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Hall Effect rpm sensor

 
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Mike Welch



Joined: 13 Feb 2011
Posts: 272

PostPosted: Mon Jun 18, 2012 2:23 pm    Post subject: Hall Effect rpm sensor Reply with quote

List guys,

Can someone direct me to "complete rpm sensor circuit", including either a digital or analog gauge
that would go along with it?
I have need of something that will display visually a rotating motor's shaft. A Hall Effect circuit
would be fine, but I'm open to anyone's suggestion if they have a better idea how to monitor rpms
of a motor. FYI, the motors will turn at a relatively slow 200-250 rpm (if that matters).
If you know of a specific gauge, or LCD display, that could read these rpms, I'd appreciate that, too.
Thanks in advance,
Mike Welch

[quote][b]


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nuckolls.bob(at)aeroelect
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PostPosted: Tue Jun 19, 2012 6:55 am    Post subject: Hall Effect rpm sensor Reply with quote

At 05:21 PM 6/18/2012, you wrote:
Quote:
List guys,

Can someone direct me to "complete rpm sensor circuit", including either a digital or analog gauge
that would go along with it?

I have need of something that will display visually a rotating motor's shaft. A Hall Effect circuit
would be fine, but I'm open to anyone's suggestion if they have a better idea how to monitor rpms
of a motor. FYI, the motors will turn at a relatively slow 200-250 rpm (if that matters).

If you know of a specific gauge, or LCD display, that could read these rpms, I'd appreciate that, too.

Thanks in advance,
Mike Welch

What is the rpm range of interest? Is the
instrument to be permanently mounted or is
it a 'test' or 'setup' environment that could
use a hand-held? See:

http://tinyurl.com/77ulekb

http://tinyurl.com/77lw4bs

If you need a permanent, panel mounted
instrument, you could use something like
this

http://tinyurl.com/7nxrh4w

but you'd need to build a sensor and
some interface electronics. As long as
you're building stuff, the data can be
displayed on a small, analog instrument
where a customized scale sized to your
task is pretty easy.








Bob . . . [quote][b]


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Mike Welch



Joined: 13 Feb 2011
Posts: 272

PostPosted: Tue Jun 19, 2012 7:33 am    Post subject: Hall Effect rpm sensor Reply with quote

Bob,

  Thank you for replying!  
Here are some of the parameters:
1)  motor shafts are anticipated to rotate between 0-300 rpm
2)  the tach-displays need to be remotely, and permanently mounted (in a console)
(I really like that digital tach you suggested!!)
3)  the 'precise' motor rpms do not have to be "highly accurate", but they do need to be consistant.
(in other words, if the shaft is actually spinning at 307 rpms, and the gauge says "320", that's fine, as long as 
each time it is consistantly off the same amount!)
  I did find a very nice electronics package that was close to what I'm looking for, but it had a couple of 
glitches.  First glitch was the rpm range it measured, which was way too high, and the second glitch was the 
two 7 segment displays, when I would prefer an actual tachometer like the one you suggested.
  See:
http://www.eio.com/p-23310-velleman-k2625-digital-tachometer.aspx
  Thanks for your help, Bob,
Mike



[quote][b]


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PostPosted: Wed Jun 20, 2012 5:38 am    Post subject: Hall Effect rpm sensor Reply with quote

At 10:32 AM 6/19/2012, you wrote:

Quote:
Bob,

Thank you for replying!

Here are some of the parameters:

1) motor shafts are anticipated to rotate between 0-300 rpm

Okay, if you were going to display on an analog instrument,
you'd want a sensor that was watching say, 10 events per
revolution so that you were measuring 3000 evenst/min or
50 events/second. It's hard to get a fast responding display
that is also free of 'wiggles' when the measured frequency
is below 20 Hz or so.

With a digital instrument, one can measure the period of time
between pulses and then calculate rpm . . . this technique
will get you a good rpm measurement for every counted event.

Quote:
2) the tach-displays need to be remotely, and permanently mounted (in a console)
(I really like that digital tach you suggested!!)

This is an automotive device that probably expects to
get a signal from the ignition system. It's scaled internally
to present shaft rpm when the engine produces 3 or 4
ignition events per revolution. The specs on this instrument
are suspect when they said, "A tach adapter may be required if
you have a multiple coil ignition system to ensure a proper signal."

It didn't mention whether the instrument had a jumper setting
to allow tailoring the installation to cars of different
engine sizes. I've built tach adapters that would convert
observed shaft RPM into a signal that would emulate an
engine . . . but that's a bit of added fuss that you
probably want to avoid if practical.


Quote:
3) the 'precise' motor rpms do not have to be "highly accurate", but they do need to be consistant.
(in other words, if the shaft is actually spinning at 307 rpms, and the gauge says "320", that's fine, as long as
each time it is consistantly off the same amount!)

Digital can and should be quite accurate and very
repeatable to +/- one least significant digit.
But how sensitive is your process to RPM variations
in the 1 LSD range? 320 real RPM on some tachs might
produce a 319-320-321 "wobble" in readings. In other
words, just how accurate dose the displayed speed
reading need to be. Again, having lots of events per
revolution (10-20 toothed gear to stroke your sensor).


Quote:
I did find a very nice electronics package that was close to what I'm looking for, but it had a couple of
glitches. First glitch was the rpm range it measured, which was way too high, and the second glitch was the
two 7 segment displays, when I would prefer an actual tachometer like the one you suggested.
See:
http://www.eio.com/p-23310-velleman-k2625-digital-tachometer.aspx

Thanks for your help, Bob,

You've probably seen the response from Jim Hausch.
He's no doubt slain this dragon many times. Why
don't you guys strike up a battle plan on the List?
I'll join in if I think I've got something extra to
contribute but I'll bet Jim can handle it.

If it turns out that you do need some kind of data
conversion device, We might be able to accommodate
the requirement with custom software in the open
source, digital wig-wag project board. Our byte
herding friends here on the List could probably
get the board to sing, dance and do dishes for your
application.


Bob . . . [quote][b]


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jhausch



Joined: 14 Jan 2008
Posts: 33

PostPosted: Thu Jun 21, 2012 3:59 am    Post subject: Re: Hall Effect rpm sensor Reply with quote

Bob,

I have been receiving Mike's responses to my email. I only receive a daily digest from the list. I will leave it up to him to post the collection/recap of our conversation on the web.

I was a bit surprised to see my work email signature pop up on the list, but I guess that's the nature of the internet.

I've contacted encoder and prox vendors looking for 100' submersible solutions. I think that is the most challenging part of this application as viewed from my world. We have items rated for high pressure washdown, but 3 atm of constant pressure is likely another story.... You'd think a fully potted solid state solution would be fine, but my gut tells me the saltwater will creep in at the cable entry point and perhaps along the mating surfaces between the housing and potting material - searching for any void it can find to get at the electronics....

I agree with you that multiple PPR (pulses per rev) are needed to provide some accuracy/display stability.

We'll see where this goes... certainly an interesting application.


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PostPosted: Thu Jun 21, 2012 3:00 pm    Post subject: Hall Effect rpm sensor Reply with quote

At 06:59 AM 6/21/2012, you wrote:


Bob,

I have been receiving Mike's responses to my email. I only receive a
daily digest from the list. I will leave it up to him to post the
collection/recap of our conversation on the web.

I was a bit surprised to see my work email signature pop up on the
list, but I guess that's the nature of the internet.

You were in a cc list and the reply-all response got you
dumped into the List data flow but not in the bucket of List
subscribed addresses.

I've contacted encoder and prox vendors looking for 100' submersible
solutions. I think that is the most challenging part of this
application as viewed from my world. We have items rated for high
pressure washdown, but 3 atm of constant pressure is likely another
story.... You'd think a fully potted solid state solution would be
fine, but my gut tells me the saltwater will creep in at the cable
entry point and perhaps along the mating surfaces between the housing
and potting material - searching for any void it can find to get at
the electronics....

If you can find a square-wave (hall effect) driven instrument
with the approrpiate features for scaling say 3000 ppm to a 300
rpm display, we can hammer a high pressure sensor together.

I agree with you that multiple PPR (pulses per rev) are needed to
provide some accuracy/display stability.
We'll see where this goes... certainly an interesting application.

Agreed. Let's see what kind of shaft is exposed
to the inquisitive world of instrumentation.

Bob . . .


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