What is an LVDT?

An LVDT is a linear variable differential transformer and is used to accurately measure linear displacement (position measurement) which is movement in a single direction along an axis. An LVDT is often also referred to as a linear displacement transducer or a linear position transducer. A device similar to this is an RVDT (Rotary Variable Differential Transformer) used to measure rotary displacement.

There are many types of LVDT sensors. LVDTs have different armatures, temperatures ranges, built-in electronics and stroke lengths. LVDT sensors with a captive guided spring return armature have been designed for measuring multiple targets. These types of armatures are ideal for measuring surface structure changes. A captive guided armature is suited to longer measurements. The armature is attached to both the body and structure it is measuring.

How does an LVDT work?

An LVDT position sensor has a primary coil and two secondary coils. This coil assembly is mounted to a stationary object while a ferromagnetic core is attached to the object whose position is being measured. The core links the electromagnetic field of the primary coil to the secondary coils. The difference from the coil outputs results in proportional voltage relative to the movement of the core versus the coils.

What are the benefits of a linear variable differential transformer?

The LVDT has a long life as there is no contact between the sensing elements
An LVDT is robust and can operate in harsh conditions
Extremely small movements are measured by an LVDT
An LVDT has excellent repeatability for performing precise applications
Analog input and output
Absolute measurement giving no position loss
An LVDT can convert the rectilinear motion of an object into an electrical signal
The LVDT can be used in a range of applications within industry or research as it can be easily modified to fulfil different tasks.

An LVDT is an electrical transformer and requires a different type of AC power (around 3 Vrms @ 3 kHz). The support electronics for an LVDT, such as a signal conditioning unit, supply this sort of excitation power. A signal conditioning unit also converts the low level AC voltage from an LVDT into higher level DC output voltage.

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Description Price Stroke Input Current Range Energising Voltage Range Output Voltage Range Sensitivity Response Time Overall Height Overall Width Overall Depth Minimum Operating Temperature Maximum Operating Temperature
RS Stock No. 803-1591
±2.5 → ±50.8mm - 3 Vrms - 94.5 mV/V/mm - 44.5mm 19.05 (Dia.)mm - -55°C +95°C