served by the facility.

Auto-Zero Feature: Some devices, such as stack gas sensors and very-low range differential pressure transmitters, periodically re-establish the zero point of their output span by simultaneously providing a zero input condition and automatically adjusting the output to a zero value.

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