Target signals

[green]

The first tests were done at an amplifier gain of 11. I've been playing with a gain of 150. The plots are similar. The quarter and the ferrite are still the same. Both change polarity when testing vertical and horizontal during on time with very little signal at off time. I still get a lot more signal with the nickel at off time.The targets were about 1 inch away. No target, nickel flat, nickel edge, quarter flat, quarter edge.

[green]

The thread TARGET TIME CONSTANTS lists the time constant for 1 inch square aluminum foil at 10 usec. My plot looks closer to 2 usec. What am I doing to cause that much difference?

[Ferric Toes]

The thread TARGET TIME CONSTANTS lists the time constant for 1 inch square aluminum foil at 10 usec. My plot looks closer to 2 usec. What am I doing to cause that much difference?

I couldn't find the thread you mentioned, but, importantly, how thick is the foil? I took a 1in square piece of baking foil (0.0005in) and it decays into the noise by 20uS. This means that its TC is about 4uS. Thinner stuff and different aluminium alloy will make it faster, or slower if thicker. It is better to use a standard coin such as a US nickel as the size, thickness, and metallic composition is very well controlled.

Eric.

[green]

{One square inch of household aluminum foil has a total discharge time of 50 uS and a 10 uS TC. Eric Foster mentioned, in one of his posts, that his Goldqust PI can detect this 1 sq inch foil at 12" using an 11" coil at 10 uS}.
I measured some other targets. quarter,10usec--nickel,10usec--dime,10usec--penny,18usec--1 inch diameter ring # 12 copper wire,21usec. The approx. time for a 63% drop in amplitude. I need to improve my setup but was wondering if the measurements are in the ball park. PiTec had some good looking plots in a thread, one showing a time constant change for a silver ring as it decayed. Maybe some of the difference is where the drop is measured

[Ferric Toes]

{One square inch of household aluminum foil has a total discharge time of 50 uS and a 10 uS TC. Eric Foster mentioned, in one of his posts, that his Goldqust PI can detect this 1 sq inch foil at 12" using an 11" coil at 10 uS}.
I measured some other targets. quarter,10usec--nickel,10usec--dime,10usec--penny,18usec--1 inch diameter ring # 12 copper wire,21usec. The approx. time for a 63% drop in amplitude. I need to improve my setup but was wondering if the measurements are in the ball park. PiTec had some good looking plots in a thread, one showing a time constant change for a silver ring as it decayed. Maybe some of the difference is where the drop is measured

Something is not right. There should be a big difference between the coins you mentioned, particularly between the quarter and nickel. I will do some plots shortly and post.

Eric.

[Ferric Toes]

Something is not right. There should be a big difference between the coins you mentioned, particularly between the quarter and nickel. I will do some plots shortly and post.

Eric.

Here are plots for quarter and nickel. The quarter has still not reached the zero line at 500uS while the nickel is at similar amplitude at 65uS. I still have penny to do but I think there are two different compositions depending of date. Also have not yet found a dime to test but recollect that they are somewhere in the middle between a nickel and a quarter.

Eric.

[Ferric Toes]

Yes, there is a difference in 1 cent (penny) USA coins. '70s and '80s pennies have a longer decay than one I have for 2003. This must be because on the later ones it is a copper plated core of some cheaper metal.

Eric.

[green]

Thanks for the reply. I'll have to find out why I'm getting low time constants for the quarter and eliminate the noise.

[Carl-NC]

Zinc

[Ferric Toes]

Zinc

I see that the quarter has a copper core with cupronickel plating. Hence the long decay.

Eric.