The reliability of strength test results depends directly on the condition of the force measurement system. Even a high-quality strain gauge load cell drifts over time: overloads, temperature cycles and ageing of the strain gauge adhesive all take their toll. Calibration is therefore not a formality for accreditation but a working tool for verifying measurement reliability.
The basic calibration interval for testing machines is once a year; it is fixed in the type approval documentation of the measuring instruments and in the accreditation criteria for testing laboratories. For heavily loaded machines (more than 40–50 tests per shift), manufacturers recommend shortening the interval to six months.
An unscheduled calibration is carried out regardless of the schedule: after repair or replacement of a load cell, after relocating the machine, after an accidental overload beyond the rated capacity, and when results systematically diverge from parallel tests. Indirect signs of trouble include zero drift after warm-up and readings failing to return to zero after unloading.
Following the work, the laboratory should receive a calibration certificate with a report: measured values at points across the range, calculated errors, the accuracy class to GOST R 8.663 (ISO 7500-1) and details of the reference force transducers with valid verification certificates. A report without traceability of the reference standards will not be accepted during an accredited laboratory audit.
In-Test arranges periodic calibration of force measurement systems from any manufacturer, with on-site visits to the customer's facility and a complete set of documentation. Requests are handled by the service department.