Temperature Sensors

There are many types of temperature sensors. They are listed in two categories. The categories are Mechanical and Electrical temperature sensors. Examples of mechanical temperature sensors are the thermometer and Bimetal. Examples of electrical temperature sensors are the thermistor, thermocouple and resistance thermometer.

I’m quite sure that almost anyone, who has graduated the fourth grade, can use a basic thermometer. It is simple. Mercury expands and contracts according to the temperature and thus this expansion and contraction can be measured. A bimetal temperature sensor however, is a little less known to most people. Bimetal temperature sensors use strips and disks of metals which convert into mechanical displacement.

Electrical temperature sensors include thermistors, thermocouples and resistance thermometers to name a few. Thermistors are types of resistors which in turn measure resistance with ensuing changes in temperature. The basic equation of  controls the sensor. Where R is resistance, T is the temperature and k is a coefficient based on other attributes of the sensor. Thermocouples consist of two conductors that yield a voltage with differences in temperature. The governing equation is . Again the equation is based on the metals in the thermocouple. Tables are easy to look up for the coefficient in the aforementioned equation. A resistance thermometer, also referred to by the acronym RTD (Resistance Temperature Detectors), correlates resistance to changes in temperature. Again variations in metals used in the product dictate the subsequent equation:  , where  .

Typically a thermostat in a small residential home uses mechanical temperature sensors in the form of bimetal technology. As fellow student Mike S. points out it is the relative cheapness of these sensors that makes them very useful in residential applications. But as a corollary, for uses in commercial and industrial applications where high accuracy, low drift, wide operating range and precision are needed, you will typically find some sort of electrical temperature sensor. These sensors tend to be more expensive based on the fact that they have to be engineered and calibrated to handle the above-mentioned qualities.

I wouldn’t be surprised to see, that when the prices of these electrical sensors come down with advancements in technology, we will see them installed into small residential homes.

It was interesting to see from other posts like C. Meraz’s post, that other sensors such as pressure sensors typically measure something other than pressure, like resistance and capacitance and then translate these changes from the change in temperature that causes this change in resistance or capacitance.

Sources:

http://en.wikipedia.org/wiki/List_of_temperature_sensors

http://www.temperatureworld.com/shci.htm