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Compensation bridge circuit with temperature-dependent voltage divider

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The bridge circuit with temperature-dependent voltage divider for compensation of cold-junction temperature of thermocouple is described. The proposed circuit allows reducing the influence of cold-junction to less than 0,1С for thermocouples of the K-type (chromel - alumel) and L-type (chromel - copel). Streszczenie. W artykule opisano mostkowy układ kompensacji wolnych końców termopary zawierający zależny od temperatury dzielnik napięcia. Opracowany układ pozwala zmniejszyć wpływ zmian temperatury wolnych końców na wynik pomiaru poniżej 0,1С dla termopar typu K (chromelalumel) i typu L (chromel-kopel). (Mostkowy układ kompensacji wolnych końców termopary zawierający zależny od temperatury dzielnik napięcia) Keywords:. thermocouple, temperature-dependent voltage divider, cold-junction compensation Słowa kluczowe: termopara, dzielnik napięcia zależny od temperatury, kompensacja wolnych końców termopary Introduction The temperature is widely measured in modern industry, scientific experiments, materials testing etc. - practically all fields of human activity are connected with temperature measuring and control. Thus the temperature is the most often measured physical quantity. The increase in accuracy of the temperature measurement drives the production quality improvement. For low and medium range temperature measurements, various types of temperature transducers such as thermoresistorsor, thermocouples etc. are employed. If thermocouples are employed, it is necessary to take into account the influence of cold-junction temperature of the thermocouple on the measurement accuracy [1]. For compensation of the influence of cold-junction temperature, the thermostatting devices or compensation circuits are used [2, 3]. Analo[...]

Improvement of dynamic characteristics of thermoresistive transducers with controlled heating DOI:10.15199/48.2019.05.27

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Microprocessor sensory systems as a component of information and communication technologies are an integral attribute of human society at the present stage. The sphere of sensory systems application is constantly expanding. Special place belongs to sensors of temperature and humidity. These sensors are widely used in automated control systems at food and light industry, agriculture, oil and gas pipelines, medical and environmental monitoring systems [1-5]. Measuring the humidity and temperature of air and industrial gases is important for ensuring the quality of final products. For example, changing the temperature of gas in gas pipelines can cause condensation of water vapour, which leads to negative consequences, such as corrosion, the formation of aggressive chemicals, etc. Changing of temperature also influence the characteristics of different sensors, for example, of capacitive sensors [6]. In order to measure humidity the sensors based on polymeric or ceramic materials that are sensitive to humidity are used [7]. The measurement of low humidity (up to 20% RH) was not sufficiently investigated, and was accompanied with difficulties due to significant errors in the nonlinearity of humidity sensors. Modelling of polymer-based capacitive humidity sensors carried out in [8] allowed to explain the nature of nonlinearity and suggests a logarithmic relationship between the relative humidity and the output value of the sensor. The combination of the results of researches of humidity sensors (in particular their accuracy and calibration [9-10]) and temperature sensors (in particular linearization of the transfer function of thermoresistive transducers [11-12], cold-junction compensation in thermocouples [13]) will allow for comprehensive control of the parameters of technological processes. It is advisable to use integrated temperature and humidity sensors in which temperature compensation can improve the accuracy of humidity [...]

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