Precision temperature calibration methodology — ISO/IEC 17025 accredited, NIST-traceable, ITS-90 compliant.
Temperature Calibration Specialists was established to address the growing need for reliable, on-site temperature calibration services across the upper Midwest. As manufacturing, pharmaceutical, and food processing operations expanded throughout Illinois and Wisconsin, a significant gap was identified between the calibration requirements imposed by regulatory agencies and the availability of accredited providers capable of meeting those demands locally.
The organization was founded on a straightforward principle: temperature measurement is foundational to product quality, patient safety, and regulatory compliance — and the calibration services supporting those measurements should be held to the highest metrological standards available. Through Temperature Calibration Specialists, on-site calibration is coordinated and performed by certified technicians operating under A2LA-accredited laboratory protocols with full NIST traceability.
From the outset, the focus has been placed on serving industries where temperature accuracy is not optional — aerospace heat treating, pharmaceutical manufacturing, food safety operations, medical device sterilization, and cold chain logistics. Each of these sectors is governed by strict regulatory frameworks, and the calibration work performed through Temperature Calibration Specialists is structured to satisfy the documentation and uncertainty requirements of those frameworks.
Today, temperature calibration services are provided across Illinois and Wisconsin, with coverage extending to major industrial centers including Chicago, Milwaukee, Aurora, Madison, and surrounding areas. All measurement results are NIST-traceable, and all calibration certificates are issued under ISO/IEC 17025 accredited laboratory scope.
ISO/IEC 17025 is the internationally recognized standard that specifies the general requirements for the competence, impartiality, and consistent operation of calibration and testing laboratories. When calibration is performed under this accreditation, it means the laboratory's technical procedures, quality management systems, and measurement uncertainties have been independently evaluated and verified by a third-party accreditation body. For temperature calibration, this standard ensures that every measurement result produced is defensible under audit and recognized across international borders.
The American Association for Laboratory Accreditation (A2LA) is a nonprofit, internationally recognized accreditation body that evaluates laboratories against the requirements of ISO/IEC 17025. A2LA accreditation is not a one-time certification — laboratories are subject to ongoing surveillance assessments and periodic reassessments to maintain their accredited status. When temperature calibration is performed by an A2LA-accredited laboratory, it provides documented assurance that the technicians, equipment, and procedures involved meet rigorous international standards. A2LA accreditation is widely accepted by regulatory agencies including the FDA, FAA, and Department of Defense.
NIST traceability refers to an unbroken chain of comparisons linking measurement results back to the National Institute of Standards and Technology. In temperature calibration, this chain begins at NIST, where primary temperature standards are maintained, and extends through reference standards and working standards down to the instrument being calibrated. Each link in the chain is documented with a stated measurement uncertainty. Through Temperature Calibration Specialists, all measurement results are NIST-traceable, meaning the calibration data recorded on each certificate can be traced through an unbroken series of documented comparisons to national standards.
The International Temperature Scale of 1990 (ITS-90) is the internationally agreed-upon practical temperature scale used to approximate thermodynamic temperature. ITS-90 defines temperature in terms of fixed points — the reproducible equilibrium states of pure substances such as the triple point of water (0.01 °C), the melting point of gallium (29.7646 °C), the freezing point of tin (231.928 °C), and the freezing point of zinc (419.527 °C). Calibration performed in accordance with ITS-90 ensures that temperature measurement results are consistent with international standards and can be compared meaningfully across laboratories worldwide. For industries requiring the highest levels of temperature accuracy, ITS-90 compliance is essential.
A comprehensive assessment is conducted prior to any calibration work. The complete temperature instrument inventory is reviewed, including all thermocouples, RTDs, data loggers, and process sensors requiring calibration. Existing calibration history and certificates are evaluated, and the required measurement range, accuracy tolerances, and applicable compliance standards are identified for each instrument. This assessment ensures that the appropriate reference standards, calibration procedures, and uncertainty budgets are prepared before any measurements are performed.
Based on the assessment results, the appropriate NIST-traceable reference standards are selected and matched to the measurement range and accuracy requirements of each instrument. Reference equipment may include Standard Platinum Resistance Thermometers (SPRTs) for the highest-accuracy applications, Platinum Resistance Thermometers (PRTs) for general industrial work, dry-block calibrators for efficient on-site comparison calibration, stirred liquid temperature baths for immersion-type sensors, and fixed-point cells for ITS-90 verification. The selection of reference standards is governed by the requirement that the uncertainty of the reference must be sufficiently small relative to the tolerance of the instrument under test.
Calibration is performed using the comparison method, in which the instrument under test and the NIST-traceable reference standard are exposed to the same stable temperature source simultaneously. Measurements are recorded at multiple temperature points spanning the instrument's operating range. Data acquisition systems are used to capture readings with high resolution and repeatability. The measurement data is then analyzed, and a complete uncertainty budget is calculated for each calibration point in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM). As-found and as-left readings are documented for every instrument.
Upon completion of the calibration measurements, an ISO/IEC 17025 accredited calibration certificate is issued for each instrument. The certificate includes all measurement data, as-found and as-left readings, calculated measurement uncertainties at each test point, the identification of the NIST-traceable reference standards used, and the complete traceability chain linking the measurement results to national standards. All certificates are issued under the scope of an A2LA-accredited laboratory and are suitable for presentation during regulatory audits, quality system assessments, and customer qualification reviews.
All calibration is performed using NIST-traceable reference equipment maintained under ISO/IEC 17025 quality management protocols. The following categories of reference standards and calibration equipment are utilized.
Standard Platinum Resistance Thermometers and Platinum Resistance Thermometers serve as the primary reference standards for temperature calibration. SPRTs are calibrated at ITS-90 fixed points and provide the lowest measurement uncertainties available. PRTs are used for general industrial calibration work where slightly larger uncertainties are acceptable. All reference thermometers are maintained on a documented recalibration schedule with full NIST traceability.
Portable dry-block calibrators provide stable, uniform temperature sources for on-site comparison calibration. These instruments are used extensively for thermocouple and RTD calibration in industrial environments where liquid baths are impractical. Temperature stability and axial uniformity specifications are verified and documented to ensure that measurement uncertainties remain within acceptable limits for each calibration application.
Stirred liquid temperature baths provide exceptional temperature stability and uniformity for immersion-type sensor calibration. Liquid baths are selected for applications requiring the lowest achievable uncertainties at a given temperature range. Different bath fluids are used depending on the target temperature — silicone oils for elevated temperatures, ethanol or methanol mixtures for sub-ambient work, and distilled water for moderate temperature ranges.
Fixed-point cells reproduce the defined phase-transition temperatures of high-purity substances as specified by ITS-90. Cells maintained and utilized include the triple point of water (0.01 °C), the melting point of gallium (29.7646 °C), the freezing point of tin (231.928 °C), and the freezing point of zinc (419.527 °C). Fixed-point cells are used for the calibration and verification of SPRTs and other high-accuracy reference thermometers.
High-resolution data acquisition systems and precision resistance bridges are employed to capture temperature measurement data with the accuracy and repeatability required for accredited calibration work. These systems provide automated data logging, real-time stability monitoring, and digital recording of all measurement values — ensuring that calibration data is captured consistently and is available for complete traceability documentation.
Environmental chambers are used for the calibration and qualification of temperature monitoring equipment under controlled conditions. These chambers provide stable, uniform temperature environments across a wide range — from ultra-low temperatures for cold storage sensor verification to elevated temperatures for industrial process instrument calibration. Chamber uniformity and stability are characterized and documented prior to use in any accredited calibration procedure.
On-site temperature calibration is available across Illinois and Wisconsin. ISO/IEC 17025 accredited calibration certificates are issued for all measurement results.