Re: Hight sensor

--- In CAD_CAM_EDM_DRO@egroups.com, John Stevenson <machines@n...>
wrote:

> On 9 Oct 2000 07:10:07 -0000, you wrote:
>
> I work on laser cutters and these have two types of sensors....
> The older ones use a hinged loop around the cutting nozzle attached

to a

> spring loaded LVDT [ hope I've got the letters right] The output > >

Sorry John, I edited out most of your text. These e-mails get long
and confusing. An LVDT is a Linear Voltage Displacement
Transformer. Its a fancy name for a small biflar wound transformer
with a moveable core. It works like this: There are two windings
that are wound out of phase with each other. A small AC signal is
imposed on both windings. When you do that in a normal fixed core
transfromer, the signals cancel out and the resulting signal is
zero. If you make the windings around a hollow bobbin and slide a
piece of iron (normally moulded powdered iron) then the miracle of
magnetics causes the signals to become unbalanced and the resulting
output is directly porportional to the linear distance the core has
moved from "zero" which is equally between both windings. Thus it
allows you to measure small changes in linear motion without getting
into proximity and complex electronics. Its been a long time since I
built anything with a LVDT. I really appreciate your feedback. I
was seriously thinking about doing something like attaching a pushrod
with a small wheel to a slide pot that is connected in one leg of a
bridge circuit. A pot could be used to "balance" the circuit to keep
the error voltage at zero when the height was correct. There would
of course need to be control circuitry that caused the stepper motor
to move and maintain the balance. There are I am sure more elegant
ways of developing the feedback but sometimes simple is better. There
are commercial LVDT's but I haven't priced one lately. I made the
last ones I used but I was working in a lab that had transformer
winding tools.