Insights
Calibration
Calibration practice, certificates, intervals and equipment.
What is CMC in calibration?
Calibration and Measurement Capability is a laboratory's best-case uncertainty, not the accuracy of your instrument.
Dry block vs environmental chamber
Two common ways to generate a temperature for calibration, suited to different sensors, ranges and uncertainties.
How to calibrate a Pt100
Calibration by comparison against a reference thermometer, and the factors that decide the uncertainty.
As-found vs as-left
Why both sets of readings matter, and what to do when the as-found data are out of tolerance.
What should a calibration certificate contain?
A checklist for reading a certificate — and the items whose absence should make you ask questions.
How to set calibration intervals
There is no universal interval. Set it from risk, manufacturer data and — above all — the instrument's own as-found history.
How thermocouples are calibrated
Thermocouples measure with the whole wire, not just the tip — which is why immersion, homogeneity and the reference junction dominate their calibration.
How temperature data loggers are calibrated
Loggers are calibrated as a system — sensor, electronics and firmware — usually in a chamber, at the points that matter for their use.
Liquid bath versus dry-block calibrator
A stirred liquid bath offers the best uniformity; a dry block offers speed, portability and no fluid — the choice is about uncertainty and practicality.
Immersion depth and stem conduction
A probe conducts heat along its stem. Insufficient immersion makes the sensor read closer to room temperature than to the medium.
Calibration, adjustment and verification are different things
Calibration measures; adjustment changes the instrument; verification compares against a requirement. Mixing them up leads to lost as-found data and unsupported claims.
Tolerance versus uncertainty
Tolerance is what you require of the instrument; uncertainty is how well the calibration could measure it. A conformity statement needs both.
Choosing calibration points
Calibrate where you measure. Points should bracket the use range and include any temperature where a decision is made.
Self-heating in resistance thermometers
The measuring current warms the sensing element. The effect depends on the medium — so calibrate at a current and condition representative of use.
Hysteresis in temperature sensors
A sensor can read differently at the same temperature depending on where it came from. Calibrations that only approach from one direction hide it.
Selecting a reference thermometer
The reference sets the floor of your uncertainty. Choose it for stability and a calibration uncertainty comfortably below what you need to deliver.
The ice-point check
A properly made ice bath gives 0 °C to within a few millikelvin — a cheap, repeatable way to watch a PRT for drift between calibrations.
Calibrating relative-humidity sensors
Humidity calibration is a temperature calibration in disguise: small temperature differences between sensor and reference become large RH errors.