Oh my goodness, Bruce, the bubble is burst <Grin>
LeRoy Cordes
AMA 16974
Chicago, IL
In God We Trust
On Wed, 28 Jan 2009 22:20:40 -0000 "Bruce McCrory" <hbm55_at_comcast.net>
writes:
> 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
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>
LeRoy Cordes
AMA 16974
Chicago, IL
In God We Trust
____________________________________________________________
Get free information on the latest in steel buildings.
http://thirdpartyoffers.juno.com/TGL2141/fc/PnY6rw29rwh8Ne43Oywy24FvKvN9cuvXD3trw8Kxz8VTO0x8i9l3t/
Received on Thu Jan 29 2009 - 11:47:43 CET