IP5 - An Accurate Readout Circuit for Sensors Based on Thermopiles/Thermocouples

SENSOR+TEST Conferences 2009
2009-05-26 - 2009-05-28
Congress Center Nürnberg
Proceedings OPTO 2009 & IRS² 2009
IRS² Poster Session
Q. Jia, X. Li, G. Meijer - Delft University of Technology, Delft, The Netherlands
295 - 299


Thermopiles and thermocouples are commonly applied in a very wide range of applications, from contactless temperature measurement, infrared gas-absorption measurement, climate control to medical equipment and home appliances.
When a conducting material is subject to a temperature gradience, the thermoelectric effect, or Seebeck effect, will generate a voltage difference between the hot and the cold end. Since this effect is material dependent, if two different types of material is connected at one end (for instance at cold end) and open at the other end (for instance at hot end). We will see a small voltage difference at the open end. A thermocouple is based on this effect to generate a voltage difference across the output terminals proportional to the temperature difference between the hot junction and the cold junction of the sensor. This voltage is very small, generally in the range of a few pVPC. So in order to have a detectable output voltage, the temperature difference should be kept high. However there are special circumstances that the temperature difference can not be made large, then the use of thermopiles become inevitable. A thermopile is a large number of serially connected thermocouples. Since the output voltage is the sum of each individual thermocouple output voltage, the total output voltage is then amplified back to a detectable level. However the total output resistance of such a sensor can be very large, depending on the materials and the number of serially connected thermocouples, up to tens of kΩ or even larger.
In this paper we propose an interface system to measure the small output signal of a thermocoupler thermopile sensor, with source resistance under 10 kΩ and an maximum output voltage less than 10 mV.