Re: Milligram digital scales- Inexpensive vs. expensive scientific

From: Max Zaluska <flyezb_at_yahoo.com>
Date: Thu, 29 Jan 2009 03:01:47 -0000

You get what you pay for, and that doesn't include just scales. I'm not rich; don't get the
wrong idea. If you can't afford it; don't buy it, if you want it; buy the best. I bought $120
pliers with tungsten-carbide inserts, not only they have a 10year replacement warranty
but I bet I'll be talking about them and using them till I die.
I have the Acculab VI-1mg, and I usually weigh components 2-3 times to make sure I'm
getting consistent readings..

--- In Indoor_Construction_at_yahoogroups.com, "Bruce McCrory" <hbm55@...> wrote:
>
> After seeing the autrageously low price for the milligram scale being
> discussed, I checked to learn why there was such a variation in cost;
> then found more information about the current discussions. The
> digital scales, for all their ease of use, seem to have some problems.
>
> There appears to be two basics types of digital scale. The less
> expensive strain gauge type– currently in 2009, a low of $25 for
> 0.001 gram – and analytical scales using electromagnetic force
> sensors with a $300 starting price tag.
>
> The following was copied from a scientific scale sales site, and
> seems to account for some of the puzzlements we face when using
> digital weighing scales. Puzzlement over drifting readouts and
> constant recalibration are a couple.
>
> Strain gauge-
> "…Unfavorable features of a strain design include susceptibility to
> instability or drift (when the numbers on the display crawl) due to
> hysteresis and temperature coefficient characteristics. The reason
> why some manufacturer's select a strain gauge for a milligram scale
> is cost."
>
> Force coil, or electromagnetic force measuring sensor-
> "…Mechanically the sensor …..is a simple lever & fulcrum. One end of
> the lever holds the weighing pan where an unknown weight is placed.
> On the opposite end of the lever is a FORCE COIL suspended in a
> magnetic field (much in the same way a speaker operates). The
> displacement detector, and power amplifier produce an appropriate
> current to hold the lever balanced in the null position for any
> weight placed on the pan. The amount of current required to do this
> is proportional to the weight on the pan.
>
> "The MICROPROCESSOR monitors the current produced in response to the
> applied load to determine the magnitude of the weight…."
>
> The force coil type scales are generally sensitive to temperature and
> humidity.
>
> All scales of centigram and lower resolution should have breeze
> shields, to minimize external interference. There is more. Besides
> the above noted issues, a level vibration free surface, and
> particularly static electricity will affect the accuracy of both
> types. Static electricity will cause erratic readings. Instruments
> should be operated on a static dissipating surface (antistatic mat)
> Avoid the use of plastic containers for items being weighed. Never
> replace broken glass doors on instruments with plastic ones.
> Maintain humidity at 65% or more.
>
> Of course, until I read all these cautions, weighing as part of model
> building was actually fun to do; especially after converting to
> digital scales. Now, I wonder if it is really worth the trouble. … :(
>
> Bruce
>
Received on Wed Jan 28 2009 - 19:01:53 CET