# Connecting 4 load cells in parallel

I have 4 strain gauge load cell to calaculate actual weight.I want to use summing method for 4 output signals. I searched at internet for summing box schematic I found this pic Now if V1 , V2 , V3 , V4 are the output signals for each load cell Why connecting them in parallel like that will make the resulting volt = (V1+V2+V3+V4)/4. ?

• Consider each bridge as a Thevenin source. Then look at what will happen to the output when one generates a signal with them all paralleled. Commented Mar 6, 2020 at 20:21

I have also found many documents related to Junction Box or Summing Box for load cells that state that connecting the bridges in parallel is the way for averaging the signals, but I found no one that provided an explanation of the working principle for this.

Motivated by what Phil G pointed about using Thevenin equivalent circuit and as I found some authors that also suggest the same as this link, I decided to follow the suggested path for the following full-bridge circuit:

First find the Thevenin equivalent circuit as seen from Sig+ and Sig-

Applying the following simplification: ∆R << R ⇒ RTH ≈ R as in this Application report

When connecting the equivalent circuits in parallel we can solve and find the equivalent output voltage

As a final result we have that Vout=Vext*(ΔR1+ΔR2+ΔR3)/(3*R), which reflects the relationship between the output and the average of the ΔRs from all the bridges.

• because each gauge load cell will have 1/4 of the load How can that be known to be true? If you have a stiff table surface, placing the weight anywhere on the table should give the same sum of all cells. But, moving the weight will distribute the contribution for each load cell differently. If the weight is completely over one cell, does it still get 25% or does it get 85%, or even more? How do we guarantee the load is evenly distributed, even if it is a set of unusual conditions? IMO, this is a big problem for calibration of sensors. Commented Sep 9, 2021 at 1:25