How to manage calibration of measuring instruments in your plant
Measuring instrument calibration is one of those quality system requirements that is either taken seriously or completely neglected in Indian manufacturing plants. When it's neglected, your quality decisions — accept or reject — are based on measurements that might be wrong. Every quality audit and customer quality requirement will check calibration.
Build a calibration register. List every measuring instrument in your plant: vernier callipers, micrometers, gauges, weighing scales, thermometers, pressure gauges, and any other instruments used to make quality or process decisions. For each, record: instrument ID, type, location, range, calibration frequency, last calibration date, and next calibration due date.
Define calibration frequency based on use and criticality. An instrument used to make final quality decisions on every batch should be calibrated more frequently than one used occasionally for reference. Manufacturer's recommendation is a starting point; adjust based on your actual use and the criticality of measurements taken.
Use an accredited external calibration lab for reference instruments and complex equipment. For simple instruments (vernier callipers, basic gauges), in-house calibration against a master reference is often sufficient. For precision measurement equipment, thermometers used in controlled processes, or any instrument whose calibration will be scrutinised by a customer or certification body, use a NABL-accredited calibration lab.
Mark instruments with calibration status. Every calibrated instrument should have a label showing the calibration date and next due date. Instruments that are out of calibration should be tagged and physically removed from the production area so they can't be accidentally used.
When calibration reveals an instrument was out of tolerance, investigate impact. If your gauge was out of tolerance for the last 3 months, what did you ship during that period? This is a critical quality question that most companies don't answer rigorously. Document the investigation and its conclusion.
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