Documentation As-found and as-left

An important gauge is good practice when documenting the value of the instrument as it was found (as-found) and how it was made (as-left) with the settings. The purpose of documenting both conditions is to make records concerning gaps or drifts during the time the instrument. If only one of these conditions will register (as-found and as-left) every time you calibrate an instrument, it will be difficult to determine how well an instrument is maintaining its calibration (accuracy) over long periods of time.

A delay or inaccuracy often is an indicator of imminent failure, which is vital for any predictive maintenance program and quality control.

Typically, the document format for the values ​​of these conditions (as-founf and as-left) is a simple table showing the calibration points or values, the ideal instrument, the current response of the instrument and the error calculated for each point. The following table is an example for a pressure transmitter with a range from 0 to 200 PSI:

Up-and Down-test test

It is common calibration tables show we usually test points on the rise and drop points, for purposes of rule and document problems and deadband hysteresis (deadband). The following example shows a transmitter with a maximum hysteresis of 0.313% (the biggest error data are shown in bold)

If we make a calibration in both directions, it is important to apply the same stimulus value (precision) at some point to proceed to quantify errors or dead band hysteresis accurately, otherwise the data may not be used for these purposes.