RE: [CAD_CAM_EDM_DRO] Repeatability of Home switches

I use hall switches with a tiny magnet on the moving part for sensing
position, but in an environment which suffers from dust, which will possibly
block optical switches, However where there are ferrous bits floating about
in the air they will always get onto the magnet and cause repeatability
problems.

If ferrous dust is not a problem, it is possible to get ordinary hall
switches pretty accurately repeatable by spreading the field from the back
of the magnet with a wide pole piece of steel, and putting a narrow pole
piece on the front of the magnet, making the front of the field "doughnut"
more pointy and thus the field gradient steeper. (also a bit of metal behind
the hall sensor will tend to concentrate the field).

I would be tempted to use a slotted opto switch for the job of home sensing.

BUT.... using either switch, remember to sense while moving only in one
direction as the hysteresis of the switch will give a different position for
the transition off-on to the position of the transition on-off.

Nig.

-----Original Message-----
From: mrgamber [mailto:mgamber@...]
Sent: Thursday, April 03, 2003 2:46 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Repeatability of Home switches


What repeatability should I expect from home switches?

I can get a Honeywell Hall Effect VX series switch in a standard
package that claims .005" repeatability. Can I do better with a
typical hall effect switch?

The output on the switch is confusing, does sink mean that it is
coupling the supply voltage to the output? Or is it contact closure
like a normal switch.

link;

content.honeywell.com/sensing/prodinfo/solidstate/catalog/c20048.pdf




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