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Author Topic: setting up a reflective object sensor for dummy's  (Read 27044 times)

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Re: setting up a reflective object sensor for dummy's
« Reply #30 on: February 02, 2008, 04:08:32 PM »
just installed newest version of mach and no change.
anybody?
Chris

Offline Chip

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Re: setting up a reflective object sensor for dummy's
« Reply #31 on: February 02, 2008, 04:42:45 PM »
Hi, Chris

Sound's like your slot isn't wide enough and not giving Mach enough time to see the pulses.

On my lathe, 5 inch dia. disk  3/4" to 7/8" slot work's up to 3000 rpm.

Hope this Helps, Chip

Offline TonyP

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Re: setting up a reflective object sensor for dummy's
« Reply #32 on: February 02, 2008, 05:08:16 PM »
Chris,
I assume that you're using the index input as opposed to the timing input. I say this because I didn't realise for some time that there were two different inputs. With one slot use index, with two or more use timing. With more than one you need one slot 50% wider than the others. I would have thought your slot width would have worked ok, certainly at low speeds. It's only when you get fairly fast that the slot size gets critical. There is information on working it out in the Mach manual.
Have you payed with the active Hi/lo setting? I seem to remember it having an effect on my setup. I'll try & run the lathe up & try it.

Tony

Offline TonyP

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Re: setting up a reflective object sensor for dummy's
« Reply #33 on: February 02, 2008, 05:14:08 PM »
Yup, that's it. If I set active lo (green tick in the box) on my index/timing input, I get no tacho.

Tony
« Last Edit: February 02, 2008, 05:15:41 PM by TonyP »
Re: setting up a reflective object sensor for dummy's
« Reply #34 on: February 02, 2008, 06:05:00 PM »
yeah Im running it on index with the one slot. I thought the slot might need to be wider too so I slowed the spindle down to approx 300 rpm and I still get crazy readings. Im getting a signal to the controler but Im either getting noise or something else needs to be tweaked. Not sure though. everything else seems to be fine. Im curiouse if the opto isolation is part of the problem. does everyone out there use a breakout board too. If so any problems with that. This is really driving me nuts because I keep hearing everyone talk about how simple it is. Yet I've been working on this thing for over a month.
Chris :-\

Offline Hood

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Re: setting up a reflective object sensor for dummy's
« Reply #35 on: February 02, 2008, 07:03:36 PM »
Thats a weird one, few things I can think of-
 Are you using screened cable and do you have it grounded properly?
 Have you tried using another pin, possible that you may have a bad Parallel cable or even the breakout of port is dodgy.
 Like you said maybe a reinstall of Mach could help.

Hood

Offline Chip

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Re: setting up a reflective object sensor for dummy's
« Reply #36 on: February 02, 2008, 07:35:42 PM »
Hi, Chris

Strait to the printer port hear, If you go direct make sure it's no more than 5 volt's to the port.

With some BOB & some Encoder's you may need a pull-up or pull-down resistor, Around a 1000 ohm's on the optical pickup side.

Thanks, Chip 

Offline TonyP

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Re: setting up a reflective object sensor for dummy's
« Reply #37 on: February 03, 2008, 05:00:07 AM »
Chris,
you didn't say whether you'd tried changing the active hi/lo. My test shows that it does matter, and can give the effect that you're seeing. The diagnostics still show the signal changing, but the tacho does not work or gives strange readings.
I'm using a bob with opto isolation.

Tony
Re: setting up a reflective object sensor for dummy's
« Reply #38 on: February 03, 2008, 08:50:25 AM »
Hi, Placing a capacitor of 0.1uf across the sensor/switch terminals will reduce any spurious interference to the signal.

The action of the capacitor is to provide a short path to ground for any AC component on a DC line.

If the value of the capacitor is chosen carefully, noise spikes and mains induced hum can be reduced whilst leaving the wanted switched DC signal (ie the pulses to determine spindle speed) still available.

If the chosen capacitor value is smaller (ie 0.01uf for instance) it will only reduce higher frequencys so you'll reduce some noise spikes but not mains hum.

If the chosen capacitor value is greater (ie 1uf for instance) it will reduce all of the above and will reduce some if not all of your wanted signal. It will also introduce a small time delay as the capacitor charges and discharges if you chose to large a value, basically it will be trying to turn the pulse speed signal into DC so at higher spindle speeds you'll start losing the signal.

The above explaination gives an idea of how it works but one must remember that this is a last resort thing.

If you have connected to a sensor using fully screened cable (with only one end of the screen connected to ground) and tried to keep signal wires away from high current wires (eg stepper/servo motor and VFD wires) and you are still getting noise spikes then the above option can help.



Re: setting up a reflective object sensor for dummy's
« Reply #39 on: February 03, 2008, 11:40:24 AM »
Yes i have tried the High low setting and it had no effect. I've looked for any sorces of noise that I can think of and the cables are shielded so I will try the capacitor filter. But In the spirit of keeping this post for dummies. where exactly in the circuit does one put the capacitor? Does it just go in line with the  input terminal? ( between the blue wire and signal terminal?) or across the the two wire's. for the sensor (Blue and white?). My terminology isnt so good so when someone says "Just bridge so and so with such and such" I tend to get confused.  "between red and purple" kind of directions or "slot A into tab B" kind of directions are what Im best at.
Chris :P
Oh yeah Im using Bob campbells break out board