Gadianton wrote:Thanks for the additional information Ben. I was struck most by this line:
"So he used a magnetic eddy current thickness gauge to measure the thickness of the papyri. His measurements - both in the width of the winding of the papyri"
I think one guy alone in a room with a ruler would be a prime target for confirmation bias, and then if using this thing goes beyond point and click, that just makes it worse.
I've sent a message to Dr. W in case he can weigh in on how these things work.
Dean Robbers,
This post is in response to your request for a consult from the Physical Sciences Department (such as it is). Realizing that the following is more than anyone not working in the field would ever wish to know about eddy current devices (ECDs), I've marked the sections so one can read only what interests them.
As you clearly surmised, using a magnetic eddy current device of any description to directly determine the thickness of a non-conductive, non-magnetic material such as paper or papyrus (both dielectrics) would be quite an achievement. Papyri are neither magnetic or conductive, so it is difficult to see how such a device could be used as claimed. I have never heard of anything like this before and so went to the literature for a quick look.
Not only could I find no literature regarding the used of ECDs for direct thickness measurement of dielectrics alone, I cannot see why one would even attempt such a feat when there are several good contact methods for making such measurements. A good quality micrometer and a set of feeler gauge standards would be a great start.
That said, here are some of the applications for which eddy current devices (ECDs) are indispensable.
Eddy Current Separators used in Recycling: Eddy current equipment for physically separating non-ferrous metals (mainly aluminum cans) from ferrous metals and from non-metals such as paper and plastic are a mainstay of the recycling industry.
We consult for one of the largest recyclers of aluminum in North America and they use eddy current for separating shredded aluminum from all the dirt, paper and plastic packaging that rides along in the bales of crushed aluminum cans they receive for re-melting.
These separators are essentially conveyors with a rapidly rotating magnetic drum inside the endcap roller. The rotating magnet induces a current in the thin aluminum shreds as they approach the endcap roller. The induced electric current creates a magnetic field (Lenz's law) that opposes the field produced by the rotating drum. The resultant repulsive force kicks the aluminum particles upward and forward over a gate into a bin while the non-metallic material falls straight down by the force of gravity as it leaves the conveyor. The ferrous metals are attracted to the magnet and only fall off the conveyor belt when no longer in the magnetic field of the roller. Thus, these machines effectively separate non-ferrous, non-metallic, and ferrous materials into three separate bins, and can do so at a surprisingly rapid rate. (See the link below)
http://www.buntingeurope.com/magnetic_separation_and_metal_detection/magnetic_separation/eddy_current_separators.aspxEddy Current Devices for Non-Destructive Testing: ECDs of a different type are used to detect corrosion or fatigue cracking in non-ferrous metal structures such as aluminum aircraft components. These ECDs are comprised of a probe and coils that induce a circulating AC current (and resulting magnetic field) in the metal. The depth of penetration of the field is proportional to the frequency. Cracks or corrosion, on or beneath the surface, disturb the uniform flow of current and the differences show up in the induced voltage and phase of the AC signal in the probe.
https://www.olympus-ims.com/en/eddycurrenttesting/https://www.youtube.com/watch?v=FbqzJ-hTtmQ
Eddy Current Devices to Determine the Thickness of Non-Conductive Coatings on Conductive Metals: Devices of similar design to the one described above are routinely used to determine the thickness of non conductive coatings on conductive metal surfaces.
Again an AC current is induced in the underlying metal by a set of coils and the strength of the field is determined by the probe. The distance between the induced current in the metal substrate and the tip of the probe affects the phase and the voltage induced in the probe and allows precise determination of the thickness of the non-conductive coating.
https://www.elcometer.com/en/coating-thickness-gauge.htmlThere are additional kinds of ECDs. Described above are three main industrial applications of which I am aware.
All require that a conductor or conductive substrate be involved in the measurement. (See ETA below).
Back to our friend Bro. Schryver: I'm at a loss to understand what he claims to have done. Again, eddy current measurements require a conductive substrate of some type in which the eddy current can be induced. Sounds like miscommunication, wild imagination, or just plain nonsense to me. If Bro. Schryver has figured out a way to induce an eddy current in papyrus, it would be a more important discovery than anything he thinks he has turned up in Mormon history.
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ETA: I suppose that one could use a ECD probe, place the papyrus on a smooth, uniform and preferably flat, metal surface, and then make some kind of thickness determination by pressing the probe against the papyrus and the papyrus against the metal surface. But why go to all the trouble when easier, more readily accepted, methods are available?
In any case, this would not be the intended use of the ECD. The use of standard measuring equipment, employing standard methods, that can be readily repeated by others is part and parcel of good science.
