Displacement Transducer and its Classification

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 

1. The physical separation between the detector & a given target element.
2. 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 

1. Easy to use
2. Rugged to attain greater precision.
3. 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

1. Highly Stable 
2. Highly Reliable
3. 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.