Calibration by Comparison of Platinum Resistance Thermometers Using Slow Resistance Bridges

Platinum resistance thermometers (PRTs) are calibrated at the highest level in fixed points, as specified in the International Temperature Scale of 1990 (ITS-90). However, in order to reduce cost and time, platinum resistance thermometers can also be calibrated by comparison. In the temperature range from ?100 °C to 300 °C, it is possible to achieve uncertainties as small as 5 mK. A PRT is calibrated by comparison by comparing its resistance reading with the temperature reading of a reference thermometer, placed at the same temperature inside the temperature-controlled calibration medium. The reference thermometer is commonly also a resistance thermometer, so the intrinsic measurement problem is the simultaneous measurement of two resistances. Four methods that perform this measurement are presented in this article. A special emphasis is given to the measurement with slow bridges. Slow bridges are not able to produce a stable resistance reading within 20 s after the connection of the PRT, so they are often considered to be unsuitable for calibration by comparison of PRTs. To overcome this problem, a special method that directly measures the ratio between the reference PRT and PRT under calibration is presented and analyzed. The analysis and measurement results proved that this method and consequently the slow resistance bridges are capable of performing calibration by comparison of PRTs at least at the same level as the conventional methods.     

Low-temperature thermometer using sputtered ZrNx thin film

A thin film thermometer using sputtered zirconium nitride has been investigated as a low-temperature thermometer. This film deposited on a sapphire substrate can be used to measure a wide temperature range from 1 to 300 K with reasonable sensitivity within a fast response time. The thermometer sensitivity can be altered by changing fabrication conditions. Moreover, the thermometer is almost insensitive to magnetic fields. The temperature error in a magnetic field of 6 T is less than 10 mK at 4.2 K.     

Thin film temperature sensor for cryogenic region with small magnetoresistance

Chromium nitride (CrN) thin films were fabricated onto Si wafers by RF magnetron sputtering equipment in pure N₂ gas. By adjusting the fabrication conditions, the film had negative temperature coefficient of resistance (TCR) below 300 K. It showed reasonable sensitivity between 300 and 1.8 K. The temperature resolution in the cryogenic temperature region was better than 1 mK. A good thermal cycle stability was observed. After 27 thermal cycles between 4 and 300 K, the coefficient of variation (CV) value was as small as 0.098% at 4 K, which corresponds to a 2.1 mK temperature shift. In addition, the thermometer was nearly insensitive to the magnetic field. The temperature shift due to magnetoresistance in a magnetic field of 9 T was less than 5 mK at 4 and 2 K. Therefore CrN can be an excellent choice of material for cryogenic temperature sensors under magnetic fields.     

Instrumentation and methods for low temperature measurements in high magnetic fields

There are several difficulties associated with the accurate measurement of low temperature in the presence of an intense magnetic field B. Most of the problems stem from the direct effect of the field on the thermometric properties of almost all of the comcommonly used sensors. Because the magnitude of the field effect, eg magnetoresistance, varies widely as a function of B, T, and the thermometer itself, a careful selection process is necessary to minimize the error. As an aid to such a process, a detailed comparison is presented of the field-dependent errors, Δ/T, as a function of T, of carbon, carbon-glass, germanium, and platinum resistance thermometers, thermistors, Si and GaAs diodes, thermocouples, capacitance thermometers, and several other less popular devices. Specific recommendations are made on the basis of the comparison. The related problem of magnetic field measurement is also examined, with emphasis on the recent characterizations of commercially available InAs, InSb, and GaAs Hall effect probes. From the results of measurements over the 1.5–300 K range and to fields as high as 23 T, several encouraging conclusions may be drawn concerning the performance of the sensors as magnetometers in the 1% accuracy range.     

Experimental Method for Determination of Self-Heating at the Point of Measurement

This paper presents a new experimental method and algorithm for the determination of self-heating of platinum resistance thermometer (PRT) when the temperature instability of medium of interest would prevent an accurate self-heating determination using standard methods. In temperature measurements performed by PRT, self-heating is one of the most common sources of error and arises from the increase in sensor temperature caused by the dissipation of electrical heat when measurement current is applied to the temperature sensing element. This increase depends mainly on the applied current and the thermal resistances between thermometer sensing element and the environment surrounding the thermometer. The method is used for determination of self-heating of a 100 \(\Omega \) industrial PRT which is intended for measurement of air temperature inside the saturation chamber of the primary dew/frost point generator at the Laboratory for Process Measurement (HMI/FSB-LPM). Self-heating is first determined for conditions present during the comparison calibration of the thermometer, using the calibration bath. The measurements were then repeated with thermometer being placed in an air stream inside the saturation chamber. The experiment covers the temperature range between \(-65{\,}^{{\circ }}\hbox {C}\) and \(10{\,}^{{\circ }}\hbox {C}\). Self-heating is determined for two different air velocities and two different vertical positions of PRT in relation to the chamber bottom.     

Uncertainty Propagation for Platinum Resistance Thermometers Calibrated According to ITS-90

A new supplement to the GUM outlines uncertainty calculations using matrix algebra for models with more than one output quantity. This technique is applied to the problem of uncertainty propagation for platinum resistance thermometers (PRTs). PRTs are calibrated at specified sets of defining fixed points dependent on the desired temperature range. The problem of uncertainty propagation from the fixed-point calibration results plus the resistance of the PRT in use as input quantities to the coefficients of the deviation function as intermediate results and the temperature as a sole output quantity is discussed. A general solution in matrix form for any temperature range of the ITS-90 defined by PRTs is highlighted. The presented method allows for an easy consideration of the input quantity correlations, which differ with the circumstances of the accomplishment of the fixed-point calibrations and the resistance measurement of the thermometer in use. An example calculation for a specific temperature range based on a simplified model for the input quantity correlations demonstrates this benefit.     

A simple engineering calibration for platinum resistance thermometers in the temperature range 4.2 K - 273 K

We describe how a simple two-point calibration of a platinum resistance thermometer can be used to deduce the resistance-temperature relationship in the range 4.2 K ? T ? 273 K. This relationship is established by comparing the unknown thermometer to two carefully calibrated platinum resistance thermometers. This technique produces an accuracy of (0.1 – 0.3) K. This accuracy should be adequate for many engineering applications.     

Low-Cost Ratiometric Front-End for Industrial PRT Applications

Cost, size, speed, and measurement range limitations make the resistance bridge not always suitable for temperature measurements with platinum resistance thermometers (PRTs) in industrial applications. However, high-accuracy resistance thermometer systems are often needed in many industrial applications, where measurement performances comparable to resistance bridges are often needed at a lower cost and size. A tiny, portable, ratiometric front-end exploiting a 24-bit analog-to-digital converter (ADC) with ?? ?? modulator is described. It was designed to measure the resistance ratio between a 100 ?? industrial PRT (IPRT) and a reference resistor with repeatability to within a few parts in 10⁶. Its small size makes it ideal for integration in the stem-handle assembly of a thermometric probe, enabling an early transmission of measurement data in digital form. The ADC-based system design, development, and performance testing are discussed. The system was investigated in the resistance ratio range from about 4 × 10^?3 to 5 × 10^?2. Furthermore, a comparison between the system performance and a commercial AC resistance bridge was carried out and the results reported in this paper. An accurate thermometer for industrial applications resulted from the above developments. The compactness of the devices enabled an implementation of the ??smart sensor?? concept in the measurement chain, where the front-end electronics was placed inside the IPRT handle together with an integrated memory to hold device identification, calibration coefficients, and the associated uncertainty. All data are transmitted to the readout module and are available to the user at a 5 Hz update rate for further analysis.     

Improving the Traceability of Meteorological Measurements at Automatic Weather Stations in Thailand

A joint project between the National Institute of Metrology Thailand (NIMT) and the Thai Meteorology Department (TMD) was established for improving the traceability of meteorology measurements at automatic weather stations (AWSs) in Thailand. The project aimed to improve traceability of air temperature, relative humidity and atmospheric pressure by implementing on-site calibration facilities and developing of new calibration procedures. First, new portable calibration facilities for air temperature, humidity and pressure were set up as working standard of the TMD. A portable humidity calibrator was applied as a uniform and stable source for calibration of thermo-hygrometers. A dew-point hygrometer was employed as reference hygrometer and a platinum resistance thermometer (PRT) traceable to NIMT was used as reference thermometer. The uniformity and stability in both temperature and relative humidity were characterized at NIMT. A transportable pressure calibrator was used for calibration of air pressure sensor. The estimate overall uncertainty of the calibration setup is 0.2 K for air temperature, 1.0 % for relative humidity and 0.2 hPa for atmospheric pressure, respectively. Second, on-site calibration procedures were developed and four AWSs in the central part and the northern of Thailand were chosen as pilot stations for on-site calibration using the new calibration setups and developed calibration procedures. At each station, the calibration was done at the minimum temperature, average temperature and maximum temperature of the year, for air temperature, 20 %, 55 % and 90 % for relative humidity at the average air temperature of that station and at a one-year statistics pressure range for atmospheric pressure at ambient temperature. Additional in-field uncertainty contributions such as the temperature dependence on relative humidity measurement were evaluated and included in the overall uncertainty budget. Preliminary calibration results showed that using a separate PRT probe at these AWSs would be recommended for improving the accuracy of air temperature measurement. In case of relative humidity measurement, the data logger software is needed to be upgraded for achieving higher accuracy of less than 3 %. For atmospheric pressure measurement, a higher accuracy barometer traceable to NIMT could be used to reduce the calibration uncertainty to below 0.2 hPa.     

Construction and Characterization of a Large Aperture Blackbody for Infrared Radiometer Calibration

A large aperture blackbody (LABB) with a diameter of 1 m has been successfully constructed for calibrating radiation thermometers and infrared radiometers with a wide field of view in the temperature range between 10 °C and 90 °C. The blackbody is a 1 m long cylindro-conical cavity with a diameter of 1.1 m. Its conical bottom has an apex angle of 120°. To achieve good temperature stability and uniformity, the cavity is integrated to a water-bath to which the pressurized water is supplied from a reservoir. To reduce the convection heat loss from the cavity to the ambient, the cavity is purged of the dried air that passes through a coiled tube immersed in the reservoir. For an uncertainty evaluation of the LABB, its temperature stability was measured by using a reference radiation thermometer (RRT) and a platinum resistance thermometer (PRT), and its radiance temperature distributions on the aperture plane were measured by using a thermal camera. Measuring the spectral emissivity of the coating material, the effective emissivity of the blackbody was calculated to be 0.9955 from 1 ??m to 15 ??m. The expanded uncertainty of the radiance temperature scale was evaluated based on the PRT readings, which vary from 0.3 °C to 0.5 °C (k = 2) in the temperature range. The temperature scale is validated by comparing with the RRT of which the temperature scale is realized by a multiple fixed-point calibration.     

Characteristics of Standard Capsule-Type PtCo Resistance Thermometers Between 0.65 K and 25 K

Standard capsule-type platinum–cobalt (PtCo) resistance thermometers represent one of the few types of resistance thermometers that have been developed for precise thermometry in the cryogenic temperature range. These thermometers remain sensitive even at 0.65 K, which is the lower limit of the ITS-90. Standard capsule-type rhodium–iron (RhFe) resistance thermometers are another type of resistance thermometer intended for use in this temperature range and have been well characterized and are the de facto standard worldwide. Existing data show RhFe resistance thermometers are more reproducible than the corresponding PtCo resistance thermometer. However, it has become difficult to obtain brand-new standard capsule-type RhFe resistance thermometers since their production was discontinued in the early 2000s. Unfortunately, information regarding the characteristics of standard capsule-type PtCo resistance thermometers is limited compared to that available for RhFe resistance thermometers. In this study, the characteristics of two standard capsule-type PtCo resistance thermometers between 0.65 K and 25 K were investigated. Because the resistance versus temperature curves for these thermometers over this temperature range exhibit two inflection points, setting break points near each of the inflection points was found to be beneficial during polynomial curve fitting to obtain mK-level precision. Special attention was paid to the reproducibility of these thermometers, and it was observed that the reproducibility of one of the thermometers within the cryogenic temperature range was ±0.5 mK over 6 years, while the second thermometer showed a larger variation. Similar trends in the resistance characteristics of the two thermometers were observed at the triple point of water.     

一等铂电阻温度计标准装置智能检定系统

一等铂电阻温度计标准装置主要用于检定二等标准铂电阻温度计,检定程序繁琐、计算量大,迫切需要改进目前的装置,实现标准铂电阻温度计的智能检定。本文系统是对传统一等铂电阻温度计标准装置的智能升级,优化了标准铂电阻温度计的检定过程,能自动采集数据、自动处理数据,能生成证书内页及分度表。     

Two-point calibration of standard capsule platinum resistance thermometers for the range 13.81 K to 273.15 K

A method of calibrating a standard capsule platinum resistance thermometer (prt) over the range 13.81 K to 273.15 K is described. Measurements of the resistance of the prt are needed at only two fixed points, the boiling point of He⁴ (4.2 K) and the ice-point (273.15 K), both of which are easy to realize. For a prt with a residual resistance ratio (R_{4.2 K}/R_{273.15 K}) of less than 4 × 10^?4, the method provides a calibration on ipts 68 with an uncertainty of 20 mK over the entire range 13.81 K to 273.15 K. For prts with residual resistance ratios between 4 × 10^?4 and 7 × 10^?4, the calibration uncertainty is 75 mK from 13.81 K to 40 K and 20 mK from 40 K to 273.15 K.     

Stability of industrial-grade platinum resistance thermometers in the range 77 – 273 K

The paper pays attention to stability of 10 two-lead industrial-grade 100 Ω platinum resistance thermometers used in the temperature range from 77 to 273 K. The static stability was checked by the method of storing the thermometers for about two years, the dynamic stability was tested by the method of cycling the thermometers in 25 cycles from room temperature to the temperature of liquid nitrogen. it has been found that the static instability of the thermometers ranged within + 2.5 to + 7.7 mK only one thermometer showed –2.5 K The dynamic instability ranged within –5 mK to –80 mK only one thermometer showed +35 mK.     

Effect of platinum oxidation on the characteristics of standard platinum resistance thermometers

Platinum oxidation in PTS-10 and PTS-25 standard platinum resistance thermometers has been studied. The experimental results show that heat treatment of a thermometer at 100–300°C can increase its resistance at the triple point of water by the equivalent of 1.5 mK. A procedure for calibration in the range 0–450°C is recommended. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 41–44, July, 1996.     

A self-calibrating rhodium-iron resistive SQUID thermometer for the range below 0.5 K

We report on experiments with a prototype resistive SQUID device which show that it can serve both as a primary noise thermometer and as a secondary resistance thermometer in the range 0.01–0.52 K. The resistor in the circuit was made from an alloy of Rh with 0.5% Fe whose resistivity has an appreciable temperature dependence in this range. The high sensitivity of the SQUID allowed the resistance to be measured very accurately with negligible dissipation of heat. Since values of absolute temperature could be obtained by noise thermometry, the device was in effect a self-calibrating resistance thermometer. This combination of features is a rarity in thermometry in general, and may be unique in this temperature range. A version of this new thermometer has been fabricated and tested in the range 0.01–0.52 K. The results of experiments with this prototype are described, its limitations are examined, and ways of improving it are outlined.Division of Quantum Metrology, National Physical Laboratory, Teddington, Middlesex, U.K.NRC-NBS Postdoctoral Associate.     

分度方法对高精度数字温度计测量结果影响的实验研究

铂电阻温度传感器用CVD方程、ITS-90国际温标、多项式方程进行分度,并采用高精度数字温度计显示不同方法的测量结果,以分析不同分度方法对于高精度数字温度计测量结果的影响.在-60～300 ℃进行了实验研究,结果表明,分度方法对于测量结果有一定的影响,在高精度测量条件下可通过方法的选择以提高稳定性和准确度.分度方法的研...     

A High-Emissivity Blackbody with Large Aperture for Radiometric Calibration at Low-Temperature

A newly designed high-emissivity cylindrical blackbody source with a large diameter aperture (54 mm), an internal triangular-grooved surface, and concentric grooves on the bottom surface was immersed in a temperature-controlled, stirred-liquid bath. The stirred-liquid bath can be stabilized to better than 0.05°C at temperatures between 30 °C and 70 °C, with traceability to the ITS-90 through a platinum resistance thermometer (PRT) calibrated at the fixed points of indium, gallium, and the water triple point. The temperature uniformity of the blackbody from the bottom to the front of the cavity is better than 0.05 % of the operating temperature (in °C). The heat loss of the cavity is less than 0.03 % of the operating temperature as determined with a radiation thermometer by removing an insulating lid without the gas purge operating. Optical ray tracing with a Monte Carlo method (STEEP 3) indicated that the effective emissivity of this blackbody cavity is very close to unity. The size-of-source effect (SSE) of the radiation thermometer and the effective emissivity of the blackbody were considered in evaluating the uncertainty of the blackbody. The blackbody uncertainty budget and performance are described in this paper.     

精密铂电阻温度计的校准方法

介绍了精密铂电阻温度计的特性及0~660.323℃温度范围内精密铂电阻温度计的校准方法。提出对测量上限温度高于450℃的精密铂电阻温度计可参考使用说明书要求进行上限温度退火,进行定点法校准时,可采用熔化点温坪替代凝固点温坪,对于无法进行定点法校准的精密铂电阻温度计,可采用比较法校准及采用简化公式计算各项参数的可行性,同时指出自热效应对测量的影响。     

The influence of a magnetic field on an AuMn resistor at low temperatures

Measurements of the magnetoresistance of an AuMn (0.9 at %) based low-temperature resistance thermometer were made at 4.2 K in a magnetic field up to 13.5 T and 2.8 K and 1.8 K in fields up to 4.2 T. The change in the scattering cross-section of the electrons by the manganese spins due to the magnetic field produces an important decrease (up to 50% at 10 T) of the resistivity. Experimental relationships for the temperature and magnetic field characteristics of the resistor are indicated