Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!ucsd!pacbell.com!pacbell!sactoh0!pacengr!americ!erk From: erk@americ.UUCP (Erick Parsons) Newsgroups: sci.electronics Subject: Re: Electonic scales question... Message-ID: Date: 24 Jul 90 23:53:22 GMT References: <25815@unix.cis.pitt.edu> <5907@videovax.tv.tek.com> Distribution: na Lines: 55 >In article <5907@videovax.tv.tek.com> bill@videovax.tv.tek.com (William K. McFadden) writes: >In article <25815@unix.cis.pitt.edu> fmgst@unix.cis.pitt.edu (Filip Gieszczykiewicz) writes: >> 2) I read in Consumer Digest of a advertising scheme that >> some companies used in similar scales. Seems some >> claimed that THEIR scales could be used on carpets. But >> in the fine-print stated otherwise, WHY? Mine seems to >> work on a carpet but the directions specify a hard, level >> surface, why? >It seems that since the carpet has a springy pad underneath, the scale will >read too low. This is because the scale will only measure the compression of >its internal spring, and some of that compression gets used up by the carpet. >Now, if the scale had pointy feet on the bottom, it would have less carpet to >compress, hence giving a more accurate reading. More than likely it is the way all scales are designed or at least the majority of them anyway. Scales usually have 4 pivot points on them to collect weight info from the platform that you stand on. These pivot points are usually reducing in nature (similiar to the way a lever makes it easier to lift a boulder- but backwards :-). The pivot points are at each corner of the platform and are in themselves miniture scales. The trick in weighing is to sum the weight on the four corners and produce a consistant weight to (in the case of an electronic scale) a load cell. If the scale is not level there will be more force applied to 2 of the pivot points. In manufacturing bathroom scales the ratios of the individual pivot points cannot be cheaply calibrated to each other so there will almost always be a differant weight reading were the weight concentrated on any individual corner. When a scale is placed in an environment where it is possible for the level to change depending on weight distribution on the platform there will always be a differance in readings due to the mismatched corner calibrations. The only way to overcome this is to make sure that the scale is perfectly level at all times and insuring that weight distribution on the four corners is consistant. Commercial scales are overseen be the munincipalities that be (Weights & Measures) and are adjustable at the individual corners. The corners MUST be within .1% tolerance of the wieght applied on it. The test wieght is usually about 25% of the full scale rating of the platform. Those that don't will be repaired OR put out of service until the repairs have been performed. -- -------------------------------------------------//------------------------- (ames att sun)!pacbell! ----> sactoh0!pacengr!americ!erk Multitasking, ucbvax!ucdavis!csusac! --/ // Never leave uunet!msac! -/ Erick Parsons \Sacramento Ca Home Without it --------------------------------------------\X/----------------------------- Please Don't Wait...