What do the letters LVDT stand for?

LVDT stands for 'Linear Variable Differential Transformer'.

What does an LVDT do?

An LVDT converts linear mechanical movement of an object connected to it, into an electrical signal proportional to the amount of mechanical movement, giving precise positional feedback.

How does an LVDT work?

An LVDT is a 'contact-less' device, which consists of one primary coil and two secondary coils symmetrically wound on a cylindrical hollow tube. The fundamental principle of operation is by induced voltage from the primary coil into the secondary coils, using a magnetically permeable core. Flying leads connected to the primary and secondary coils allow for the Primary coil to be energised with an AC signal, and the secondary output signals to be monitored using appropriate test equipment. Because of the way LVDT's work they can accurately sense miniature movements of the core (down to microns).

Fig 1,2 and 3 below show a simple schematic drawing of an LVDT in 3 positions of travel.

• (Fig 1) Core retracted, more Voltage induced into coil 'b')
• (Fig 2) Core at the electrical Null, (induced Voltages in coil 'a' and 'b' is identical)
• (Fig 3) Core extended, more voltage induced into secondary 'a'

Click image to enlarge

Please continue to read the next section, Connecting and operating an LVDT.

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