Analytical Instrumentation
Displacement Transducer and its Classification
Table of Contents
- What is a Displacement Transducer?
- Working Principle of Displacement Transducers
- Classification of Displacement Transducers
- Classification of Inductive Transducer
- Circuit Diagram of Displacement Transducer
- Difference between LVDT & RVDT
- Advantages of Displacement Transducer
- Disadvantages of Displacement Transducer
- Applications of Displacement Transducer
- What is a Displacement Transducer?
- What are the types of Displacement transducers?
- What are the types of Inductive transducers?
What is a Displacement Transducer?
- A Displacement Transducer is an electro-mechanical device to metamorphose mechanical motion, specifically rectilinear motion or vibration into dynamic electrical current signals, voltage signals, or electrostatic, magneto-electric, or electromagnetic signals.
- These signals obtained from displacement transducers are scanned and elucidated into information.
- Usually, these displacement transducers can determine
- The physical separation between the detector & a given target element.
- The static & dynamic displacements measure the vibration of an object or target.
- The output value of the displacement transducer ranges from a few micro-inch to a few feet.
- Through these displacement transducers, both direct displacement and indirect displacement can be measured easily.
- The main benefit of displacement transducers is
- Easy to use
- Rugged to attain greater precision.
- Yields reliable measurement in production, R&D sectors
Working Principle of Displacement Transducers
Displacement Transducers function on the law of measurement of extremely reliable inductance.
Classification of Displacement Transducers
Classification of Displacement transducers is done on the basis of linear & rotary motion.
Strain Gauge
- A Strain Gauge is a kind of Displacement Transducer that transforms the sensed physical quantity to equivalent mechanical strain and finally to a measurable electronic signal.
- Usually, this Strain Gauge type Displacement Transducer is clamped on an elastic body.
- This Strain Gauge type Displacement Transducer measures the displacement for up to 10 mm.
- This Strain Gauge transducer has a shorter length in contrast to Linear Variable Differential Transducer.
- This strain gauge transducer is
- Highly Stable
- Highly Reliable
- Free from electromagnetic effects.
Resistive Transducer
- A Resistive Transducer is acclaimed as a changeable resistance transducer.
- The working principle of this resistive transducer is based on the transduction of variable resistance.
- It encompasses resistive elements along with movable contact.
- This transducer is the most often exploited displacement transducer.
- The motion of this transducer is perhaps translational, rotational, helical, or a combination of these motions.
- This transducer measures various physical quantities such as displacement force, pressure, temperature, and vibrations, and transforms it into proportional measurable electrical signals.
Capacitive Transducer
- A capacitive transducer is a kind of passive transducer.
- The working principle of this capacitive transducer is based on the transduction of variable capacitance.
- This capacitive transducer can determine various process parameters such as motion, chemical composition, acceleration, electric field, & pressure.
- Equal & Opposite charges are produced on the plates of the capacitive transducer isolated by dielectric material as a consequence of an applied voltage across the capacitor plate.
- Here an external power supply is used for this capacitive transducer.
- Some more parameters such as displacement, force, movement, pressure, & velocity can be determined by this transducer.
- The capacitance is based upon dielectric constant, plate overlapping.
Inductive Transducer
- In differentiation to Capacitive Transducers, & Resistive Transducers this Inductive Transducer is another type of displacement transducer.
- The working principle of this inductive transducer is based on electromagnetic induction.
- Measurement of various physical quantities such as acceleration, displacement, force, mutual inductance, pressure, self-inductance, torque, and velocity may also vary.
Classification of Inductive Transducer
Inductive Transducer is categorized into two types as
- Linear Variable Differential Transducer (LVDT)
- Rotary Variable Differential Transducer. (RVDT)
But in most cases, this Linear Variable Differential Transducer is considered the best example of an Inductive Transducer.
Linear Variable Differential Transformer
- Linear Variable Differential Transformer (LVDT) is an electromechanical device, a kind of displacement transducer.
- This coil produces an equivalent voltage as an output signal compared to the displacement of the iron core and transformer.
- This transducer comprises three coils placed uniformly among each other.
- The coil located at the center is a primary coil, & remaining two coils placed aside are secondary coils.
- The secondary windings are similar with reference to the turning number, and placement of both sides of the primary winding.
- Generally, these coils linked are in series & are fixed uniformly around the main coil.
- The primary coil is electrified by the application of a sine wave signal.
- A movable core produces a proportional electrical signal with respect to its displacement.
- When the core is at the center a sinusoidal voltage emerges across these two secondary coils.
Rotary Variable Differential Transducer.
- The working principle of both LVDT & RVDT is the same which means both work on the same principle.
- It is also a type of electromechanical transducer that furnishes a dynamic AC output voltage proportional to the angular displacement as a linear function.
- A Rotary Variable Differential Transducer (RVDT) measures only rotational angles.
- RVDT incorporates one primary, & two secondary windings.
- RVDT makes use of rotary-type ferromagnetic cam-type core, but
- LVDT makes use of a flexible cylindrical iron core.
- RVDT detects the angular displacement & transforms this signal to an equivalent electrical signal.
- RVDT characterizes linearity properties between -40 and +40 degrees.
- The sensitivity of RVDT lies between 2mV to 3mV per degree of rotation
Circuit Diagram of Displacement Transducer
- The displacement transducer indicated in the diagram shown below represents an inductive transducer.
- This circuit of Displacement Transducer determines actual displacement with an Inductive Transducer.
- This transformer encompasses an
- Primary Winding 01 no’s.
- Secondary Winding 02 no’s.
- The terminals of secondary windings are coupled to each other in a series position.
- The Primary Voltage “VP” is given to the transformer’s primary winding.
- The two voltages developed across these two secondary winding of the transformer are VS1 & VS2
- Finally, output voltage V0 generated across transformer secondary winding is the difference voltage between VS1 & VS2. This voltage is dissimilar between VS1 & VS2 because the transformer used is a differential type.
- Mathematically, this output voltage V0 is given by V0 = VS1 – VS2.
- The induced voltages across two windings S1 & S2 are identical if the core is located at the center.
- Since the displacement doesn’t exist at this condition when the output voltage V0 becomes zero.
- Here the maximum amount of induced voltage across S1 is produced, if the core is located above the center which is (V1>V2).
- Similarly, the lesser amount of induced voltage across S1 is produced, if the core is located below the center which is (V1< V2).
- In the above-shown conditions, there are two displacements one is upward displacement & the other is downward displacement.
- Hence, the magnitude of output voltage “V0” is proportional to the position of the core relative to the center.
- To determine the displacement, it is required to link to the central core
- The middle point of the core changes when the body moves in a straight line path causing the output voltage V0 to change.
Difference between LVDT & RVDT
LVDT Vs RVDT
Parameter | LVDT | RVDT |
Sensing | Linear type Displacement transformer | Angular type Displacement transformer |
Full-Form | Linear Variable Differential Transformer | Rotatory Variable Differential Transformer |
The shape of core | Rectangular core | CAM shaped core |
Range | +100 micro-m to + 25 cm | +40 degrees to -40 degrees. |
Sensitivity | 2.4 mV/Volts/degree of rotation | 2 mV to 3mV /Volts/degree of rotation |
RMS input voltage | 1 V to 24 V | 3 V |
Frequency Range | 50 Hz to 20 KHz | 400 Hz to 20 KHz |
Application | Weight & Pressure Measurement | Fire Controlling, Antenna & Radar Systems |
Advantages of Displacement Transducer
- Excellent Linearity.
- Higher Accuracy in wide temperature ranges.
- The resolution is about 0.01 µm.
- Un-bias able to have a high magnetic field.
- Stronger design.
- Excellent stability.
- This transducer can be mounted in any direction.
- Low power consumption.
- Low hysteresis loss.
- Friction is minimum.
- High measurement range.
- High Sensitivity
- Alignment & Maintenance is very easy.
Disadvantages of Displacement Transducer
- Limited dynamic response.
- Requires external demodulator to produce DC output signal.
- Requires maximum displacement to produce high voltage.
- The performance of the displacement transducer is distressed due to vibrations & temperature changes.
Applications of Displacement Transducer
Displacement transducers are used to
- Determine the comparative movement between the tip of the sensor to the rotating shaft.
- Measure displacement in CNC machines.
- Measure the thickness of rolled metal sheets
- To measure force, acceleration & pressure in flight control systems.
What is a Displacement Transducer?
A Displacement Transducer is an electro-mechanical device to metamorphose mechanical motion specifically rectilinear motion or vibration into dynamic electrical current signals, voltage signals, or electrostatic, magneto-electric, or electromagnetic signals.
What are the types of Displacement transducers?
Displacement Transducers are classified as
- Strain Gauge
- Capacitive Transducer
- Inductive Transducer
- Resistive Transducer
What are the types of Inductive transducers?
Inductive Transducer is classified into
- Linear Variable Differential Transducer (LVDT)
- Rotary Variable Differential Transducer. (RVDT)