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I see that there are "pinless" moisture meters on the market, e.g., http://www.omega.com/pptst/HHMM257.html that look like this

enter image description here

My understanding is that they measure the amount of reflected RF. Perhaps, it's because liquid absorbs RF. However, different materials absorb RF differently - how could this type of measurement be reliable?

Also, why do they use a round RF transceiver rather than a dish for receiving?

Thanks

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  • \$\begingroup\$ Best moisture meters I ever used uses TDR - time domain reflectometry. A pulse is sent, then the DSP process data from RF reflection. Quite expensive device, don't believe the one on the picture uses TDR. \$\endgroup\$ – Marko Buršič Jan 14 '16 at 9:11
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    \$\begingroup\$ That fancy looking rod and ball just scream "Marketing thinks you'll believe anything!". \$\endgroup\$ – Olin Lathrop Jan 14 '16 at 12:09
  • \$\begingroup\$ Take a look here wagnermeters.com/flooring/wood-flooring/pin-moisture-meter \$\endgroup\$ – johnnymopo Jan 14 '16 at 15:56
  • \$\begingroup\$ The "shiny mystery ball" makes it look like something out of an esoterics magazine, but this seems to be a serious device. The local building inspectors wield those (yes, I initially thought this was a hoax). They are meant for "building materials" (i.e. concrete) only. You have to preselect for the known material to analyze. The glossy brochure calls the principle "capacitive high-frequency measuring method", see for example this selection at gann.de. The ball is likely to be just an electrode (one side of a capacitor). \$\endgroup\$ – David Tonhofer Jun 10 '17 at 18:04
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As it happens the SignalPathBlog recently looked at a different moisture detector. That one uses a capacitive sensor (just a plate of metal) and detects when it is near a conductive object which could be something that contains moisture.

This detection probably works using an oscillator circuit which would change frequency when the (coupled) capacity of the sensor plate changes.

Although the device you show looks very different from the FLIR device I expect that it works in a similar way. For both it is a relative measurement so it is only usefull to find wet and dry areas on the same material.

I also think this has nothing to do with RF, the steel rod an ball may look fancy but it does not look like an antenna to me.

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As far as I know The meter you're showing doesn't necessarily have anything to do with RF. What the picture is showing is this if I'm not mistaken. It consists of two bulbs, wet and dry. The way it works is below (copied from Wikipedia):

At temperatures above the freezing point of water, evaporation of water from the wick lowers the temperature, so that the wet-bulb thermometer usually shows a lower temperature than that of the dry-bulb thermometer. When the air temperature is below freezing, however, the wet-bulb is covered with a thin coating of ice and may be warmer than the dry bulb.

Cheers!

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  • \$\begingroup\$ I don't think that is how it works. The product write up says: "High frequency sensing technology" and can measure the moisture content below the surface of a solid material such as wood. \$\endgroup\$ – Icy Jan 14 '16 at 8:40
  • \$\begingroup\$ You have big imagination:) \$\endgroup\$ – Marko Buršič Jan 14 '16 at 9:19

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