Inductive Transducer: Types, Working Principle and Applications
Table of Contents
What is an Inductive Transducer?
An inductive transducer is one that operates according to the electromagnetic induction or transduction mechanism. To measure the necessary physical quantities, such as displacement (rotary or linear), force, pressure, velocity, torque, acceleration, etc., a self-inductance or mutual inductance is adjusted. So These tangible amounts are referred to as measurands. An illustration of an inductive transducer is the linear variable differential transducer (LVDT). By moving the core in one direction, the LVDT measures displacement in terms of the voltage that is induced in the winding.
Types of the Inductive Transducer
There are two types of inductive transducers: passive and self-generating. So An example of a self-generating inductive transducer is a tachometer. An illustration of a passive type inductive transducer is the LVDT.
So There are two different categories of inductive transducers. It’s them,
Simple Inductance Type
A single coil is utilized in this type of transducer to measure the necessary parameter. The inductance of the coil and the output change when the displacement modifies the permeability of the flux generated in the circuit. So It is possible to calibrate the output using the measurand that will be measured. Below is a diagram of a basic inductance circuit. Once more, two types are created from a single inductance type.
Single Coil Inductance Type
The air gap between the magnetic materials and the permeability of the flux generated in the circuit change when the circuit’s armature is moved. The inductance in the circuit changes as a result. So This type is primarily used to count the number of objects. Below is a diagram of a single-coil inductance type circuit.
Hallow Coil Inductive Type Circuit
The hallow material, which has a coil wound around it, allows the magnetic core to be moved inside of it. So The output can be calibrated in terms of the measurand and is inversely proportional to the input. The air gap controls how the coils’ and the flux linkage’s magnetic fields change.
Mutual Inductance Transducers (two coils)
For mutual induction in this type, two coils are utilized. One is used to create excitement, and the other is for output. The movement of the armature affects the voltage difference between the two coils. The inductance changes when the armature position is altered by connecting to the movable mechanical component. So The voltage induced in the coil and the air gap between the armature and the magnetic material are both dependent on changes in armature position. The differential mutual inductive transducer is another name for this kind.
Inductive Transducer Working Principle
Inductive transducers typically operate on the basis of eddy current generation, change in mutual inductance of two coils, and self-inductance of one coil. So The change in flux in the coils (secondary or primary coils) causes the voltage difference and the change in inductance. The inductive transducer’s operating system is described below.
Change in Self-inductance
Consider the self-inductance of the coil be,
L = N2/R
The expression for the reluctance of the coil is,
R = l/µA
L = N2µA/l
L = N2µG
Where ‘N’ represents no.of turns
‘R’ represents the magnetic circuit’s reluctance
‘μ’ represents permeability of the coil (medium in and around the coil)
G= A/l = geometric form factor
‘A’ represents a cross-section area of the coil
‘l’ represents the length of the coil
The aforementioned equations show that altering the number of turns, geometric form factor, or permeability of the coil will alter or change the self-inductance. So Any of the three aforementioned variables (turns, form factor, and permeability) can be changed to directly measure the displacement in terms of inductance. The instrument can also be calibrated using a measurement.
Change in Mutual Inductance
Inductive transducers operate on the same basis as multiple coils’ mutual inductance. We take into account the two coils with self-inductances L1 and L2. The coils’ mutual inductance is determined by,
M = K √L1L2
Where ‘K’ represents the coefficient of coupling.
Therefore, the self-inductance of the individual coils can be changed, as well as the coefficient of coupling, to alter the mutual inductance. So The distance between the coils and their orientation both affect the factor K. One coil is fixed, and the other is attached to a moving object to measure displacement. The mutual inductance of the coils changes as a result of the factor K changing as the object moves. For an instrument, this change can be calibrated in terms of displacement.
Eddy Current Production
By altering the conductive plate placed close to the coil, the inductive transducer’s ability to produce eddy current can be changed. Eddy currents are created in the conductive plate when it is placed close to an alternating current coil because the plate’s own magnetic field works against the coil. And Eddy current refers to the conductive plate that transports circulating current.
Eddy current is created with its own magnetic flux when the conductive plate is brought close to the coil, which lowers the coil’s magnetic flux and inductance. So Higher eddy currents are produced and more reduction in the coil’s inductance as the distance between the coil and the conductive plate is reduced, and vice versa. As a result, shifting the conductive plate allows for the measurement of inductance change. So This Change can be calibrated to determine an instrument’s displacement, a physical quantity.
Advantages/Disadvantages of Inductive Transducer
The advantages of the inductive transducer include the following.
- These have high accuracy and stable operating range with good life-span
- So Any environmental conditions, including high temperatures and humidity, can be handled by inductive transducers. These can perform well in an industrial setting as well.
- So These types of transducers are applicable in a wide range of applications.
- These can be used in industrial applications at high switching rates.
The disadvantages of the inductive transducer include the following.
- It depends on the magnetic field of the coil.
- So The construction and temperature conditions determine the inductive transducer’s operating range.
Applications of the Inductive Transducer
Inductive transducers are used in,
- Detection of metals and missing parts
- Counting the no.of objects.
- Proximity sensors to measure position, dynamic motion, touchpads, etc.
- Linear and Rotary Motor
- Pressure and airflow sensors
- Electroactive polymers
- LVDT and RVDT
- Micro-electro-mechanical systems
- Powered generators etc.
- Potential meters
- Sequential counters
- PB monitors, heart monitors, etc