small targets

[Anonymous]

When searching for small targets (small gold earrings, chains, etc.) what would be the better choice for a detector? A PI? A high frequency VLF w/ small coil?
I've heard that the VLF/IB nugget machines that operate above 25kHz are good for small gold, etc. but would also think a PI would be a good detector choice for this too.

 

[Anonymous]

Hi Jeff,
A lot depends on where you are searching. In dry sand you can use a high frequency IB machine to good effect but on wet ocean beach sand there would be far too much falsing due to the salt conductivity. Wet sand around fresh water lakes and river should be OK as fresh water is not very conductive. At the moment there is not a treasure hunting PI that would match a high frequency IB detector for sensitivity to very thin chains, earrings etc. One could be made, however, without too much difficulty. I have designed industrial PI

 

[Anonymous]

I second the motion.
what do you believe the compromises would be on such a detector (loss of depth on larger objects, less depth on silver,slower sweep speed,ETC.) ?
Russ

 

[Anonymous]

Hi Russ,
I would expect some loss of depth on bigger or more conductive targets as the coil would be smaller; probably 8in at most with less turns. However, the sweep speed should be no worse and could even be better due to a higher pulse rate. It should be possible to have a control that you can set to the type of object and where you are searching. i.e. fine chains and very thin rings in dry sand or fresh water - normal rings etc in salt water - heavier rings and coins at greater depth in salt water. Maybe even do a coil change depending on the type of object. Many possibilities.
Eric.

 

[Anonymous]

Eric, Can you explain what you mean by an "industtrial PI" as opposed to a treasure hunting PI? What is the difference in your unit that detected fine gold chains with no problem? Thanks for all your help, Fred

 

[Anonymous]

Hi Fred,
Industrial metal detectors vary widely depending on their application. At one end there is the detector in a quarry or mine which is there to protect rock crushing machinery. This is set to detect rock drill bits, gear wheels, parts of metal pit props etc. which can do serious damage if ingested by the machine. They are not worried by 1/2in bolts, Coke cans and things of that size or smaller. At the other end of the scale is a detector for the food or pharmaceutical industry where they want to detect metal particles to 0.5mm diameter and less. This latter application is still largely the province of induction balance detectors operating at frequencies of 100kHz or more. As well as quarries, sawmills and plastics industries, PI detectors are used by textile manufacturers for finding broken off needle tips and carding wires and also in some areas of the food industry to find stainless steel nuts and washers that may have worked loose from processing machinery. Stainless steel is a difficult metal to detect due to its non-magnetic properties and its high resistivity. Usually, industrial PI coils are rectangular and are mounted either under or over a conveyor belt that carries the product. The control unit is mains powered and on detecting metal, switches off the conveyor and sounds an alarm. In some cases the detector operates a diverter flap or valve which shunts the portion of product containing the metal into a reject bin.
High sensitivity industrial PI