# Load cell and wheatstone bridge

Discussion in 'Beginner Electronics' started by James Dill, Sep 29, 2006.

1. ### James DillGuest

Need therory help.!!!!!

I work with load cells to weigh the weight in hoppers. These load cells are
wheatstone bridge-type strain gauges. I can find the formulas to work out
the resistence and voltage drops of the gauges. But, when you parallel the
load cells, the voltage output is addative or as the scale book says "summed
together". This is where the problem lies...... I have never run into the
situation where parallel voltages are added togetrher in DC this only
happens in series circuits like voltage dividers. Can someone tell me how
or where to find the information about summing parallel voltages together.
Thanks for any suggestions to this problem.

P. S. I have Googled this problem and come up with a blank.

2. ### James DillGuest

These are electrically in parallel not mechanically. I built two Wheatstone
Bridge circuits out of resisters. After applying voltage to one of these, I
had 15 MV output. I then soldiered the second bridge on top of the first
bridge and I got a 31 MV output. I then soldiered 4 resisters between the
bridges to make a box like circuit. I was looking for some kind of strange
recirculating curcuit. I came up blank.

I know the two bridges in parallel double the output voltage or summed as
the scale books say but I have no ideal why.

3. ### James DillGuest

Yes I agree with your above equations but I think I have led you off track.
My experimental circuit was to just prove that the output voltages of the
bridges were additive (yes I used 5% resistors) a balanced bridge should
have 0 output. The two bridges had the same basic current draw and roughly
the same output. When I paralleled them, the current was additive and the
voltage was also????

Please look at the following link. This is similar to the summing box that
I used. There are no active parts. All the connections are in parallel on
the back of the circuit board. We have three load cells in parallel on our
scale. If one of them is removed the other two will continue to sum
weight??