Choosing the optimal method for measuring the temperature of medical devices parts during certification tests

The issues of choosing the optimal method for measuring the temperature of medical devices parts during their certification in accordance with the requirements of the general standard DSTU EN 60601-1:2019 are considered. Such measurements should be provided both during the normal operation of medical devices and for conditions of a single violation. It is proposed to carry out a preliminary temperature assessment of the medical device’s internal components using a thermal imager, which makes it possible to determine the components of the devices with a higher temperature. Furthermore, only then carry out an accurate temperature measurement of certain product components using a set of calibrated thermocouples of the TXA (K) type connected to a modern data acquisition and switching system. This greatly simplifies the process of measuring the temperature of medical devices parts and reduces its complexity. Practical examples of such tests are given.


Introduction
It is necessary to measure the temperature of medical devices parts during testing to protect the patient and medical personnel from possible excessive and dangerous temperature values [1,2] .
Temperature is often a determining factor in the performance of a medical device. For modern equipment, heat dissipation is becoming more and more important as electronic components (e.g., microprocessors) that generate a significant amount of heat become smaller. Due to overheating caused by insufficient cooling, unstable operation occurs, and sometimes even failure of product components.
Problem areas should be identified early in develop-ing and implementing medical devices. Temperature measurements of medical devices parts are carried out for this, and based on the analysis of the data obtained, appropriate optimization measures are taken, if necessary. One such measure is the use of cooling systems, which mainly consist of fans. In medical products, from one (of the high-frequency surgical equipment HFSE-300 «Nadiya-4», model -300BI/V2) to six (functional magnetic stimulation device StarFormer) or more ventilators are used. If temperature measurement during testing of medical devices, including certification ones, is performed inaccurately and incompletely for various reasons, this may adversely affect such indicators as efficiency, reliability, consumption and, as a result, quality. The standard DSTU EN 60601-1:2019 establishes the permissible maximum temperature values for   medical devices parts both during their normal operation (Subsection 11.1 and Tables 22 and 23) and for single violation conditions (Subsections 13.1.2, 13.2.7) [2] . Note that the maximum allowable temperature of medical devices parts under the condition of a single violation in accordance with Subsection 13.2.7 (malfunction of the cooling system when using fans) must be measured when blocking the operation of these fans in turn. The temperature measuring process of the product components is quite lengthy and laborious, also because the product must operate until temperature stabilization is achieved, as well as at a voltage equal to both 90% of the minimum rated voltage and 110% of the maximum rated voltage. As a rule, temperature measurement is performed using a primary transducer (usually a thermocouple or resistance thermocouple) and a measuring transducer. It should be noted that the use of a modern data acquisition and switching system as a measuring transducer (e.g., 34970A from

Main body
The process of measuring the temperature of medical devices parts during certification tests can be divided into two stages: 1. The first stage is a preliminary assessment of the temperature of medical devices parts (primarily their internal components).  process, the temperature of certain components of the product is accurately measured using a set of calibrated thermocouples (e.g., type TXA (K)) that are connected to a data acquisition and switching system (e.g., Agilent 34970A, Agilent 34972A, etc.).
Thermocouples are widely used to measure the temperature of various objects. Temperature measurement using thermocouples has become widespread due to the reliable design of the sensor and ease of installation, the ability to operate in a wide temperature range, and low cost [4,5] . Thermocouple chromel-alumel (TXA) is one of the most common thermocouples used in industry and research. It allows to measure temperatures up to 1000 °C for a long time. The thermoelectric characteristic of the thermocouple is practically linear, the sensitivity is about 40 µV/°C [6,7] . Thermocouples are available with standard tolerance class 2 (accuracy ± 1,0 °С in the range from -40 °С to 1200 °С) or special tolerance class 1 (accuracy ± 0,5 °С in the range from -40 °С to 1000 °С).
Thermocouples are securely fastened to certain product components according to the procedure [8] .

Examples of the proposed method application for measuring the temperature of medical devices parts
It should be noted that in the examples given, the preliminary temperature assessment of the product's internal components was carried out using the FLIR-T62101 thermal imager, and the final temperature measurement of products certain internal components was carried out using the Agilent 34970A data acquisition and switching system with the Agilent34901A module (for 20 channels) and software BenchLink Data Logger 3 Version 4.3. A set of calibrated thermocouples of the ТХА(К) type of the first accuracy class was connected to the system. The tests were carried out at an ambient temperature of (23 ± 2) °С.

Example 1
Let us consider the tests HF apparatus HFSE-300 «Nadiya-4» (model -300BI/V2) manufactured by TOV «MNVK «NDI PE», Kyiv, Fig. 1a) shows the internal view of the product, and Fig. 1b) shows one of its obtained thermograms. The results of the final temperature measurement of certain internal components of the product with the fan blocked are shown in Table 1. Operating mode: cutting, output power P = 300 W at a load of R = 100 Ohms, control was carried out using a pedal: 10 s -activation, 30 -pause. 1) product operation time; 2) numbers of thermocouples installed on specific components of the product.  Figure 2a) shows one of the internal views of the product and Fig. 2b) shows one of its obtained thermograms. Fig. 2c) shows graphs of these components' temperature changes for one of the product's operating modes. The results of the final temperature measurement of the product's specified internal components are presented in Table 2.  Supply voltage: 90 V, 60 Hz.

Fig. 1. Electrosurgical HF device HFSE-300 «Nadiya-4» (model -300BI/V2): a) internal view; b) one of its thermograms
Operating mode: period, the wavelength of working radiation λ = 940 nm, output power P = 10 W; the wavelength of radiation of the pilot laser is λ = 650 nm, and its power P = 5 mW; fiber optic SMA-905 with a diameter of 600 µm; nozzle OL1; working time: 30 min -activation, 10 min -pause (three cycles). 1) numbers of thermocouples installed on certain components of the product; 2) the number of the blocked fan (1, 2 -internal, 3, 4 -external); 3) the normal state of the product when all the fans are working.

Temperature compliance of medical devices
components with the established regulatory requirements both under normal conditions and under conditions of a single violation is the key to their safe and high-quality operation.

During certification tests of medical devices, it
is proposed to measure the temperature of their internal parts in two stages: to determine the components with the maximum heating temperature, first carry out a preliminary temperature assessment by analyzing the thermograms obtained, using a thermal imager, and then using calibrated thermocouples, connected to the collection system data and switching to produce an accurate temperature measurement of these components. 4. Authors hope that the article will be useful to everyone involved in the production and operation of medical devices and employees of testing laboratories and accredited service centers for their maintenance.