SPONSORED FEATURE Cover story ACHIEVING PRECISION IN
TEMPERATURE MEASUREMENT: ISOTECH’S HIGH-ACCURACY TRACEABLE SOLUTIONS
Resistance Thermometers (PRTs) offer many advantages. At higher temperatures, Noble Metal Thermocouples outperform lower-cost base metal alternatives.
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One area where greater accuracy is crucial is environmental control systems in buildings. Historically, an accuracy of around 1°C may have sufficed, but today, improving measurements to within a few hundredths of a degree can save tens of thousands of pounds.
PLATINUM RESISTANCE THERMOMETERS (PRTS) AND THERMOCOUPLES The IEC 60751:2022 standard, “Industrial platinum resistance thermometers and platinum temperature sensors,” defines tolerances for industrial PRTs, with the tightest being 0.1°C at 0°C rising to 0.53°C at 250°C. PRTs operate on the principle that platinum’s electrical resistance changes predictably with temperature, making them ideal for precise measurements. While a 0.1°C to 0.5°C tolerance is good, many applications demand even greater precision. By individually calibrating a PRT's coefficient to characterise its resistance- temperature curve, its temperature can be uniquely calibrated rather than using IEC 60751 table values. This can improve measurement accuracy by a factor of 10.
ccurate temperature
measurements require suitable sensors and measuring instruments. For high-precision measurements from around -200°C to 660°C, Platinum
MEASURING INSTRUMENTS
While a high-precision digital multimeter (DMM) could measure PRT resistance or thermocouple voltage, a dedicated thermometer offers advantages. Good thermometer designs allow the entering of calibration coefficients for the PRT or thermocouple, enabling direct display of the corrected temperature.
BENEFIT FROM ISOTECH PRTS AND THERMOCOUPLES
Drawing from four decades of industry-leading expertise, our semi-standard Platinum Resistance Thermometers (PRTs) incorporate hand crafted, high-stability platinum coils, facilitating an extensive temperature range, exceptional accuracy, and minimal drift. Post-assembly, these PRTs undergo a rigorous process of annealing, proprietary thermal treatments, and multi-cycle stability testing, ensuring industry leading accuracy. Our thermocouples are engineered with the finest available metal alloys and like the PRTs, undergo a proprietary post-production process, delivering outstanding performance.
ISOTECH MILLIK PRECISION THERMOMETER
The Isotech milliK precision thermometer boasts industry-leading accuracy for PRTs and thermocouples. It also supports current transmitters and thermistors. The milliK can store probe correction coefficients. It also features a colour numeric display and built-in logger for easy use.
DRY BLOCKS AND CALIBRATION BATHS The milliK, when paired with a heat source, enables calibration of industrial sensors across an extensive temperature range of -200°C to 1,300°C. Our comprehensive calibration solutions include a range of dry block calibrators and stirred liquid baths, accommodating probes of varying sizes – from compact portable devices to larger laboratory units. We offer portable models for on-site calibration as well as laboratory models, ensuring versatility and precision across for all types of temperature sensors.
EXPERIENCE
Selecting the correct equipment for traceable measurements and calibration is a critical decision that can significantly impact the accuracy, efficiency, and reliability of the calibration process. With over 40 years of experience in designing, manufacturing, and operating a world-leading temperature calibration laboratory, we can guide you in choosing the most appropriate solutions for your specific needs.
THERMOCOUPLES
Thermocouples work on a different principle: the Seebeck effect. When two dissimilar metals are connected with their junctions at different temperatures, a small voltage is generated. Noble metal thermocouples can perform well at high temperatures and can be calibrated by producing an error curve to correct them against IEC 60584-1:2013, “Thermocouples - Part 1: EMF specifications and tolerances.”
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CALIBRATION To achieve higher accuracy, sensors must be precisely calibrated, with the option to use calibration results to correct errors. Correct calibration also provides traceability. The instrument can be supplied with UKAS (United Kingdom Accreditation Service) ISO 17025 calibration from our leading in-house laboratory. Visit
isotech.co.uk to see the performance achievable with different thermometers.
Isotech
isotech.co.uk/consultancy/ May 2024 Instrumentation Monthly
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