Correction of dynamic characteristics of temperature measuring devices

Oksana BOYKO, Oleksandra HOTRA
Danylo Halytsky Lviv National Medical University, 69 Pekarska str., Lviv, 79010, oxana_bojko@ukr.net
Lublin University of Technology, ul.Nadbystrzycka 38 A, 20-618 Lublin; o.hotra@pollub.pl

Temperature measurement has long been used in medicine for the diagnosis of many diseases. The complexity of temperature measurement is connected with the specificity of living organism as an object of temperature measurement. RTDs with low time constant τ (approximately 1 s) are widely used in temperature measurement but in practice the time of temperature setting is much longer due to peculiarities of heat exchange between a living organism and the environment. To reduce the time of heat exchange and to improve the fast operation of temperature measuring device we propose to conduct the preheating of RTD to a temperature value close to the temperature to be measured. It is also proposed to measure the RTD resistance value at a certain moment of the beginning of the transition process with subsequent calculation (by developed algorithm) of the given RTD resistance value corresponding to the measured temperature value.
The temperature measuring device with formation of the standard measuring current and additional heating current was developed. The control of the heating and measurement processes is carried out by analogue-digital methods. In order to convert the RTD resistance change into the voltage the differential circuit based on operation amplifier with subsequent conversion into the digital signal by ADC is used. The calculation of the measuring temperature is performed by microprocessor.
The accuracy of temperature determination is mainly dependent on the accuracy of the temperature measuring at the time t of the beginning of the transition process, which is chosen from the calculation of t <τ. It has been found that the developed temperature measuring device provides the measurement accuracy of 0.1 °C at the measurement time t = 0.2τ.