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Barry Lennox
Guest
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 Posted:
Fri Feb 11, 2005 2:38 pm Post subject:
Re: Measure Small Weight? |
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On 10 Feb 2005 01:15:15 -0800, "Brad" <bevernon@aol.com> wrote:
| Quote: | Anybody aware of some very inexpensive sensors or other devices that
can be used to measure weights of about 8 ounces to a 0.01 ounce
accuracy? I need the gizmo to be robust, reliable, linear and
monotonic.
I have looked at piezoelectric sensors but the ones from Honeywell and
SensorOne are way too pricey. The one's that aren't really expensive
seem to lack the accuracy or repeatability I want. Any idea on the
cost of the devices from Cooper Instruments? Are there other
manufacturers (Yahoo isn't much help here...)
I have considered magnetics, beam balances and so on but haven't come
up with a strategy that I am sure will work. Any ideas?
Brad
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There was one in the Amateur Scientist columm in Scientific American
several years back. It used a gutted moving coil meter and a an op-amp
to servo the pointer back to center. Can't recall the resolution and
accuracy, but I think it did much better than .01 oz, the top end of 8
oz may be a problem though, and I'm not sure about the "robust" bit.
I could find the article if you are interested.
Barry Lennox
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martin griffith
Guest
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| Posted:
Fri Feb 11, 2005 3:38 pm Post subject:
Re: Measure Small Weight? |
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On Fri, 11 Feb 2005 21:38:06 +1300, in sci.electronics.design Barry
Lennox <rianz.15.barryl@neverbox.com> wrote:
| Quote: | On 10 Feb 2005 01:15:15 -0800, "Brad" <bevernon@aol.com> wrote:
Anybody aware of some very inexpensive sensors or other devices that
can be used to measure weights of about 8 ounces to a 0.01 ounce
accuracy? I need the gizmo to be robust, reliable, linear and
monotonic.
I have looked at piezoelectric sensors but the ones from Honeywell and
SensorOne are way too pricey. The one's that aren't really expensive
seem to lack the accuracy or repeatability I want. Any idea on the
cost of the devices from Cooper Instruments? Are there other
manufacturers (Yahoo isn't much help here...)
I have considered magnetics, beam balances and so on but haven't come
up with a strategy that I am sure will work. Any ideas?
Brad
There was one in the Amateur Scientist columm in Scientific American
several years back. It used a gutted moving coil meter and a an op-amp
to servo the pointer back to center. Can't recall the resolution and
accuracy, but I think it did much better than .01 oz, the top end of 8
oz may be a problem though, and I'm not sure about the "robust" bit.
I could find the article if you are interested.
Barry Lennox
see: |
http://www.amasci.com/amateur/sciam1.html
martin
NOT EVEN YOUR
RINGTONES ARE SAFE. |
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Boris Mohar
Guest
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| Posted:
Fri Feb 11, 2005 7:08 pm Post subject:
Re: Measure Small Weight? |
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On Fri, 11 Feb 2005 21:38:06 +1300, Barry Lennox
<rianz.15.barryl@neverbox.com> wrote:
| Quote: | On 10 Feb 2005 01:15:15 -0800, "Brad" <bevernon@aol.com> wrote:
Anybody aware of some very inexpensive sensors or other devices that
can be used to measure weights of about 8 ounces to a 0.01 ounce
accuracy? I need the gizmo to be robust, reliable, linear and
monotonic.
I have looked at piezoelectric sensors but the ones from Honeywell and
SensorOne are way too pricey. The one's that aren't really expensive
seem to lack the accuracy or repeatability I want. Any idea on the
cost of the devices from Cooper Instruments? Are there other
manufacturers (Yahoo isn't much help here...)
I have considered magnetics, beam balances and so on but haven't come
up with a strategy that I am sure will work. Any ideas?
Brad
There was one in the Amateur Scientist columm in Scientific American
several years back. It used a gutted moving coil meter and a an op-amp
to servo the pointer back to center. Can't recall the resolution and
accuracy, but I think it did much better than .01 oz, the top end of 8
oz may be a problem though, and I'm not sure about the "robust" bit.
I could find the article if you are interested.
Barry Lennox
|
Looks like they have removed it. If you have it could you send it to me?
Regards,
Boris Mohar
Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca
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Brad
Guest
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| Posted:
Fri Feb 11, 2005 7:46 pm Post subject:
Re: Measure Small Weight? |
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Boris Mohar wrote:
| Quote: | On Fri, 11 Feb 2005 21:38:06 +1300, Barry Lennox
rianz.15.barryl@neverbox.com> wrote:
On 10 Feb 2005 01:15:15 -0800, "Brad" <bevernon@aol.com> wrote:
Anybody aware of some very inexpensive sensors or other devices
that
can be used to measure weights of about 8 ounces to a 0.01 ounce
accuracy? I need the gizmo to be robust, reliable, linear and
monotonic.
I have looked at piezoelectric sensors but the ones from Honeywell
and
SensorOne are way too pricey. The one's that aren't really
expensive
seem to lack the accuracy or repeatability I want. Any idea on the
cost of the devices from Cooper Instruments? Are there other
manufacturers (Yahoo isn't much help here...)
I have considered magnetics, beam balances and so on but haven't
come
up with a strategy that I am sure will work. Any ideas?
Brad
There was one in the Amateur Scientist columm in Scientific American
several years back. It used a gutted moving coil meter and a an
op-amp
to servo the pointer back to center. Can't recall the resolution and
accuracy, but I think it did much better than .01 oz, the top end of
8
oz may be a problem though, and I'm not sure about the "robust" bit.
I could find the article if you are interested.
Barry Lennox
Looks like they have removed it. If you have it could you send it
to me?
Regards,
Boris Mohar
Got Knock? - see:
Viatrack Printed Circuit Designs (among other things)
http://www.viatrack.ca |
The Scientific American article was a follow up to an earlier S.A.
piece. Both versions used gutted galvonometers, and the second was
much easier to use. That article is what got me thinking about trying
to weigh larger masses. The S.A. devices were microgram scales and
were incredible in terms of their capability. You could wet a piece of
thread, then watch the weight change as the thread dried out. Very
nice! They didn't explain how it was so incredibly accurate, but I
think they got a little help from the fact that that the drive circuit
kept the galvo constantly vibrating and the vibration could overcome
the friction in the bearings.
S.A. has removed all external links to this article. It is available
on the S.A. web site along with a hand full of other articles from the
Amateur Scientist. I don't have the link, but read the article a week
or so ago.
None-the-less, I'm looking for grams and a converted galvo is not
robust enough. I'm considering making a similar device using needle
bearings/jewel bearings with a more powerful coil. I need to lift
about 8 ounces maximum. If the original device can measure a few
micrograms I should be able to measure a few hundred grams....
Regards, |
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Daniel Haude
Guest
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| Posted:
Fri Feb 11, 2005 8:50 pm Post subject:
Re: Measure Small Weight? |
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On 10 Feb 2005 03:33:01 -0800,
Brad <bevernon@aol.com> wrote
in Msg. <1108035181.223214.217050@g14g2000cwa.googlegroups.com>
| Quote: | I am looking into the magnetic approaches, but as an earlier responder
pointed out, alignment is critical and slop is unacceptable.
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I'd go for the voice coil (loudspeaker) servo feedback approach.
Guaranteed to be linear, and cheap. I recall having seen it in Elektor
magazine several years ago.
--Daniel |
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Brad
Guest
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| Posted:
Sat Feb 12, 2005 5:06 pm Post subject:
Re: Measure Small Weight? |
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Daniel Haude wrote:
| Quote: | On 10 Feb 2005 03:33:01 -0800,
Brad <bevernon@aol.com> wrote
in Msg. <1108035181.223214.217050@g14g2000cwa.googlegroups.com
I am looking into the magnetic approaches, but as an earlier
responder
pointed out, alignment is critical and slop is unacceptable.
I'd go for the voice coil (loudspeaker) servo feedback approach.
Guaranteed to be linear, and cheap. I recall having seen it in
Elektor
magazine several years ago.
--Daniel
|
I'm leaning towards this approach. I looked at the Elektor site for
any construction article that seemed related and couln't find any.
They have them all online from 1998 and later. When was the article?
Any idea on the details?
Thanks for the suggestions everyone!
Regards, Brad |
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