I'm thinking of a similar sort of thing.

But wouldn't you add the individual outputs to get the total?
If so - you may be able to add the strain elements together - depending on
what type etc they are - you'd need access to the individual strain arm so
this may be more difficult. If connected in parallel I guess you'd get some
sort of average but if very unequally distributed I think the accuracy may
go well off. - Not sure.
By using an analogue mux you should be able to get away with one amp and one
A/D anyway - and do the division? summing in software anyway.

Just comments - I haven't got any special knowledge of these things but I
have a project tucked away in the back of my mind to look at someday!

Richard

> -----Original Message-----
> From: Brent Brown [mailto:brent.brown@CLEAR.NET.NZ]
> Sent: Monday, August 16, 1999 12:15 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [OT] Load cell averaging
>
>
> Hi,
>
> I'm working on a new project that will be using 4 load cells to
> measure the weight of a piece of machinery during operation.
>
> I've seen weighing platforms that use a load cell on each mounting
> foot - presumably they just average the four readings to get the
> total weight eg. (A+B+C+D)/4 ?
>
> Can I minimise the electronics by putting the outputs of the four
> strain gauge bridges in parallel (maybe with some series resistors)
> and then just use one bridge amplifier and one ADC input on my
> micro? (Rather than 4 x bridge amps, 4 x ADC's)
>
> Would this affect linearity much?  My dynamic range of weight is
> very small, I'm looking to measure 0-20kg change (product) on top
> of a constant 500kg or so (the machinery itself), and 0.1 or 0.2kg
> resolution would be fine enough.
>
> Also, what are your favourite bridge amplifier's for a job like this?
>
> Hope these are simple questions to answer for people with
> experience here, and interesting for the rest of us!
>
> Thanks in advance, Brent.
>
> Brent Brown
> Electronic Design Solutions
> 16 English Street
> Hamilton, New Zealand
> Ph/fax: +64 7 849 0069
> Mobile: 025 334 069
> eMail:  brent.brown@clear.net.nz
>