Transformer Induction coil (COIL CONSTRUCTION)

In summary, the conversation discussed creating an efficient induction coil for a circuit that imitates a transformer. The circuit is given two very thin strips of wire which can be used to create a primary and secondary coil. A ball passing through the coil(s) will generate a numerical output based on the strength of the sensed magnetic signal. The main question was how to build the coil(s) in the most effective and efficient way without changing the signal threshold. Various suggestions were given, including using standard epoxy or bondable wire to hold the coil shape, and using a twist-tie or beeswax to temporarily hold the coils in place. The conversation also touched on the possibility of using a scope and signal generator to demonstrate the coils' operation and changing the
  • #1
jegues
1,097
3
Hello all,

I'm currently working on a project and I have a question in regards to creating an efficient induction coil for our circuit.

Without going into the specific details of the circuit(We aren't given the details anyways, just the circuit itself), it basically imitates a transformer.

We are given two VERY THIN strips of wire 15m long which we can then create two coils out of. A primary coil and a secondary coil. SEE FIGURE

When a ball passes through the coil(s) (either a metal ball or non-metal ball) the sensor gives a numerical output between 0 and 255 (or 1024 I don't recall off the top of my head) based on the strength of the sensed magnetic signal. This strength depends on how we "make" our coils, so this will also generate our "signal threshold" to determine whether the ball is metal or non-metal.

That being said, I have to be certain that the coils aren't going to change or deform, in turn changing our "signal threshold".

Now the heart of my question is, what is the most effective and efficient way to build this coil(s)?

Again, the wire is extremely thin, so if I was to wrap it around an object like a highlighter, and then remove the highlighter the wire doesn't hold its shape as well as it should and falls out of place.

Is there anything we could spray the coil with so that it will hold its shape, but at the same time not decrease the signal strength it generates?

Should we be looking to wrap the coils as close together and as tight together as possible?

Should we overlap the two coils?

Can we tape the coils without ruining the signal?

Any ideas/tips/suggestions/comments?

Thanks again!
 

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  • #2
Just use standard epoxy. wind your coils and then brush it on. Are you not allowed to use a coil form? depending on how large the coils need to be (Im guessing not very since its only 15M of thin wire) you could use a couple of empty spools that are used for solder, plumbers tape, etc.
 
  • #3
Just use standard epoxy

Will the epoxy affect the magnetic signal produced by the coils?

Also, what is the best way to produce our coils? Does it matter if they wire overlaps while wrapping?

Thanks again,
 
  • #4
You can wind the coils any way you like. It doesn't matter if the turns are wound on top of each other. The last turn can even be wrapped around the rest of the coil to hold it in place.

Epoxy should not affect the operation of the coil at normal frequencies (below 30 MHz).

The classic coil former is the cardboard tube inside toilet paper rolls.

Also, garden "pop-up" sprinklers have some nice plastic formers in them. The outer case can be very useful.
 
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  • #5
Hello VK,

It sounds like you want free standing coils. This is commonly done with bondable wire. The wire has a thin coating that is easily melted with heat or weak solvents (even IP alcohol as I recall). You can check for this stuff at mwswire.com under round magnet wire polyester or polyurethane bondable.

You'll need to hold it in place with something that doesn't want to bond. Delrin, teflon, or aluminum have all worked for me.

Best of Luck,

- Mike
 
  • #6
Any other ideas?

I think I'm going to end up using epoxy to get the wire to hold the coil shape. I might try using a "twist-tie" to hold the coil in place as well.
 
  • #7
Well, an old method was bees wax. I've used it for accelerometers and just generally holding stuff together temporarily. Then again, good ol' two part epoxy will hold it right.
 
  • #8
Is your metal ball magnetic, or just conductive?
 
  • #9
The two balls passing through both the secondary and primary coil are metal ball bearings, and marbles.

Apparently if the coils aren't wrapped properly or efficiently you won't produce a consistent signal and it's impossible to set the proper threshold to accurately determine whether the ball is metal or non-metal.
 
  • #10
I see. With a magnetic steel and a low excitation frequency, one coil will be coupled more tightly to the other as the ball falls in between. However, if you turn the frequency up too high, or use a ball that's conductive (but not magnetic), the ball will shield on coil from the other.
 
  • #11
Are you using a scope and a signal generator to demonstrate?
 
  • #12
Also, are you allowed to change the orientations of the coils?
 
  • #13
We are given a circuit board that is similar to that of a transformer.

We are given two strips of 15m long VERY THIN wire.

From these two strips of wire we are expected to make a primary coil and a secondary coil which are attached the circuit board in order to create an analog signal as a ball passes through the coil.

We are allowed to create the coil in any manner we chose, of course we want to do so in a manner that will create a strong and consistent signal as either a marble or metal ball bearing passes through it.
 
  • #14
This shows the field structures for two orthogonal coils with the ball off center. That will reject a lot of back ground coupling, but give you two peaks as the ball rolls by.
 

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  • #15
I don't know if I would be able to position the two coils like that.
 
  • #16
Maybe with 1/2 inch PVC? The Excitation coil wrapped around the PVC while the Pick up is wound on a separate piece of PVC and epoxied so that it is centered over the Excitation coil. If your allowed to use a little extra circuitry, you can add a POT and trim out the alignment error.
 
  • #17
That sounds a little too complicated, I think the solution is simplier than that.
 
  • #18
You can do it either way, or even make an E shaped structure. I know most all of em'. But the sensitivity difference with orthogonal coils will be several orders of magnitude better, depending on how well you can align your coils.

Then again, if your doing this for a class, your prof would likely get suspicious if it were too advanced.
 
  • #19
I'm confused on how I would make the coils orthogonal to one another? Would be the balls simply pass by them then?

I need a better picture of just the physical coil setup, not the fields and such.
 
  • #20
If neither coil is excited, a metal ball will not induce any signal in either coil unless the ball has a permanent magnetic moment.

Are you planning on exciting either coil (the "primary") with an ac frequency? What frequency and amplitude? Solid metal balls will reduce the inductance because of eddy currents (unless frequency is very low). A ferrite ball would increase the primary inductance. Any kind of metal ball will change the mutual inductance between the two coils. A dielectric ball (marble) will have no effect. Please be more specific on your design objective.

Bob S
 
  • #21
I'm not sure about all the details behind the circuit generating the signal. (Mainly because we weren't given them)

All I know is that there is 2 wire connections for the primary coil, and 2 wire connections for the secondary coil. (as depicted in FIGURE)

To identify whether the ball is a metal ball bearing or a marble, we are suppose to create and implement a coil with the circuit in order to generate different signal strengths.

The metal balls, creating a significantly "stronger" signal strength, would allow us to develop a threshold for accurately determining which balls are metal and which are simply marbles.

Does that clear things up? Sorry if I'm not giving out enough information, I'm limited in what we actually know.

I'm looking for the most efficient way to make and implement our coil in order to generate a strong/consistent signal so that my threshold for determining whether the balls are metal or marbles is accurate.

EDIT: After rereading your post again Bob, I believe this is what we're looking at,

Any kind of metal ball will change the mutual inductance between the two coils. A dielectric ball (marble) will have no effect.

So what would be the best orientation to create these coils in order to obtain a strong an consistant inductance between the two coils?(when a metal ball passes through it)
 
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  • #22
This is pretty much it.

If the ball is mostly magnetic, it will react to the excitation winding to set up a dipole field. If the ball is on either side of the sense winding, it will be indicated.

If the ball is mostly conductive, it will distort the field on either side of the excitation winding which will also give an indication.
 

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  • #23
What is the tubing made out on which the wire is wrapped around?
 
  • #24
Most likely, the tubing is plain 1/2" PVC from a plumbing store - very cheap stuff. Use some ordinary office tape to hold the wire in place so that you may wind it. Then, place another piece over the last turn to hold the wire until you can adjust it or glue it.

For the orthogonal design, use a sharp knife to make a 1/4" V-cut in opposite sides of the tube. This, and a little tape, will hold it in place to glue.

In either design, the signal will die as the ball rolls into the very center, but will be very strong on either side.
 
  • #25
You may want to get some sandpaper to help you remove the insulation from the wire before you solder it. Or, you may be able to use a cigarette lighter to burn the insulation away, followed by a quick scrub with a wet towel to get the suet off.

Also, they generally want to sell you 10 feet of tubing (for about US $1.50 as I recall). To get a shorter piece, you might want a plastic "riser" or plastic "pipe nipple." Check over in the water sprinkler area for these.

Sometimes, the hardware man will have mercy and simply cut the pipe for you.
 
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  • #26
Thank you for the coil layouts Mike.

Would simply placing the primary coil before the secondary as indicated in the figure work as well, or is it necessary to follow one of the design patterns you've demonstrated?

Initially that is how we were "told" to do it, but it's up to us to make the final decision. Are you certain the other designs will create a stronger signal? Will the plastic PVC tubing interfere at all?

Thanks again.
 
  • #27
The coils work equally well when placed either way. I'd tune the primary (or excitation winding) with a capacitor. Not knowing any better, I'd try tuning it around 1-2 MHz using ceramic caps. Why? Because you'll get more current in the primary if it's ringing into a cap. That makes for far more signal.

The PVC is a plastic material, and you won't see any signal aberration due to it. In fact, just about any plastic is great.

This configuration won't get more signal as such, BUT you'll get a more discrimination. If you get your coils centered, you won't see much signal until a metal ball comes along.

As the ball rolls into the coils the output will reach a peak, suddenly drop to zero, and then suddenly reach another peak and taper off as the ball rolls away. Very definite. The marble will make no difference at all.If you do decide to do this, make sure you have a feel for WHY this works. Someone's bound to ask. The idea is to reject the signal from the primary - until the ball disturbs the field.
 
  • #28
Okay so now I'm confused.

Is it going to make a big difference if I use the orthogonal layout as opposed to simply placing the primary coil followed by the secondary coil?
 
  • #29
Sorry Jeques,

They're any number of ways to do this. Either one of the two I showed you will work good. A lot of people like the orthogonal coil because they can adjust it easily. Just move it along the other coil until the output disappears, then tape and glue.

The other method would probably be simpler to construct - just keep track of which way the wire is wound, make sure you have the same number of turns on each of the side windings, and that their fairly centered about the primary. If you see a bit of signal squeaking through, you can push the windings about a bit with your thumb nail while watching the signal. When the signal has nulled out, tape and glue your coils

Again, the orthogonal one will adjust better, the other takes less finesse to build. Either one will do a great job of detecting the bearing.
 
  • #30
So aside from you designs, I can't simply place a primary coil followed by a secondary coil in sequence to generate a signal? (NO EXICITATION WINDING. See figure)
 
  • #31
jegues said:
So aside from you designs, I can't simply place a primary coil followed by a secondary coil in sequence to generate a signal? (NO EXICITATION WINDING. See figure)

You might get a small signal if the steel ball happened to have some residual magnetism, but generally, no. There would have to be a magnet there somewhere.

This is sounding a little like a metal detector design project.

I saw a metal detector coil in a magazine. It had coils about the size of compact disks (ie about 12 cm) but they were flattened on one side to make a "D" shape. The two coils were then laid over each other with the curved parts facing away from each other.

like this:
http://dl.dropbox.com/u/4222062/metal%20detector%20coils.PNG [Broken]

The idea was that the vertical part of each "D" would get opposing signals from the vertical and curved parts of the other "D" shape and you got a cancellation.

The rectangular coils at right would probably give the same effect. You would feed the signals in where the gaps are in the vertical sections. You would only feed the ends of the windings, of course.

When you had cancellation, bringing any metal into the vicinity would cause the signal radiated from one coil to be reradiated into the other coil.

I have never tried it but it seems like a good idea.
 
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  • #32
Mike's coil-3.jpg in Post 22 is the right way to do it. The two pickup coils, if properly balanced (bucking mode), will give a null signal unless a conducting ball rolls inside the pipe. It is important that the two pickup coils be symmetric about the excited coil. If necessary, the coils could be moved back and forth on the PVC pipe to get a null.

Bob S
 
  • #33
Hey VK,

Yep, the twin D is common for metal detectors. With the sensing coil overlapping the excitation coil's loop, you can get rejection. It's just a matter of tweaking.

What's really interesting about these detectors is that you can amplify / limit the output of the sensing coil and run that through synchronous detectors. The end result is that you get the phase relationship between the excitation signal and the return signal. This tells you natural time constant (L/R) of the target. Hence you get a good idea what kind of metal is present ;)
 
  • #34
It is useful to look at the circuit design used in the coin pass/ fail detection units in vending machines. They use half a pulsed ferrite pot core on one side of the coin, and a L/R sensing pickup (the other half of the pot core) on the other. It is very fast.

Bob S
 
  • #35
Bob S said:
Mike's coil-3.jpg in Post 22 is the right way to do it. The two pickup coils, if properly balanced (bucking mode), will give a null signal unless a conducting ball rolls inside the pipe. It is important that the two pickup coils be symmetric about the excited coil. If necessary, the coils could be moved back and forth on the PVC pipe to get a null.

Bob S

So this is the design I should be aiming for in order to obtain the best consistent signal?
 
<h2>1. What is a transformer induction coil and how does it work?</h2><p>A transformer induction coil is a device that uses electromagnetic induction to transfer electrical energy from one circuit to another. It consists of two or more coils of insulated wire wrapped around a core made of iron or other magnetic material. When an alternating current is passed through the primary coil, it creates a changing magnetic field which induces a voltage in the secondary coil, allowing for the transfer of energy.</p><h2>2. What materials are commonly used in the construction of transformer induction coils?</h2><p>The most common materials used in the construction of transformer induction coils are copper wire for the coils and an iron core. Copper is an excellent conductor of electricity, allowing for efficient energy transfer, while iron is a highly magnetic material that helps to amplify the magnetic field created by the current in the coils.</p><h2>3. How are transformer induction coils designed and constructed?</h2><p>The design and construction of transformer induction coils involves careful calculations and considerations to ensure efficient energy transfer and proper functioning. The number of turns in the coils, the size of the wire, and the type of core material all play a role in the design process. The coils are then wrapped around the core and insulated to prevent short circuits and ensure safety.</p><h2>4. What are the main applications of transformer induction coils?</h2><p>Transformer induction coils have a wide range of applications, including power distribution, voltage regulation, and electronic devices. They are commonly used in power plants, electrical substations, and household appliances such as televisions and computers. They are also used in various industrial and scientific equipment, such as welding machines and particle accelerators.</p><h2>5. What are some common issues or problems with transformer induction coils?</h2><p>One common issue with transformer induction coils is overheating, which can be caused by excessive current or poor insulation. This can lead to damage to the coils and affect their efficiency. Another issue is voltage drop, which can occur due to factors such as the length of the wires or the quality of the core material. Regular maintenance and proper design can help prevent these problems and ensure the proper functioning of transformer induction coils.</p>

1. What is a transformer induction coil and how does it work?

A transformer induction coil is a device that uses electromagnetic induction to transfer electrical energy from one circuit to another. It consists of two or more coils of insulated wire wrapped around a core made of iron or other magnetic material. When an alternating current is passed through the primary coil, it creates a changing magnetic field which induces a voltage in the secondary coil, allowing for the transfer of energy.

2. What materials are commonly used in the construction of transformer induction coils?

The most common materials used in the construction of transformer induction coils are copper wire for the coils and an iron core. Copper is an excellent conductor of electricity, allowing for efficient energy transfer, while iron is a highly magnetic material that helps to amplify the magnetic field created by the current in the coils.

3. How are transformer induction coils designed and constructed?

The design and construction of transformer induction coils involves careful calculations and considerations to ensure efficient energy transfer and proper functioning. The number of turns in the coils, the size of the wire, and the type of core material all play a role in the design process. The coils are then wrapped around the core and insulated to prevent short circuits and ensure safety.

4. What are the main applications of transformer induction coils?

Transformer induction coils have a wide range of applications, including power distribution, voltage regulation, and electronic devices. They are commonly used in power plants, electrical substations, and household appliances such as televisions and computers. They are also used in various industrial and scientific equipment, such as welding machines and particle accelerators.

5. What are some common issues or problems with transformer induction coils?

One common issue with transformer induction coils is overheating, which can be caused by excessive current or poor insulation. This can lead to damage to the coils and affect their efficiency. Another issue is voltage drop, which can occur due to factors such as the length of the wires or the quality of the core material. Regular maintenance and proper design can help prevent these problems and ensure the proper functioning of transformer induction coils.

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