I have been experimenting with using eddy currents to differentiate between copper and zinc pennies. Here is a link to the history of penny composition. http://en.wikipedia.org/wiki/Penny_(United_States_coin)
I built a little jig and circuit to attempt to measure the time it takes a penny to slide the length of its diameter while passing through a magnetic field. That setup is shown in the attached photos.
I selected three pennies: a 1958 "wheat" penny, a 1977 "copper" penny, and a 2006 "zinc" penny. I cleaned and polished each of the pennies. (I know that I ruined the collector value, but that's a cost I can bear .)
Then, I placed each penny into the slide, and it moved down the slide until it was stopped by the paper clip. Then, I pulled the paper clip up to release the penny and allow it to slide under the magets and between the LED and the phototransistor mounted in the slide. The time was measure by the PIC. I repeated the process 20 times with each penny with the "tail" down, and 20 times with each penny with the tail up.
Attached is the data that I recorded. I am no statistician, so I am not sure how much credibility to place in it, or exactly what to make of it. I would appreciate any input.
Specifically, I am concerned with the variance between the results of the 20 trials for a specific penny, and how I can reduce the variance as much as practical.
Thanks.
I built a little jig and circuit to attempt to measure the time it takes a penny to slide the length of its diameter while passing through a magnetic field. That setup is shown in the attached photos.
I selected three pennies: a 1958 "wheat" penny, a 1977 "copper" penny, and a 2006 "zinc" penny. I cleaned and polished each of the pennies. (I know that I ruined the collector value, but that's a cost I can bear .)
Then, I placed each penny into the slide, and it moved down the slide until it was stopped by the paper clip. Then, I pulled the paper clip up to release the penny and allow it to slide under the magets and between the LED and the phototransistor mounted in the slide. The time was measure by the PIC. I repeated the process 20 times with each penny with the "tail" down, and 20 times with each penny with the tail up.
Attached is the data that I recorded. I am no statistician, so I am not sure how much credibility to place in it, or exactly what to make of it. I would appreciate any input.
Specifically, I am concerned with the variance between the results of the 20 trials for a specific penny, and how I can reduce the variance as much as practical.
Thanks.
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