Someone know how a common cheap 4-wire load cell is made? I'm referring at one that it is in the cheap Chinese scale, like this.

In particular, using a multimeter, I would try to identify the structure of load cell for simulation purpose.

I know that there is the Wheatstone bridge under the load cell, but I'm unable to identify correctly the shape of it (eg how many strain gauges are in the load cell) and the resistor values.

What kind of measures is useful to identify this kind of load cell?

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    \$\begingroup\$ Question can easily be answered with a Google search. Should be closed - insufficient research. \$\endgroup\$ – Leon Heller Nov 5 '18 at 10:27
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    \$\begingroup\$ I'm sorry sir, but google tell me more and more thing. After good searching i'm unable to know how idenfity this kind of load cell. But If you are a google guru, please, link me some useful page, document or similar, because i'm a stupid man and i'm unable to find that i search. \$\endgroup\$ – Luca80 Nov 5 '18 at 10:38
  • \$\begingroup\$ On the page you linked, there's a documents tab, under which there is a link for "Getting Started with Load Cells". What gaps remain after you read that? [sparkfun: Getting Started with Load Cells] (learn.sparkfun.com/tutorials/getting-started-with-load-cells) \$\endgroup\$ – Chris Knudsen Nov 5 '18 at 13:18
  • \$\begingroup\$ @Christ Knudsen, I have already read this page. The problem is that this page speak in general terms and not into specific terms. This page not tell nothing about how to identify the load cell and what measure one should do for identify the bride resistors. Using a multimeter i measure two different resistor values, depending on what legs of the load cell i using to acquire the value. In this case how i identify the resistor value? Also, this tell me that the strain gauges used in my load cell aren't the same and maybe the number of they are two or four? \$\endgroup\$ – Luca80 Nov 5 '18 at 13:47

A typical 4 wire load cell has 4 resistors in a bridge.
They are wired so that opposing resistors are to experience the same strain and adjacent resistors are to experience the opposite strain. This results in the excited load cell being forced out of a balanced condition under load and a voltage to appear on the sense pair under load.

When measuring a load cell you can find opposite terminals by measuring the largest values between two terminals. This will be equal in value to the element resistance R=(R+R)||(R+R). If you measure across two adjacent terminals you should read a value of R'=R||R+R+R=0.75R.

If the top and bottom pairs are not equal in value you will have a much harder time determining the exact values as you will have to take more readings and possibly short out other terminals to gain enough known values to calculate the unknowns. It is certainly possible but less fun.

Once you have found the opposite pairs of terminals you need to provide a excitation current and then see which polarity the sense pair supplies and determine the gain of the bridge with applied maximum load. If you plan to use some cheap devices with little documentation then I would purchase a bunch, and test them to load and current and temperature destruction (dielectric insulation too), check the gain and resistance tolerance and yield and THEN if they meet your need I would order a lifetime supply hoping to receive the same type and redo the tests in case they are from a different batch.

If you need to reorder do so from a reputable source with a data sheet and pay for them from the profits of your first successful run.

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    \$\begingroup\$ your answer make sense to me. I know the load cell cable signatures, so i know what are the adjacent and opposite terminal. Also i obtain the same result of your formulas that are ~996 ohm for the opposite terminals and ~750 ohm for the adjacent terminals. Now this values make sense to me. I not have buyed this load cell, but i have obtained it from cheap chinese scale, so i haven't any documentation except the maximum scale loads. I need it for an university project. The main problem is modelling the load cell and make some simulation before design the conditioning circuit. \$\endgroup\$ – Luca80 Nov 5 '18 at 17:48
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    \$\begingroup\$ You can gain a lot of information about the excitation needs by examining how it was connected in the original circuit. \$\endgroup\$ – KalleMP Nov 6 '18 at 10:59
  • \$\begingroup\$ This is a bit complicated! The strain gauge is attached to the load cell by a white material (like silicone) so i can't see how the circuit connections are made. I can only measure voltage and resistance between the load cell terminals. \$\endgroup\$ – Luca80 Nov 6 '18 at 11:18
  • \$\begingroup\$ No need to expose the strain elements, search for pictures on the net if curious. I was suggesting measuring and inspecting the original circuit that was powering it to see what the drive voltage or current was. \$\endgroup\$ – KalleMP Nov 6 '18 at 11:28
  • \$\begingroup\$ Ah! ok, I can do this! \$\endgroup\$ – Luca80 Nov 6 '18 at 11:48

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