Spark Generator

[wizard]

You are probably correct in thinking that a spark would be an almost ideal point source of sound, whereas the sound of an impact would radiate from the entire surface, depending on how mechanically damped it is. I think that the peak amplitude would still be highly localized to the point of impact, so you could still locate it accurately.
I am not advocating this method. I was just trying to give you something else to think about.

I am not sure he is able to do so easily, the sound (noise) would be generated along the arc too (proportionate to the freq which the arc is generated at).

If he wants to use mechanical waves he has to go for much more frequencies, much more than 20kHz. I am suspect to the mechanical waves for the said task though.

 

[Roff]

I am not sure he is able to do so easily, the sound (noise) would be generated along the arc too (proportionate to the freq which the arc is generated at).

If he wants to use mechanical waves he has to go for much more frequencies, much more than 20kHz. I am suspect to the mechanical waves for the said task though.

I would think the length of the arc would be short relative to the resolution required, but I am only speculating.

 

[alireza]

Ali, An Arc generates sound or noise by air molecules not by the connected surfaces. I mean if you want to use a sounded spark to calculate the distance between the surface and the probe (i.e. the start point of the spark) then you should consider that the sound is produced at the whole points of the spark not just at the surface. Besides did you consider that the audible sound is not narrow for your job?

I think youre confusing my mean. in some earlier posts, I put an image about my idea. the distance that I want to determine is between arc and microphones.

you should consider that the sound is produced at the whole points of the spark not just at the surface.

You are right. But I think, this error is negligible in comparison with the measured distance. The arc length is about 5mm but the distance is about 1m. so the error is just 0.5%.

Why don't you use ultrasonic for the said task?

Maybe ultrasonic is better. I will test it

 

[alireza]

I am not sure he is able to do so easily, the sound (noise) would be generated along the arc too (proportionate to the freq which the arc is generated at).

Wizard!
Can you tell me, in which frequencies the arc is generated?

If he wants to use mechanical waves he has to go for much more frequencies, much more than 20kHz. I am suspect to the mechanical waves for the said task though.

If the sound is much more than 20kHz, its not hearable. is there any microphones can hear it?

 

[wizard]

Hi Ali,

I was not able to see the picture. It was not opened for me.

I think it is no matter where the microphone is mounted at. If you need a NARROW beam of sound for your job, you should know that audible sounds are not narrow (due to their low frequencies) at all. Audible sounds are propagated spherically in the medium, not cylindrically. It is no matter if the transducer is a speaker or a narrow spark.
I never have worked with a CMM device before. But I guess it uses a narrow beam of light like laser to determine the shape of an object, Right?
Unfortunately sound beams are diffracted and refracted as they travel in the medium. Are you thinking that the sound would not be refracted to the other dimensions of the measure object? Or maybe you have an extremely sensitive device which is able to detect the MAX of the audible sound!?
Please let me know how much of sound directivity do you expect and or need for the said project.

What do you mean by "Can you tell me, in which frequencies the arc is generated?"?
At several projects I used a variable arc between 5 kHz to more than 50 kHz. When we are talking about the arc frequencies we are talking about the frequencies which the high voltage transformer is swing at (We have to use alternating current for any transformer, otherwise the transformer will not work at all. You know that the alternating current has to have frequency). According too the transformer the higher the frequencies the much more magnetic flows will be cut and (that's why the fly back transformers are so small). So the arc frequency is proportional to the limitations of the transformer too. Are you thinking that the DC currents are not able to generate arc at higher frequencies? They do.
If you want to use ultrasonic waves, then I am seriously suspect of the abilities of a fly back at mega hertz frequencies.
Can you let me know why did you decide to use an ARC for your project?
Why didn't you go for electromagnetism (laser for instance)?

 

[alireza]

Hi wizard!
Thank you for your reply

I was not able to see the picture. It was not opened for me

I upload my pictures in tinypic website. why have you problem to se that?

Please let me know how much of sound directivity do you expect and or need for the said project.

There is no obstacle between generated sound an receivers, so I think the little error in directivity is negligible. It is not very important for me.

What do you mean by "Can you tell me, in which frequencies the arc is generated?"?

I mean that which sonic frequencies does exist in the spark?
I think there is a full range of defferent frequencies in the spark, but its better exist a short length spike in it.

We have to use alternating current for any transformer, otherwise the transformer will not work at all

It is not correct. If you connect and disconnect a dc battery to an ignition coil quickly, it generates a spark in secondary coil. you know that an arc is Continuous but a spark has very short leght of time.

Can you let me know why did you decide to use an ARC for your project?
Why didn't you go for electromagnetism (laser for instance)?

I would like to build a Sonic CMM not laser os other stuff, because there are several types of CMM that work with laser, light, tought trigger and etc. I want to work with sound. (not with arc obligatory!). other things that produce audible or not audible sound is applicable.

 

[wizard]

Hi Ali,
Why don't you try to attach your picture at this forum?

Why do you think that there is a small error due to the audible sound?
Please tell me why did not you go for a small speaker rather than a spark? Is it due to your assumption of thinking that the spark will generate sound waves which are more directive than a small speaker? If the response is nope so please let me know the reason?
You told me that the directivity is not important for you! Why you are thinking so? Are you sure that the sound would not be picked up by the other microphones but just with one?
Do you consider the bending of the sound by the edges of the measured object?

"It is not correct. If you connect and disconnect a dc battery to an ignition coil quickly, it generates a spark in secondary coil. you know that an arc is Continuous but a spark has very short leght of time."
I don’t know what are you desire to tell me?
Do you think that we are not able to have an arc if we use DC voltages at the secondary of the transformer?
The arc can be generated at both DC and AC.
According to your above example (i.e. battery and spark),
The spark is generated due to due to AC voltage i.e. joining and cutting the battery which cases frequencies in the ignition coil and thus on the spark…

At my above post, I tried to tell you if you use a suitable device to generate a proper spark, you will not be able to hear it if the frequency is mounted at the upper range of human hearing.

 

[Roff]

I think he wants an impulse of sound that radiates in all directions, so he can receive it with multiple microphones and compute the origination point (location) of the sound by using the arrival times at all microphones. A speaker is not a point source, and most are not omnidirectional.

 

[alireza]

Hi wizard!
I agree with you. you are right. My opinion is the same as you. Maybe there is a misunderstanding.

never mind

Wizard! here is my idea:

Please tell me your idea exactly

 

[alireza]

I think he wants an impulse of sound that radiates in all directions, so he can receive it with multiple microphones and compute the origination point (location) of the sound by using the arrival times at all microphones.

This is my opinion exactly

A speaker is not a point source, and most are not omnidirectional.

Waht can I do?

 

[alireza]

Hi everyone
I tested my opinion with ultrasonic transmitter, but I couldnt locate the position of emitted point exactly

why?

 

[Roff]

Hi everyone
I tested my opinion with ultrasonic transmitter, but I couldnt locate the position of emitted point exactly

why?

How can we even guess, when you provide no details of your circuit or location calculation algorithm?

 

[duffy]

Trying to hit the accuracy of a CMM machine with this seems like a pretty tall order. A typical transducer resonant frequency is 40khz, that gives a wavelength of 8.5mm, which means you are going to have to hit a point in that curve with repeatable 1/8,500th accuracy to get to micrometer resolution. Ultrasonics become useless much over 100khz because of coupling problems (impedance mismatch) with air.

You might be better off using that spark to sense the distance to the surface electrically by monitoring current flow through the tip.