PRACTICAL LIMITS OF MEASUREMENT UNCERTAINTIES IN CALIBRATION OF STANDARD PLATINUM RESISTANCE THERMOMETERS BY COMPARISON

Usually, SPRTs are calibrated at fixed points, but due to the high cost of a primary realization of physical quantities and time needed for the calibration at fixed points, it can be reasonable to calibrate them by comparison at the highest level. The calibration by comparison is a technique most widely used to calibrate measuring instruments, not only in industry but also in many secondary calibration laboratories. Calibration procedures of a typical secondary laboratory are based on the use of transfer standards, which are usually calibrated in a primary laboratory, thus providing traceability to (inter)national standards through a process of dissemination of a unit with an associated uncertainty. The aim of the paper is to show that temperature calibrations by comparison, in the range from -95 °C up to 300 °C, can result in a calibration uncertainty (k=2) of 0,005 °C, which is sufficiently low for many industrial applications and secondary calibration laboratories.