We have load cell with three wires (black, red, blue) coming out of it. It looks there’s a strain gauge between each pair of wires:

black —/\/\/\— red: ~1kohm

blue —–/\/\/\— red: ~1kohm

black—-/\/\/\—blue: ~2 kohm

Moreover, the resistances change when we compress the load cell. In the following photographs, you can see a circular load cell, and it gets covered with a blue clamp – which is what I am using to exert a force.

It looks like the resistance of the black–red gauge increases on compression, but the blue—red’s decreases. Similarly, if we put both these resistors / strain gauges in series, and put 5 volts across them, we find the voltage drop across one to increase, and the other to decrease, when we apply compression!

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From our ME buddy, consider two wires, one normal, and the other pre-strained, such that applying force would strain the first one while relaxing the second! That’s one way to think about why one of the resistances goes up, and the other goes down.

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