There is always a need to monitor the temperature of your system – whether due to temperature dependent electrical changes or to protect equipment against overheating – and temperature sensors are the best tool to monitor accurately and effectively. Not surprisingly, the demand for quality temperature sensors market continues to grow and not utilizing them in a wide range of applications is becoming rare.
There are many different types of temperature sensor – thermocouples, thermistors, resistance temperature detectors (RTDs) and infrared sensors. We’ll examine four common applications, and see how one or more of these temperature sensor types can be utilized for them.
Thermocouples: Gas Regulation
Thermocouples consist of two wires of different metals connected at two points — both ends and one junction. One junction is set at the temperature to be measured and the other is held at a fixed lower temperature. The voltage generated in the circuit between the two junctions is proportional to the temperature difference. Thermocouples are rugged and can measure over a diverse range of temperatures, but accuracy can be inconsistent.
Thermocouples are one of the most widely used temperature sensors for many applications, including gas boilers or ovens to regulate whether the pilot flame is burning or not. If the thermocouple detects a drop in the temperature, the resulting decrease in voltage will trigger the valve close and shut off the gas supply.
Thermistors: Automotive Warnings
Thermistors are often called negative temperature coefficient (NTC) sensors. A thermistor is a semiconductor device made of materials whose resistance varies as a function of temperature. They can be used to compensate for temperature variation in other components of a circuit.
Because of their low cost and the simple circuitry required, they are preferred in many applications to more expensive thermocouples and RTDs. In addition, they can be produced in very small designs with a fast response and low thermal mass.
The automotive industry is one major user of thermistors for detecting issues with the temperature of oil and coolant. The warning lights you see on your car console are triggered by thermistor detection of a temperature change outside the set normal range which can avoid costly engine damage.
Resistance Temperature Detector (RTD): Critical Accuracy
Resistance temperature detectors or resistive thermal devices (RTDs) are temperature sensors that consist of a wire coil wrapped around a ceramic or glass center. The sensor exploits the predictable change in electrical resistance of some materials with changing temperature. The most widely used sensor is the 100 ohm or 1000 ohm RTD platinum resistance thermometer.
RTDs are the most accurate sensors for scientific and many other applications and also offer the best long term stability. A representative value for the accuracy of a platinum resistance is +0.5 percent of the measured temperature. After one year there may be a shift of +0.05°C through aging. Platinum resistance thermometers can cover temperature ranges from -200 to 800°C.
RTDs big calling cards are accuracy and stability. Each RTD also provides the same readings which makes replacing one with a new component easier since it does not require recalibration. They are optimal for many industrial applications, where long term reliability and accuracy are critical.
Thermal Switches: Temperature Regulation
Thermal switches consist of two wires of different metals that control glow plug operation. A thermal switch is an electromechanical device which opens and closes contacts to control the flow of electrical current in response to temperature change.
Commonly used on applications like compressors or hot water heater units; if the temperature exceeds a set limit, the switch would cut off the flow for safety considerations and operational efficiency.
Predicted to top seven billion in sales in 2023, temperature sensors are extremely useful devices for a very wide range of applications in many industry segments.
Please contact Probes for any of your thermistor, thermocouple, RTD and thermal switch requirements; our experienced technicians can also assist with calibration, design or engineering needs.