A temperature sensor is a gadget important in the kitchen, in science laboratories, in manufacturing plants and other industries. This gadget measures the amount of heat energy or its lack within an object or system. Temperature sensors are classified according to their physical appearance and according to how they function.
The two basic physical types of temperature sensors are the Contact Types and the Non-contact Types. The Contact Type Temperature Sensor functions when in contact with the object being sensed. It uses conduction in monitoring changes of temperature. This type of sensor can be used to mointor solids, liquids or gases in a wide range of temperatures. An example of this is the usual thermometer used to determine body temperature. Another very common example of a Contact Type temperature sensor is the Lollipop Thermometer used in the kitchen to test the temperature of food being cooked. Any solid or liquid materials that emit radiant energy can make use of this type of temperature sensor in measuring its heat energy.
The Contact Type and Non-contact Type Temperature sensors are subdivided into three groups of sensors namely, Electro-mechanical, Resistive and Electronic.
- An example of electro-mechanical temperature sensor is the Thermostat. This kind of non-contact temperature sensor consists of two different metals such as Nickel, Copper, Tungsten or Aluminum that are connected together to from a bi-metallic strip. Since the two metals have different properties, the strip bends or produces a mechanical movement when the it is subjected to heat. The bi-metallic strip is usually used to control hot water heating elements in boilers, furnaces, storage tanks for hot waters and also in radiator cooling system of vehicles.
- The Thermistor on the other hand is made up of a resistor that is thermally sensitive in that it changes its physical resistance with temperature. This type of temperature sensor is made up of ceramic type semiconductor materials like oxides of nickel, manganese or cobalt. This type of temperature sensor is very quick in responding to any changes in temperature as well as very accurate in its reading. Since this type of temperature resistor is a passive resistive device, it needs to be connected in series with resistors. A current is needed to pass through it so as to produce a measurable voltage output.
- The Resistive Temperature Detectors or RTDs are temperature sensors that are very precise, made from conducting metals like platinum, copper or nickel. The said metals are wound to form a coil, and its electrical resistance changes with temperature as with the thermistor. This type of temperature sensor is very costly because of its material, the platinum. This device is also passive resistive, meaning it has to be connected to the circuit so that current will pass through it.
- The thermocouple is the simplest among the temperature sensors, thus commonly used. This type of temperature sensor is very easy to use and quickly responsive to changes in temperature. Of all the different types of temperature sensors, a thermocouple has the widest temperature range, from -200oC to over 2000oC. Like the thermostat, it consists also of dissimilar metals, such as copper and constantan, which are welded together or crimped.