[Trebleplink]

I am building a Smithy 1240 mill.

In the full "factory"package Smithy cnc, they are using cylindrical Hall-effect switches which detect the passing of a piece of steel barstock. They use this for zeroing and hard limit switches.

I am an electronics guy, but only somewhat familiar with Hall-Effect devices - there are both linear and logic outputs, along with open collector, etc. OC would seem to interface to the PMDX 131 board well.

But do you know if this type of sensor requires permanent magnet bias to detect passing steel? Is it a special "proximity" sensor which has an integral magnet? Is there a proven type?



http://www.scott-inc.com

[neilw20]

Have a look at:
http://www.allegromicro.com/en/Produ...ories/Sensors/

[Al_The_Man]

You can get magnetic sensors, but most of the type used are ferrous metal proximity detectors, although there are type that will sense non-ferrous also.
The open collector 3 wire come in PNP & NPN (sink/source).
If you are using them in an application that inputs into relatively high impedance, such as logic input etc, the 2 wire type can be used, the three wire are only necessary if an appreciable load is being switched.
The advantage with the 2 wire is that they can be used in a sink or source input.
Al.

[Trebleplink]

The position bars are ferrous - and I can use npn or similar fet outputs, three wire are fine - A ferrous metal proximity switch is what I think Smithy uses. These are cylindrical, approximately .300 diameter, with leads exiting the rear. I've an inquiry into Smithy, but they apparently don't stock them, don't know exactly what they are, and are emailling the factory. I have a feeling if I buy through Smithy I may be paying $60 each for $15 sensors ...

I've been reading the information provided by the previous poster, which seems to indicate that magnetic bias is required, and these are built in to the "ferrous metal detector" package. I'm not seeing packaged sensors from that vendor though - I would have to build up mountings for the very small leaded packages ...

You can get magnetic sensors, but most of the type used are ferrous metal proximity detectors, although there are type that will sense non-ferrous also.
The open collector 3 wire come in PNP & NPN (sink/source).
If you are using them in an application that inputs into relatively high impedance, such as logic input etc, the 2 wire type can be used, the three wire are only necessary if an appreciable load is being switched.
The advantage with the 2 wire is that they can be used in a sink or source input.
Al.