I.

Introduction
A temperature transducer is employed to measure the temperature of a physical object.
Ordinarily, a transducer is nothing but transforming a physical quantity into electrical energy.
Thus, a temperature transducer is an instrument used to convert the thermal energy of the
substances into electrical form. In other words, it is a piece of electrical equipment applied for
automated measuring of temperature. The latest purpose of the temperature transducer is to
measure the heat of the material in a readable format.

Principle Features of Temperature Transducers

Although there are various types and applications for temperature transducers, the basic
principle and features of them are quite similar, which can be summarized as the following:
 The input to a temperature transducer is invariably the thermal quantities
 They regularly transform the thermal amount into an electrical one
 They are typically utilized for the determination of the temperature and heat flow
Transducer vs. Sensor: Basic Differences & Advantages of Them
A Temperature Transducer is a device that transforms thermal energy into physical
quantities including mechanical energy, pressure, and electrical impulses, among other things. A
temperature Transducer is a Vital Component of Using Industrial Tools. Temperature
Transducers are available from a variety of Suppliers and Companies, as well as various
manufacturers and distributors.
Transduction Element
A transduction element is an element that converts the output of the sensing component
into electrical quantity. The variation in the feature of the sensing component performs as the
output for it. It measures the variation in the property of the sensing component. The outcome is
then calibrated to produce output, representing the change in the thermal quantity. For example,
in the thermocouple, the potential diversity generated across the two terminals is measured by a
voltmeter. The magnitude of voltage generated after calibration provides the idea of temperature
change.

II. Discussion
Types of Temperature Transducers

Generally, contact and noncontact temperature transducers are the two classes of
temperature transducers. The sensing element of the contact types is in direct contact with the
material, therefore, they work based on the heat conduction mechanism for transferring thermal
energy. As in the non-contact transducer the element does not make direct contact with the
thermal source, hence non-contact temperature transducer works on convection mechanism for
heat transfer. Read here to learn about different kind of heat transfer.
 Based on the function and structure of the sensor, there are various types of temperature
transducers, which can generally be classified into the following categories:

 Thermistor
 Resistance Thermometers
 Thermocouples

Thermistor
The word thermistor is a summarized form of “Thermal Resistor”. As the name implies,
it is a device in which resistance varies with the temperature change. They are extensively
employed for the measurements of the temperature due to their high sensitivity. They are
regularly called the ideal temperature transducer. Thermistors are commonly comprised of a
mixture of metallic oxides.
The thermistor is a type of resistor whose resistance varies with the temperature. The
resistance is measured by passing the small measured direct current, and this current causes the
voltage drop across the resistance.

How Does a Thermistor Work

The working principle of a thermistor is that its resistance is dependent on its
temperature. We can measure the resistance of a thermistor using an ohmmeter. By
understanding how temperature changes affect a thermistor’s resistance, we can measure its
resistance to determine the temperature. How much the resistance changes depends on the type
of material used in the thermistor. The relationship between a thermistor’s temperature and
resistance is non-linear.
If we had a thermistor with the above temperature graph, we could simply line up the resistance
measured by the ohmmeter with the temperature indicated on the graph. By drawing a horizontal
line across from the resistance on the y-axis, and drawing a vertical line down from where this
horizontal line intersects with the graph, we can hence derive the temperature of the thermistor.
Characteristics of Thermistors
Thermistors have various types and applications; however, they have some common
characteristics as follows:

 They have a “Negative Thermal Coefficient”, i.e. the thermistor resistance decreases with an
increase in temperature.
 Semiconductor materials used to produce them.
 Generally more sensitive than “Thermocouples” and “Resistance Thermometers”.
 Ohmic range: 0.5 Ω ~ 750 KΩ
 They are generally employed in applications with a temperature range between -60 ° C to 15
°C .

Some most important applications of thermistors are as the following:

 They can be utilized as current-limiting devices for circuit security as replacements for fuses.
 They can be employed as a heater in the automotive industry to produce additional heat
inside the cabin with a diesel engine.
 They can also be utilized in the protection circuits of lithium batteries.
 They can be used as a resistance thermometer for very low-temperature measurements in the
order of 10 K.

Resistance Temperature Detectors

Resistance Temperature Detectors (RTDs) are another sort of temperature transducer.
RTD’s are relatively high accuracy temperature sensors fabricated from high-purity conducting
metals, such as copper, platinum, or nickel, bound into a coil. Their electrical resistance varies
similarly to that of the thermistor corresponding to the temperature change.
An RTD commonly uses platinum, nickel or any resistance wire whose resistance is a
known function of temperature, and has a high intrinsic accuracy. The most commonly used
RTD is that with the element platinum due to its high stability and large working range.
Resistance thermometer detectors RTDs are connected in Wheatstone bridge circuit

RESISTANCE THERMOMETER

Common characteristics of RTDs are as the following:

They are profoundly sensitive and relatively affordable compared to thermocouples and
thermistors.
They are able to measure the temperature in the range of -182.96 C to 630.74 C.
The relationship between temperature and resistance of conductors in the temperature range near
0C can be calculated using the equation

𝑅𝑡 = 𝑅𝑟𝑒( 1+ α Δt)

𝑅𝑡 = resistance of conductor at temperature at t °C

𝑅𝑟𝑒𝑓 = resistance of the reference temperature , usually 0 °C

α = temperature coefficient of resistance.
Δt = difference between operating and reference temperature

A high value of α is desired in a temperature sensing element, so that sufficient change in

resistance occurs for a relatively small change in temperature. This change in resistance can be
measured with a Wheatstone’s bridge which can be calibrated to indicate the temperature, that
caused the resistance change rather than the resistance itself.
RTDs have the following advantages:
• Platinum RTDs provide high accuracy and stability.
• Linearity over a wide operating range.
• Wide operating range.
• Higher temperature operation.
• Better stability at high temperature.
Disadvantages of RTDs:
• Low sensitivity .
• It can be affected by contact resistance, shock and vibration.
• Requires no point sensing.
• Higher cost than other temperature transducers.

How does RTDs works?

When the temperature of a metal increases, the resistance to the flow of electricity increases as
well. An electrical current is passed through the sensor, the resistance element is used to measure
the resistance of the current being passed through it.

Thermocouples
A thermocouple is a versatile temperature sensor made up of two metal wires connected
to a thermometer. It can measure temperatures over a wide range, making it useful in various
applications. Understanding its structure, functions, and ranges helps determine the appropriate
type and material for your application.

How does a thermocouple work?

When two wires composed of dissimilar metals are joined at both ends and one of the
ends is heated, there is a continuous current which flows in the thermoelectric circuit. If this
circuit is broken at the center, the net open circuit voltage (the Seebeck voltage) is a function of
the junction temperature and the composition of the two metals. Which means that when the
junction of the two metals is heated or cooled a voltage is produced that can be correlated back to
the temperature.
Thermocouple Uses:
Thermocouples are sensors that measure temperature. Their applications range from
industrial manufacturing and experimental settings to the meat thermometer you use at home.
They are often used anywhere it is important to be able to reliably monitor or record temperature
data.
Thermocouple Types
 Thermocouples are available in different combinations of metals or calibrations. The
most common are the “Base Metal” thermocouples known as Types J, K, T, E and N. There are
also high temperature calibrations - also known as Noble Metal thermocouples - Types R, S, C
and GB.

B-Type Thermocouple
The alloy combination is of Platinum (6% Rhodium) and Platinum (30% Rhodium). This
thermocouple exhibits a temperature range between 1370 to 1700 °C. It is mainly used in
applications executed at extremely high temperatures, such as glass production.

E-Type Thermocouple
Chromel and Constantan are the alloys that form an E-type thermocouple. The temperature
range is between 0 to 870 °C. This thermocouple does not focus on the oxidation in the atmosphere
and can be used in an inert environment. However, they need to be protected against the sulfurous
environment. They are commonly used in power plants.

J-Type Thermocouple
J type of thermocouple is formed with Iron and Constantan. 0 to 760 °C is its temperature
range. Owing to the low-temperature range of the thermocouple, its life span reduces in high
temperatures. J types thermocouple is best suited for vacuum and inert environment. Injection
molding is one of the most common applications of such types of the thermocouple.

K-Type Thermocouple
Chromel and Alumel form a K-type thermocouple. The temperature range is between 95
and 1260 °C. The neutral or oxidizing environment is best suited for these types of the
thermocouple. It generates an EMF variation below 1800°F due to hysteresis, which restricts its use
in an inert and oxidizing environment below this temperature. They are most commonly used in
refineries.

CONCLUSION:

Temperature transducers are crucial instruments for making temperature measurable and
accessible for applications ranging from environmental conditions in homes and offices to
making sure industrial processes like material melting can be carried out with precise control.
Because they convert temperature readings into electrical signals through either thermo-elements
or resistors, temperature transducers allow for accurate detection and monitoring. If integrated
with a control system, then temperature transducers will make automation possible, for instance,
activating air-conditioning or controlling temperatures in sensitive environments such as cold
storage for gastronomy. They are versatile and accurate tools in everyday as well as industrial
temperature management, aiming at favorable conditions and efficient process control.

Why Do We Use Temperature Transducers?

When dealing with severe heat, risks, or inaccessible measurement sites, temperature
sensors are used to guarantee that a process is either remaining within a specified range,
providing safe usage of that application, or satisfying a mandated requirement.

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