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| Design for a Homebrew Paint Thickness Tester |
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| StuartA:
I’d like to own a Paint Thickness Tester for use on car paintwork. There are some very cheap ones available on-line (using ultrasonics), but they almost certainly don’t have the resolution required to be very useful. My guess is that the ones I’d like to own cost more than I want to pay, but my gut instinct is that something adequate could be built at home for not very much money at all. That lead me to search for detailed information on how they work, and ideally, a design to construct one. The best I’ve been able to do is find a few interesting patents, which reveal quite a variety of designs, working at both AF and RF frequencies and measuring either frequency shift, or the extent of coupling via eddy currents. I suspect that, starting from scratch, this could make an interesting but very time consuming project. I wonder if anyone has ever seen a design for a homebrew thickness tester? S |
| MosherIV:
Hi Firstly, no I have not seen any home brew thickness testers. I worked in the NDT test industry in the past, in ultrasonics. The thickness meters have become commodity items, hence they have dropped in price. The cheapest way to do thickness measurement is with ultrasonics, hence you will not find commercial solutions with rf. You can certainly get resolution down to .01mm with a high ultrasonic freq, as far as I know. If by "very cheap" you mean less than £80, yes I would avoid it. Anything decent will be at least that price. Check the unit can do the resolution (thickness) that you need first. |
| StuartA:
Thanks for that insight. As you may know, there are ultrasonic testers on eBay for £10, but the claimed resolution is nowhere near what you need for paint. My impression is that anything less than ~£100 won't be worth having. |
| Conrad Hoffman:
If you always shoot the same kind of paint, and are willing to do some tests for calibration, a capacitance measurement through the layer might do it. Put a 20 mm square plate or similar against the surface, then measure to the metal behind. Yeah, only works with metal, but the resolution should be quite good. The downside is the dielectric constant of the dry paint would have to be the same, and that might change with color and the degree of dryness. If it could do the job, the circuit could be a simple bridge with a calibrated pot. |
| tunk:
Whey not get one of the cheap ones and see if you can hack or calibrate it? |
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