🚀 go-pugleaf

In article <4145@ash31.UUCP> svoboda@motcid.UUCP (David Svoboda) writes:
>bill@videovax.tv.tek.com (William K. McFadden):
>> 
>> 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.
>
>Wait a second.  Think about this for a moment.  What EXACTLY do you mean by
>"compression get used up by the carpet"?  We are talking about forces here.

	I took one of these apart (the strain gage kind), and found
the load force was transmitted through levers to a calibrated, temperature
compensated (four lead) strain gage.  Those levers had a fulcrum near each
foot, and used the CENTER of the bottom cover plate as the fixed end
for the strain gage.
	So, if you support the scale on a carpet, the bottom plate is
bowed (by the carpet pressing in its middle), and the geometry of
the levers changes (by the bow angle).  The top plate was VERY heavy
plastic construction (I'd have thought steel would work better);
the bottom plate wasn't, so it would probably deflect considerably
on a thick rug.  
	Parenthetically, I found the electronic construction/design
to be quite adequate.  The mechanical design, though, was only 
so-so.  I disassembled the thing because someone had stepped on it
too hard, and broken the strain gage.  It looked like that was
guaranteed to happen by the attachment mechanism of the strain
gage (too high stress at the dowel pin onto the foil of the gage).

			John Whitmore