Instrument calibration is the process of correcting a measuring device or instrument, usually by adjusting it to match or confirm to a dependably known or unvarying measure. The calibration process generally involves using the instrument to test samples of one or more known values called ‘calibrators’; just like any equipment that may be used to repair a watch.
To understand calibration process, we need to first understand that most instruments do not work in isolation. They work together in a cluster, also known as “loop” in industry parlance. So calibration essentially means calibrating instruments in a loop. Because of complicated interconnection, loops frequently undergo drift which requires their calibration.
If you want to calibrate instruments in a loop there are two ways of going about it – you can either calibrate each of the instruments individually (known as individual instrument calibration) or you can calibrate the loop as a whole (known as loop calibration).
Given below is a more detailed explanation of both loop calibration and individual instrument calibration along with their advantages and disadvantages.
Individual instrument calibration
It is a calibration performed only on one instrument. The input and output are disconnected. A known source is applied to the input, and the output is measured at various data points throughout the calibration range. The instrument is adjusted, if necessary, and calibration is checked.
Disadvantages of Individual Instrument Calibration
- Entire loop is not verified within
- Mistakes on re-connect
- Less efficient use of time to do one calibration for each loop instrument as opposed to one calibration for the loop
Advantages of Individual Instrument Calibration
- Correct instrument will be adjusted
- More compatible with multi-function calibrators
A loop calibration is a set of instruments that are grouped and calibrated together. The input and output of the whole group determines the pass or fail status of the calibration. This means, if there is an error in one it will lead to a domino effect of errors on all other instruments that are part of the loop. Loop calibrator thus requires a special kind of calibrator, known as loop calibrator, that is equipped to handle and effectively calibrate instruments in loop. Loop calibrators, can again, be portable (i.e. handheld) or stationary. Portable calibrators are more popular, obviously because they are more convenient to use.
Advantages of Loop Calibration
- Entire loop, including sensor, is verified within tolerance
- Mistakes on re-connect minimized
- More efficient use of time to do one calibration for, loop as- opposed to one calibration for each loop, instrument
Disadvantages of loop Calibration
- Wrong instrument may be adjusted to bring the loop within calibration
- Not as compatible with multi function calibrators used-for “paperless” data collection