Temperature control and stabilization in the cryodielectrometer for temperatures 0.5 – 300 K
To meet requirements, which arise while design of equipment for research the dielectric parameters of low-loss materials in the millimeter waveband, the necessity of high-precision temperature stabilization and measurement appear. Despite the fact that a lot of attention [1,2] is devoted to this task already, it reminds still actual, due to a plenty of specific features, which each given measuring complex possess.Thermometers intended to measure low and very low temperatures, as a rule use the temperature dependence of certain physical properties of basis substances. There is known quite large amount of temperature controllers [3-6], which are able to operate in a wide temperature range. However, some of them operate in direct current DC-mode [4], and others, which are used AC-mode, intended for operation in too narrow temperature range ≈ 1 K [3, 6]. Besides, they are able to use only one type of sensor and possess, in our opinion, too complicated feedback scheme for the temperature stabilization [5]. In this paper we consider the scheme of the temperature regulator-stabilizer with two temperature sensors having both positive and negative temperature coefficients of resistance (TCR). It designed for low temperature measurements on the cryodielectrometer “TORNADO” in the temperature range 0.5-300 K. As well results of the low-temperature radiospectroscopy experiment using the device designed are given.
Low-Temperature Thermocouple Thermometry
Precision temperature measurements are becoming increasingly Important in industrial and military cryogenic engineering. Of the many ways of measuring cryogenic temperatures, thermocouples are among the simplest and most useful. Four general considerations are of importance in designing and determining the feasibility of thermocouple systems. First, the selection of the best thermocouple pair depends on the temperature range since both the sensitivity and reliability of a junction change markedly with temperature and are quite different for different systems. Second, a calibration curve must be obtained for each junction pair since the thermoelectric potential differences are not primary temperature scales, Third, estimates must be made of the effects of inhomogeneities and other sources of error that will affect the reliability of the temperature readings. And fourth, for high accuracy at the lowest temperatures the electrical circuitry and measuring apparatus must be carefully designed. The last item is one of instrumentation and will not be discussed here. The other three considerations are discussed for gold-cobalt and constantan versus copper or “normal” silver, chromel versus aiumel, and iron versus constantan.
Traceability strategy for gear-pitch-measuring instruments: development and calibration of a multiball artifact
There is a strong demand to ensure the traceability of gear-measuring instruments (GMIs). We propose a multiball artifact (MBA) for the evaluation of pitch-measuring accuracy. The aim of the MBA is to transfer the minimum uncertainty from a calibrated value at the National Metrology Institute of Japan (NMIJ) to a measured value of GMIs at a shop floor. The MBA is composed of equally spaced high-accuracy balls around an axis. The pitch-measuring accuracy of GMIs is evaluated by measuring the angular pitch deviation of the balls instead of the angular pitch deviation of a gear. We calibrated the angular pitch deviation using a coordinate measuring instrument (CMM) at the NMIJ and adapting a multiple-orientation technique. We proposed a calibration strategy of the angular pitch deviation. The calibration value of the pitch deviation for the MBA at the NMIJ was obtained with a measurement uncertainty (U95) of 0.2 µm. We evaluated the pitch-measuring accuracy of a GMI using the calibrated MBA. Each value of U95 for the cumulative and single pitch deviations for the left and right flanks was less than or equal to 0.5 µm. The small uncertainty was transferred from the NMIJ to the GMI.