Calibration is the comparison of an instrument against a known standard. It is a process that involves comparing the measurements of two instruments: standard/s (with a known magnitude of correctness) and a test instrument (one that you would like to ascertain).
You can compare the process with setting the time on a clock. When your time has gone out, (with the passing of time or due to a power failure, perhaps) you check it against a known standard, such as phoning the time standard or another known accurate timepiece, compare it with the time displayed and adjust it if necessary.
A field check is a simple comparison between two meters. It can sometimes point out a problem, but is not an accurate calibration. For calibration to be effective, the calibration standard must be more accurate than the instrument being tested. Calibration typically involves a standard of at least 10 times the accuracy of the test instrument.
An NIST-traceable standard is one that has paperwork showing it compares correctly to a chain of standards going back to a master standard maintained by the National Institute of Standards and Technology.
If a test instrument does not conform to the standard, then correction and repairs will need to to be performed to bring the instrument back into calibration.
If the report shows significant calibration errors, the user may need to go back and redo the measurements taken since the previous calibration.
Why do you need to calibrate your testing instruments?
The major components of test instruments can shift over time. This shifting is usually minor and is corrected during regular calibrations.
Other reasons to calibrate:
- Testing a new instrument
- After an instrument has been repaired or modified
- Prior to / after a critical measurement
- When measurements / data seems to be inaccurate
- When an instrument has been exposed to an event – such as a shock, vibration, was dropped heavily or sudden weather changes
- As per the manufacturer’s instructions
- For audits
Precision is the degree to which repeated measurements under unchanged conditions show the same result.
Accuracy is the degree of closeness of measurements of a quantity to its actual true value.
Thus, calibration is important for Precise and Accurate measurements.
How often should instruments be calibrated?
The norm is once annually. Calibration frequency is often specified by the quality auditors.
If you have a pH meter, you may be interested in reading How to make your pH Electrode last longer
Trackback from your site.