The Linear Variable Differential Transformer (LVDT) is a type of sensor which converts linear displacement into an variable electrical signal. An LVDT consists of a sliding ferromagnetic core which sits inside 3 electrical coils, a primary coil in the middle and two identical secondary coils at either side.
Since the design of an LVDT is based on the transformer principle of Mutual Inductance, an LVDT device will only function with a AC voltage supplied to the primary coil.
The secondary coils are interconnected so that any current induced by the primary coil will be 180 degrees out of phase between the two secondary coils, and the resulting output will be zero when there is no displacement. If the core is moved to the left or the right, the mutual inductance between the primary and secondary coils will increase in one and decrease in the other, creating a differential voltage across the two secondary coils. The differential voltage output produced is directly proportional to the amount of displacement of the core.
There is very little friction generated by the movement of the core which makes it ideal for incorporating into sensor technologies where high precision and repeatability are important requirements. The lack of friction also reduces mechanical fatigue extending the working life of the sensor.
The resolution of an LVDT is considered to be infinite and the null point is extremely repeatable, these qualities make it possible to incorporate the technology into other devices such as pressure sensors without compromising on measurement precision or stability.
LVDT technology is used by some manufacturers of pressure measurement instrumentation. An LVDT is incorporated into a pressure measurement device by connecting the core of the LVDT to the centre of a pressure sensing diaphragm, so that any flexing of the diaphragm due to changes in pressure will be detected as a position change by the LVDT.
Glossary of Pressure Sensor technical terms
- Ceramic Pressure Sensors
- Digital Compensation
- Dry Cell
- Dry/Dry
- HART®
- Isolation Diaphragm
- Pressure Sensors
- SOI – Silicon on Insulator
- Stainless Steel Pressure Sensors
- Static Line Pressure
- Wet/Dry
- Wet/Wet
Help from Pressure Sensor resources
- Pressure Sensor Technology Comparative Guide
- How do you choose the correct pressure range for a pressure sensor
- Measuring vacuum as a negative gauge pressure using a dp sensor
- How to get a 10 volt signal from a 4-20mA output pressure sensor
- Transforming a 2 wire Current Loop into a Voltage Output Signal
- How do you measure flow rate with a dp cell
- Measuring liquid level in a tank using a dp sensor
- Measuring density of a liquid using a dp sensor
- Pressure Sensor Accuracy Specifications
- Supply voltage and load resistance considerations for pressure transmitters
- How to Connect a 4-20mA Current Loop Pressure Transmitter
- What is difference between working, burst and over pressure
- What can a DP sensor be used to measure beyond differential pressure?
