What is a Transducer? Classifications of transducers:

What is a Transducer?

A transducer is a device that senses a physical parameter and converts it into a measurable form. Simply we can say that it is a device capable of converting physical quantity into a proportional convenient form or state.

Transducers are also known as “Pickups” and there are several types of transducer because there are varieties of parameters to measure. The transducer or the response tool may be electronic, electrical, optical, acoustic, magnetic, thermal, radioactive, chemical or all of its variations, but for the following purposes electrical devices are favoured:

  • The signal can be conditioned

  • A remote operation is possible, as well as multiple readings.

  • Device, like Op-Amps are available to ensure reduced device load.

  • Observer, independent data acquisition and accurate process management with the aid of microprocessors are essential with machines, for that matter.

Block diagram of transducer:

  • Transducer contains two sections directly connected, i.e. the element for sensing and the element for transduction.

  • The entity which detects is called the sensor. It is a system which produces a measurable reaction to changes in physical conditions.

  • The transduction factor converts the output of the sensor to the correct electric form.

Transducer performance characteristics:

Sensitivity: It is generally the ratio between a small change in the electrical signal to a small change in physical signal. The transducer needs to be flexible enough for detectable output.

Operating Range: The transducer will satisfy the necessity for range and provide reasonable resolution over the whole area.

Span: The dynamic range or period is the spectrum of physical inputs which the sensor may translate to electrical signals.

Accuracy: Uncertainty is commonly defined as the greatest error predicted between the real and calculated output signals. High accuracy is assured.

Precision: Precision is an instrument’s ability to repeat a specific series of readings within a given range.

Resolution: The smallest change in the measurable value that can be detected. The output signals for certain sensors can shift in small steps if the input changes continuously across the range.

Stability: Power of a sensor when used to quantify a constant signal over a period of time to provide the same output.

Repeatability: The flexibility of the sensor to provide the same output for repeated applications with the same input value.

Dead Band: Range of input values for which there is no output.

Dead time: Length of time from the application of input until the outputs begins to respond and change.

Role of a transducer in a control system:

  • Provides position, velocity and acceleration information of the measuring element

  • Give the indication of the presence of components

  • To replace complicated and inefficient feeding and processing devices

  • Provides real-time information

  • Used as a protective device

What is the difference between transducer and sensor?

The sensor is a system that detects a physical quantity and transforms it into an analog quantity that can be electrically measured, such as voltage, capacitance, inductance, and ohmic resistance.

The transducer is a sensor-connected system to transform the quantity measured into a regular electrical signal such as 0-10V DC, -10 to+ 10V DC, 4 to 20mA, 0 to 20mA, 0-25mA etc. The device manager will use the transducer’s o / p right away.

Classification of transducer:

Transducers can be classified on the basis of:

  • Active and passive transducers.

  • Primary and secondary transducer

  • Analog and digital transducers.

  • On the basis of transduction principle used.

  • Transducers and inverse transducers

Active & Passive transducers:

Active transducers:

Active transducers are self-generating devices, their functioning being based on the conversion of energy from one form to another. Active transducer doesn’t need any external power to excite them.

Eg: thermocouple, Thermoelectric, piezoelectric, photovoltaic, Electromagnetic transducer

Passive transducer:

Passive transducers, on the other hand, do not generate any energy They need be excited by the application of electrical energy from outside.

Eg: Photoresistor, Hall Effect based, Photoconductive, Thermoresistive Elastroresistive transducers.

Primary & Secondary transducer:

Primary transducer:

Such transducers contain both the mechanical and the electrical equipment. The mechanical tool transforms a mechanical signal to the actual quantity to be measured. These mechanical instruments are called main transducers as they deal with the determined physical quantity.

Secondary transducer:

The electrical device then transforms this mechanical signal to an electrical signal correspondingly. This electrical equipment is known as a secondary transducer.

Analog and digital transducers:


Analog transducer converts the quantity of input into an analog output that is a continuous function of time.

Eg:LVDT, Thermocouple, Pressure Gauge, Thermistors.

Digital transducer:

Digital transducer converts input quantity into an electrical output is in the form of pulses eg: Glass scale, Metallic scale.

On the basis of transduction principle used

Capacitive transducer:

The measurement spectrum is translated into a transition inefficiency in capacitive transduction transducers.

Electromagnetic transducer:

The electromagnetic transducer is self-generating active transducers. Throughout electromagnetic transduction, the measurement spectrum is transformed to voltage caused by a change in the magnetic flux in the conductor, in the absence of excitation.

Inductive transducer:

In inductive transduction, the measurand is transformed into a transition in a single coil’s self-inductance. It is accomplished by shifting the centre of the coil fixed to a mechanical sensing element.

Piezoelectric induction

In piezoelectric induction, the measurement range is transformed into a change in electrostatic charge q or voltage V produced by crystals when it is stressed mechanically.

Photovoltaic transduction

In photovoltaic transduction, the measurand is converted to voltage generated when the junction between dissimilar material is subjected to light above particular intensity.

Transducer and Inverse Transducer:


Transducers convert non electrical quantity to electrical quantity

Inverse Transducer:

Inverse transducers convert electrical quantities into quantities other than electrical ones.

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