Platinum resistance thermometers: converting ohms to degrees Celsius

摘要

Platinum resistance thermometers (PRTs) are the most common reference standards used in Thermometry calibration laboratories. They are calibrated either directly in terms of resistance, producing a table of "actual temperatures" (determined by higher-level standards, for example, standard PRTs or fixed points) and "measured resistances" of the Unit Under Test (UUT), or together with a readout (as a system) that displays the "indicated temperature" of the UUT using one of a number of equations to convert measured resistance to temperature. In both cases, significant errors can arise during use, if interpolation between resistance-temperature data pairs is performed using an overly simple technique, or if the conditions of calibration and use of a PRT + readout system are not precisely defined and carefully adhered to. This paper discusses the methods of converting resistance to temperature, drawbacks of each, and techniques to reduce the possibility of error when using a calibrated PRT.