Electronics > Projects, Designs, and Technical Stuff
Design for a Homebrew Paint Thickness Tester
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StuartA:
From what I can find out, the "banana" gauge was a device which used to be made by Elcometer, but their website makes no current mention of it. It worked using a magnet and a mechanism for detecting how much force was needed to pull the magnet off a painted surface. Your guess would probably be better than mine as to why it seems to have been replaced with electronic gauges.

Paint on modern cars seems to be typically around 100um (4 thou), consist of three layers and I'd guess that you really want a resolution of ~10um. This may be thinner than on infrastructure like pipelines and might be asking a lot of a banana gauge?
techman-001:

--- Quote from: StuartA on October 01, 2019, 10:36:50 pm ---From what I can find out, the "banana" gauge was a device which used to be made by Elcometer, but their website makes no current mention of it. It worked using a magnet and a mechanism for detecting how much force was needed to pull the magnet off a painted surface. Your guess would probably be better than mine as to why it seems to have been replaced with electronic gauges.

Paint on modern cars seems to be typically around 100um (4 thou), consist of three layers and I'd guess that you really want a resolution of ~10um. This may be thinner than on infrastructure like pipelines and might be asking a lot of a banana gauge?

--- End quote ---

I imagine that the 'banana guage' could work very well  providing it had the sensitivity needed, which means precision bearings in the force balance mechanism and so on. Cheap and nasty bearings would mean a lot of non repeatability.

Battery less for sure and probably simple but also fragile like all sensitive mechanical instruments I'll wager. Once dropped it was probably useless.

A perfect case for robust and cheaper electronic device replacement.
MosherIV:
Hi. If you had good results with the inductive approach, why have you stopped?

I think that the inductive appraoch needs individual tunning/calibration for each inductor.
This means it is not cost effective to mass produce but perfectly ok for individuals to build at home.

Interresting to see so many approaches to the problem.
techman-001:

--- Quote from: MosherIV on October 02, 2019, 06:51:03 am ---Hi. If you had good results with the inductive approach, why have you stopped?

I think that the inductive appraoch needs individual tunning/calibration for each inductor.
This means it is not cost effective to mass produce but perfectly ok for individuals to build at home.

Interresting to see so many approaches to the problem.

--- End quote ---

I'm quite sure the 'Banana Guage" would also need individual calibration due to manufacturing tolerances including magnet strengths. In this regard it would be no different to a inductive meter needing calibration.
Kleinstein:
The inductive and also some other meters would need individual calibration. This may be needed just once but possible even later. By providing a piece of coated steel, the calibration could be done by the user, possibly just before use to also compensate drift with aging. This would not add much costs.


I did a quick test with a tape head:  it did not work  :(, at least not really sensitive, but only some 10% change in inductance (tested at 1.6 kHz).
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