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Combining/paralleling wheatstone bridges

Y

You Know Who

Jan 1, 1970
0
Hi

I have recently been told that you can combine a number of wheatstone
bridges (load cells) conforming a multipoint weight scale.

Are the bridges paralled direct or are the signals mixed with serial
resistors?

regards
Jens
 
J

John Larkin

Jan 1, 1970
0
Hi

I have recently been told that you can combine a number of wheatstone
bridges (load cells) conforming a multipoint weight scale.

Are the bridges paralled direct or are the signals mixed with serial
resistors?

regards
Jens

If you have, for example, a platform with 4 load cells, one on each
corner, and you want indicated weight to be independent of load
position, each load cell must be individually gain tweaked, so you
wouldn't want to just slap them in parallel. I've seen "mixing" pots
used here, but I'd imagine they would be a serious pain to adjust.

John
 
C

ck

Jan 1, 1970
0
John Larkin said:
If you have, for example, a platform with 4 load cells, one on each
corner, and you want indicated weight to be independent of load
position, each load cell must be individually gain tweaked, so you
wouldn't want to just slap them in parallel. I've seen "mixing" pots
used here, but I'd imagine they would be a serious pain to adjust.

John

I worked in a scale shop for awhile, we used juntion boxes similar to these
http://www.ricelake.com/docs/browse.php?categoryID=147

And yes they do have pots to *balance* the cells. Rather common in truck
scales. For truck scales to be certified legal for trade they need to pass a
section test to prove the same readings regardless of the position of the
vehicle on the scale. This is where *mixing the pots* is needed.

Unfortunately I never really bother to investigate the circuit design.

Chris
 
J

Jamie

Jan 1, 1970
0
You said:
Hi

I have recently been told that you can combine a number of wheatstone
bridges (load cells) conforming a multipoint weight scale.

Are the bridges paralled direct or are the signals mixed with serial
resistors?

regards
Jens
That is a common practice, we have hopper units that sit on
three load cells, they are all tied together into one signal.
with these cells, you simple zero each unit with the others
not plugged in. when completed, we just plug them all in afterwards.

they are all joint together via a network at which point, should be
balanced to a zero point. when ever any one of these units change it
alters the balanced and if one cell is much more than the other.
Basically, you get a very accurate reading with load shifting and so
on because the three cells will differentiate the value.

We do have another set up where each cell is a DeviceNet link, these
units are all combined via communications and talk to via an device
number to read, calibrate, zero etc.. these work good for a single
control process unit to indicate load imbalance if you wish to do so.
 
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