NTC thermistor used in body temperature measurement instrument
Body temperature measurement instruments are mainly divided into two types. The first is an electronic body temperature detector based on thermistor. The second is an infrared radiation thermometer, including an infrared skin thermometer, an infrared eardrum thermometer, and an infrared thermal imager. The temperature measurement range in -10 ~ 50℃, and the measurement error is 0.2 ℃.
The basic principle of the thermistor temperature measurement system: the thermistor and the reference resistor are connected into an unbalanced Wheatstone bridge temperature measuring circuit, and the resistance variable value with temperature change is converted into a voltage variable. Thermistor temperature measurement is a measurement of temperature by utilizing the physical properties of a conductor or a semiconductor whose resistivity changes with temperature. The resistance increases with increasing temperature is a positive temperature coefficient thermistor, and vice versa is a negative temperature coefficient thermistor. For example, medical body temperature probes are generally made of a semiconductor material having a negative temperature coefficient.
As a sensitive component for temperature measurement, NTC thermistor is widely used in medical equipment. NTC thermistor has the characteristics of small size, high precision, good reliability and quick response. On electronic thermometer with NTC thermistor usually centered on 37 ℃ adjustable resistance value, to ensure that the paragraph in the temperature of 25℃～50℃ accuracy can be controlled within the plus or minus ±0.2℃～±0.4℃, temperature of 37℃±5℃ in precision can be controlled in ±0.5%.
Since the manufacturing process of high-precision NTC thermistor is relatively complicated and costly, the resistance of the NTC thermistor is usually within ±1%, and the temperature change of one-thousandth degree can be detected with the help of amplifying circuit.