Re: Effect of Moon on balance -- electronic balances

[Bernard Cleyet <anngeorg@PACBELL.NET>]

there's more.  Electrical "balances"  these balance the weight against a
force generated by a current.  One may make a crude one from a d'Arsonval
meter.

more on the so called electronic balance (possible to be electrical balance
if the detector has a high output).

The one's I've seen bend or stretch a beam and an attached motion
detector.  The one I've disassembled uses a resistor whose resistance
increases when stretched (Sr. moment here), therefore, analog.  If one
placed it in series with a d'Arsonval meter and a battery it would be
electrical.  I doubt if any are so connected, instead an a2d chip is used
and an LCD.  I don't doubt that an optical encoder could also be used in
that case it would be completely digital instead of hybrid.

bc who thinks the term "balance" should be reserved for mechanical direct
comparitor ones only, e.g. equal arm, JC's "vertical", etc.  In HS chem &
physics, our knuckles were rapped (figuratively) if we confused them.


Michael Edmiston wrote:

> I disagree with John Clement's assertion that an electronic balance is
> not a balance.
>
> The electronic balance and the equal-arm balance are almost the same
> thing.  The difference is the electronic balance has a temporal
> displacement and the equal-arm balance has a spatial displacement.
>
> The equal-arm balance compares two masses as the same time, but at
> slightly different locations.  The electronic balance compares two
> masses at the same location, but at slightly different times.
> .
> I make two assumptions here... (1) By "balance" we mean we are making a
> mass comparison.  We are comparing unknown masses to standard masses.
> (2) The electronic balance is calibrated with standard masses at the
> same location the balance is used.
>
> I don't see any reason to prefer one method over the other in terms of
> physics principles.  In terms of making accurate mass comparisons the
> electronic balance might be preferred because it is faster and more
> likely to be well calibrated.
>
> Electronic balance manufacturers recommend calibration whenever the
> balance is moved, whenever it loses power, and at regular intervals even
> if it has not been moved or has lost power.  If this advice is followed,
> the electronic balance probably makes better mass comparisons than an
> equal-arm balance.  This is because equal-arm balances take long enough
> to calibrate that people don't do it.  They check it once and forget
> about it.  I check our electronic balances roughly monthly, or whenever
> they are moved.  Also, the electronic calibration can easily check for
> linearity as well as accuracy at a fixed point.  The linearity of an
> equal-arm balance can be checked and adjusted, but often is not.
>
> Also note that an electronic balance will work just fine on the moon if
> calibrated on the moon...and if the manufacturer's software does not
> detect an error.  Some balances indicate an error condition if they call
> for a particular calibration mass and you give it a mass that produces
> significantly different results than it expected.  If your balance asks
> for a 1000g calibration and you give it 160g and it takes it, then your
> balance will work just fine on the moon.
>
> If your electronic balance will not accept calibration masses that give
> only 1/6 the response of the anticipated response, then your balance
> won't work on the moon.  But this is not a physics problem.  It is a
> software problem.  If this is not clear, e-mail me and I will explain
> how electronic balances work and why software sometimes limits where
> they will work.
>
> Michael D. Edmiston, Ph.D.
> Professor of Physics and Chemistry
> Chair of Sciences
> Bluffton College
> Bluffton, OH 45817
> (419)-358-3270
> edmiston@bluffton.edu