OPTIMIZING THE UNCERTAINTY DUE TO THE SELF-HEAT OFPLATINUM RESISTANCE THERMOMETERS IN PRACTICAL USE

摘要

Self-heat of platinum resistancernthermometers (PRTs) is a well-known phenomenon thatrnoccurs when measurement current additionally heats up arnPRT sensor. This temperature increase depends onrnmeasurement current, PRT design, operating temperaturernand surrounding medium. Self-heat temperature increase canrnbe corrected with some residual uncertainty, but this appliesrnmainly to calibration of PRTs, while in practical temperaturernmeasurements self-heat measurement or estimation isrndifficult due to poor temperature stability and/or shortrnmeasurement time that does not allow temperature transientrneffects to fade away. If not handled properly, self-heatrnuncertainty can be one of the largest, but often neglectedrnuncertainty contributions in temperature measurement. Arnstudy of uncertainty optimization is presented for arnmeasurement system composed of up to twenty PRTs thatrnare connected to the ohmmeter via a scanner andrnsequentially measured. The optimal measurement procedurernis discussed and the uncertainty analysis is given.