from:larrybsp@aol.com (Larry Stark)
Years ago I worked in the auto industry developing test
instrumentation. In short you'll be lucky to get 5% accuracy and
repeatability out of portable scales.
Although I haven't taken a set apart I'll bet they use strain gauges in a
wheatstone bridge configuration for temperature compensation. This method
goes back years
and is subject to all kinds of errors. Any instrument tracable to recognized
standards
has to be calibrated at least once a year. I'll bet the scales we use have
never been recalibrated. The scale accuracy is also subject to leveling,
crudely done if at all at a divisional. Positioning of the wheel on the
center of the scale effects accuracy. I could go but you get the point. You
are NOT going to get laboratory results with
portable scales that are handled like hammers, not delicate instruments.
FWIW.
Larry
In a message dated 5/6/02 4:52:55 PM Pacific Daylight Time,
john@harlie.idsfa.net writes:
> Subj:Re: scales
> Date:5/6/02 4:52:55 PM Pacific Daylight Time
> From:<A HREF="mailto:john@harlie.idsfa.net";>john@harlie.idsfa.net</A>
> To:<A HREF="mailto:ba-autox@autox.team.net";>ba-autox@autox.team.net</A>
> Sent from the Internet
>
>
>
> On Mon, May 06, 2002 at 07:15:20PM -0400, ERito@aol.com wrote:
> > i think that it is incredible that we would demand a 1/2% repeat
> > accuracy from a portable sale. we are talking lab accuracy here in
> > something that gets hauled from place to place.
>
> What prevents a portable scale from having good accuracy? I don't
> think that it's at all incredible. It seems like it's the quality and
> design that are important to accuracy, and not the size.
>
> If they're going to penalize people for errors that are below the
> repeatability/accuracy of the scales, then they need to measure and
> publish the error range for the scales that they are using. If not,
> people are going to trust that the scales are accurate to the last
> decimal place on the display: 1 pound.
>
> Or do you expect each competitor to figure out how good the scales are
> on their own? If I were in that position, I'd weigh my car 5 times on
> friday afternoon, 5 times on friday night, 5 times saturday morning,
> and 5 times just before I ran on Saturday. People might start to get
> annoyed.
>
> If a company made a scientific instrument that read out to 3 decimal
> places but was only good to 2, their customers would crucify them,
> unless there were a plaque on the front that said "+/- 0.005"
>
> --
>
> john@idsfa.net John Stimson
> http://www.idsfa.net/~john/ HMC Physics '94
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