What is a temperature sensor and what is it used for?

Concept of temperature

Temperature is a magnitude associated with notions of heat, measurable by a thermometer. From the standpoint of physics, it is a scalar magnitude related to the internal energy of a thermodynamic system like air.

It is directly related to the part of the internal energy known as kinetic energy, which is the energy associated with the movement of air particles, whether in translational, rotational motion, or in the form of vibrations. As this movement increases, the kinetic energy also increases, so the object, in this case, air, becomes hotter and therefore its temperature rises. When the movement of these particles decreases, the temperature also decreases, even reaching absolute zero, at which the movement of the particles is null.

Temperature is measured with thermometers, which can be calibrated according to a multitude of scales that give rise to units of temperature measurement. In the International System of Units, the unit of temperature is Kelvin (K), and the corresponding scale is the Kelvin scale or absolute scale, which associates the zero Kelvin value with "absolute zero". However, outside the scientific context, it is common to use other scales. The most widespread scale is the Celsius scale, also called Centigrade. To a lesser extent, and practically only in the United States, the Fahrenheit scale is used. Often the heat or cold perceived by people has more to do with thermal sensation than with temperature. The thermal sensation is the result of how our skin perceives the temperature of the objects around us.  

Temperature sensors: types and operation

A sensor is an object capable of detecting physical or chemical magnitudes called instrumentation variables, which can be light intensity, temperature, distance, acceleration, etc. The most commonly used temperature sensor is the thermocouple sensor. It consists of very simple mechanisms formed by two metallic materials of different nature joined by junctions called cold junction and hot junction. The degree of temperature detected by these junctions generates a potential difference closely dependent on the nature of the materials. The thermal sensor transforms this potential difference into a electrical signal.

When temperature sensors are used in natural ventilation systems, they measure the temperature inside and outside the residence. The difference between both determines the air flow that should be introduced into the building. When natural ventilation is not sufficient to achieve acceptable comfort levels throughout the year, mechanical conditioning systems need to be used. In these cases, the temperature sensor analyzes two temperature levels or "set points", one below the temperature required for heating (for example 21°C), and another above the temperature required for the conditioning of the residence in summer (for example 23°C). Based on that, the ventilation system defines the priorities: if the temperature is above 23°C, depending on the temperature differences between the outside and inside, it first uses natural ventilation, and if it is not sufficient, it activates the auxiliary air conditioning system. If the temperature drops below the heating level (22°C), the heating system will start to activate.