A Transducer is defined as a device which converts one form of energy into other. The broad definition of a transducer includes devices which converts mechanical forces or physical changes into a proportional electrical signal. This essentially means that the input of transducer may be physical changes and output is electrical signal. The output may be voltage, current or frequency.
Explanation of Transducer:
From the definition, one may think that transducer’s input is always a physical change. This is not true. A transducer may have electrical input and electrical output. Suppose, you want to measure the voltage of 220 kV Bus and indicate the same in Control Room. You will need, a voltmeter and a transducer. If you check the specification of a voltmeter, you will notice that the entire scale (say 0-250 kV) is divided for 4-20 mA input current range. This means that you will need to have a transducer which will convert voltage into current. Similar may the case in the measurement of other electrical parameter measurement.
However, there exists various other cases where one may want to convert a physical change into electrical signal. For example, you may need to monitor temperature of a system. An RTD or Thermocouple may be used for this purpose. Here, RTD and Thermocouples are example of transducer which convert temperature into electrical signal. Similarly, to measure the flow of fluid, one need a transducer (flowmeter) whose output is again an electrical signal.
Components of a Transducer:
A transducer, as per definition, coverts physical change into corresponding electrical signal. This means, it must have two components: One which can respond to physical change and other which can convert the response of first one into electrical signal. These two parts / components are called Sensing Element and Transduction Element respectively.
Sensing element is also known as Detecting Element of transducer. It is a part of transducer which responds to a physical phenomenon or change in physical phenomena. The response of sensing element must be closely related to the physical phenomena to have accurate measurement.
A sensing element is the first in the process of conversion of one form of energy into other, it is also known as primary transducer.
A transduction element is the part of transducer which converts the output of sensing element into electrical signal. Since, it is the second component used in the process of conversion, it is also known as Secondary Transducer.
Working Principle of Transducer:
A transducer, combination of detecting and transduction element, has to change one form of energy into other. The sensing element responds to the physical change and generates its output. This output may be in the form of displacement, angular displacement, strain etc. The output of the sensing element is then linked to the transduction element. This element is so designed to act upon the response of sensing element and generate a proportional output in the form of electrical signal.
Let us take an example to better understand the working of a transducer. LVDT (Linear variable Differential Transformer) is a transducer which converts the linear displacement into output voltage. In LVDT, an arm is attached to the soft iron core. This arm responds to the linear motion. Hence, it is the sensing or detecting element.
Due to the movement of arm, displacement of soft iron core take place which causes change in generated emf in the secondary of transformer. Here, the transformer along with core is Transduction Element.
In most of measurement systems, there is a suitable working combination wherein a mechanical device acts as a primary detector and the electrical device acts as secondary transducer with mechanical displacement serving as the intermediate stage.
Why Physical Changes Converted into Electrical Signal?
There are a number of transducers which transform a variety of physical quantities and phenomena into an electrical signal. The reason for transforming a physical phenomenon into electrical forms are numerous. The advantages of converting physical quantities into analog electrical quantities are as follows:
- Electrical amplification and attenuation can easily be done.
- The mass-inertia effect is minimized. This is because, when dealing with electrical signals, the inertia effects are due to electrons which have negligible mass. In many situations, we don not come across mass or inertia problem at all.
- The effects of friction are minimized.
- The processing and controlling of electrical signal require less power.
- The electrical output can easily be used, transmitted and processed for the purpose of measurement. Modern digital computers make use of these transducers absolutely essential.
Application of Transducer:
A transducer finds a great application in industries. In fact, control and automation would not have been possible without the use of transducer. Some of the major applications of transducers are as follows:
- It is used in various home appliances such as Air Conditioner to sense room temperature and control it.
- In microphone, the sound wave is converted by a transducer into an electrical signal. Similarly, in speaker, electrical signal is converted into sound wave.
- Thermocouple / RTDs are used in industries to monitor and control system temperature.
- In medical industry, acceleromyograph is used to measure the muscle movement after nerve stimulation.
- In industries, various kind of transducers viz. Frequency, Active Power, Reactive Power, Voltage, Ampere, Power Factor Transducers are used in conjunction with CT and / or PT to indicate these values in control room meters.
- Transformer oil and winding temperature is measured using OTI and WTI respectively.
- It is used to sense the pressure of process fluid (gas / liquid) and converts it into electrical signal.
- In communication system, electromagnetic wave gets converted into electrical signal using transducer in Antenna.
- In digital thermometer, body temperature is converted into electrical signal.
- Photovoltaic cell is an example of transducer which converts sun light into electrical signal.
- Changes around the circumference of the chest is measured with a pneumograph that has a photodiode which acts as transducer.
- Used in Robotics and Automation to convert movement into electrical signal.
- Nuclear Radiation is measured using transducer which transforms the radiation energy into electrical signal in Direct Reading Dosimeter (DRD).
These are only few applications of transducer. In fact, it has a vast use and it is not possible to list all of them at one place.