V. Batagelj

Methods of reducing the uncertainty of the self-heating correction of a standard platinum resistance thermometer in temperature measurements of the highest accuracy

Self-heating of resistance thermometers is a well-known phenomenon, which occurs when the measuring current additionally heats up the sensing element. In the paper, the self-heating of standard platinum resistance thermometers (SPRTs) is studied with special emphasis on the investigation and evaluation of factors which contribute to the uncertainty of the self-heating correction. The basic two-current method for self-heating correction is analysed and additional correction methods are proposed, based on the optimal selection of currents and the use of more than two different currents. Using the advanced methods we can decrease the uncertainty of the self-heating correction from 0.04 to 0.01 mK. This decrease may not be significant in routine SPRT calibrations, but it can present an improvement in measurements of the highest accuracy, such as intercomparisons.

Automated system for measuring temperature profiles inside ITS-90 fixed-point cells

The defining fixed points of the International Temperature Scale of 1990 (ITS-90) are temperature reference points for temperature calibration. The measured temperature inside the fixed-point cell depends on thermometer immersion, since measurements are made below the surface of the fixed-point material and the additional effect of the hydrostatic pressure has to be taken into account. Also, the heat flux along the thermometer stem can affect the measured temperature. The paper presents a system that enables accurate and reproducible immersion profile measurements for evaluation of measurement sensitivity and adequacy of thermometer immersion. It makes immersion profile measurements possible, where a great number of repetitions and long measurement periods are required, and reduces the workload on the user for performing such measurements. The system is flexible and portable and was developed for application to existing equipment in the laboratory. Results of immersion profile measurements in a triple point of water fixed-point cell are presented.

Automation of reading liquid-in-glass thermometers

In this paper, the automation of calibration of liquid-in-glass thermometers (LiGTs) is discussed. Temperature readings are taken automatically with the use of a measuring system that consists of a standard calibration setup, a video camera and illumination, an image acquisition module and a computer that executes the algorithm for image processing and analysis. Once the reading of the temperature is extracted from the acquired image, this value can be passed to any other data processing program, which includes the comparison with the values from the reference thermometer and determination of correction and combined uncertainty. Data achieved in this way can be directly used to prepare the calibration certificate.

Influence of SPRT Self‐Heating on Measurement Uncertainty in Fixed Point Calibration and Calibration by Comparison

The following paper describes the influence of the self‐heating of standard platinum resistance thermometers (SPRTs) on the uncertainty in fixed point calibration and calibration by comparison. The self‐heating is a well‐known phenomenon, which occurs, when the SPRT resistance is measured with a measurement current that dissipates power and therefore additionally heats up the SPRT sensor. A value of the self‐heating at the measurement current of 1 mA is typically in the range from 0.2 mK to 5 mK, depending on the SPRT design, temperature and the surrounding medium. A series of measurements was performed in order to understand the behavior of the self‐heating with different SPRT designs and measurement conditions. Procedures to reduce the uncertainty of self‐heating correction are discussed and conclusions regarding uncertainty estimation are presented.

A large aperture blackbody bath for calibration of thermal imagers

Thermal imagers are becoming widely used instruments for noncontact absolute temperature measurements as opposed to previous practice when they were mostly used to measure temperature differences. To assure accurate and reliable absolute temperature measurements, a calibration procedure including evaluation of the thermal imager entire field of view (FOV) is needed. The challenge was to construct a large aperture blackbody, covering the complete FOV of the thermal imager and having better stability and non-uniformity than the thermal sensitivity of the imager. The blackbody calibration bath was designed on hypothesis analogous to the multi zone furnace, where the role of electrical heaters was superseded by electrically controlled valves. The experimental work showed that the designed system enables traceable calibration of thermal imagers in the temperature range from 10 to 70 °C with the expanded uncertainty of 0.2 °C, while further investigations are needed to cover ranges beyond that.

A Custom-Made Automated System for Accurate Spatial Positioning in Laboratory Experiments

Abstract Accurate and repeatable spatial positioning of measurement equipment is required in many laboratory experiments and measurement procedures. Although such mechanical manipulation can often be performed manually, by using special equipment such as different mechanical tripods, an automated spatial positioning system offers several advantages, such as higher accuracy and repeatability, reduced operator workload, and possibility to implement more complex measurement procedures. Many adequate spatial positioning systems are commercially available, but our aim was to produce a high quality, low cost, and measurement oriented solution, with special emphasis on correct evaluation of all metrological parameters.

On-Site Environmental Conditions—Do They Really Affect the Measuring Accuracy?

According to requirements of the ISO/IEC 17025:2005 standard, environmental conditions while calibrating are monitored and stated in the calibration certificate. In this paper we present an experiment for evaluation of the behavior of our on-site measuring equipment regarding its specifications and the suitability of these specifications for our typical on-site work. We built a measuring setup for determining the temperature and relative humidity dependence of our on-site equipment. Main units of the equipment were placed in a climatic chamber, while temperature sensors and humidity sensors were placed into an ice bath and humidity generator, respectively. The temperature and relative humidity conditions in the climatic chamber were changed incrementally from 5°C to 45° and from 80 % to 20 %. Results are presented and evaluated. The built measuring setup was proven to be a useful tool for determining the temperature and relative humidity dependence of our on-site equipment. By observing the dynamic transitions of the instrumentation between changes of conditions possible dynamic effects could be evaluated also.

Using a CCD camera for the determination of the target size in radiation thermometry

The objective of this paper is to present the new objective method for the determination of the target size in radiation thermometry using a charge-coupled device (CCD) camera and the custom-made software. The target size is one of the essential components needed for the proper calibration of a radiation thermometer, as well as for everyday measurements. In practice, most of the radiation thermometers have a small black ring engraved on the ocular, and the interior of the ring defines the target area. Usually, manufacturers state how much radiation is gathered from the target area. Typical values stated are from 90% to 99%. The existing method was very subjective. A person determining the target size looked through the radiation thermometer and tried to read the target size of the thermometer from the millimeter grid paper. In our case, three different people in our laboratory, using this existing method, determined different target sizes. The new method uses a predefined mask of known dimensions, printed on millimeter grid paper and positioned in front of the radiation thermometer. Instead of a person looking through the ocular, a CCD camera and the custom-made image processing software are used. This target size can be used as an indication of target size in cases when other information is unavailable or to check manufacturers data.

Automation of reading of liquid-in-glass thermometers

In the proposed paper a possibility of automation of calibration of liquid-in-glass thermometers is discussed. Temperature readings are taken with the use of a measuring system that consists of a standard calibration facility, the video camera and illumination and the personal computer that executes the program for image processing and analysis. Once the reading of the temperature is extracted from the acquired image, this value can be passed to any other data processing, which includes the comparison with the values from the reference thermometer and determination of overall uncertainty. Data achieved in this way can be directly used to prepare the calibration certificate.

Usage of Reference Datasets in Testing and Validation of Thermometry Software Modules

The objective of the following paper is to discuss the preparation and usage of adequate input parameters (called reference data sets) for efficient testing of temperature measurement software modules, applying the white‐box software testing strategy. Furthermore, the extension of the suggested approach is presented in an area of intercomparison of temperature measurement software modules. With this new approach better equivalence of the results of the software modules will be possible.