Detecting through metal

  • Thread starter Michael Griffin
  • Start date
M

Thread Starter

Michael Griffin

Can anyone suggest a method of detecting the presence or absence of a small iron object behind a sheet of steel? The object of interest is a
small (10mm diameter) sphere of iron located behind and in contact with a sheet of steel which is approximately 2mm thick. The purpose is to determine if the small iron object is missing, so the method must be very reliable.
It is not possible to view inside the assembly, so means such as optical sensors cannot be used. The sphere is rigidly mounted, so it cannot be "rattled". There are no other externally visible indicators (but yes, it does need to be installed in the assembly).
I doubt that a normal inductive sensor could pentrate the sheet of steel (but I would be willing to consider any suggestions along that line). X-rays sound dangerous and expensive. Does anyone have any other ideas?


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Michael Griffin
London, Ont. Canada
[email protected]
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Gerald White

You might try doping the iron ball with a detectable substance a slight radioactive trace and detector might work.
 
A

Anthony Kerstens

We have double blank detectors on our lines by Syron. According to old literature I have they're in Michigan. The phone number is 313-429-4989, although the area code could have changed.

These devices are essentially an analogue version of an inductive prox switch. They can be set to sense different thickness' of metal and trigger on something greater than the setting. It's a die protection devices that ensures only one sheet of metal is inserted into the press. It might just
do what you need.

Anthony Kerstens P.Eng.
 
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Michael,

Provided the ball is indeed in good contact with the steel plate, then an ultrasonic thickness gauge should detect it, (at one point only!). Don't know much about magnetometers but presumably this technology should be able to detect a 10mm iron ball additive to the existing steel plate. (Any inductive prox detector with analog output should show some, albeit very small, variation).

Hope this helps,

Tony Firth,EE,
Quester Technology Inc.,Fremont,CA
 
Just a wild thought, but what about looking at an infrared thermal image? Maybe heat the sheet, and look for a distinct heat loss pattern that would be different if the piece were not there.
Mike Milton
 
Y
How heavy is the part as compared to the over all weight? If it is significant, then simply weight the assembly to determine if the part is present.
 
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Michael Griffin

We are considering ultrasonic, but don't have any recent experience with it (at least not for about 15 years for me). The ultrasonic equipment that I have seen (weld testing) requires some sort of coupling fluid, which is not practical for this application.
Can anyone suggest any particular ultrasonic equipment we should look at? The criteria are that it must be quick, easy to use, and can be interfaced directly to a PLC to give a pass/fail output.


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Michael Griffin
London, Ont. Canada
[email protected]
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B

Bruce Axtell

Interesting problem....these are just a couple of off the cuff & off-the-wall brainstorming ideas that might generate some really constructive ideas from others. Without knowing the construction, it's hard to say.

1) Magnetic imaging? There may be several ways to do this depending on the construction, and what else is inside...of which I'm not familiar.

2) View the sheet with an infrared scanner and blow warm air on it. The spot with the metal disk has more mass, and should show up as a cooler circle. This may not give a precise
measurable position...just a yes/no, is it there sort of indication.

Good luck.
Bruce
 
A

Anthony Kerstens

Only use radioactive devices if you are prepared to install radiation detectors for your trucks at the gate. The last time I saw such a detector, the truck had to inch through at <3MPH. :)

Anthony Kerstens P.Eng.
 
C

Clark Southoff

Michael:
Check with U. Of Waterloo or Queens U, A air coupled Ultrasonic transducer is available but it is not cheap.
Also check CSNDT.org or NDT.net and search for Air coupled UT transducers.

Best regards
Clark Southoff
Technology Wranglers Inc.
Calgary, Alberta
 
R
Know any radio hams? They will soon knock you up an oscilator whose LC resonant tank, placed close to the surface, will be pulled off frequency by the presence of the sphere.
 
M

Michael Griffin

At 11:19 01/06/00 -0400, Anthony Kerstens P.Eng. wrote:
>We have double blank detectors on our lines by Syron.
>According to old literature I have they're in Michigan. ....<clip>

We saw some data on a Keyance double sheet feeder a few days ago - there are probably several companies that make them. At the time we thought we wouldn't be able to get something like that to work in this application, but on second thoughts, its definitely worth a try.

"Yuzna, Ray" wrote:
<clip>
>How heavy is the part as compared to the over all weight? If it is
>significant, then simply weight the assembly to determine if the
>part is present.
<clip>
The weight of the iron ball is small compared to the weight of the overall assembly. The sensitivity would not be good enough.

Several people suggested some sort of thermal means. I think the iron ball is too small relative to the steel sheet to make much difference.

I think we should try out the double sheet feeder sensor idea. I would like to thank all the people who have taken the time to contribute a suggestion.

**********************
Michael Griffin
London, Ont. Canada
[email protected]
 
S

Steve Monnet

Hi,

I think you can use vibration to detect the presence of the sphere. By appling a certain signal (hit the sheet of steel with a small hammer for exemple), the resulting sound must be recorder and analysed to determine if the sphere is here or not.

Hope this idea can help

Regards

S.Monnet
[email protected]
 
K
Hi Michael... This may be a long shot and I am not sure if the technology is up to snuff... but in the food industry we use some very precise metal detectors. These detectors have the ability to capture a signal from a product stream and then "phase" it out using digital signal processors. Any signal seen by the detector that is not "phased" out will then trip the detector.

You mentioned that the sheet was made of steel and the ball was made of iron. You may be able to phase out the steel sheet (without the iron
sphere) so that the detector ignores the presence of the steel sheet. If you are able to do this... the detector would go off on the presence of the iron sphere. You could then watch for the "Metal Present" signal to ensure that your sphere is where you want it to be.

Again... I am not sure if the technology can do this for you. A name and number for you is John Nolan at Gorring-Kerr at (905) 470-7599. Let me know what they tell you.

Best Regards... Rick Kelly

Chief Technician
Natural Cuts
Cheese Operations
Kraft Canada
(613) 537-8069 V
(613) 537-8057 F
[email protected]
http://trondata.on.ca
 
M

Michael Griffin

This sounds like a custom made proximity sensor. It is worth considering though.

I have been contacted off list by someone who manufactures a "missing part detector". This detector is intended to inductively sense
missing metal parts which are located behind another sheet of metal (does this sound familiar?). I intend to check if the specs will meet our application (the 2mm thickness I mentioned was just a guess - their detector
though is limited to 1.5mm). The company's name is "Prime Controls". Has anyone used one of their products before?


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Michael Griffin
London, Ont. Canada
[email protected]
**********************
 
B

Bruce Durdle

Michael,
Check out Pepperl and Fuchs. I was glancing through a glossy of theirs and saw an inductive sensor that supposedly can detect through a magnetic material - so it may be worth a look.

Bruce
 
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