Path: utzoo!attcan!uunet!ns-mx!iowasp.physics.uiowa.edu!maverick.ksu.ksu.edu!zaphod.mps.ohio-state.edu!math.lsa.umich.edu!sharkey!mailrus!hellgate.utah.edu!croc.utah.edu!gunderse From: gunderse%croc.utah.edu@cs.utah.edu (Eric Gundersen) Newsgroups: sci.electronics Subject: Message-ID: <1990Jul20.100536.445@hellgate.utah.edu> Date: 20 Jul 90 16:05:36 GMT Lines: 32 References: <5907@videovax.tv.tek.com> <4145@ash31.UUCP> <3861@kitty.UUCP> Sender: Eric H. Gundersen (gunderse@cs.utah.edu) Organization: University of Utah CS Dept Keywords: Digital Scales Subject: Re: Electonic scales question... >stress will most likely cause an erroneous weight reading due to >spurious stress and/or deformation imparted upon the spring mechanism >and/or LVDT or load cell in the case of an electronic scale. In regards to the hum mentioned in the first aricle, I took apart our GE dig. scale at home and took a look. Its "load cell" (or whatever you want to call it) consisted of 2 parallel stretched wires with a thin metal strip placed across these wires. At each end of this metal stip there was a coil that was connected to the electronic circuitry. When the scale was turned on by standing on it, the metal strip vibrates (like a paddle laying across a rocking canoe. A lever system stretches the wires so that the tension of these supporting wires is proportional (or at least related) to the pressure on the scale. Anyway the final effect is that the frequency of this vibrating strip varies depending on the weight on the scale. Most probably one of the coils forces this vibration and the other is a sense coil. It seems that the digital stuff (mostly built into the LED display module) is just a frequency counter sort of circuit. Looks like someone did some real engineering to make it work. Just thought it might be of interest. Eric Gundersen PS my scale also says not to use it on the carpet. I wondered why it said that too.