Temperature Transmitter Working Principle

By  //  May 13, 2023

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The temperature transmitter is a device that converts heat from one body into an electrical signal.

The transmitter receives heat from a temperature sensor and converts it to an alternating current where power levels are proportional to the local temperature.

This article will explain how the temperature transmitter works, its uses, and who might find a use for it.

A Temperature Transmitter is a device that can convert natural or generated heat into electric signals. The functions of such devices are to measure differences in temperatures of different surfaces on which they exist and work as controllers and warning signals in accordance with an environmental condition or value (such as a fire).

Temperature Measurement Techniques

Temperature is a measure of the amount of heat energy. In the case of a temperature transmitter, heat obtained from a temperature sensor receives an electric current proportional to the amount of heat produced. To understand how such devices work, one must realize that every practical measurement contains two essential concepts – a thermometer and a calorimeter.

The thermometer describes instruments used for measuring temperatures. A thermometer measures temperature with a semiconductor crystal whose composition and structure are specific for each type of instrument. On the other side stands a calorimeter, which determines the quantity and quality of heat energy that passes through it.

Temperature Transmitter Basics

The thermocouple is a temperature transmitter device used to measure an object or surface’s thermal energy (heat). It is comprised of two dissimilar metals with different heat expansion coefficients. One wire from the pair serves as the input, while the other is the output. As heat flows through the wires, they warm and transfer their thermal energy to their respective metals. It creates a voltage potential across each of them due to the changing temperature differential. These voltages are transmitted by wire to a measuring device, a multimeter or digital recorder, where the actual measurements are displayed. The thermocouple also has a thermal overload protection device to prevent damage in case of abnormally high temperatures.

In areas where temperatures are extreme, there is a need for temperature transmitters so that proper functioning of equipment and machinery can be ensured. For example, the process of refrigeration used today could not be possible if it were not for the application of temperature transmitters. Their important role in this field must be emphasized with their importance in industry and transport rule out any form or disorder without them. In industry, these transmitters control systems such as blast furnaces and heating plants operating at very high temperatures.

Temperature Transmitter Working Principle

A temperature transmitter works on the principle of thermocouples. Thermocouples are made of two dissimilar metals joined together, which create a small voltage drop when heated. When the two wires of the temperature transmitter are connected to a measuring instrument, it is possible to measure temperature changes from –180°C to 1800°C. As with thermistors, NTC, and RTD temperature sensors, such devices are considered non-linear, but they have higher linearity ratings than thermistors and RTD sensors.

Temperature Transmitter Uses

The major applications of temperature transmitters are thermal measurement for industrial and domestic supply systems, the industrial process control system, and checking the environment’s ambient temperature. In vehicles, they are used in thermostats to control air conditioners or to measure engine temperature. Temperature transmitters also find their uses in agriculture, where they help control power consumption while working on a farm. They also act as auxiliary sensors in automobile engines. So these instruments are used in automotive industries along with other instruments such as pressure transducers, gas analyzers, flow meters and etc., which are commonly called integrated sensor systems. The exact specifications of the temperature transmitter depend on its application; hence there is no fixed amount of power i.e.

Types of Temperature Transmitter Outputs

There are mainly two output types of temperature transmitters: the open circuit voltage (V oc ) and the current (I oc ). V oc is common in automotive systems, whereas I oc is more common in process control systems.


A basic function of any temperature transmitter is to convert heat energy into an alternating current, which varies proportionally to the local temperature. This first step is achieved by adjusting a potentiometer (a variable resistor) until it produces a pure sine wave at the frequency determined by multiplying it 25 times. The output waveform received from the potentiometer amplifier has a voltage or relative potential difference proportional to the heat produced by a temperature sensor. The voltage output comes from a potentiometer or a rheostat, both adjustable resistors used for adjusting the current flow through the thermocouple.


Temperature transmitters offer either open-circuit voltage or closed-circuit current outputs. The open-circuit voltage output is generally used in applications requiring high power and low current. In contrast, closed-circuit current is used in applications requiring high precision and low power. For example, car engines use the open circuit voltage output to control the temperature of the coolant flowing within the engine. On the other hand, the industrial cooling system requires highly precise control, so they use only closed-circuit current outputs.

Advantages and Disadvantages of Temperature Transmitters

Temperature transmitters come with similar advantages and disadvantages as the other types of temperature sensors. The open circuit voltage output has a high power, which makes it perfect for applications that require high strength, while the closed circuit current output is easier to measure accurately. On the other hand, the closed circuit current output is limited in terms of power since it cannot produce a short-circuit current higher than 10mA. It is also incapable of transmitting magnetic interference, making it reliable for use in non-magnetic conditions.

Factors to Consider When Selecting a Temperature Transmitter

Temperature transmitters come in various specifications depending on brand and model type. Therefore, it is essential to consider several factors when choosing among the available temperature transmitters. First and foremost, the accuracy required by your application should be considered. This will help you determine which kind of output suits your specific needs. The measurement range is also important when selecting a transmitter, as it determines whether you need a linear or logarithmic result. In addition, the output of your transmitter should have good linearity over the entire range of measurement for it to be effective for your needs.

The next factor to consider is the cost of the transmitter. It is important to choose a reliable product that will offer good durability and long-term performance, making it ideal for your application.

The last factor is the kind of wires and connectors used by your transmitter. The wires should have adequate strength and be able to withstand heat and other corrosive elements that can affect their performance.


Temperature transmitters are simple devices that convert heat energy into an alternating current, which is proportional to the local temperature. Their wide range of applications makes them a vital part of the industrial, agricultural, and automotive industries.

In most cases, temperature transmitters are used as part of integrated sensor systems that contain highly accurate sensors and transducers, such as pressure transducers, gas analyzers, and flow meters. They also act as auxiliary sensors alongside other instruments in automobile engines, controlling power consumption while working on a farm and acting as auxiliary sensors in automobile engines.