Why Use a Standard Platinum Resistance Thermometer (SPRT)?

An Industrial Platinum Resistance Thermometer (IPRT) can make an ideal working standard for temperature measurement and calibration. The most common type of IPRTs will have a resistance of 100 Ohms at 0 °C. Most IPRTs will be metal sheathed and the best performing will use a sensor with a coil of platinum wire that will have superior performance than the lower cost ‘film’ types. All Isotech IPRTs use coil type temperature sensors. IPRTs are commonly constructed with a metal sheath, perhaps 3 – 6 mm diameter, in a range of lengths and are suitable for different temperature ranges. Whilst the standard, EN 60751: 2008 covers the temperature range to 850 °C, it is unusual to see working standards with a range higher than 660 °C. EN 60751: 2008 specifies tolerances. At 0 °C for example, the tightest tolerance for a complete resistance thermometer is 0.1 °C while at 600 °C this increases to 3.3 °C. With individual calibration using appropriate calibration standards IPRTs can be calibrated with uncertainties of 0.01 °C at 0 °C and 0.05 °C at 660 °C. Isotech would not offer an uncertainty lower than 0.01 °C for an IPRT due to the limitations of the sensing elements. This level of uncertainty is suitable for many applications and IPRTs have benefits of lower cost and are more rugged than Standard Platinum Resistance Thermometers. IPRTs do require careful handling but are much more robust than SPRTs.