Re: under100 Hz transmitter
thanks for your helps.
http://obrazki.elektroda.pl/5400485000_1479651401.jpg
This is the real key; unfortunately I do not know if there is a standard software that can simulate the attenuation of the signal.
I wonder if similar calculation that are useful for computing the skin depth can be used as an approximation.
Without some rough idea to guide us, the problem is intractable.
GPS = Global Positioning by Satellite but I said GPR.
GPR = Ground Penetrating Radar.
Intense but narrow beam pulses are directed into the ground from a mobile (sometimes hand held) device and the timing and intensity of echoes gives you the distance to and density of underground structures. GPR would tell you where the pipe was but not the PIG inside it but if the PIG vibrated the pipe wall in some way it would show as a modulation on the GPR reflection and that could be used to find it's location.
VLF acoustic waves may pass through the wall of the pipe but EM waves will be highly attenuated as FvM explained. If say 99.9% of the signal didn't reach the outside of the pipe, the chances of the remaining 0.1% being detected through 5m of soil as well is almost zero.
Brian.
but all PIG locating systems use ELF EM waves to detect the PIGs. A 22Hz transmitter is located in the PIG and the hand-held receiver detects the EM waves.
see the below link.
http://www.pigging.com/X100-1N.html
hi everyone.
which frequencies can pass metals and soil with the lowest attenuation?
thanks
Hi,
I know nothing of your subject area, don't want to waste your time too much, from what I see one problem is the pipe material, besides the seemingly big hurdle of signal attenuation, I guess there's no way of adapting some of the more sophisticated metal detector designs to locate the "pig" (if made of/encased in a specific metal whose signature is easily identifiable) and ignore the steel/iron pipe, as both systems seem to rely on a similar Tx Rx system?
The difficulty is that the inductive coupling between two coils only works provided there is nothing in the way that provides a much easier and shorter magnetic path for the magnetic field than through the remote coil.
A two inch steel pipe (shedule 40) has a 3.9mm wall.
A twelve inch shedule 40 steel pipe has a 10.3mm thick wall.
Larger pipes are even thicker.
As stated earlier, the main near field coupling medium at these frequencies will be completely magnetic.
It seems pretty unrealistic to expect the available energy from a couple of AA cells to magnetically penetrate at least 4mm of mild steel.
If you try to induce an eddy current around the circumference of the pipe, I cannot see how there would be much of a magnetic field extending beyond the pipe itself. The magnetic flux will find a much easier path through the steel than radiating out externally.
In answer to an earlier question about what moves the pig. The pig is like a free piston in the pipe, it moves along the pipe as the fluid moves. Sometimes there might be a different type of fluid ahead and behind the pig, so you can use the same pipeline to alternately transfer very different fluids with very little mixing.
In a gas pipeline, water or condensate sometimes accumulates at low spots which can be a problem. Passing a pig through the line powered by differential gas pressure, will sweep any water ahead of the pig and clear the line. This is often done on a routine basis.
thanks a lot. do you have any functional idea? it's very very important to me.
The only way I can see this working is as already suggested in post #8 by Betwixt
A tuned tank circuit with axial coil might be made to couple into the pipe and induce a circulating current around the circumference of the pipe. That part is easy, but I just cannot see that producing much of an external magnetic field around the outside of the pipe.
This would work well if the pipe was non ferrous (non magnetic). But a very thick steel pipe is going to be a very big problem for you.
As there are commercial devices that claim to already do this, it must be possible, but it is going to be far from easy to make a receiver sensitive enough to be useful.
If you want to explore the outer fringes of technology, scalar waves might offer a possibility, but I have absolutely no idea how those are either generated or detected.
Anyone here know ?
Is this related to cable location?
That depends on the coupling medium, and what you are trying to do.
Three possibilities.
Direct electrical coupling through stakes driven into the ground.
Magnetic coupling through coils.
Electromagnetic coupling through antennas.
All are very different and each presents unique problems.
Found a manufacturer's article giving some quantitative data about relation of wall thickness and detection distance. http://www.pigging.tools/Aprodit-Art...ing_a_Pig.html
It shows that the intended project specification is basically feasible, but also that the field attenuation by the pipe walls is rather challenging. It seems usual to specify the detection range of low frequency electromagnetic pig transmitter/receiver systems by a free a air range. This allows a simplified calculation of design properties.
Post #9 brings up the idea of sound transmission. I once heard the sound of a plumber's 'roto rooter' going through an underground pipe, a few feet below ground. The sound of scraping was easy to hear, and its position in the pipe.
To use the same idea with the pig, you could have a solenoid tapping against the pipe.
Also post #13 suggests tapping against the pipe wall.
It depends.
DC (zero frequency) is blocked by a conducting enclosure- the electric field is not felt outside.
On the other hand, very high electromagnetic radiation is also blocked by the conducting metal.
Somewhere in between, metals show some transparency to EM radiation. And that depends on the frequency.
The peak (wavelength) depends on the conductivity of the metal, the thickness and the polarization.
The metal body acts like an antenna and radiates the exciting frequency.
So vague the question, so incomplete the answer.
E-field is blocked, DC M-field passes conductive enclosures, but is affected by ferromagnetic metals.
no, but it's something likes that.
I want to send signals underground to the surface.the transmitter is located into a steel pipeline.but I am baffled which choice is better. E field, M field or EM? Which frequency should I choose?
I think 22Hz is the best choice. help me.
thanks
If possible, shortly describe all 3 possibilities to me. thanks.
do you have any functional idea? I'm so tired by this project but I must complete it till February 2017.
Electric currents can be sent through soil directly, mainly due due to moisture, most soils are electrically conductive to a greater or lesser extent.
If you drive stakes into the ground separated by some reasonable distance, and pass a current between them, the current does not all travel in a direct path, but spreads out horizontally and vertically in a large cross section.
These currents can be detected at a distance by driving other stakes into the ground, so its possible to communicate through the ground directly without wires over some short distance. All this requires a direct electrical connection to the ground. Its interesting, but not particularly useful.
Another method is to generate a low frequency magnetic field around a coil. If there is another coil in the vicinity, the signal can be received. The magnetic field always takes the easiest path, and may be readily distorted by magnetic objects.
And that would be very unfortunate for you if one coil is surrounded by a thick steel pipe. In this case the coupling will be entirely magnetic, no direct connection to the ground is requires, so hand held receiver is possible.
Third method is by electromagnetic propagation (radio waves) which is also non contact, but it requires a very log antenna at very long wavelengths to work efficiently. At 22 Hz a half wave antenna would need to be roughly 7,000 Km long, which is obviously a practical impossibility.
Thanks a lot, I think utilizing of magnetic field is the only way. in this way, I am thinking on Wireless Power Transmitter (WPT) method. now I have 2 questions:
1- what is your practical proposal about utilizing magnetic field?
2-as I said, the WPT technology is a choice in my mind.what's your advice?
As commercial devices to do this already exist, your best bet is to research those.
As they probably represent a fair bit of experimental research and development, its unlikely that you are going to achieve or discover some better solution.
The research may have been done "in house" in which case you probably may not be able to discover much.
If you are really lucky it may have been part of someone’s thesis and its all there ready to scoop up if you can find it.