Low Voltage Traceability and Uncertainty Evaluation for High Accuracy Thermocouple Calibration Utilizing a Modern Automated Potentiometer

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Low Voltage Traceability and Uncertainty Evaluation for High Accuracy Thermocouple Calibration Utilizing a Modern Automated Pote (569.52 KB)

The Hart Scientific Division of Fluke Corporation manufactures a family of high quality noble metal thermocouples intended for laboratory applications. The calibration laboratory is required to calibrate these thermocouples to very low levels of uncertainty. Noble metal thermocouples are calibrated by fixed point over the range of 0 °C to 1000 °C. The temperature uncertainty components that contribute to the total uncertainty are easily dealt with in this laboratory because the laboratory has the capability for low uncertainty calibration of SPRTs. The equipment and procedures used in the SPRT process were easily adapted to thermocouple calibration. However, the voltage measurement aspects of the calibration are not so simple. The voltages generated vary between 1.7 mV and 16 mV, and the sensitivities vary between 8 V/°C and 24 V/°C de-pending on thermocouple type and temperature. With expanded uncertainty requirements be-tween 0.01 °C and 0.15 °C, nanovolt measurement accuracy is required. To further complicate matters, the Hart Scientific laboratory is an accredited laboratory with a high volume workload (relatively speaking) and strict quality control requirements; any solution proposed would have to be suitable for such an environment.