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# Is it possible to determine the location of metal object on an inductor cable

## Is it possible to determine the location of metal object on an inductor cable

(OP)
Lets say I have a long inductor cable and I put a metal object somewhere along the inductor cable. Is there a way I can find the location of where the object is? I know you can detect that the metal object is near the inductor but can you detect where along the inductor it is?
Also I am not allowed to put any sensor device on the metal object. So basically I'm placing random metal objects along the inductor and need to find its location.

Thanks for all your input, I greatly appreciate all responses.

Replies continue below

### RE: Is it possible to determine the location of metal object on an inductor cable

What's an inductor cable? Assuming it's just a long inductor, then sure - in the proximity of the metal object the inductance will change since inductance is proportional to the magnetic permeability of the medium through which the magnetic field passes. This will create an impedance mismatch, which causes signal reflection. If you pass a high frequency pulse down the inductor, there will be a reflection at the point of impedance mismatch. By timing the arrival of the reflection, you can determine how far away it is. Of course, in practice the impedance mismatch will be both small and spread out, so the quality of the reflection will be poor. The specifics of the situation will determine whether the measurement is actually feasible.

What's the application?

### RE: Is it possible to determine the location of metal object on an inductor cable

The location of objects along a cable consisting of parallel wires can be determined using TDR techniques. The location along a parallel wires can be determined more precisely if the structure forms a transmission line. The position along a solenoid coils can also be determined as this can form a slow-wave transmission line. There are many linear position sensing devices that use a transmission line probe with a metal reflector, metal short, or dielectric change for the position element.

### RE: Is it possible to determine the location of metal object on an inductor cable

(OP)
Basically, my project requires me to send multiple metal objects along a path. From this I have to map the instantaneous position of the multiple objects (however many) onto a display. I am currently just brainstorming ideas I could use to detect these metal objects. Radar is one option but this would project any object onto the screen not just metal. and I thought of using an inductor system. would you folks have any ideas?

### RE: Is it possible to determine the location of metal object on an inductor cable

Your requirement is very vague: no object dimensions or metal properties, position detection accuracy required, etc. If you can tag the unspecified objects, how about an RFID system?

### RE: Is it possible to determine the location of metal object on an inductor cable

The description of the problem ("inductor cable" and "metal object(s)") will naturally suggest some sort of TDR type system. But if there are multiple objects (how many?), then a good strong reflection from the first leaves less power for the second, and so on.

A practical solution is likely something completely different, such as a vision system. Depending on all the details not yet mentioned.

Is this an actual real-world real application?

### RE: Is it possible to determine the location of metal object on an inductor cable

(OP)
Lets say the path which the metal objects travels is very long (I know its vague but bare with me), I am allowed to put several(fewer the better to reduce costs) emitters/reciever stations along the path. the number of metal objects that can travel along on the path can vary depending on how wide the path is and how long it is. and heres the catch... I CANNOT put any aditional device/tag on the objects.

To give you a perspective on the size of the objects, consider a standard letter size sheet of paper as the width of the path (length is infinitely long as mentioned); 8.5 by 11 in (216 mm x 279 mm), where the width of the path is 8.5in the size of the metal object relative to the path would be roughly as putting your keybord mouse on the piece of paper.

Originally, my thought was to put a inductor below the path to detect the objects. but TDR system would diminish the signal depending on the number of objects

### RE: Is it possible to determine the location of metal object on an inductor cable

If the path is "infinitely" long, then it might take quite a while to get position detections or reports back from the most distant objects.

### RE: Is it possible to determine the location of metal object on an inductor cable

(OP)
Thats why I said there can be multiple emitters/reciever or detection stations along the path

### RE: Is it possible to determine the location of metal object on an inductor cable

Your original post stated you wanted to 'find the position of the metal object'. Are you effectively just trying to count how many are in a section (relatively easy) or are you trying to identify the position of a specific object? If you are trying to identify a specific object anywhere along the line how do you intend to differentiate it from the others if you cant' mark it or attach anything to it?

### RE: Is it possible to determine the location of metal object on an inductor cable

By using TDR the reflection from first metal object would be significant. What about other objects down the inductor length? Secondly are you interested in the size of the the metal object placed? It will make things a bit complicated.

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