BAPI Recommended Humidity Transmitter Calibration Interval – Application Note


Building Automation Products Incorporated (BAPI) certifies that our humidity transmitters have been produced, inspected, and tested in compliance with applicable drawings, specifications, and standards by the manufacturer. These products meet or exceed published specifications and have been calibrated using applicable quality standards, such as but not limited to, the National Institute of Standards and Technology (NIST), natural physical constants, or established ratio type self-calibration techniques.

However, due to the critical monitoring nature, some uses require re-certification or re-calibration according to the manufacturer’s recommendations. This document shall serve notice that under the normal operating conditions (relatively clean) all humidity transmitters drift slightly with time and installation conditions. Due to this slight drift, BAPI recommends that any humidity transmitter should be tested and re-certified after 3 years using a minimum of a one point NIST certification process and as needed recalibration. If the environment is very dirty or dusty or the control is critical, then this re-certification time could be as short as 1 year. Due to unpredictable field conditions, NIST certified recalibration can only be done in a laboratory conditions using NIST traceable equipment, procedures and standards. One point calibrations can be done in the field using a trusted hand held reference (Preferably NIST traceable) and offset adjustment, but will not be considered an NIST traceable calibration due to the lack of a controlled environment such as an environmental chamber.

A quick field check once a year can be conducted with an NIST traceable hand held solid state RH meter. Compare the hand held meter results to the field installed humidity transmitter output. If the transmitter under test is greater than 6% different from the hand held meter, then a laboratory test and/or recalibration would be recommended. Possible replacement may be required depending on the severity of the application wear and tear.

If you have any questions about this procedure, please call your BAPI representative.


Printable pdf Version of this Application Note

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