Smart Sensor Systems

6

Thermal Sensors

Sander (A.W.) van Herwaarden

6.1 The Functional Principle of Thermal Sensors

In this chapter we describe thermal sensors based on silicon and related technologies, having an electrical output signal. Their input signal can belong to any of the six signal domains defined by Middelhoek and Audet [1], i.e., the mechanical, magnetic, chemical, radiant, thermal and electrical signal domains. In thermal sensors, the input signal is transduced into the output signal in two steps: first, the input signal is transduced into a thermal signal, which is then transduced into the electrical output signal.

After reviewing the two types of thermal sensors in the sense of transduction types, we will describe the physics of heat transfer mechanisms, in many cases the first transduction step. Then we will discuss temperature-difference sensing elements, with the emphasis on thermopiles, since transistors are discussed in Chapter 7. Finally, the various thermal sensors are discussed with some examples and applications. A more extensive treatment of this subject can be found, for instance, in ref. [2].

6.1.1 Self-generating Thermal-power Sensors

An important distinction in thermal sensors is that between thermal-power sensors and thermal-conductance sensors. In thermal-power sensors, the input signal measured by the sensor generates thermal power in the sensor. The thermal power is also used to generate the electrical power for the sensor's output signal. Because of this, the sensor ...