On a 3-wire load cell that has a black , red, and white wire......... I would think if I ohmed out the resistance between the red and white or red and black or any combination there of, that I would see some kind of change in resistance when putting as much as 200 lbs load on the load cell.No change in resistance at all, so how does the load cell develop a voltage drop,even in the milli-volt range if there is no change in resistance as weight is put on the cell?

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• There is a change in resistance, but it's very, very, very small and not easily measurable with your normal mulitmeter. – brhans Jun 21 '17 at 21:12

I would expect that you found the largest resistance was red to black, with the white wire being more or less the centre tap of the total resistance.

Load cells are not designed to be measured as resistance. While the resistance does change with load, it is too small to be measured reliably, and certainly too small to be detected above the noise and digit resolution on a standard multimeter.

It is designed to be measured by a Wheatstone Bridge

Your strain gauge comprises the two resistances R1 and R2, one increases, the other decreases with strain. You supply R3 and R4, and they are nominally equal. The output voltage proportional to strain is taken across Vg, with a high gain low drift differential amplifier.

Changes of strain gauge temperature will affect both resistors equally, and will not be measured at Vg. Changes of excitation voltage across A-C will affect the gain of the measurement, but will not add an offset.

You have not shared the details of the load cell so its hard to comment on how much the resistance should change.

But usually, in the data sheet, it is mentioned that what is the minimum change in load that will cause a change in resistance.

And as @brhans mentioned in comment, the resistance is usually too small to measure through your normal multimeter, that's the reason Wheatstone's bridge is used to measure the change.

Probably you can look on this website for more details.