Difference between Sensor and Transducer

Sensors and transducers are indeed a concept that can easily be misunderstood. A sensor is distinguished from a transducer by subtle differences in the module’s input, output, and construction. A sensor and a transducer share a lot of features and functionalities in common. The following article delves deeper into the similarities and differences between a sensor and a transducer.

Contents:

  1. Superficial Differences and Similarities between a Sensor and a Transducer
  2. Difference between a Sensor and a Transducer Based on Input and Output Types
  3. Variation of Construction of a Sensor and a Transducer
  4. Sensors vs Transducers Based on Working
  5. Special Sensors which are also Transducers
  6. Transducers which could be Sensors
  7. Temperature Sensor vs Temperature Transducer
  8. Selection of a Sensor and Transducer Based on the Requirement

Superficial Differences and Similarities between a Sensor and a Transducer

One of the main differences between a sensor and a transducer is that the sensor measures a physical quantity and converts the measured data into a signal which can be analyzed. While a transducer converts the quantity itself to another form after measuring. The below diagram is a pictorial representation of both sensors and transducers.

Inner view of sensors and transducers
  • As the above figure states, a transducer contains a sensor and a sensor senses a physical parameter.
  • A calibrated (calibration is a process in which a sensor’s output and input are analyzed and modified according to the requirement) sensor reads input from a physical parameter such as heat, sound, wave etc. and converts it into current or voltage as they’re easily readable. The accuracy of the sensor depends upon the efficiency of the calibration done.
  • A process of converting one form of energy to a related form is known as transduction. A transducer is a device that does transduction. A transducer either converts electrical signals (voltage & current) to a physical parameter (force, motion, position, etc.) or converts such physical parameters to electrical signals.

Difference between a Sensor and a Transducer Based on Input and Output Types

Both sensors and transducers take a physical parameter as an input. For instance, a microphone is an example of a combination of sensor and transducer. The working of a microphone is explained below diagram.

working of a microphone
  • As shown above, a microphone contains both a sensor and a transducer. The sensor part of the microphone is that which recognizes the sound wave from the atmosphere, and it is processed by the internal circuit of the microphone which contains a diaphragm, magnet, coil etc.
  • The processed sound wave is then sent to an amplifier which is a transducer. There, the sound wave gets amplified. With the help

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Variation of Construction of a Sensor and a Transducer

Though there are many sensors and transducers available in the market in recent times, to understand the constructional variance, the construction and working of a Hall effect sensor and a Hall effect transducer are explained below.

  • Hall effect sensors are used as a switch in circuits that involves magnetism. This sensor works based on the Hall effect. A Hall effect sensor consists of a thin semiconductor plate which usually is made of a P-type semiconductor. When this sensor is connected within a circuit, a magnet is placed above the plate in a perpendicular direction.
  • At this position, when the current is passed through the circuit, the induced magnetic flux affects the movement of electrons and holes in the semiconductor and disturbs the flow. Thus, a Hall effect sensor allows the current to flow through only when it is maintained in a certain position and thus it is used as a switch.
  • While a Hall effect transducer is used to measure the current flowing through the circuit without disturbing the flow, measure the displacement of an element (more like a proximity sensor) etc. Just like a Hall effect sensor, a Hall effect transducer contains a semiconductor strip. But the difference is that the strip is permanently placed in the magnetic field, unlike the sensor in which the magnet is movable.
  • When the current flows through the strip, both the magnetic flux and the current will affect each other. In the end, an emf is induced in the strip and is known as Hall effect emf and is used to measure the current flowing through the circuit.

Sensors vs Transducers Based on Working

The working of a pressure sensor and a pressure transducer is explained below to indicate the difference between a sensor and a transducer based on working.

  • A pressure sensor is used to measure the pressure of fluids. There is a pressure-sensitive membrane in the sensor. The edges of the membrane are connected to four resistors which are connected in the form of a Wheatstone bridge.
  • When pressure is applied to this membrane, the voltage which is proportional to the amount of pressure applied is created in the bridge. By analyzing the amount of voltage produced, the amount of pressure applied can be calculated.
  • A pressure transducer is most commonly known as a pressure transmitter. It is used to measure pressure and to control the amount of pressure exerted. Many related parameters such as flow, level, speed can also be controlled using a pressure transmitter.
  • One of the most commonly used pressure transducers is the differential pressure transducer. This transducer consists of two pressure sensors that are connected to various parts of the system. The difference between the amount of pressure measured in the two spots is known as differential pressure.

Special Sensors which are also Transducers

Though sensors and transducers are different modules, certain devices have an integrated characteristic of both a sensor and a transducer. Some of them are listed below.

  • A tacho generator is used to measure the speed of an AC or DC motor and coupler circuits are used to measure the same in stepper motors.
  • The intensity of the light can be measured using a photodiode, LDR or a photo-transistor.
  • An LVDT (Linear Variable Differential Transformer) is used to measure the position of a structural element.
  • Microphones and piezo-electric crystals are used to measure and analyze sound waves.
  • Other than the above said, many other modules like strain gauge, thermistor, encoders, etc. are used to measure force, temperature, and position.

Transducers which could be Sensors

Though there are very minimal chances for a transducer to be a sensor, it’s not a definite no. As a transducer does something more than a sensor along with the functionality of a sensor, a transducer can’t act as a sensor. In other words, a sensor senses a parameter but a transducer converts it into another form, thus a transducer cannot do the sensing part alone without conditioning the data.

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Temperature Sensor vs Temperature Transducer

A temperature sensor measures the temperature of a certain element or the environment and converts it into an electrical signal and sends it to another circuit. There are different kinds of temperature sensors.

  • A temperature sensor can be a contact sensor and it can also be a non-contact sensor. A non-contact temperature sensor uses infrared radiation for the measurement of temperature. Pyrometers are examples of infrared thermometers.
  • A temperature transducer does the same operation but not only that. The measured temperature can also be converted into any type of physical parameter. A thermocouple is an example of a temperature transducer.
  • When two different temperatures are measured in the two terminals of a thermocouple, a potential difference is produced across the terminals and is used for further analysis.

Selection of a Sensor and Transducer Based on the Requirement

While selecting a sensor or a transducer for a requirement, the first parameter to be considered is the sensitivity of the module. Sensitivity is technically calculated using the slope of the output characteristic curve of a sensor.

  • For an application requiring a lot of accuracy and precision, the sensor must have high sensitivity to provide such efficiency. But for applications requiring measurement with not much accuracy, sensors and transducers with minimal sensitivity can also be used.
  • The sensitivity of a sensor is reduced by external disturbances such as noise. Amplifiers can reduce noise and increase the sensitivity of the sensor and a transducer.

Key Points to Remember

Here is the list of key points we need to remember about “Sensors vs Transducer”.

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  • A sensor just senses a parameter while a transducer converts it into another form.
  • A sensor can function without a transducer while a transducer is just a signal conditioning circuit without a sensor.
  • The primary difference between a sensor and a transducer lies in the output of the module.
  • A sensor always provides an electrical signal as an output while the output of a transducer can be of any form.
  • Sensors and transducer that are measuring the same parameter don’t differ a lot in terms of construction.
  • Certain modules can act as a combined unit of a sensor and a transducer.
  • The efficiency of a sensor is measured by the sensitivity of the module.

If you find any mistake above, kindly email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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