NTC sensor used in forehead thermometer
The thermopile is made up of multiple pairs of thermocouples in series, and the thermoelectric potential output by each thermocouple is superimposed on each other. The thermocouple must have a reference temperature or cold junction temperature when measuring temperature. In general, the reference temperature of the thermopile is 25°C.
When measuring human body temperature with a forehead thermometer, first put it under standard test conditions, that is, the temperature of the measured object is 37°C. The output voltage measured when the stack reference temperature (ambient temperature) is 25°C is written into the infrared temperature measurement signal processing chip.
Then use the actual measured output voltage of the thermopile and the ambient temperature where the thermopile is located to obtain the actual temperature of the measured object through calculations.
There is the following approximate relationship between the temperature of the measured object and the ambient temperature of the thermopile:
Tb is the temperature of the measured object (K)
Ts is the ambient temperature of the thermopile measured by the NTC thermistor (K)
Vout is the output voltage of the thermopile (V)
A is the scale factor
Ts in the above formula is the ambient temperature measured by the NTC thermistor packaged in the thermopile. The accuracy of the forehead thermometer's temperature measurement is outside the conversion error of the thermopile system. It is closely related to the reference temperature, that is, the accuracy of the ambient temperature of the thermopile. The higher the accuracy of the NTC sensor to measure the ambient temperature, the higher the accuracy of the final temperature displayed by the forehead thermometer. Therefore, the accuracy of the NTC sensor plays an important role in the temperature measurement accuracy of the forehead thermometer.
YAXUN Electronics mass-produced this kind of small-size and high-precision NTC sensors. It adopts blue film packaging, suitable for bonding process, and has been widely used in thermopile packaging.