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Author Topic: Hall Effect or Slotted Opto?  (Read 2804 times)

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Hall Effect or Slotted Opto?
« on: March 29, 2015, 08:45:04 AM »
My break out board calls for a Hall Effect sensor to get the spindle pulses into Mach3, however my old TCL160 under conversion already has a nice big encoder disc mounted directly on to the end of the spindle shaft.
It has 100 holes on the inner and 1 slot on the outer ring and uses two slotted opto switches.

I really don't want to use magnets mounted onto my encoder ring for fear of introducing a balance issue.
Can I use the slotted opto switches with my break out board. And if so can you suggest a hook up method.
I have attached some pictures which may help.

I understand I can then calibrate the spindle speed by running the spindle and comparing the speed from Mach3 with the actual speed recorded by an electronic speed gauge and then applying a difference offset into Mach 3. Is that correct?

Many thanks

George
Re: Hall Effect or Slotted Opto?
« Reply #1 on: March 29, 2015, 09:02:32 AM »
The weight of the magnet required would be inconsequential. If concerned though, you could place a small steel slug of the same mass directly opposite.
I prefer the Hall to the optical myself. I fitted two machines with the optos and both, over time became contaminated to the point that they  would operate intermittently. One by oil mist and dust accumulation and the other from light rubber dust form the belts and other ambient particulates.

Russ

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Re: Hall Effect or Slotted Opto?
« Reply #2 on: March 29, 2015, 10:51:43 AM »
Agree with Russ. The Hall's are more expensive, make sure you look at the specs as some have faster repsonse than others. The Hall's are easy to mount and align so you can get away with an installation  that otherwise couldn't be done. The rare earth magnet I used was only 1/8" dia x 1/16" thick and was grazy glued to a pulley.

BTW, you only can use one / single slot and there is no advantage to multiple slots.

I don't use a BOB. Mach's rpm is good to probably 4 places is probably more accurate than your indicator.

RICH.
Re: Hall Effect or Slotted Opto?
« Reply #3 on: March 29, 2015, 11:05:09 AM »
Thanks gents,

Ok, looks like its the Hall Effect route I'll adopt, thanks for the advice.

Rich, excuse me if I'm being a bit dumb. I'm not sure by what you mean when you say 'You don't use the BOB' Are you suggesting that I don't use either the Hall or the Opto at all? Are we relying on the 0-10V input to my Inverter drive.
I will be using this on a Lathe (TCL160) so I will want to do some 'threading'

George

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Re: Hall Effect or Slotted Opto?
« Reply #4 on: March 29, 2015, 11:51:09 AM »
No, I just stated that I don't have or use a break out board.
You must use something to get an index pulse for Mach to know the spindle speed.
 Sorry for the confusion...

RICH
Re: Hall Effect or Slotted Opto?
« Reply #5 on: March 29, 2015, 01:35:49 PM »
I'd have thought that it would be just as easy to connect the optical sensor, since the output circuit is much the same as a hall d=sensor, effectively open collector.  However, I've built a Hall sensor for my big mill for a tachometer, it uses a tiny neodymium magnet about 4 x 2 mm araldited to the spindle pulley, and the sensor "sees" it from about 5 mm away - so you dpon't need a big heavy magnet.  And just stick an equivalent weight bit of steel diametrically opposite to balance if it's a concern.
Re: Hall Effect or Slotted Opto?
« Reply #6 on: March 29, 2015, 03:19:53 PM »
Thanks for the replies,
I have ordered some 3mm neo magnets and will glue that to my disc which is attached to the shaft as in the picture. I should think I will get a better resolution if I attach it close to the original holes. ?


Thanks

George