Disassemble a load cell?

[mrburnzie]

I would like to experiment with some strain gauges, but don't really want to wait months for an order to come from China.
I have a load cell at hand, and was wondering if anyone was successful by removing the white goo from the load cell and extracting the strain gauge?

A load cell like this: https://electropeak.com/pub/media/catalog/product/cache/fa232c603e0403143aafcf902b42df2f/_/s/_s_e_sen-13-045-1.jpg

[jonpaul]

DIY make thin PCB, see typical strain guage pattern, bond to any desired metal beam, sheet, extrusions.

Use 4 wire resistance measures or 6.5 digits DVM

Bon courage

Jon

[mrburnzie]

I want to measure on a length of 550mm, maybe even the 1.6mm standard size would be okay? What kind of performance can I expect from soemthing like this?
I haven't found any larger strain gauge for those dimensions.

[Kleinstein]

1.6 mm wire is rather thick and would mean very small resistance.

Just for demonstration one could try some thin (e.g. 0.2) constantan or manganin wire. The restance would still be relatively small (e.g. 10 Ohms range).

The train effect for metalls is relatively similar: a resistance change of about 2 times the strain.  So 0.5% of strain (which is about the maximum for a strong material) would result in 1% of resistance change. To avoid creepage and with softer maerials one may have to use less strain.

One usually uses a bridge with 2 or 4 equal resistors to compensate the temperature effect.

edit: The glue to attach the strain gages need to very strong and it would be very hard to remove them, with a large chance to damage the strain gage.

[mrburnzie]

Sorry, I meant 1.6mm thick PCB with a strain gauge pattern on it.

[Kleinstein]

Using PCB material has 4 problems:
1) The FR 4 material can show creepage / elastic relaxation
2) pure copper can not withstand much stress and will also plastically deform, so the maximum strain is limited (e.g. 0.01% or 8 m bending radius)
3) copper resistance is quite temperature dependent
    this could be partially compensated by building a bridge circuit, with resistors on both sides of the PCB.
4) the copper resistance is quite low  - so it would need a relatively fine wire pattern to get a reasonable voltage.

[jonpaul]

Hello again: in 60 sec found

$12 Amazon....Culler Strain Gauge Used in Mechanics Experiment for Material,

https://www.amazon.com/Culler-Mechanics-Experiment-Material-Industry/dp/B01FUNXN0K

 They are  stick on ready made strain guages,     on Mylar or Kynar?

  similar are used in   aviation and materials stress tests.

Not precision but fine for familizaration...

Jon

[mrburnzie]

Yeah, I found other ones too, I just wanted to see what can I make now without waiting for the shipping.

[Kleinstein]

With a PCB one may have to wait for the PCB to be made. With thin lines and double sided PCB etching at home is not that much fun.

[mrburnzie]

I guess ordering is the option here.