Air testing metal detectors

[satdaveuk]

Air testing......... What use is it for the metal detectorist, or engineer
Well it shows you that you switched it on, and you have batterys on board with juice in them.
It tells you it can detect metal in the air in some cases from very long distances.

What else ?????? Nothing unless ive missed something.

Please give your opinions on the subject engineers and anyone who uses detectors alike, theres normally two sides to a coin but me can only see one

Regards

[kliner]

It does tell you that if you can't detect deeper than 20cms in the air your never going to get more than that in the ground!

[wam]

Hi,
http://www.itep.ws/pdf/STEMD_Interim_Lab.pdf

[WM6]

It does tell you that if you can't detect deeper than 20cms in the air your never going to get more than that in the ground!

Sorry not true. There are some detectors (especially PI) which can go deeper in soil than distance achieved in air on same test target.

Air test can tell you if detector is working in sensitivity mean, but how it works in real world (stability etc.), this can tell you field test only.

[Skippy]

It allows you to compare two identical detectors. Example: if your friends' Deus will find a coin at 35cm, and yours only manages 25cm, you may have a fault, or have some function not set correctly.
It allows you to check your machine for changes in performance. Example you know it will find a coin at 30cm. You took it to the beach, got it wet, it didn't seem so good afterwards. Repeat the airtest - only 25cm - maybe the saltwater got in it?
Suppose you have two 8 inch coils for your machine, a new one and a battered old one. An airtest will allow a comparison, and show if your old one still works like new.
You've tinkered with the front-end amp gain, and increased it by 25 %. The airtest will show this improvement, in accordance with the 'inverse 6th power' relationship.
We know that flat things like coins that are at an angle can be found less deep, and pinpoint badly. An airtest can give a decent indication of how much depth is lost, and how far off the pinpoint can be for differently angled coins,at different depths.
You buy a small 5 inch coil for your machine. The depth gauge on the detector is calibrated for the 10 inch coil. Doing an airtest will give you an idea of how to translate indicated depths into real ones, when using the small coil.

[Jerry]

While there is no substitute for testing in actual ground, air tests are of value in making a determination as to if the test detector is working properly.

It becomes valid when people build a detector like the TGSL, IGSL and then test it to see how it compares to what others have got with the same detector. It at least lets you know what is possible.

I admit that there are many variables that can skew the test results but if one can obtain an air test of 30 cm or whatever versus say 4 or 5 cm, it does tell you something about the detector.

Testing in the same spot in exactly the same manner as changes are made gives you a relative scale as to improvement or not of your changes. I have gone as far as building a machine that does just that.

We have at least two people on here that have taken great pains to travel to a quiet location just for the purpose of seeing what their detector with do under quiet conditions. That is dedication

I was hoping to improve a little on my methods for air testing this winter but so far for reasons beyond my control I cannot get out to my shop for any experimenting.

Jerry

[satdaveuk]

While there is no substitute for testing in actual ground, air tests are of value in making a determination as to if the test detector is working properly.

It becomes valid when people build a detector like the TGSL, IGSL and then test it to see how it compares to what others have got with the same detector. It at least lets you know what is possible.

I admit that there are many variables that can skew the test results but if one can obtain an air test of 30 cm or whatever versus say 4 or 5 cm, it does tell you something about the detector.

Testing in the same spot in exactly the same manner as changes are made gives you a relative scale as to improvement or not of your changes. I have gone as far as building a machine that does just that.

We have at least two people on here that have taken great pains to travel to a quiet location just for the purpose of seeing what their detector with do under quiet conditions. That is dedication

I was hoping to improve a little on my methods for air testing this winter but so far for reasons beyond my control I cannot get out to my shop for any experimenting.

Jerry

I agree with you its not a substitute, I been doing detector repairs since 1987 and dug the first test bed back at the same date and without it id be truely knackered because you can get two identical machines air testing a sixpenny bit pre 1947 silver one comes in at 30cm one at 26cm, how they react in real conditions is anyone guess, and thats not one off situations its common, wether be coil problems or control box problems and theres no quicker and more accurate way than to drop a coin in a hole and go from there. ie real conditions.
Thats normally the first thing i do with the customer when they bring them in.
Im lucky i know because my workshop has land round it, but to be honest theres no substitute, How people like skippy manage to do repairs/mods ill never know, its ok to see if a machine basically works as said earlier but thats where it ends.
Ive done that 30cm air with the TGSL using two 6mh coils just altering frequency with CX and nulling with the second hit, works fine in workshop apart from the odd chirping, disc works, lacking small silver.
Soon as you take to real conditions its unstable reducing gain to just short of halfway, £1 coin 15cm.
Properly set up coil gives 26cm air and 21 in ground, so i rest my case.

Regards

[Skippy]

I do have a coin garden as well, I just wish I had a decent PC oscilloscope/datalogger to make better use of it.

[satdaveuk]

Scope data logger

I do have a coin garden as well, I just wish I had a decent PC oscilloscope/datalogger to make better use of it.

Do you know im sure somewhere here ive got a circuit and construction details for a scope data logger, was looking at it a few months ago and thinking that could be useful, if your interested will try to dig it out for you.
It will be copyright so will email it.
Regards

[Jerry]

Ive done that 30cm air with the TGSL using two 6mh coils just altering frequency with CX and nulling with the second hit, works fine in workshop apart from the odd chirping, disc works, lacking small silver.
Soon as you take to real conditions its unstable reducing gain to just short of halfway, £1 coin 15cm.
Properly set up coil gives 26cm air and 21 in ground, so i rest my case.

Regards

Let me turn the question around a little. What besides ground balance can you adjust on a detector in real ground that you cannot with an air test that will provide significant improvement over the air test alone?

This is an interesting subject for me. I am not taking a position that air testing is better than in ground testing. However, it is a quick means of obtaining some information about the over all condition/adjustment of a detector.

A lot of people get concerned if someone posts on the forums that their TGSL is getting a 30 cm air test and they are only getting say 25 cm. With all of the variables involved that is not significant. Likewise, if one persons TGSL gets 12 cm in the ground and anther gets only 10 it probably has more to do with the ground makeup than the detector.

However, if one gets 30 cm on an air test and someone else only gets 4 or 5 that probably means that more work is needed. I don't think you have to take it to an outside test bed to verify that and it is easy for me to test either way.

I am fortunate enough to live in the country in a quiet location and have lots of land. I have two test gardens and one is in an area where I normally plow the snow so it is accessible all winter long.

Jerry

[detecto]

Garrett

Sorry not true. There are some detectors (especially PI) which can go deeper in soil than distance achieved in air on same test target.

Air test can tell you if detector is working in sensitivity mean, but how it works in real world (stability etc.), this can tell you field test only.

One of those metal detectors is
Garrett Infinium Land & Sea
i tryed him in the air and on the real soil, preformances in the soil are much much much betther.
Regards

[Jerry]

One of those metal detectors is
Garrett Infinium Land & Sea
i tryed him in the air and on the real soil, preformances in the soil are much much much betther.
Regards

I wont debate that point at all since I have no experience with PI detectors. My comments were directed towards vlf detectors.

Jerry

[mario]

Air testing is important for configuration purposes.

On some PI equipment, you air test to null out emi. Once you've nulled out emi, you then ground balance. And yes, some PIs will detect deeper on ground vs air.

I do like kliner's comment on the issue: if you detect something in the air at 20cm, you can not detect it by much more in the ground.

[wam]

Hi,
On page 15 is a table to compare number of VLF and PI detectors for depth in air and depth in soil for 7 types of soil.
http://www.itep.ws/pdf/GICHD_MDCatalogue2007AnnexSTEMD.pdf
Regards,