Temperature sensors vary in their accuracy and responsiveness.
Certain applications, such the equipment that creates life-saving medicines, require temperature sensors to respond and be accurate to ensure critical quality control. However, there are some applications, such your car’s thermometer, which don’t need as precise or responsive sensors. These are the four most popular types of temperature sensors. They range in accuracy and responsiveness from high to low.
- Negative Temperature Coefficient, (NTC), Thermistors
- Resistance Temperature Detectors
- Semiconductor-Based Sensors
Temperature Sensor Types
1. Negative Temperature Coefficient (NTC), thermistor
A thermistor, a thermally sensitive resistor, exhibits a constant, small, incremental change of resistance in response to temperature variations. An NTC thermistor offers higher resistance at lower temperatures. According to the R-T table, resistance decreases with increasing temperature. Large changes in resistance per C can cause small changes to reflect well. An NTC thermistor’s output is not linear due to its exponential nature. However, it can be linearized depending on the application. The range of effective operation is between -50 and 250 degC in glass l atedthermistors, and 150 degC in standard thermistors.
2. Resistance Temperature Detector
A resistance temperature detector (or RTD) changes the resistance of an RTD element with temperature . It consists of either a film or, for greater precision, a wire wrapped around the core of a ceramic or clear glass. Platinum is the most precise RTD, while copper and nickel make RTDs at a lower price. However, nickel and copper can be less repeatable and are less stable than platinum. Although they offer a high-quality linear output, Platinum RTDs are more costly than nickel or copper.
A thermocouple is made up of two wires from different metals that are electrically bonded at 2 points. Temperature changes are reflected in the varying voltages created by these dissimilar metals. When used for temperature control or compensation, thermocouples are not linear and must be converted with a table. This is usually done using a lookuptable. Although accuracy is very low (0.5 to 5 degrees Celsius), thermocouples work across the entire temperature range (-200 to 1750 degrees Celsius).
4. Semiconductor-based temperature sensors
Typically, integrated circuits (ICs) incorporate a semiconductor-based temperature sensor. These sensors utilize two identical diodes with temperature-sensitive voltage vs current characteristics that are used to monitor changes in temperature. These sensors have a linear response, but the lowest accuracy of all the basic types. These temperature sensors are also the most responsive across the smallest temperature range (-70 C to -150 C).
Temperature sensing for everyday life
Temperature sensors are essential to daily life. These sensors measure how much heat an object or system emits. These measurements allow us to sense temperature changes. Preventive action is another important function of temperature sensors. Temperature sensors can detect when there is a high temperature and alert you to take preventive action. Fire detectors are a good example.