Temperature sensors are a simple instrument that measures the degree of hotness or coolness and converts it into a readable unit.
As a definition, temperature sensors are electronic devices that measure the temperature of its environment and convert the input data into electronic data to record, monitor, or signal temperature changes.
There are many different types of temp. sensors. Some of them require direct contact with the physical object that is being monitored (contact temp. sensors). While others indirectly measure the temperature of an object (non-contact temp. sensors).
Among the contact temp. sensors are thermocouples and thermistors.
A thermocouple is comprised of two conductors. Each made of a different type of metal, that are joined at an end to form a junction. When the junction is exposed to heat, a voltage is generated that directly corresponds to the temperature input. This happens on account of the phenomena called the thermoelectric effect. Thermocouples are generally inexpensive, as their design and materials are simple.
The other type of contact temperature sensor is called a thermistor. In thermistors, resistance decreases as temperature increases. There are two main types of thermistors: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). Thermistors are more precise than thermocouples (capable of measuring within 0.05-1.5 degrees Celsius), and they are made of ceramics or polymers. Resistance Temperature Detectors (RTD) are essentially the metal counterpart of thermistors, and they are the most precise and expensive type of temperature sensors.
Temperature sensors are used in HVAC systems and devices, automobiles, medical devices, computers, cooking appliances, and other types of machinery.