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Eric Foster's PPD1

Reg

New member
While we are discussing pulse units of the 80's that were unique, I feel we need to discuss the PPD1, which was Eric's ferrous discriminating PI that appeared to work reasonably well on many salt water beaches. The unfortunate problem with this detector was once a person took it inland, the ground signals made it impossible to use. So, the detector never really caught on.

What a lot of people don't know about the PPD1 is, it was the foundation for the initial design of Dave Emery's Pulse Devil. The PPD1 gave the idea of sampling during the on time to obtain information useful in determining whether the metal was ferrous or non ferrous. To do this, you need to use a separate TX and RX coils.

So, in simple terms, the target response of ferrous and non ferrous were/are dramatically different during the pulse when using DD or balanced concentric coil. Actually, the same thing is true if one uses a coaxial coil, which is what was on the original PP1 if I am not mistaken. Eric mentioned that he built a later design using a shielded concentric coil that worked better.

Because sampling during the on time, the ground signals became a problem that were the primary downfall for this detector.

One thing I also remember is another design engineer, George Payne, also developed a ferrous/non ferrous discrimination several years before Eric and Dave. George's design was also patented. Here is the patent number for those interested. Patent number is 4,110,679. Again, google this number as a patent number and you should be able to download the pdf of that design.

Now, what made the Payne design interesting was the fact he both sampled during the on time, but also was able to develop a ground balance feature as well as ferrous/non ferrous determination. It is my understanding from talking to George, no energy recovery system was in place so the design was power hungry. This was one of the main reasons the design never became a product to be sold.

Now, I decided to mention all of these detectors at this time to point out to those wondering why no one has built a discriminating PI for sale.

There is one more design being worked on that I know of and that is being discussed on the Geotech forum. This idea is being developed by Moodz.

What I find interesting is Moodz is accomplishing this iron ID feature while eliminating the need for a damping resistor. The reason I believe he is able to determine ferrous vrs non ferrous has to do with just when the sample occurs. I have been working on something similar but uses the present PI design. My initial design gave me hope but I got sidetracked by personal issues and I never have gotten back to that idea.

The bottom line is, I feel a working iron id type feature is possible and the basis may be hidden in one or more of the designs mentioned above.

So, getting back to the PPD1, it would be nice to hear from someone who has or used one of these detectors to find out more as to how well they worked.

Reg
 
I call Her, ......"The Screamer"

THe PPD1 is one heavy detector by todays standers, 8 D cells is the reason. This detector was Given to me by a friend, (VLAD) I restored it and use very little, but once retired, very soon, she will get more action....

Coin was foreign, and was badly wore....As far as depth, it was at about 8 to 9 inchs....

http://www.youtube.com/watch?feature=player_embedded&v=wRcnEiHvMBw
 
I can see why you call it the Screamer! In the Youtube video the threshold setting is way too high and should be set back to just ticking, to get the best sensitivity. It is also much easier on the ears. Look for small increases in the tick rate for deep targets. Closer targets cause an increase in rate which will eventually reach a scream when just a few inches from the coil. Some users, though, found it hard to get used to a ticking threshold after using other detectors that used a continuous tone threshold.

Eric Foster
 
Hello and Seasons greetings.
I have bought a PPDI in a spares /repair condition, the battery top cover is missing , otherwise it is complete, and I managed to get the needle to move on the red section of the dial about a quarter way.is there anyone I could contact in the uk to have a look at it for me. I have tried to upload some pictures unable to do this at the moment , will try again later
Regards Keith
 
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