Temperature Sensors and Thermostats

What are the Temperature Sensors?

Have you ever heard the noise of your laptop or PC when they are operated at a high load? If so, it is due to the presence of a tiny embedded temperature sensor that measures the internal temperature of your device. Once the inside of the device strikes a specific temperature (common PCs shut down at approximately 90 degrees Centigrade, for instance), the temperature sensor transmits an electronic signal to an implanted computer. This, in turn, limits users from obtaining any applications or characteristics until the device has cooled back down, as operating programs would only additional damage to the interior components of the device.

A temperature sensor is a piece of electronic equipment that measures the temperature of a physical object. Generally, a temperature sensor is nothing but equipment that converts temperature into an electrical signal. It is utilized to record, monitor, or signal temperature variations. The ultimate purpose of the temperature sensor is to measure the heat of the material in a readable form. There are many diverse types of temperature sensors. Some temperature sensors require direct contact with the physical object named contact temperature sensors, while others indirectly measure an object's temperature, designated as non-contact temperature sensors.

Types of Temperature Sensors

Some applications, such as devices employed to create life-saving medications, need temperature sensors to be sensitive and accurate for critical quality control; however, other applications, like the thermometer in your car, do not require highly accurate or sensitive sensors. The four most typical types of temperature sensors, varying in responsiveness and accuracy from high to low, are:

• Negative Temperature Coefficient (NTC) Thermistors:

It is a thermally sensitive resistor that presents a continuous, tiny, incremental variation in resistance correlated to temperature variations. An NTC thermistor offers higher resistance at low temperatures. As temperature increases, according to its R-T table, the resistance diminishes incrementally.

• Resistance Temperature Detectors (RTDs)

A resistance temperature detector (RTD) adjusts the resistance of the RTD element with temperature. An RTD typically consists of a film or, for higher precision, a wire wrapped around a ceramic or glass core. Platinum RTDs propose a highly accurate linear output across -200 to 600 °C but are much more costly than copper or nickel.

• Thermocouples

A thermocouple typically consists of two wires of dissimilar metals electrically bonded at two points. The different voltage produced between these two disparate metals returns proportional variations in temperature. Thermocouples are nonlinear and need conversion with a table when applied for temperature control and compensation, typically achieved using a lookup table. Accuracy is relatively low, from 0.5 °C to 5 °C, but thermocouples operate across the most extended temperature range, from -200 °C to 1750 °C.

• Semiconductor-Based Sensors

A semiconductor-based temperature sensor is regularly included in integrated circuits (ICs). These sensors employ two same diodes with temperature-sensitive voltage vs. current features used to monitor temperature changes. They propose a linear response but have the lowest precision of the primary sensor types. These types of temperature sensors also have the slowest responsiveness over the narrowest temperature range (-70 °C to 150 °C).

Temperature Sensors Working Principles

Despite several types and applications for temperature sensors, the fundamental principle and features of them are pretty similar, which can be summarized as the following:

• The input to a temperature transducer is regularly the thermal quantities
• They typically transform the thermal amount into an electrical one
• They are usually employed for the determination of the temperature and heat flow

A temperature sensor generally consists of a sensing element and a transduction element. The sensing part in a temperature sensor is the element whose features alter with temperature change. As the temperature changes, the corresponding variation happens in particular properties of the element. For instance, in a Resistance Temperature Detector (RTD), the sensing element is the Platinum metal.

A transduction component is an element that transforms the output of the sensing element into electrical quantity. The change in the feature of the sensing element acts as the output for it. It measures the difference in the property of the sensing component. The outcome is then calibrated to produce output, describing the change in the thermal quantity. For example, in the thermocouple, a voltmeter can measure the potential difference made across the two terminals. The magnitude of voltage produced after calibration gives the idea of temperature change.

Temperature Sensor Applications

Some most essential applications of temperature sensors are as the following:

• They can be used as current-limiting accessories for circuit security as replacements for fuses.
• They can be employed as timers in the degaussing coil circuit of most Cathode-ray tube (CRT) displays.
• They can be applied as a heater in the automotive industry to generate additional heat inside the cabin with a diesel engine.
• They can also be employed in the protection circuits of lithium batteries.
• They can be utilized as a resistance thermometer for very low-temperature measurements in the order of 10 K.
• They are also used as sensors in automotive applications to monitor fluid temperatures like the cabin air, engine coolant, engine oil temperature, or external air, and supply the relative readings to regulate units like the ECU.
• Thermistors are also regularly employed in modern digital thermostats and monitor battery packs' temperature during charging.
• They are employed during the purchaser appliance industry for estimating temperature. Toasters, freezers, refrigerators, hairdryers, etc., depending on thermistors for precise temperature control.
• They are applied to determine the temperature profile inside the sealed hole of a convective (thermal) inertial sensor.
• They are decent for measuring over a broad temperature range, from −270 °C up to 3000 °C.
• They can be applied in furnaces, diesel engines, gas turbine exhaust, other manufacturing processes, and fog devices.
• They are applicable for applications where fewer temperature variations require to be measured with high accuracy.