What is a Transducer? Types of Transducers and Applications

Types of Transducers

There are two types of transducers, as follows:

• Input Transducer
• Output Transducer

What is an Input Transducer?

An input transducer or a sensor takes in physical energy and converts it into an electrical signal that can be read. A microphone, for example, converts physical sound waves into an electrical signal that can be transferred through wires.

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What is an Output Transducer?

An output transducer, or an actuator, takes in electrical signals and converts them into other forms of energy. A lamp converts electricity into light and a motor, on the other hand, converts electricity into motion.

Types of Transducer based on the Principle of Operation

Transducers are divided into different types based on the principle of operation.

Photovoltaic Transducer

A photovoltaic cell is an active transducer that converts light energy into electrical energy. It is made of semiconductor material having a PN junction. When a light particle enters the junction, it energizes the junction and releases current into the connected load. The current is known as photoelectric current.

It is also known as solar cells used in solar panels. They are used for converting solar energy into electrical energy to power electrical equipment. They are the source of green energy.

Photoconductors Transducer

A photoconductor transducer is a device whose conductivity depends on the light intensity. LDR (light-dependent resistor) is a photoconductor whose conductivity increases with an increase in the intensity of light. LDR can be used to convert the light intensity into an electrical signal.

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Piezoelectric Transducer

A piezoelectric transducer works on the principle of the piezoelectric effect. It generates electrical energy that is proportional to the pressure, force, and strain on it.

There are various materials that produce the piezoelectric effect. One of the most used substances is quartz crystal made from silicon oxide SiO₂. It produces a charge on its surface when a force is applied on it. The charge can be utilized by connecting electrodes to its surface.

A piezoelectric transducer is used for measuring the change in pressure, acceleration, etc. They are used in automatic doors for sensing footsteps. It is also used in a lighter to generate necessary sparks to ignite the fuel. Microphone also operates on piezoelectric effect to sense the sound energy pressure and convert it into an electrical signal.

Electromagnetic Induction

An inductive transducer works on the principle of electromagnetic induction. It measures the change in inductance between the two coils. This can be done by either self-induction or mutual induction. A movable core is used between the coils of a transducer to vary the inductance between them. Physical quantities such as displacement, force, torque, acceleration can be measured.

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Hall Effect Transducer

Such transducer works on the principle of the Hall Effect. it can detect a magnetic field and convert it into an electrical signal that is proportional to the magnitude of the magnetic field.

Hall Effect transducers are used for proximity and position sensing, speed detection in the tachometer, etc.

Thermoelectric Transducer

It is a temperature transducer that converts thermal energy into electrical energy. A thermocouple is a thermoelectric transducer that has two terminals. It produces electrical energy based on the temperature difference between its terminals.

Electrostatic Transducer

An electrostatic transducer is made of two electrodes i.e. fixed and movable electrode charge with opposite polarities. When the movable electrode moves, it changes the capacitance between the electrodes that varies the applied voltage. The voltage change is proportional to the electrode displacement.

Electromechanical

An electromechanical transducer converts the mechanical motion into an electrical signal. It is used for sensing and measuring mechanical displacement and positioning.

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Based on Quantity to be measured

There are different types of transducers used for measuring various physical quantities.

Pressure Transducers

The transducer that converts the pressure exerted into an electrical signal is called a pressure transducer. It consists of an elastic material that bends when pressure is exerted on it. The bending is translated into an electrical signal.

Pressure transducers are used for the following applications.

• It is used to measure the pressure inside a gas tank and detect any leak in case pressure drops.
• It is used for monitoring the flow of substances.

Temperature Transducers

The temperature transducers convert the surrounding temperature into an electrical signal. It can measure the temperature as well as any change in it. A thermocouple, thermistor is  example of a temperature transducer used for temperature measurement.

It is used for monitoring the temperature of equipment. It is also used to control and maintain the temperature inside a room.

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Ultrasonic Transducers

An ultrasonic transducer converts ultrasonic waves into an electrical signal. The ultrasonic waves are reflected from a surface that is detected by this transducer.

It is used for detecting an object in front of it. It is also used for measuring the distance between the object and the transducer. The speed of ultrasonic waves is equal to the speed of sound that is used in the calculation of distance.

Displacement Transducers

A displacement transducer converts linear motion or vibration into an electrical signal. It can sense change in displacement and also measure the precise position of an object. It uses different principles of operation to measure the change in displacement such as resistive, capacitive, and inductive etc.

An LVDT (linear variable differential transformer), potentiometer is an example of displacement transducer used for measuring linear displacement.

Flow Transducers

A flow transducer converts the flow of a gas, liquid into an electrical signal. It is used for measuring the flow velocity of any gas or liquid.

Inductive Transducer

An inductive transducer works on the principle of electromagnetic induction to detect a change in its self-inductance. It has a coil that develops a magnetic field due to its own current flow. When an object such as a metal comes in its magnetic field, its inductance varies that is detected by a deflecting needle.

It is used in proximity sensors, metal detectors, object counters, etc.

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Strain Gauge Transducer

A strain gauge transducer converts physical quantity like mechanical stress or strain into an electrical signal. It is made of an elastic material with trace of conductor that does not break when force is applied on it. It works on the principle of change in electrical conductivity or resistivity of the conductor.

When force is applied, it bends and the conductor lengthens and gets narrower. Therefore, the resistivity of the conductor changes. The change in resistivity is translated into the electrical signal using a formula that is proportional to the stress applied on it.

Strain gauge transducers are mainly used for measuring stress and strain in the field of civil engineering.

Acceleration Transducer

Acceleration transduces or accelerometer is a transducer that converts the acceleration of a body into an electrical signal. It can sense the change in velocity. Accelerometer uses various operating principles.

Acceleration is caused when force is applied on an object. A piezoelectric crystal can sense the force acting on it and generate an electrical signal proportional to the force. Therefore, it can translate the acceleration into an electrical signal.

Factors to consider while selecting a transducer

• Transducers should have high input impedance and low output impedance to avoid the loading effect.
• A transducer should be highly sensitive to desired signals and insensitive to unwanted signals.
• Transducers should be able to work in corrosive environments.
• The transducer circuit should have overload protection to withstand overloads.

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Characteristics of Transducer

There are some characteristics of a transducer that determines the overall performance of a transducer.

It is divided into two types;

• Static Characteristics
• Dynamic Characteristics

Static Characteristics

These characteristics do not depend or vary with variation in the input signal or with time. Here are some of the static characteristics.

Accuracy

The accuracy of a transducer is the maximum difference between its actual value and the indicated value. It is expressed in a percentage of the actual value. A transducer must have high accuracy to measure the physical quantity accurately.

Linearity

The ability of a device to vary its output linearly with the input signal is called linearity. The output is in proportional with the input signal. A transducer having linearity has a more accurate reading and it can easily translate the signal to its corresponding output value.

Robust

A transducer must be able to withstand extreme environmental conditions and mechanical stress. A rugged and robust transducer’s performance Is not affected by its environment.

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Repeatability

The ability of a transducer to generate an identical output signal multiple times when applied with the same input signal. The output signal must repeat itself and do not vary with time.

Stability

The capability of a transducer to provide a stable output and does not fluctuate.

Sensitivity

The ability of a device to sense the smallest change in a physical quantity and translate it efficiently into an electrical signal is called sensitivity. A device having higher sensitivity can measure more accurately and precisely.

Size

A transducer having a small size is crucial for installing compact devices without taking much space.

Dynamic Characteristics

The dynamic characteristics of a transducer are dependent of time and they may vary little. Here are some of the dynamic characteristics of a transducer:

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Dynamic Range

The dynamic range is the ratio between the highest amplitude and the lowest amplitude the device can efficiently convert. A transducer having a high dynamic range has better performance and sensitivity.

Error

The error is the difference between the measured reading and the actual reading. The error can be caused by various factors.

Speed

The speed of a transducer plays a vital role in its performance as it shows how quickly it translate a physical quantity into a stable electrical signal. 

Noise

Noise is a random unwanted signal that distorts and inflicts error in the original signal. A transducer adds noise in its signal. A low amplitude signal is more affected by noise than a high amplitude signal.

Hysteresis

Hysteresis is the ability of a device whose output not only depends on its current input but the previous input as well.

Efficiency of Transducer

The efficiency of a transducer is the ratio of output power to input power. The percentage efficiency of a transducer is never 100% as some of the energy is wasted during the process of conversion. For example, the efficiency of a photovoltaic cell is below 30%. Most of the energy is wasted in the form of heat and reflection.

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Advantages and Disadvantages of Transducers

Advantages 

Here are some advantages of Transducer

• The electrical signal of a transducer can be easily and quickly processed using electrical circuits and microprocessors.
• It requires less energy to control electrical signals thus more energy efficient.
• The electrical signal is easier to transmit and receive over long distances.
• The electrical signal can be easily amplified, added, mixed with other signals.
• Modern tech is becoming smaller and more compact day by day. Thus electrical signals can be processed and stored using very small gadgets and devices.
• There are no mechanical parts involved, thus it reduces the mechanical wear and tear problem.

Disadvantages

Here are some disadvantages of a transducer

• Some transducers especially the more accurate ones are relatively very expensive.
• Transducers are not reliable as compared to mechanical instruments in long-term use.
• Noise in an electrical signal can affect the accuracy of the measurement.
• The battery-operated transducer’s performance is affected by the charge remaining in the battery.

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Applications of Transducer

The conversion of any physical quantity into an electrical signal is used in almost every field. Here are some applications of transducers.

• In Biomedical Instrumentation, different transducers are used to help patient diagnosing such as ultrasound machines, thermometers, ECG, ECHO, CT, MRIs, and other instruments. They convert various signals generated from our body into electrical signals and display them on a screen.
• In civil construction, stress gauges are used to measure the stress on a building, bridge, etc.
• The temperature is converted into an electrical signal that is processed to maintain temperature in a room. They are also used in fire alarms.
• A transducer such as an antenna converts the electromagnetic signal into an electrical signal that enables data transmission over a long distance.
• The pressure of any liquid or gas is easily measured using a transducer.
• Transducers such as microphones convert sound waves into electrical signals that can be amplified as well as processed, modified, and stored.
• Photoelectric transducer such as solar cells is a source of green energy. They are used to produce electrical energy from solar energy. Other LDR, photodiodes and photo-transistors are used in various electrical projects.
• Modern driverless cars operate on transducers that convert different signals from its surrounding into electrical signals and process them to make decisions.
• In robotics, Robots depend on transducers to understand and process real-world quantities using their microprocessors.

In general, we use multiple transducers in our daily life such as the lighter we use in our kitchen has a piezoelectric crystal that generates a spark when hit with a spring-loaded hammer. Almost every electrical equipment or gadget has a transducer embedded in it. different types of transducers are used in electronic measurement devices.

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