Temperature sensors and transmitters are the instruments at the heart of indoor air management in buildings. Temperature is the first air parameter to be controlled and the first target for the tuning of an air conditioning system. 

Within a building, top-of-the-range fixed thermometers can be found in a number of key locations within an air-conditioning system, from an air-handling unit or boiler, right through to the rooms supplied by the air-conditioning and/or heating systems, and sometimes even outside to optimise the energy efficiency and power consumption of the air-conditioning or heating systems. 

Types of temperature transmitters

There are several types of thermometer for professional use. They differ mainly in terms of their function and the nature of their measurement technology, which often also determines the temperature range covered by the device. 

In terms of use, there are three types of fixed thermometer: 

  • Sensors: these instruments are commonly called sensors because they simply measure and display one or more temperatures. 
  • Transmitters: these devices are sensors capable of transmitting their measurements over a digital or analogue network. They form the basis of indoor air management systems known as BMS (building management systems). Simply put, building automation is large-scale home automation for buildings. 
  • Thermostats: these fixed thermometers measure a temperature and send a signal to activate or deactivate an associated system (ventilation, air conditioning, etc.), depending on a set threshold value. 

There is a wide range of temperature measurement technologies, and top-of-the-range professional instruments use only the most reliable ones in their temperature range: 

  • Thermocouple: a device that uses the electrical difference of potential generated by two conductors of different metals to measure temperature. These sensors can reliably measure extremely low and high temperatures over very wide measurement ranges, but they are sensitive to electromagnetic interference and their accuracy is not the finest in the sector. These sensors do, however, have the advantage of being highly responsive to temperature variations, as well as being affordable. 
     
  • Resistance: also known as RTD (Resistance Temperature Detector), this type of sensor is based on the change in electrical resistance of a metal as a function of temperature. These sensors are more accurate than thermistors, but also more expensive. The different metals used in these sensors offer different temperature ranges: 
    . Tungsten: -100°C to 1400°C 
    . Platinum: -200°C to 600°C 
    . Nickel : - 60 °C to 180 °C 
    . Copper: - 190°C to 150°C 
    The most widely used metal is platinum, whose temperature range is the most functional in many situations. These are the famous Pt100 or Pt1000 probes (Pt meaning "platinum"). 
     
  • Thermistor: this is also a resistor that changes as a function of temperature, this time on metal oxides. These NTC (negative temperature coefficient) or PTC (positive temperature coefficient) sensors are inexpensive and offer excellent sensitivity: responsiveness and precision are therefore their main qualities. However, thermistor sensors are limited to a very narrow temperature range, which varies according to the oxide used.
     
  • Infrared or IR: this type of sensor measures temperature by detecting the heat radiated in the infrared spectrum by the surface of an object. It has the advantage of measuring temperature at a distance, without requiring physical contact and without being at the same temperature as the target. An IR sensor is optical, and therefore highly sensitive and responsive. However, its accuracy depends on a number of factors that need to be taken into account: it can only measure the temperature at the surface of a subject, not at its centre. It is also easily disrupted if the target or its lens is not clean (dust, liquid, rust, etc.). The space between the sensor and the target can also interfere with the measurement if it is saturated with smoke, dust or even humidity, which can diffract infrared rays.