What is the difference between calibrating the sensor and the loop?

A sensor calibration compares the probe against a reference at known temperatures. A loop calibration verifies the whole chain — sensor, transmitter, wiring and what the control system finally displays or records. A sensor can be perfect while the loop is wrong, usually because of a configuration or wiring error, so we normally do both.

Do you have to remove the sensor from the process?

For a comparison calibration the sensor has to reach the reference temperature, so it is withdrawn from its thermowell — which usually does not require breaking process containment. Where the sensor cannot be withdrawn, we calibrate the transmitter and loop by simulation and assess the installation separately.

How many set points do you use?

Typically three to five across the actual working range, including points near the operating setpoint and near the tolerance limits. Calibrating only at ambient tells you almost nothing about behaviour at 150 °C.

Can you calibrate thermocouples in place at high temperature?

We can compare against a reference probe inserted in the same well or an adjacent one, which is valid where the two see the same temperature. For tight tolerances a withdrawn comparison in a dry-block or bath is more reliable, and we will say which applies to your point.

Why do my two sensors on the same line disagree?

Most often it is installation rather than sensor error — different immersion depths, one sensor reading wall temperature through stem conduction, or a transmitter configured for the wrong sensor type. Calibration separates a genuine sensor fault from an installation effect, which is the difference between replacing a probe and moving it.

Is the calibration traceable?

Yes. Our reference probes and dry-blocks carry their own accredited calibration certificates, and every report names the reference used and its traceability chain. Our procedures are built to ISO/IEC 17025 requirements, and our ESYD accreditation is in progress.

Temperature measurement

Temperature Sensor & Transmitter Calibration

Temperature decides reaction rates, product safety and energy cost, and its sensors fail in ways that look like normal operation. A thermocouple drifts as its junction ages, an RTD shifts after thermal shock, a transmitter is configured for the wrong sensor type, and a badly fitted thermowell reports the temperature of the pipe wall instead of the fluid. SEMAC calibrates the sensor, the transmitter and the loop together, on site.

What we calibrate

Pt100 / Pt1000 resistance sensors

The workhorse of process temperature. We check the element, the wiring configuration (2/3/4-wire) and the effect of lead resistance.

Thermocouples — types K, J, T, N, E, S

Junction ageing and inhomogeneity cause slow, one-directional drift. Comparison against a reference probe at working temperature is the only reliable check.

Temperature transmitters

Sensor-to-output conversion, sensor type and range configuration, and linearisation — verified by injecting known resistance or millivolt values.

Dial thermometers and thermostats

Local indicators and switching devices, including the actual switching point of a thermostat rather than its dial marking.

Thermowell and installation assessment

Immersion depth, contact and stem conduction. A perfectly calibrated sensor in a bad well still reports the wrong temperature.

How we do it

Comparison in a portable dry-blockSensor and traceable reference probe are brought to the same temperature at several set points across the working range, and the difference is recorded at each.
Liquid bath comparisonFor better uniformity, short sensors, or multiple sensors at once — the preferred method where accuracy requirements are tight.
Ice-point checkA fast, highly reproducible 0 °C reference used to confirm sensor stability between full calibrations.
Simulation and loop calibrationInjecting known resistance or millivolt signals verifies the transmitter and the control-system reading independently of the sensor.
Multi-point profilingFor chambers, tanks and rooms, several sensors are logged simultaneously to map uniformity and identify cold or hot spots.

What you receive

Calibration certificate per sensor or loop
As-found and as-left deviation at each set point
Set points covering the actual working range, not just ambient
Reference probe used, with its traceability chain
Stated measurement uncertainty per point
Sensor type, wiring configuration and transmitter settings recorded
Installation findings — immersion depth, well contact, stem effects
Pass/fail against your tolerance, plus recommended interval

When you need it

Product safety and HACCP

Pasteurisation, cold chain and sterilisation records are only as defensible as the sensor that produced them.

Suspected sensor drift

Two sensors on the same duty disagree, or a reading moved without a process reason.

Energy and efficiency work

Heat balance, boiler efficiency and heat-recovery calculations amplify a small temperature error into a large money error.

Audit and qualification

ISO 9001, HACCP/IFS/BRC and equipment qualification all expect documented, traceable temperature calibration.

After maintenance

A replaced sensor, a rewired transmitter or a swapped thermowell needs verification before it is trusted.

Calibration intervals

Thermocouples drift faster than RTDs and should be checked more often — typically every 6 to 12 months in hot service, against 12 to 24 months for a stable RTD loop. Safety-critical and product-release points sit at the short end regardless of sensor type. As with flow, the honest interval comes from your own as-found history rather than from a default number.

Calibration procedures follow ISO/IEC 17025 methodology; ESYD accreditation is in progress.

Industries served

Where we operate

Common questions

Tell us about the measurement point you need checked

Describe the instrument and your plant, and we will tell you what can be verified in-situ, what needs a workshop calibration, and what it will take.

Keep your instrumentation performing at its best

Speak with SEMAC's service team to discuss your maintenance needs and plan your verification & calibration service.

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