What is a LVDT?

What is a LVDT?

An LVDT (linear variable differential transformer) is an electromagnetically sensor used to convert mechanical motion or vibrations, specifically rectilinear motion, into a variable electrical current, voltage or electric signals, and the reverse. Actuating mechanisms used primarily for automatic control systems or as mechanical motion sensors in measurement technologies.

Principle of LVDT:

LVDT works under the principle of mutual induction, and the displacement which is a non-electrical energy is converted into an electrical energy.

LVDT consists of a cylindrical former where it is surrounded by one primary winding in the center of the former and two secondary winding at the sides. The number of turns in both primary and secondary are equal, but they are opposite to each other, i.e., if the left secondary winding is in the clockwise direction, the right secondary winding will be in the anti-clock wise direction, hence the net output voltages will be the difference in voltages between the two secondary coil. The two secondary coil is expressed as S1 and S2. Esteem iron core ids placed in the center of cylindrical former which can move in to and motion. The AC excitation voltage is 5 to 12V and the operating frequency is given by 50 to 400 HZ.

Conversion Principles:

• Electromagnetic
• Magnetoelectric
• Electrostatic

Output Signals:

• Analog and discrete output
• Digital

Measurement Ranges: 0.02", 0.02 to 0.32", 0.32 to 4.0", 4.0 to 20.0", ±20.0" (range of measurement or maximum distance measured)

LVDT accuracy: Describes percentage of deviation from the actual/real value of measurement data.

Output: Voltage, Current, or Frequency

Interface: Serial—Standard digital output protocol (serial) like RS232, or Parallel—Standard digital output protocol (parallel) like IEEE488.

Type of LVDT: Current Balance AC/AC, or DC/DC, or Frequency Based

Application: There are many other application of LVDT like in the measurement of thickness of metal sheets being rolled out in industry, in the measurement of tension of a wire in a wire-drawing machine, automatic opening and closing of gates at railway crossings, etc.