Temperature Sensors, What are The Functions, How They Work, and Types?

Temperature sensors have various functions. Not only for measuring body temperature, temperature sensors are also useful for vehicles, rooms, and others. Check out the functions, how it works, and what are the types of temperature sensors through the following article TransTRACK!

What is the Temperature Sensor Feature?

Temperature sensors are devices that detect and measure cold and heat and convert them into electrical signals. Temperature sensors are used in our daily lives, whether it is a household water heater, thermometer, refrigerator, or microwave. There are various applications of temperature sensors, including the field of geotechnical monitoring.

Temperature sensors can also be defined as simple instruments that measure degrees of cold or heat and then convert them into readable units. There are specialized Temperature Sensors that are used to measure the temperature of boreholes, soil, large concrete dams, or buildings.

Function of Temperature Sensors in Vehicles

There are many types of temperature sensors, but the most common way used in their categorization is based on the connection mode which includes contact and non-contact Temperature Sensors. Examples of contact sensors include thermistors and Thermocouples as their contact with the object being measured is direct, whereas non-contact type temperature sensors measure the radiation of the heat source.

Such temperature gauges are mostly used in hazardous environments such as thermal power plants or nuclear power plants. Temperature Sensors are used to measure the heat of hydration in bulk concrete structures, in the field of geotechnical monitoring. They can also be utilized to monitor seepage or groundwater migration.

One area where they are commonly used is in concrete maintenance as concrete needs to be relatively warm to be properly installed and maintained. Seasonal variations cause expansion or shrinkage of the structure, bringing about an overall change in its volume.

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How the Temperature Sensor Works

The way this temperature sensor works is based on the voltage at the diode terminal. If there is an increase in voltage, the temperature also increases. This is followed by a voltage drop between the base and emitter transistor terminals in the diode. There are also Temperature Sensors that work on the principle of voltage change due to temperature change.

In vibrating wire temperature gauges, different metals have different linear expansion coefficients. It mainly consists of a magnetic wire stretched with high tensile strength and two ends fixed to different metals so that any change in temperature will directly affect the tension in the wire and its natural vibration frequency.

The dissimilar metal can be made of aluminum as it has a greater coefficient of expansion than steel. When the conversion of temperature signals into frequency occurs, the same readout unit used for other vibrating wire sensors can also be used in temperature monitoring.

Custom-made vibrating wire sensors are sensors that sense temperature changes and then those temperature changes are converted into electrical signals that are then transmitted to the readout unit as frequency.

Types of Temperature Sensors

Contact and non-contact temperature sensors are further divided into the following mentioned Temperature Sensor types.

The Resistance Temperature Detector (RTD)

These are known as resistance thermometers and use the resistance of the RTD element with temperature to measure temperature. Different types of materials can be used to make metals.

The materials include nickel, platinum, and copper. However, platinum is the most accurate and therefore the most expensive.

Thermocouple Sensor

Thermocouple Sensors have two wires made of different metals connected at two points. The voltage between the two wires reflects the change in temperature.

While their accuracy may be slightly reduced to a lesser extent than RTDs, their temperatures range from -328 °F to 3182 °F (-200 °C to 1750 °C) and are generally more cost-effective.

Thermocouples are separated into several types, with each type suitable for specific temperature conditions. Different classes of Thermocouples are built to meet specific application needs.

Usage for Thermocouple Type:

• E: suitable for vacuum, inert, mild oxidizing or reducing conditions J: used in places with limited oxygen
• K: requires metal or ceramic protection
• N: resists oxidation from sulfur
• T: used in oxidizing or reducing environments
• S, R, and B: must be shielded with a tube shape and are used for high temperature applications
• C (tungsten/renium): very commonly requires a protective casing and is used for high temperature applications.
• A: a variant of type C and of limited use

Type R Thermocouple – Type R thermocouples are made of platinum and rhodium and can be used for temperatures up to 2700° (1480° C) F. They must be protected by a gas-tight ceramic tube and secondary outer tube. Type R thermocouples have better stability, increased temperature range over Type S thermocouples, and are often used in place of Type S thermocouples. Applications for Type R are heat treatment, control sensors, semiconductor industry, glass manufacturing, and ferrous and non-ferrous metals.

Type K Thermocouple – Type K Thermocouples are made of Chromel®-Alumel® with a small percentage of manganese and silicon. They are general purpose Thermocouples with a temperature range of -328°F to 2462°F (-200°C to 1350°C). Type K thermocouples need to be carefully calibrated and have a small output signal. They are used in an assortment of environments including water, mild chemicals, gases, and dry conditions. Common industries that use type K Thermocouples are hospitals and food preparation. Despite the wide temperature range, type K Thermocouples are mostly used for temperatures above 1004 °F (540 °C).

Type J Thermocouple – Type J Thermocouples, like type K Thermocouples, are general-purpose Thermocouples made of iron and constantan, with a positive iron leg and a negative constantan leg. They can be used exposed or unexposed with recommended protective tubing. Type J Thermocouples are used in vacuum, inert, and reducing environments. Like type K Thermocouples, type J Thermocouples must be carefully calibrated and do not react well to noise.

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Thermistor Sensors

This type of temperature sensor displays precise, predictable and large changes in different temperature changes. With changes of this magnitude, it means that temperature reflection occurs quickly and accurately.

NTC thermistors require linearization due to the size and speed involved, so some calculations are involved.

Temperature Sensor Thermometer

This type of temperature sensor is a standard Temperature Sensor, specifically a mercury-filled glass tube. However, thermometers come in several types. Glass thermometers can contain ethanol or mercury, although currently the main liquid used in these thermometers is ethanol.

Bi-Metal Thermometer

This type of thermometer consists of a gauge and a connected rod. There is a spring attached to the rod at the sensor end, leading to the gauge needle.

When heat is applied to the sensing coil, there is movement in the coil, which causes movement of the needle in the gauge – thus the temperature is displayed.

Thermometers Containing Gas and Liquid

These types of thermometers work similarly. Both have a gas- or liquid-filled bulb located inside the sensing end of the probe. When heat is applied, the gas expands or the liquid heats up, which signals the attached rod to move the needle to the measured temperature.

Digital thermometer

This type of thermometer uses probes such as Thermocouple or RTD. The temperature is measured by the probe (sensing end) and displayed as a digital reading.

Infrared Sensor

This type of temperature sensor detects temperature remotely by measuring the amount of thermal radiation emitted by a hot source or object.

This Temperature Sensor finds its application in high temperature or hazardous environments, where a safe distance must be maintained from certain bodies.

Thermal Imaging

These temperature sensors are the most common type of non-contact Temperature Sensor. They are used in the following circumstances: when the target object is in motion (such as inside a moving machine on a conveyor belt); if the object is far away; if the surrounding environment is dangerous; or in extreme temperatures where contact sensors are not appropriate.

Negative Temperature Coefficient (NTC) Thermistor

Basically, a thermistor is a sensitive Temperature Sensor that precisely reacts to very small temperature changes. At very low temperatures, it provides a very large resistance. That is, once the temperature starts to rise, the resistance starts to drop rapidly.

Due to the large resistance change per degree Celsius, even small temperature changes are accurately displayed by negative temperature coefficient thermistors. Thermistor Negative Temperature Sensors require linearization because their working principle is exponential. Their working temperature range is typically -58 to 482 °F (-50 to 250 °C).

Semiconductor-Based Sensors

Semiconductor-based Temperature Sensors work with dual integrated circuits. They consist of two similar diodes, with temperature-sensitive voltage and current characteristics to effectively measure temperature changes.

Semiconductor-based sensors provide a linear output; however, they are less accurate at 1 to 5 °C. This type of Temperature Sensor has the slowest response (5 to 6 seconds) over the narrowest temperature range (-94 °F to 302 °F or -70 °C to 150 °C).

Vibrating Wire Temperature Sensor

This type of temperature sensor is used to measure the internal temperature inside water or concrete structures. It exhibits a resolution better than 0.1°C and works similarly to the Temperature Sensor Thermocouple.

The temperature range is also high ranging from -20°C to 80°C.

How is it? Do you already understand about the temperature sensor along with its functions, workings, and types? If you understand it, then you can use it. Temperature Sensor will be useful anywhere including in the fleet. If you want to use a temperature sensor on your fleet or vehicles, you can try using TransTRACK’s  fleet management system or  cargo tracker for cargo vehicles. Which, not only with the Temperature Sensor feature, you will get other excellent features!