Standardized Tests for Metal Detectors

[green]

In the test above the solder sample was simply a 39mm straight piece of the 8mm solder, resin core. Did not form it into a loop. I wonder if it would be detectable if it was pounded into a 6mm wide strip?

Dan

I'll try flattening one latter today. Did you try a solder ring? My tests show it should be a lot easier to detect. .8 mm not 8 mm

[baum7154]

No I didn't because as you point out that geometry is way easier to detect.

Dan

[Davor]

Yes, a loop is an equivalent of eddy current in a bulk target of the loop radius. In fact, one may make a coil and put a small potentiometer connected to it by a twisted pair to mimic any target metal. It may come useful for calibrating various VDI-s

[green]

Reply #129 I recorded some data using lead solder, couldn't plot the time constant for a straight piece. Today I recorded some copper wire targets to see how much shorter the time constant is for a straight piece vs a loop. Don't know if the ratio would be the same for lead. If it is the time constant for a straight piece of lead would be less than .3 usec. (reply 135, Tried to flatten the solder, couldn't get it wide enough).

[baum7154]

Reply #129 I recorded some data using lead solder, couldn't plot the time constant for a straight piece. Today I recorded some copper wire targets to see how much shorter the time constant is for a straight piece vs a loop. Don't know if the ratio would be the same for lead. If it is the time constant for a straight piece of lead would be less than .3 usec. (reply 135, Tried to flatten the solder, couldn't get it wide enough).

----------------------

Just for fun I melted the 39mm piece of .8mm 60/40 solder into a .133" X .090" naturally flattened bead and my detector set wide open and at 8us delay sees it pretty solidly at .5 inch, a very tough target. Then pounded it on an anvil to a .256" X .022" disk and it was solidly detected at 1.375". Pounded it again into an oval .378" X .320" X .015" thick and it is detected at 2". It would be good to know how a pure tin target responds.

Regards,

Dan

[baum7154]

Took another 39mm piece of .8mm 60/40 solder and pounded it on an anvil to a nominal thickness of .0045 X .160" wide and a length of 2 3/16" and it was only very sporadically detected by my detector in contact with the coil housing.

Dan

[Nupi]

Maybe someone will find this PDF's interesting.
Can someone tell me how I can post a PDF from 6 and 3 Mb?

[green]

Personally I'm not so interested in producing a chart indicating how various commercial detectors react to our standardized tests. I think it's up to the individual to carry out their own tests and see the results first hand. Any chart we create will be hotly contested anyway by the those that find their favourite detector didn't quite cut the mustard, and that's not really the purpose of the exercise. However, I do think a comparison chart would be most useful for some of the projects presented here on Geotech. It might also give some direction for future development of these projects, as we work to develop methods of passing the various tests. Some of the tests will only be relevant for PIs, whereas others will be more appropriate for VLFs.

As far as soil tests are concerned, I suggest we have a maximum of three for inland soils: light (1), medium (2) and high mineralization(3). Previously I suggested a panel covered in iron ferrite cores for test 3.

Has anyone tried the "wood, coin (nickel) and iron nail test"? ->
https://www.youtube.com/watch?v=qWen...ature=youtu.be
I tried this yesterday ... and the results were very interesting.

The thread seems to have died. What would be a good core size and spacing for the high mineral soil test? Just comparing build project detectors sounds good to me. If nothing else it would be a way to see if the detector was operating properly.

[Qiaozhi]

The thread seems to have died. What would be a good core size and spacing for the high mineral soil test? Just comparing build project detectors sounds good to me. If nothing else it would be a way to see if the detector was operating properly.

I was thinking of using cores of 19mm outer diameter, 11mm inner diameter, and 6mm thick, but (to be honest) that was based on one core I happen to have here. In the end the actual size will probably be determined by what's available, and at what cost. Or it might even be better to use a number of different sizes. It depends on how homogeneous you want the mineralization test to be. As to the spacing ... well that's part of the experiment.

[baum7154]

I guess a perfect standard soil equivalent could be plain tap water. Conductivity can be adjusted by adding salinity.

____________________________________

I would like to know more about this water and salt simulator. What salt would be the standard? Would the use of other salts Potassium Chloride, sea salt, etc. adversely effect the standard simulation? It seems we would have to specify a salt to use at a certain concentration at a certain depth to simulate a few soil conditions. Have you tried this simulator method?

Also I'm sure some might be reluctant to subject their coils to the corrosive salt environment.

Regards,

Dan

[Koala]

____________________________________

I would like to know more about this water and salt simulator. What salt would be the standard? Would the use of other salts Potassium Chloride, sea salt, etc. adversely effect the standard simulation? It seems we would have to specify a salt to use at a certain concentration at a certain depth to simulate a few soil conditions. Have you tried this simulator method?

Also I'm sure some might be reluctant to subject their coils to the corrosive salt environment.

Regards,

Dan

I tried adding salt to water to test my IDX. No matter how much salt is added to a cup of water my detector works fine not the same as on the beach though where ever damp patch causes a signal unless I turn the threshold down?

[Koala]

steel and stainless steel ball bearings should be the same the world over.

[Tinkerer]

Salt water is a high resistance conductor when compared to metals.

As target, one cup of salt water represents a small surface compared to the damp sand on the beach. The response is mostly proportional to the size of the target.

In general, a delay longer than 10 us shows little response on the beach, but, 50 feet deep in the ocean it shows still a significant response.

So, what does all that tell us?

It tells us that we do not really know what the TC of salt water is.

This is because we measure the signal amplitude with a traditional PI, not the TC of the target.

So, what is the actual TC of sea water? Does anybody know?

[green]

[So, what is the actual TC of sea water? Does anybody know?]

I don't think a material has a time constant. If I measure the time constant of squares cut from an aluminum can the time constant changes with area. Which brings up the question of what should our test targets look like? For a PI I think we should have short and long time constant targets. Maybe we could define what type targets we need for the different type detectors.

[Tinkerer]

If you take a square of copper and an identical square of lead you will see the difference of TC.

I use targets of the same surface area but different thickness or different metals or different alloys. They have different TC's.

Titanium in general, for example has a very short TC, but the different alloys of titanium again have different TC's.

Gold alloys, and there are hundred of different ones, all have different TC's.

But we need to look at the TC, not the amplitude of the target response.