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From: bkoball@cup.portal.com (Bruce R Koball)
Newsgroups: sci.electronics
Subject: Re: velocity sensing for robotic joints
Message-ID: <32758@cup.portal.com>
Date: 14 Aug 90 01:46:26 GMT
References: <1990Aug7.205751.21206@ecf.utoronto.ca> <19481@well.sf.ca.us>
  <140483@sun.Eng.Sun.COM> <8441@ccncsu.ColoState.EDU>
Organization: The Portal System (TM)
Lines: 17

The term LVDT mentioned by Joel Nevison stands for Linear Variable
Differential Transformer. It typically consists of three windings
and a movable core piece. The central, primary winding is excited
by an AC signal, typically of several kHz. The two secondary windings
are located on either side of the primary. The displacement to be
measured is physically connected to the movable core. As the core
moves, the coupling between the primary and the two secondaries
changes. A phase detector is usually used to difference the two
secondary signals and produce a DC output proportional to the core
displacement. Its main advantages are excellent linearity and resolution.

Bruce Koball
Motion West
2210 Sixth Street
Berkeley, CA 94710
415-540-7503
bkoball@cup.portal.com