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Assessing ESL coatings
Assessing ESL coatings
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Old 18th July 2018, 09:37 AM   #1
bentoronto is offline bentoronto  Canada
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Assessing ESL coatings
Default Assessing ESL coatings

How do you assess the correctness of ESL diaphragm coatings? What tools or measurement strategies enable builders to know if their coating is suitable? How and to what degree does performance deteriorate when the coating isn't right?

B.
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Old 18th July 2018, 03:19 PM   #2
alexberg is offline alexberg
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Then you need to define what's proper and what's not.
1. Painted a stripe. Tried to measure, no contact.
2. Painted contacts using aerosol graphite through stencil.
3. Diluted to a proper resistance. Painted, dried, tried to remove by folding.
Coating stays no matter what was done mechanically to the coated film.
Measured thickness using angled cut and microscope.
BTW Rainbow exhibiting wet coat (read really thin one) was O'K resistance wise when dried.
Did not care about the rest. No longevity tests were performed.

Last edited by alexberg; 18th July 2018 at 03:22 PM.
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Old 18th July 2018, 04:05 PM   #3
bentoronto is offline bentoronto  Canada
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Assessing ESL coatings
Great ideas, thanks... using a fixed-sized stripe as a standard.

But what would be a sensible resistance for a stripe say, one cm wide and 100 cm long? How to make a super-meg-Ohm tester? Using high voltages?

Just how does sound quality deteriorate if diaphragm resistance is too high or low?

B.
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Old 18th July 2018, 08:32 PM   #4
lcsaszar is offline lcsaszar  Hungary
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Too high -> very slow charge build-up time, i.e. long time until full sensitivity is reached
Too low -> charge migration, leading to distortion (no constant charge condition)
Too high is always better than too low, and a plastic diaphragm will naturally adsorb moisture from air, this has less than infinite resistance.
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Old 19th July 2018, 12:29 AM   #5
alexberg is offline alexberg
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Yep. I've used 3kV and uA meter. 10 cm wide and 1 cm long. I tied black polyurethane foam from semi packaging as well pressed by heavy copper pieces to make contact reproducible. I think thin foam/felt under the film will promote contact with heavy copper electrodes the very same way so you can move contact fixture across the whole area. Later on, by a chance, I've borrowed Fluke 1550 isolation meter, with up to 10kV voltage.
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Old 19th July 2018, 01:37 AM   #6
bentoronto is offline bentoronto  Canada
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Assessing ESL coatings
More great details.

BTW, use of that conductive plastic foam sounds like a good way to make contact with the diaphragm in the final construction. If high resistance keeps the charge from "moving" around, then it must make sense to have a wide-area contact at the edges of the diaphragm to supply and re-supply the charge.

B.
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