Calibrating temperature probes and loggers for pharma storage

What calibration is — and isn't

Calibration compares a device's readings against a reference of known accuracy at defined temperatures and records the difference. It tells you how far off the device is; it doesn't necessarily fix it. Some devices can be adjusted afterwards; others are simply replaced if the error is too large.

Calibration is also different from temperature mapping. Calibration checks one sensor; mapping uses many calibrated sensors to find out how temperature varies across a space.

What a useful calibration certificate shows

• The device's model and serial number, so the certificate can't be confused with another unit.
• The calibration date and the laboratory that performed it.
• The temperature points tested — they should cover the range you use, for example points around +2 to +8 °C for a refrigerator logger, and colder points for freezers.
• The measured error at each point and the measurement uncertainty.
• A statement that the device passed against the stated tolerance, or the data you need to judge that.
• Traceability to national or international measurement standards.

Accreditation in India: NABL

In India, calibration laboratories are accredited by NABL, the National Accreditation Board for Testing and Calibration Laboratories, a constituent board of the Quality Council of India. NABL accredits calibration laboratories against ISO/IEC 17025, the international standard for the competence of testing and calibration laboratories, and is a signatory to the ILAC mutual recognition arrangement, so its accreditation is recognised internationally.

Accreditation is granted for specific parameters and ranges. Before relying on a certificate, check on NABL's accredited-laboratory search that the lab's scope covers temperature over the range you need — a scope that starts at 0 °C does not cover a −70 °C freezer probe.

How often to calibrate

Many quality systems calibrate monitoring probes annually. Recalibrate early if a device is dropped, damaged or disagrees with a reference.

Simple in-house checks between calibrations

Keep one calibrated reference thermometer or logger that is used only for checks. Place it beside the working probe, inside the same buffer if possible, and compare readings once both have settled. Record the difference. If it exceeds your tolerance, take the working device out of service and send it for calibration.

These checks don't replace calibration — they catch drift and damage between visits, which is when most errors appear.

Don't forget the controller

The refrigerator's own controller sensor decides when the compressor runs. If it drifts, the cabinet will run warm or cold even while the display looks normal. Include controller checks in maintenance visits by comparing the display with your calibrated logger, and ask the service technician to adjust the controller offset if needed — then record what was changed.

Practical tips

• Keep a spare calibrated logger so monitoring continues while one is away.
• Stagger calibration dates across devices so you never lose all of them at once.
• Store certificates with the temperature records for each cabinet.
• Note any battery change on the logger record; the CDC notes battery changes may affect accuracy.