Maintenance Calibration Record

This record covers instruments the maintenance function uses to set, test and judge physical conditions. It is deliberately narrow, because the neighbouring records answer questions it cannot.

Calibration is one of the few requirements written into almost every management system standard in nearly identical terms, and always with the same two-part shape: keep the equipment fit, and deal with what you measured while it was not.

Very little law tells a maintenance department to calibrate a torque wrench. The requirement arrives instead through legal metrology for trade instruments, through sector regulation where the measurement protects product or people, and through customer standards.

Every field on this form can be answered truthfully and the record can still be indefensible. Four judgements decide which it is.

Calibration is heavily audited, and the findings are consistent across sectors: the instruments are calibrated, the consequences are not managed.

A ready-meals site sent its workshop torque wrenches out for annual calibration each March. One of them, a 40 to 200 Nm click wrench used for compressor and gearbox work, came back with a certificate showing it clicking at 158 Nm when set to 180, well outside the tool's stated deviation. The technician logged the record, recorded pass after adjustment, applied the new label, entered the next due date and closed it. Out of tolerance as found was answered no, so the two conditional fields for reviewing work done and listing affected work orders never appeared.

In June the head gasket on a chill store compressor blew during a Sunday run. The cover bolts had been retorqued in January, using that wrench, to a figure that had in fact been applied some twelve per cent light. Reconstructing which other joints were affected took a week of reading work orders, because nobody had bounded the window at the time. Three further jobs were found and redone: a pump baseplate, a gearbox and a set of flange bolts on a glycol line.

The calibration was done properly, on time, by an accredited laboratory. What failed was the single answer that opened the review, and it was answered wrong not out of dishonesty but because the record already said pass and the field looked like a duplicate of the result. The corrective action was a rule rather than training: an adjustment or a fail forces out of tolerance as found to yes, which forces the affected work review to open, which forces the window to be bounded on the day.

The calibration itself is usually done well and on time. What fails is the schedule that lets an instrument stay in the tool store past its date, and the review of past work that nobody raises because the record already says pass.

KnowMaintain

Holds the instrument population against the asset register, drives calibration from due dates rather than memory, and withdraws anything overdue from the workshop.

KnowQuality

Takes an out-of-tolerance finding through to product and process impact where the instrument touched anything that reached a specification.

KnowSafe

Owns the instruments that clear people to work, gas detectors and insulation testers among them, and blocks entry or isolation work on a lapsed calibration.

Ella

Bounds the exposed window on an out-of-tolerance result, pulls the work orders raised since the last good calibration, and opens the review with them attached.

As found reading

The instrument's indication at a test point before any adjustment, which is the figure describing its accuracy during the period just ended.

As left reading

The indication after adjustment or repair, which establishes fitness for the period ahead and says nothing about the period behind.

Tolerance

The maximum permissible deviation you accept for the way the instrument is used, stated on the record so the pass decision can be re-derived.

Out of tolerance

A deviation beyond the accepted limit, which triggers the duty to determine whether earlier measurements made with the instrument remain valid.

Metrological traceability

An unbroken chain of comparisons from the instrument to a national or international measurement standard, each with a stated uncertainty.

Measurement uncertainty

The quantified doubt about a result, which must be considered when a deviation sits close to the tolerance limit rather than ignored.

Calibration interval

The period between calibrations, set initially by manufacturer guidance and criticality and revised on drift history rather than convention.

Bump test

A functional check that a gas detector responds and alarms on exposure to target gas, which confirms response but does not calibrate span.