Realization of 22Hz transmitter by using magnetic coupling

[betwixt]

I strongly suspect that Royer oscillator will be completely impractical. The values may be calculated correctly (I didn't check them) but the physical size and availability of them would make it impossible to build. Even a 100uF non-polarized tuning capacitor would be tough to buy but add to that the two 100H chokes and you are talking of something the size and weight of a small car. Theoretically you could make the tuning capacitor from two back-to-back 200uF polarized ones but I doubt you would find it stable enough for tuning purposes anyway. The problem is the transmitter (Pig) and receiver have to be on exactly the same frequency because the receiver bandwidth would be very narrow and a Royer oscillator would be very prone to drift with temperature and age if electrolytic caps were used. Even a few Hz difference would stop it working.

Are you constrained to using this method? I still feel an acoustic solution would be better.

Comparisons with ISS and interplanetary links are not really valid. The signal attenuation through 4m of soil is probably more than that from Mars to Earth!

And yes, I heard Sputnik in my earlier years - and that infernal Chinese satellite that sent a looped tape recording of their national anthem all day and night until it's batteries gave out. These days it's easy to hear the ISS downlink on a hand portable receiver.

Brian.

 

[Warpspeed]

Something like a 350 Farad ultra capacitor and 150uH air cored coil might work.
It would need to be pulsed with a short pulse of direct battery to ring at 22 Hz.

The 22Hz excitation frequency would need to be divided down from a very accurate crystal oscillator.

A similar tuned circuit in the receiver, and then using an identical crystal frequency divided down to drive a box car averager should be able to detect coherent signals down to below the average noise floor.

 

[FvM]

I strongly suspect that Royer oscillator will be completely impractical.

Me too.

Besides feasibility of inductor and capacitor values used in the design, it's unlikely that a free-running oscillator achieves the efficiency of a class-D amplifier driven by a precise analog or preferably digital oscillator.

At least the receiver bandwidth has a lower limit by the required detection speed for the moving pig. As mentioned in literature, the transmitter coil circuit will be partly detuned by the embedding steel tube. A high Q circuit might need electronic tuning means. Or you decide for a switch-mode coil circuit without resonance capacitor.

The comparisons with long-distance radio transmissions are only true in very general regard. Actual properties of the inductive near field are quite different from electromagnetic wave transmission.

There's effectively no attenuation of a VLF magnetic field by soil, steel tube is the dominant problem.

 

[Mohammad_Pirzadi]

I strongly suspect that Royer oscillator will be completely impractical. The values may be calculated correctly (I didn't check them) but the physical size and availability of them would make it impossible to build. Even a 100uF non-polarized tuning capacitor would be tough to buy but add to that the two 100H chokes and you are talking of something the size and weight of a small car. Theoretically you could make the tuning capacitor from two back-to-back 200uF polarized ones but I doubt you would find it stable enough for tuning purposes anyway. The problem is the transmitter (Pig) and receiver have to be on exactly the same frequency because the receiver bandwidth would be very narrow and a Royer oscillator would be very prone to drift with temperature and age if electrolytic caps were used. Even a few Hz difference would stop it working.

Are you constrained to using this method? I still feel an acoustic solution would be better.

Comparisons with ISS and interplanetary links are not really valid. The signal attenuation through 4m of soil is probably more than that from Mars to Earth!

And yes, I heard Sputnik in my earlier years - and that infernal Chinese satellite that sent a looped tape recording of their national anthem all day and night until it's batteries gave out. These days it's easy to hear the ISS downlink on a hand portable receiver.

Brian.

Mr. Brian I agree with you.but I have no information about acoustic method.how it works? how to design it?

- - - Updated - - -

Me too.

Besides feasibility of inductor and capacitor values used in the design, it's unlikely that a free-running oscillator achieves the efficiency of a class-D amplifier driven by a precise analog or preferably digital oscillator.

At least the receiver bandwidth has a lower limit by the required detection speed for the moving pig. As mentioned in literature, the transmitter coil circuit will be partly detuned by the embedding steel tube. A high Q circuit might need electronic tuning means. Or you decide for a switch-mode coil circuit without resonance capacitor.

The comparisons with long-distance radio transmissions are only true in very general regard. Actual properties of the inductive near field are quite different from electromagnetic wave transmission.

There's effectively no attenuation of a VLF magnetic field by soil, steel tube is the dominant problem.

thank you. what is your recommendation?

 

[betwixt]

The acoustic method is similar to sonar. It uses Time Domain Reflectometry to find the distance from a known place or places.

Basically, from a fixed location (maybe where the Pig is dropped into the pipe) you send a short but powerful burst of tone then start a timer and start listening for a reply. The Pig also contains a microphone and a loudspeaker (possibly combined as one transducer), it listens for the tone and as soon as it hears it, it sends a tone back again. When the fixed point hears the reply, it stops the timer. From the velocity factor of the fluid in the pipe and how long it took before hearing the reply, the Pig's distance along the pipe can be calculated. If the reply from the Pig is at a different frequency, the receiver can eliminate echoes of it's own signal by filtering them out. It doesn't give you the Pigs coordinates but it tells you how far down the pipe it has travelled. Presumably you know where the pipe is so it should be easy to work out where it is located.

Brian.

 

[Mohammad_Pirzadi]

The acoustic method is similar to sonar. It uses Time Domain Reflectometry to find the distance from a known place or places.

Basically, from a fixed location (maybe where the Pig is dropped into the pipe) you send a short but powerful burst of tone then start a timer and start listening for a reply. The Pig also contains a microphone and a loudspeaker (possibly combined as one transducer), it listens for the tone and as soon as it hears it, it sends a tone back again. When the fixed point hears the reply, it stops the timer. From the velocity factor of the fluid in the pipe and how long it took before hearing the reply, the Pig's distance along the pipe can be calculated. If the reply from the Pig is at a different frequency, the receiver can eliminate echoes of it's own signal by filtering them out. It doesn't give you the Pigs coordinates but it tells you how far down the pipe it has travelled. Presumably you know where the pipe is so it should be easy to work out where it is located.

Brian.

Mr. Brian I have almost examined all brands of PIG locator systems. all them use ELF-band electromagnetic waves. you opened a good aperture for me and I think using magnetic coupling is the only possible way for now! what are your practical recommendations for realizing this nightmare project via EM waves?

best regards
Mohammad

 

[PlanarMetamaterials]

Since there is a device inside the pipe (the PIG), I assume it is mostly empty.

Could you not excite a cylindrical waveguide mode (at microwave frequencies) and use the pipe to guide it? You could extract positioning information from the phase of the signal, or even two-way communication with readily available radio modules may be possible.

 

[Mohammad_Pirzadi]

Since there is a device inside the pipe (the PIG), I assume it is mostly empty.

Could you not excite a cylindrical waveguide mode (at microwave frequencies) and use the pipe to guide it? You could extract positioning information from the phase of the signal, or even two-way communication with readily available radio modules may be possible.

hi. I agree but not economic.

 

[Mohammad_Pirzadi]

The acoustic method is similar to sonar. It uses Time Domain Reflectometry to find the distance from a known place or places.

Basically, from a fixed location (maybe where the Pig is dropped into the pipe) you send a short but powerful burst of tone then start a timer and start listening for a reply. The Pig also contains a microphone and a loudspeaker (possibly combined as one transducer), it listens for the tone and as soon as it hears it, it sends a tone back again. When the fixed point hears the reply, it stops the timer. From the velocity factor of the fluid in the pipe and how long it took before hearing the reply, the Pig's distance along the pipe can be calculated. If the reply from the Pig is at a different frequency, the receiver can eliminate echoes of it's own signal by filtering them out. It doesn't give you the Pigs coordinates but it tells you how far down the pipe it has travelled. Presumably you know where the pipe is so it should be easy to work out where it is located.

Brian.

Mr. Brian plz answer my latest question.I'm waiting for 2 days!!!

 

[Warpspeed]

Some of us are getting just a little bit tired of your continual DEMANDS.

 

[CataM]

Besides feasibility of inductor and capacitor values used in the design, it's unlikely that a free-running oscillator achieves the efficiency of a class-D amplifier driven by a precise analog or preferably digital oscillator.

[...] A high Q circuit might need electronic tuning means. Or you decide for a switch-mode coil circuit without resonance capacitor.

Indeed more eficiency, but more complex solution.
Obviously becuase of the low frequency constraint, magnetic components are bulky.
Anyway, I do not see the inductive coupling a solution for such a distance, but it may worth a try with a sensitive reciever as described in previous posts.

 

[betwixt]

Mr. Brian plz answer my latest question.I'm waiting for 2 days!!!

Please remember that I do this as a volunteer and I have to do other work to make a living. I have just come back from a two hour meeting that took 11 hours to travel to, thats why I haven't been able to answer. I got home late this evening and need some sleep before my brain will work properly again (if it ever did!)

Brian.

 

[Warpspeed]

Yesterday just for fun, I actually had a go at building a 22Hz resonant tank circuit.

First attempt was with the high voltage secondary winding removed from the EHT transformer of a black and white TV, slid onto an eight inch ferrite rod.
The dc resistance of this coil being 90 ohms just completely killed the Q.

Next attempt was with a full spool of 0.63mm diameter enamel copper wire on the same ferrite rod. this resonated with a 470uF uF electrolytic, but the Q was still far too low to be worthwhile.

Third attempt was a massive 120 turn winding of 3mm diameter copper wire that was originally the primary winding of a welding transformer. Inserted into the middle of that that were three 30mm x 30mm x 90mm ferrite I cores. That resonated at around 22 Hz with a 22,000uF electrolytic. The Q was still pitifully low.

At that point I gave up.
Reaching a Q of even 2 or 3 seems to be very difficult.
Probably a laminated iron (or mumetal) core, with a large number of turns of very thick wire, but that is going to be very large and very heavy.

Maybe there is a different approach ?

At least in the receiver, a capacitance multiplier circuit would offer small size and the possibility of potentiometer frequency tuning. The transmitter tank capacitor is a whole different problem.

 

[betwixt]

I'm heading off into dreamland here but I wonder if a different approach might work: instead of thinking of the pipe as a barrier to the EM field, to use it as a single turn coil resonator. So instead of driving at 22Hz, the frequency would be much higher, maybe hundreds of MHz with the RF capacitively coupled on opposite sides of the pipe wall so it induced currents around the pipe itself. I can see it working on a small scale, it would be similar to driving the center of a folded dipole but looking at it 'sideways on', it would be a folded dipole with huge element thickness. My guess is even if that principle worked, the soil attenuation at higher frequencies would limit the range to maybe a few cm anyway.

Well done for trying the experiments Tony, it confirms our fears about the resonance of bulk inductors and capacitors, it just isn't feasible.

If I understand commercially available Pigs, they actually have a very short range and rely on the sensor being clamped around the pipe. That makes the problem much easier to solve of course becuase magnetic and vibration sensors can easily 'hear' the signal but as soon as the physical contact with the pipe is lost, the attenuation rockets upwards. Picking up to source of vibrations 4m under ground with a portable device would be virtually impossible.

Brian.

 

[FvM]

If I understand commercially available Pigs, they actually have a very short range and rely on the sensor being clamped around the pipe.

You have both, clamp on sensors, particularly used in plants with many pipelines and hand held sensors. According to manufacturer catalogs and applications literature, some meters detection distance are feasible with thick walled large pipelines for the VLF type. Links have been given earlier in this thread.

I imagine that detection range is effectively limited by pig travel speed, the requirements may vary. The apparently large offer of VLF pigging systems with various vendors and many different pig sizes convinces me that the method is working in practice. So it's just a matter of engineering (electromagnetic and electronic design) to make it work.

Many years ago, I made a sensitive inductive 50 Hz detector to locate underground power cables. I believe it had a resonant receiver coil circuit, but I'm not sure. Of course it used a low noise band-pass amplifier. In any case it worked quite well and served it's purpose.

Alternative methods (acoustical, guided HF along the pipeline) seem to be used as well. Exciting a tube as electric dipole might work theoretically, I expect that the RF power is mostly eloping up and down the pipe. And the respective VHF to UHF frequencies will be strongly absorbed in soil. But the idea might be worth to be calculated in an EM solver (perhaps after processing the VLF problem, which is considerably less complex, as previously mentioned).

 

[CataM]

Many years ago, I made a sensitive inductive 50 Hz detector to locate underground power cables. I believe it had a resonant receiver coil circuit, but I'm not sure. Of course it used a low noise band-pass amplifier. In any case it worked quite well and served it's purpose.

Do you remember (more or less) what could have been the maximum distance between the cables and reciever ?

 

[FvM]

Unfortunately not. Several meters for sure.

But you can't compare the setups. A power cable has only a small residual field caused by the center distance of the individual conductors which is even cancelled at some distance because the conductors are stranded. On the other hand there's no shielding ferromagnetic tube around it.

 

[Warpspeed]

Maybe we are all being dazzled by the secret mysteries of electronics.

I wonder if a really powerful revolving (at exactly 1,320 rpm) rare earth magnet could induce anything worthwhile into the pipe wall at 22 Hz?

 

[betwixt]

That's a great example of lateral thinking! It would certainly allow a small battery powered motor to spin the magnet and have a reasonable life expectancy. I'm thinking the magnet would have to be aligned so maximum N and S fields radiated at 90 degrees to the pipe. I'm no expert in 'power' magnetism but I wonder if the pipe might form a shorted magnetic loop around the field and counter-drive the motor, making it harder to rotate. There is also the issue of the body of the Pig counter-rotating as well but there might be a solution in using two magnets, presumably spaced as far apart as possible but rotating in the opposite directions. Please don't ask me to calculate the resulting field pattern, it would be a nightmare to work out.

Brian.

 

[Warpspeed]

Yes, I think it would become like an alternator with one huge shorted turn.

Whatever eddy currents could be induced into that pipe, all the energy would have to come from the motor and the battery anyway, no free lunch there, unfortunately...

But there might just be enough external magnetic radiation to be detectable outside of the pipe. Its a bit agricultural, but it may possibly be the most compact and power efficient way to do it.