Re: [CAD_CAM_EDM_DRO] Machine mounted Tachometer with Surface Meter Per minuteThis

On 09/11/2010 01:22 AM, Gaston Gagnon wrote:

> Hi David,
> On 2010-09-10 22:09, David G. LeVine wrote:
>
>> On 09/10/2010 10:49 AM, Gaston Gagnon wrote:
>>
>>> Yeah, I know, I will have to take the plunge: open up the router, install
>>> something (?) and make hole in the body for the sensor but I was hoping
>>> (secretly) someone would come up with a way to derive the actual speed from
>>> router's internal speed control electronic. ;-)
>>> Gaston
>>>
>> Most routers have a nut at the collet. If using non-ferrous metals (or
>> wood or plastic), a hall effect sensor can pick up the points or cuts
>> (for ER type collets.)
>>
> Can you elaborate a little on how this would work since Hall effect sensors
> are only sensitive to change in magnetic field.
> Gaston
>

Sure, assuming a magnetic nut (note, not magnetized, but capable of
being attracted to a magnet), many Hall Effect sensors have a built-in
"bias magnet" which provides the magnetic field needed for the sensor to
operate. See the ATS616
<http://www.allegromicro.com/en/Products/Part_Numbers/0616/index.asp>
for an example and fuller write-up. The "gear-tooth" sensors (used for
engine timing, for instance), are cheap and pretty rugged.


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