Measure Small Weight?

B

Brad

Guest
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
 
On 10 Feb 2005 01:15:15 -0800, in sci.electronics.design "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
ISTR moving coil loudspeakers, with an opto feedback system seemed
Click to expand...
like a good idea(at the time).


martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.
 
"Brad" <bevernon@aol.com> wrote in message
news:1108026915.441908.6750@f14g2000cwb.googlegroups.com...
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
Click to expand...
Another vote for a capacity based system - use the capacitance to vary the
frequency of an oscillator, don't try to measure it directly. If you use a
differential design of capacitor, then some of the errors cancel out to
first order. Getting the accuracy you want will not be easy - prepare for a
significant learning curve !

The other approach that might work is a servo'd torsion balance.

Dave





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"Brad" <bevernon@aol.com> wrote in message
news:1108026915.441908.6750@f14g2000cwb.googlegroups.com...
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.
Click to expand...

Mmmm... Interested in getting into the drug dealing business I see. Drug
dealers need scales that measure to around 0.01 "oh-zee" accuracy with a
maximum weight of around 8 oh-zees. Strangely there do seem to be legal
stores that cater to the "needs" of this part of society.
 
I read in sci.electronics.design that Brad <bevernon@aol.com> wrote (in
<1108035181.223214.217050@g14g2000cwa.googlegroups.com>) about 'Measure
Small Weight?', on Thu, 10 Feb 2005:
No, It is not for that type of activity. Why would you make such an
assumption about my motives? There are easier ways to obtain a scale to
measure that sort of stuff, I'm sure, than making a post to a news
group. Thank you very much!
Click to expand...
Look up 'joke' in the dictionary.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
On Thu, 10 Feb 2005 04:08:37 -0700, in sci.electronics.design "Fritz
Schlunder" <me@privacy.net> wrote:

"Brad" <bevernon@aol.com> wrote in message
news:1108026915.441908.6750@f14g2000cwb.googlegroups.com...
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.


Mmmm... Interested in getting into the drug dealing business I see. Drug
dealers need scales that measure to around 0.01 "oh-zee" accuracy with a
maximum weight of around 8 oh-zees. Strangely there do seem to be legal
stores that cater to the "needs" of this part of society.

Just because he is measuring in ounces, Does Not mean he is a drugs
Click to expand...
dealer (around here they measure in KG)




martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.
 
On Thu, 10 Feb 2005 15:43:58 GMT, in sci.electronics.design
donald@pearce.uk.com (Don Pearce) wrote:

snip
Pearce Consulting
http://www.pearce.uk.com
Kgs are for the bottom feeders here. You should see when a boat gets
lost, loads of little RIB's scouring the sea for contraband. One
kitesurfer found some dope floating in the sea, but it was too heavy
to carry to shore.

Ah - we're obviously not talking about the white stuff, then.

d

Pearce Consulting
http://www.pearce.uk.com
Click to expand...
Nope, I'm no longer in the TV biz, so no more temptations.
But going back to the OP, I tried to find the SciAm/amateur scientist
article about a DIY microbalance(it used a mA meter, an excellent
article)

All deleted AFAICS, bastards


martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.
 
On Thu, 10 Feb 2005 11:54:55 +0000, John Woodgate wrote:

I read in sci.electronics.design that Brad <bevernon@aol.com> wrote (in
1108035181.223214.217050@g14g2000cwa.googlegroups.com>) about 'Measure
Small Weight?', on Thu, 10 Feb 2005:
No, It is not for that type of activity. Why would you make such an
assumption about my motives? There are easier ways to obtain a scale to
measure that sort of stuff, I'm sure, than making a post to a news
group. Thank you very much!

Look up 'joke' in the dictionary.
Click to expand...
With or without the quotes? ;-)

Cheers!
Rich
 
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
Click to expand...
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
 
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.
Click to expand...
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
 
Daniel Haude wrote:
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
Click to expand...
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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