Moisture meters are (not?) capacitance meters? or radio transceivers? - SailNet Community

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Old 12-10-2011
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Moisture meters are (not?) capacitance meters? or radio transceivers?

I don't mind if there's a man behind the curtain, I just want to know what he is capable of doing.

So on the one hand Im told that moisture meters for wood and FRP boats are :just: capacitance meters, of unspecified range. Including the Electrophysics ones.

But on the other hand I've seen comments that they are not capacitance meters, but rather they broadcast a small radio signal and look for the attenuation caused by mousture in the return signal path.

For all I know, either scheme might work. But I'm curious to know if anyone has "for sure" knowledge of what's done behind the curtain. And especially if anyone like Maine Sail, who has the meter and probably has a multimeter with capacitive scales on it as well, has ever compared the two, getting a result like "ell, the EP says :dry: when the cap meter says <50mfd and it says :wet: when the cap metere shows >200mfd, there are correlations.

I'd hate to waste money on an EP meter only to find my purpose built capacitance meters alreay could do the same job, and do it with digital numbers instead of waving a needle.

My iPhone S5 has a moisture meter built in, but I'm under NDA to Apple not to discuss it or use it until June 8th of next year, so that won't hel at all.

Anybody? Got the real skinny, or the two tools and an hour to do some compares?
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Old 12-11-2011
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would be interested in this information myself...
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Old 12-11-2011
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I'm sure MS will chime in here.. from some very basic research it looks like they use a resistance measurement for the pin styles (obviously not used on marine surveys) and a somewhat vague 'electromagnetic wave' technique which could technically range from ultrasonic to infrared.. some of the literature I found seems to be working on a backscatter principle - ie moisture reflecting emissions back to the source, the amount of backscatter inferring moisture presence...

No doubt the manufacturers feel their technique is proprietary and are unwilling to share details.
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Old 12-11-2011
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"No doubt the manufacturers feel their technique is proprietary and "
Well, 20 years ago a capacitance meter was an expensive piece of electronics. These days it is just one more function in a $10 multimeter...so I can understand that someone might not want to put themselves out of business.
Kinda like the magic lotions you can add to motor oil. :-)
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Old 12-11-2011
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I've worked with many different meters over the years, Take a look at my "Moisture Meter Mythology". it might help explain things.
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Old 12-11-2011
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Thanks, boatpoker.

Small brass hammer? Other than rough antiskid, I've used two fingers on my right hand, the same ones that do studfinding in plasterboard.

I suppose the real answer is to gut a microwave oven. Apply the business end to the hull and see if steam comes out. No steam? No swelling? Dry core. :-)
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Old 12-11-2011
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Not sure if it is the same device you are talking about but we use moisture meters at my jobsites, generally to determine if a substrate is dry enough to paint. The devices I'm familiar with have two probes that you stick in to the substance to be measured and measures capacitance between the two points. I believe that a multimeter can be used to the same effect with the proper offset for ohms to damp conductivity.
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Old 12-12-2011
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I borrowed an EP meter and a Ryobi meter a couple of years ago. So what I'm about to say is based on some limited actual field experience.

You need the EP one if you want to make quantitative comparisons with the results that surveyors give (since they all use EP meters). All capacitance devices need to be tuned for different depth of penetration into different materials, and you'll never match the EP results unless you use the EP meter.

For general non-quantitative use, I've used a household studfinder to track down moisture. It works on the same capacitive principle as the pinless moisture meters. I found the patent numbers stamped on the units and pulled up the patents to verify how they work. So while they may be "proprietary" (as in protected by patents), their designs are not totally secret.

If you want somewhat more quantitative results (but still won't duplicate the EP results), I found the Ryobi capacitive moisture meter ($50 at Home Depot) to give nicely repeatable results. You'll get reliable, repeatable numbers, but they will be different numbers from what the EP gives you. The nice thing about having the numbers is you can sometimes follow the gradients to the source of the leak - just like you follow the gradients to find a stud in a wall.
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Old 12-14-2011
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I have a CT-33 unit that was invaluable when hunting for a boat and has paid itself off many times over by finding a problem early after I bought my boat. It certainly appears to be a capacitive device. It is very easy to use and the results are obvious. I know the condition of my decks and hull...without the meter you have no idea until a problem gets serious.

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Old 12-14-2011
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Quote:
Originally Posted by RhythmDoctor View Post
I borrowed an EP meter and a Ryobi meter a couple of years ago. So what I'm about to say is based on some limited actual field experience.

You need the EP one if you want to make quantitative comparisons with the results that surveyors give (since they all use EP meters). All capacitance devices need to be tuned for different depth of penetration into different materials, and you'll never match the EP results unless you use the EP meter.

For general non-quantitative use, I've used a household studfinder to track down moisture. It works on the same capacitive principle as the pinless moisture meters. I found the patent numbers stamped on the units and pulled up the patents to verify how they work. So while they may be "proprietary" (as in protected by patents), their designs are not totally secret.

If you want somewhat more quantitative results (but still won't duplicate the EP results), I found the Ryobi capacitive moisture meter ($50 at Home Depot) to give nicely repeatable results. You'll get reliable, repeatable numbers, but they will be different numbers from what the EP gives you. The nice thing about having the numbers is you can sometimes follow the gradients to the source of the leak - just like you follow the gradients to find a stud in a wall.
Every surveyor I know ( I know a couple of hundred) uses a capacitance meter. Relative readings are all you are going to get on a survey. There is simply no way to get quantative results without weighing and burning a piece of the boat. After over 2500 surveys, I have yet to finds someone who would let me do that

I'd suggest you google The "Code of Practice for the Measurement and Analysis of the Wetness of FRP Hulls" ( * International Institute of Marine Surveyors (1998) Witherby & Co., London, 17p. )
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