Calibration

Temperature Calibration: Methods, Standards and Singapore Requirements

Temperature is one of the most widely measured physical quantities in Singapore industry, from pharmaceutical cold chains to HVAC systems and food processing. This guide covers temperature calibration methods, the ITS-90 scale, traceability requirements, and how to choose the right calibration service.

Unitest Instruments·Updated 24 June 2026·11 min read

Temperature calibration is the process of comparing a temperature measuring instrument against a reference standard traceable to the International Temperature Scale of 1990 (ITS-90) and recording the errors and measurement uncertainty across the instrument's operating range. Temperature is one of the most fundamental and widely regulated measurements in Singapore industry. Pharmaceutical cold chains, food processing environments, cleanroom monitoring, industrial ovens, HVAC systems, and marine cargo all depend on accurate temperature measurement. An incorrectly calibrated thermometer or temperature sensor can lead to product spoilage, regulatory non-compliance, or process failures.

The International Temperature Scale of 1990 (ITS-90)

All temperature calibrations traceable to national standards ultimately link to ITS-90, the internationally agreed approximation to thermodynamic temperature, defined by fixed points (reproducible physical phenomena at known temperatures) and interpolating instruments (typically platinum resistance thermometers and thermocouples) between them. Key fixed points include the triple point of water (0.01°C / 273.16 K), melting point of gallium (29.7646°C), melting point of indium (156.5985°C), melting point of tin (231.928°C), melting point of zinc (419.527°C), freezing point of aluminium (660.323°C), and freezing point of silver (961.78°C). National metrology institutes, including Singapore's A*STAR National Metrology Centre (NMC), maintain primary realisations of ITS-90; calibration laboratories such as Unitest Instruments calibrate their reference thermometers against NMC standards, creating a traceability chain from the customer's instrument back to the ITS-90 fixed points.

Types of Temperature Instruments

RTDs (most commonly Pt100 or Pt1000 platinum resistance thermometers) are among the most stable and accurate industrial temperature sensors, calibrated by measuring resistance at known temperatures against the relationship defined in IEC 60751; widely used in pharmaceutical manufacturing, food processing, semiconductor fabrication and HVAC, and often used as transfer standards for their excellent stability. Thermocouples generate a small voltage proportional to temperature difference and are used at high temperatures where RTDs aren't suitable — common in ovens, furnaces and process heating; they require more careful calibration since they drift with use, especially when exposed to contamination or mechanical stress, and IEC 60584 defines the thermocouple types (J, K, T, N, E, R, S, B) and tolerance classes. Liquid-in-glass and digital thermometers are typically calibrated by immersion in a temperature-controlled bath or dry block alongside a reference standard, with readings compared at multiple points. Infrared thermometers and thermal cameras measure emitted thermal radiation and are more complex to calibrate since the reading depends on target emissivity and distance, typically calibrated using a blackbody radiator. Data loggers used extensively in Singapore's pharmaceutical cold chains and food storage are calibrated for probe accuracy, display and internal clock, and are subject to HSA GMP and NEA requirements.

Temperature Calibration Methods

Two primary methods are used. Comparison calibration in a controlled medium is the most common: a liquid bath (oil or water, depending on range) or dry block calibrator holds both the reference standard and instrument under test at a series of target temperatures, with readings recorded at each point. Liquid baths provide excellent stability and uniformity for high-accuracy work; dry block calibrators are more portable and common for on-site probe calibration, using a metal block with precisely drilled holes heated or cooled to target temperature. Fixed-point calibration uses melting or freezing points of high-purity materials as the reference, providing the highest possible accuracy since phase transitions occur at a precise, reproducible temperature; it's typically used for reference-grade thermometers that will serve as transfer standards, performed by national metrology institutes and top-tier laboratories.

Temperature Calibration in Singapore's Regulated Industries

Pharmaceutical manufacturing (HSA GMP): temperature-monitoring equipment in production, storage and QC (cold rooms, autoclaves, incubators, stability chambers) must be calibrated at defined intervals with traceable standards and records maintained for inspection. Cold chain logistics (HSA, SFA, NEA): data loggers monitoring pharmaceutical, food and biological transport must be calibrated to provide confidence in the records they generate, accompanying audit evidence that the chain stayed within limits. Food processing (SFA): thermometers checking cooking and cold storage temperatures need documented calibration evidence for inspections. HVAC and building systems (BCA): temperature sensors controlling HVAC and building management systems feed into Green Mark energy performance requirements. Marine and offshore: vessels under Singapore flag or calling at Singapore ports face class society requirements (Bureau Veritas, Lloyd's Register, DNV) covering engine room monitors, reefer cargo systems and exhaust monitoring.

Calibration Intervals

General guidance: laboratory reference thermometers (Pt100, SPRT) annually, extendable on stability records; industrial RTD probes 6–12 months, more frequently for safety-critical use; thermocouples 3–12 months depending on temperature and environment, with base-metal thermocouples in harsh conditions sometimes needing quarterly calibration; handheld digital thermometers 12 months or per your quality system; cold chain data loggers typically annually or per regulatory standard; IR thermometers annually, more frequently for food safety decisions.

What to Expect from a Certificate

A well-prepared certificate from a SAC-SINGLAS accredited laboratory includes full instrument identification, the calibration points, the reference standard used with its traceability statement, measured temperature and error at each point, expanded measurement uncertainty, environmental conditions during calibration, calibration and due dates, and the accreditation number and SINGLAS mark. Unitest Instruments issues certificates meeting all these requirements under accreditation LA-2023-0845-C, and calibrates Comark food temperature instruments and Rotronic environmental monitoring probes among others. Contact us or visit our calibration services page to discuss your requirements.

Frequently asked questions

What is the difference between calibrating a thermocouple and an RTD?

RTDs (resistance temperature detectors) are calibrated by measuring their electrical resistance at known temperatures and comparing the measured resistance-temperature relationship to the standard defined in IEC 60751. Thermocouples are calibrated by comparing the voltage output at known temperatures to the thermocouple type curve defined in IEC 60584. Thermocouples are generally less stable than RTDs and require more frequent calibration, especially in high-temperature or chemically aggressive environments, because the thermoelectric properties of the alloy can change with prolonged use or contamination.

How accurate does my temperature calibration need to be for pharmaceutical cold chain compliance?

HSA GMP guidelines and the international guidance documents for pharmaceutical cold chain (such as WHO Technical Report Series guidelines for temperature-sensitive pharmaceuticals) typically require that monitoring equipment used to verify cold chain compliance be accurate to within ±0.5°C or better for temperature-critical storage applications. The measurement uncertainty of the calibration must be sufficiently small relative to this accuracy requirement. In practice, most pharmaceutical-grade temperature data loggers are calibrated to uncertainties of ±0.1°C to ±0.3°C under SAC-SINGLAS accredited conditions.

Can a temperature calibration be performed on-site without removing the sensor?

Yes, many temperature sensors can be calibrated in situ using portable dry block calibrators or reference thermometers. The dry block is placed adjacent to the installed sensor, and both the sensor and a reference probe are inserted into the block simultaneously. This method is practical for immersion-type probes in process equipment, cold room sensors, and HVAC sensors. For sensors integrated into process pipelines or safety systems, partial isolation may be required. Unitest Instruments offers on-site temperature calibration services across Singapore.

Why does my thermocouple read differently after cleaning or annealing?

Thermocouples develop inhomogeneities in the thermoelectric properties of the wire with use. Mechanical stress, contamination by process gases, or cold-working can alter the Seebeck coefficient of the alloy along the length of the wire. Cleaning removes surface contamination, while annealing at high temperature can partially restore the original thermoelectric properties, but neither process returns the thermocouple exactly to its original calibrated state. After any mechanical or thermal treatment, a thermocouple should be re-calibrated before returning to service in a measurement application where accuracy matters.

What is temperature mapping and how does it relate to calibration?

Temperature mapping is a validation exercise that characterises the temperature distribution within a space (a storage room, freezer, oven, incubator, or autoclave), by placing multiple calibrated temperature loggers throughout the space and recording temperatures over a representative period. Temperature mapping is required for pharmaceutical storage rooms under HSA GMP and for many food storage facilities. The temperature loggers used for mapping must be calibrated before and after the mapping exercise to confirm their accuracy during the study. Unitest Instruments can calibrate temperature loggers for mapping exercises and advise on appropriate placement strategies.

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Temperature Calibration for Pharma, Food and Industry

SAC-SINGLAS accredited temperature calibration with 3–5 working day turnaround. On-site service available.