Igor Pušnik

Infrared ear thermometers?parameters influencing their reading and accuracy

Infrared ear thermometers (IRETs) are extensively used for measuring the temperature of a human body. For accurate measurements with IRETs they have to be calibrated regularly with an appropriate and traceable calibration system. Such systems are neither widely available nor are there many competent (accredited) laboratories which can provide traceability for IRETs. This paper describes some important influential parameters in the calibration and use of IRETs, which were observed during the extensive research on IRETs and have not been reported in the literature yet. IRET readings, and consequently also their most important metrological characteristics, accuracy and uncertainty of measurement, depend on these influential parameters. According to our findings, we would like to warn users of medical radiation thermometers, not only IRETs but also forehead thermometers and infrared temperature scanning systems, that they should be extremely careful in selection, maintenance and use of medical radiation thermometers. Measurement accuracy, as it is required by several technical standards, is hard to achieve with the majority of currently available medical radiation thermometers.

Dilemmas in Measurement of Human Body Temperature

Abstract Measurement of human body temperature seems rather trivial until we become parents or medical professionals. If we use different thermometers, which are used at different body sites, inevitably we come across to different measurement results. Then we ask ourselves which result is the right one. The answer is far from trivial because there are a few dilemmas in measurement of human body temperature. To none of these dilemmas exists a straight answer. The article describes dilemmas in measurement of human body temperature and thermometers used for its measurement. Presented are also calibration results of certain clinical radiation thermometers and their improvement in the past few years in terms of accuracy and uncertainty.

System for the determination of the size-of-source effect of radiation thermometers with the direct reading of temperature

The paper describes a system for the determination of the size-of-source effect (SSE) of radiation thermometers with the direct reading of temperature, which form the majority of commercial radiation thermometers. Optics in every radiation thermometer (RT) gathers radiation from a larger area than is defined by the nominal target size. Thus, a measured temperature is more or less dependent on available target area. Every radiation thermometer suffers from the SSE. We developed a system, based on a water-cooled holder, for measuring the SSE by a direct method. The system could be placed in front of any blackbody. Manufacturing of such a system was relatively easy and could be important for users of commercial radiation thermometers because the majority of those thermometers have direct reading of temperature. We measured the SSE characteristics by the direct method for a radiation thermometer with a linearized signal and direct reading of temperature. The results of the SSE were analysed for the direct method without correction of the background radiation and with correction of the background radiation. Knowledge about the SSE characteristic of a radiation thermometer is one of the key elements for correct temperature measurement.

Measurement uncertainty, traceability and evaluation of test results in testing laboratories

The objective of this paper is to elaborate new elements related to metrological analysis in the field of testing, such as measurement uncertainty and traceability. Until now the international standard ISO 45001 did not explicitly require the uncertainty specifications in the area of testing to such an extent as the newly implemented standard ISO/IEC 17025. Therefore several additional steps should be performed in specifying the measurement and testing results, especially concerning performance of testing and other conformity assessment activities. The paper is focused on uncertainty analysis of a test procedure of the electrical safety of household appliances according to the European standard EN 60335-1. The traceability of measurements is presented. The example is chosen as a useful case study, as well as a very illustrative example, where many dilemmas could be highlighted. This particular case is relatively straightforward to evaluate due to the relative ease of traceability of electrical and thermal quantities. It is important that the measurement result and its uncertainty are correctly evaluated and on that basis the right conclusion of conformity or nonconformity with specifications is made. Therefore, knowledge and awareness of all facts about calibration, testing requirements and traceability are essential.

Bilateral comparison of blackbody cavities for calibration of infrared ear thermometers between NPL and FE/LMK

The paper describes the comparison method and analyses the results of comparison in terms of agreement between the blackbody of the National Physical Laboratory (NPL), United Kingdom and four different blackbody cavities of the Laboratory of Metrology and Quality (LMK), at the University of Ljubljana, Faculty of Electrical Engineering (FE), Slovenia. Three cavity shapes are suggested in different standards as suitable for calibration of infrared ear thermometers (IRETs), while one cavity shape was proposed by the LMK. The agreement between blackbody cavities was determined with the help of platinum resistance thermometers. Two reference IRETs were used to check their stability and level of agreement between calibration results at different institutes and against different blackbody cavities. Measurements were performed with two IRETs, at the NPL in one cavity and at the LMK in four different cavities. The comparison was initiated to solve the problem of assuring proper traceability for IRETs and to present the solution to their users.

Simultaneous calibration of a large number of thermocouples

The objective of this paper is to analyze major error sources in the process of simultaneous calibration of a large number of thermocouples (TCs). The main reason for the occurrence of additional error sources when a large number of TCs are simultaneously calibrated is due to additional inhomogeneity effects and characteristics of a particular measuring setup. The need for such calibrations is due to the fact that, often, a large number of relatively low-cost but traceably calibrated TCs are needed for monitoring purposes and measurements of temperature profiles in applications, such as evaluation of temperature and humidity chambers, wind channels, tunnel furnaces in steel plants, etc. The fact is that the overall uncertainty attributed to each particular TC during simultaneous calibration exceeds the uncertainty assigned to a TC during a calibration process of a single TC. Nevertheless, in most cases, the proposed solution is highly acceptable, especially in the area of testing, due to a significant decrease of calibration costs yet still meeting testing requirements.

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.

Automated system for evaluation of climatic chambers

In this paper an automated system for the evaluation of climatic chambers is presented. Besides automation, a basic emphasis is given to the reliability of operation, flexibility and the possibility of achieving a minimal uncertainty for the given application. The system is developed to completely satisfy all standards and requirements concerning evaluation and/or calibration of climatic chambers in the laboratory as well as on site.

Automation of a precision temperature calibration laboratory

The objective of the paper is to discuss the automation of a precision calibration laboratory in the view of achieving maximal quality of metrological performance. Besides automation of measurement equipment for ease of operation, communication and data processing, basic emphasis is given to reliability of operation, flexibility, and possibility of achieving minimal uncertainty for given measurement equipment. Several software design guidelines are discussed in the case of automation of a high-precision temperature calibration laboratory.

Acceptable traceability of a distributed national metrological system

Traceability of national standards to the international level, as well as the quality of the dissemination of these values to lower level working measurement standards has to meet primarily the requirements of a particular country, but equally importantly has to comply with strict and explicit rules of international accreditation bodies. In this respect vertical, hierarchically organised traceability links are usually properly evaluated in terms of added uncertainties, but horizontal connections, forming closed loops could be overlooked. It is essential to assure minimal influence from one physical quantity to another by proper uncertainty ratios. In many countries, especially in small and developing countries in transition period from one economic system to another, national metrology systems, as a key technology for development, production and technology transfer are often organised as distributed systems of laboratories; holders of national standards, as opposed to centralised systems, which are traceable to the international level, i.e. laboratories, where primary standards are realised. It is usually also not foreseen to realise SI units according to the definitions but on the highest level of transfer technology and disseminated with minimal additional uncertainties.