When we send an instrument for calibration, we expect the metrology lab to bring the instrument back into calibration. Engineers should also receive a report showing how far out of calibration the instrument was before, and how far it is after adjustment. If the report shows significant calibration errors, it may be necessary to redo a project that was completed with the instrument just prior to calibration and take new measurements.
How often is calibration required?
There is no one answer to this query, because instruments, environments and applications vary. Test instrument manufacturers recommend calibration intervals for typical conditions; extreme conditions and very critical measurements may require more frequent calibration. Here are some general categories of calibration intervals:
Routine calibration as required by customer contract, quality standard organisation, military specifications, or other industry requirements. It is necessary to review the applicable requirements before the test to ensure that the calibration or certification for the test equipment is met.
Before and after a key measuring project. For example, when a new product pilot run is complete, a design engineer will characterise the product to ensure that it meets specifications and will optimise the test procedure. Final test adjustments made here can substantially decrease test time and affect profitability. Complete and reliable testing requires that the state of the instruments be verified both before and after the test period.
When you suspect a measurement is faulty or when the instrument has been overloaded or dropped. It is important to check the calibration and safety fidelity (such as a wire shorting to the case if it was dropped).
Accurate calibration is not a needless luxury—it ensures the reliability of test instruments and even the safety of personnel. For example, before working on a piece of equipment, one might measure a meter’s voltage to be sure it is safe. If a meter is broken or gives inaccurate information, it could result in injury or death. Additionally, calibration assures quality. It guarantees the accurate test results necessary to verify that products in final test and those shipped to customers indeed meet specifications.
The author is a strategic applications engineer at Maxim Integrated
