Re: Probing

["Ian Wright" <Ian-at-iw63.freeserve.co.uk>]

HI,

Wouldn't accuracy be a big problem here? Unless one is using a very high
precision sensor, I would think that it would be difficult to find any
reasonably priced optical sensor which would give accuracy down to even 1
thou. Having said that, it has started me thinking about the possibilities
of modifying the optics out of an old CD ROM drive - six or more
phototransistors on one chip in an exact pattern, perhaps wire four of them
up for null detection (equal outputs on a bridge circuit) and pop a lens in
front of them to focus returned light to the smallest spot
possible..........  Even with this though there must be some 'depth of
field' effect which would limit sensitivity.

Ian
--
Ian W. Wright
Sheffield  UK
www.iw63.freeserve.co.uk
----- Original Message -----
From: "Doug Fortune" <pentam-at-home.com>
To: "Multiple recipients of list" <emc-at-nist.gov>
Sent: 18 January 2002 06:08
Subject: Re: Probing


>
> Pete Cook wrote:
> >
> > Has anyone thought of a non-contact probe - One of the infrared type
prox
> > switches might work - they bounce a signal off the surface and trip at
some
> > distance from the surface - might have to be close to perpendicular for
the
> > best results - Might be a bit more pricy but somewhat harder to smash...
>
> These analog sensors are not too expensive:
> Inexpensive: $15, cheaper in packs of four
> Simple to Use
> Small (3 x 1.5 x 1.4 cm)
> Connects directly to any microcontroller with A/D