High Quality EMF Meter

[kwired]

'

however, a 10' long piece of pipe laying parallel under a
230 KV bus 30' overhead on a warm day when the air
conditioners were on, had a strong enough field to induce
90 volts in that pipe, and you could clip on, and run a
milwualkee drill with it. you couldn't touch the service
truck parked there without gloves on.

And if one lives right under the line like that - why bother paying for a service connection, make your own "transformer" on your own roof or patio and power your house with it

Back in early satellite TV days when they used to change the "descrambling codes" periodically to keep people from stealing service - I often heard - if they can bounce a signal off my roof, why can't I intercept and use it if I know how? Making the person selling any codes the only one doing anything illegal.

IDK, how far are you from Offut AFB?

I think he is a little further then I am, but we both would be better off to be at ground zero and get it over with quick if it should happen.

 

[gar]

170821-1955 EDT

Dennis Alwon:

The primary supply lines have currents that largely cancel each other. So daytime vs nighttime may not show a large difference.

A bigger difference might be seen where a three phase wye feeds single phase to a neighborhood. Here a substantial neutral current (better to call it the grounded primary current from the wye center point) will flow in the earth as well as on what is the neutral wire of the transformer secondaries that is shared between the pole transformers secondaries center taps. This center tap neutral wire is usually run about midway up the pole and the primary hot wire that is at the pole top. Thus, we have some large spacing between the forward and return current paths relative to where you would make flux measurements. Thus, possibly larger flux measurements at ground level or on a second floor near power lines.

In my neighborhood we have essentially three phase delta at the top of the pole, and no ground path except for the secondary ground path between neighbors on the same transformer. My readings tonight below the primary lines are 10 to 30 microvolts. The same as earlier today.

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[gar]

170823-1300 EDT

Ravenvalor:

When I use the word quantize it means the smallest incremental change in reading that I can see. My meter that quantizes to 10 microvolts is a 4.5 digit RMS meter made by Beckman, and probably over 20 years old.

You titled this thread "High Quality EMF Meter". Possibly it should read "Sensitive EMF Meter". I don't think you need high quality or high accuracy.

I think you might want resolution of 0.5 to 0.1 milligauss, filtering at 50 Hz to substantially reduce harmonics, repeatability of 1 to 5 %, and accuracy of possibly 10 %.

You can make your own sensing coil to provide good sensitivity with a square clear white pine wood bobbin 16" on a side and 1000 turns of #28 magnet wire. I have one with 200 turns. Also this can be used to measure the earth's DC magnetic field. A meter that resolves 0.1 millivolt, average reading like a Fluke 27 is fine.

You can do your own calibration of this sensing coil.

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[gar]

170823-2136 EDT

My last post had a typo that I had thought I had corrected. 50 Hz should be 60 Hz.

With the 200 turn coil 16" on a side I get higher signal levels than with my smaller calibrated sensor. To be expected because of the greater flux linkage.

To filter some of the high frequency noise I added a simple RC filter using 100 K and an adjustable capacitor from 0 to 1 ufd.

Looking at the waveform on a scope there appears to be something that probably can be described as a 60 Hz carrier with a random sort of lower frequency modulation. There does not seem to be a dominate direction for the point of origin.

Looks like I might need a correlation detector synced to my line voltage.

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[gar]

170825-1400 EDT

Using my scope to look at the sensor output, filtered and unfiltered, I see lots of different signals that voltage wise are of the magnitude of my residual 60 Hz base level. At times larger. These various unknown signals are what cause fluctuations in the readings I get with with a simple AC meter.

Some of these may result from submarine communication. See https://en.wikipedia.org/wiki/Communication_with_submarines .
United states 76 Hz, and Russia 82 Hz for carrier frequencies.

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[gar]

170825-2144 EDT, 170826-1406 EDT

Playing around with an 18" square coil of 30 turns which has close to an inductance of 5 millihenrys I see a signal that looks around 50 kHz. With about 0.0018 ufd of parallel capacitance the resonance is about 50 kHz and rough tuning seems to peak this signal.

The peak to peak signal is about 100 millivolts for this mostly continuous carrier. Then there is short pulse modulation every varing period around 8 milliseconds, and a more consistent pulse period of about 16 milliseconds. The pulses vary considerably in peak value and damp fairly quickly. There are time periods when the pulses almost disappear.

These were dimmers exciting the sensing coil and its tuning capacitor.

Is this the time signal from NIST at 60 kHz? See http://tf.nist.gov/general/pdf/1383.pdf WWVB is listed at 60 kHz. So no it is not NIST-WWVB.

At this point in time I had not turned off all noise generators in the housee --- CFLs, LEDs, Comcast cable TV modem power supply, dimmers, a COSTCO 4' LED, and various computers. After midnight I turn off all the junk and used a 250 W flood and flashlight. This eliminated a lot of confusing signals.

Then I started to learn more about my scope. I had never tried the digital filter before.

For the following plots I used a sensing coil 18" on a side and 20 turns. This has an inductance of about 5 millihenrys, and self resonance probably in the several hundred kHz range without any added capacitance except scope input and wires from coil to scope. Self resonance to be determined.

The interesting results of my most recent experiments are signals at about 4 and 8 Hz, and the expected 60 Hz. The submarine frequencies did not pop out, but I did not filter for them.


Plot 1 no filtering:







Plot 2 low pass below 80 Hz:



Here you see the 60, 8, and 4 Hz signals.




Plot 3 low pass below 20 Hz:



Now only the 8 and 4 Hz signals show up.
.


Plot 4 FFT of the signals:



You can clearly see the peaks at 4, 8, and 60 Hz.


.

 

[Ravenvalor]

170821-1955 EDT

The primary supply lines have currents that largely cancel each other. So daytime vs nighttime may not show a large difference.

A bigger difference might be seen where a three phase wye feeds single phase to a neighborhood. Here a substantial neutral current (better to call it the grounded primary current from the wye center point) will flow in the earth as well as on what is the neutral wire of the transformer secondaries that is shared between the pole transformers secondaries center taps. This center tap neutral wire is usually run about midway up the pole and the primary hot wire that is at the pole top. Thus, we have some large spacing between the forward and return current paths relative to where you would make flux measurements. Thus, possibly larger flux measurements at ground level or on a second floor near power lines.

In my neighborhood we have essentially three phase delta at the top of the pole, and no ground path except for the secondary ground path between neighbors on the same transformer. My readings tonight below the primary lines are 10 to 30 microvolts. The same as earlier today.

.

gar,

We have roughly the same setup in my neighborhood. The three 3phase lines are at the top and the center tap neutral wire is about midway up. Interestingly enough all of the transformers in my neighborhood are being fed from only one of the 3phase lines. None are being fed from the other 2 with the exception of a single residence that has a residential shop in the backyard with 3phase. So it looks like 3phase was run throughout my entire neighborhood in order to feed one shop that probably rarely if ever uses it.

I ended up getting the LATNEX MG-2000T EMF Meter. It was under $200 and I can toggle inbetween single and triple axis to help pin down the source of an EMF problem.
https://www.amazon.com/Professional-Interference-Industrial-Appliances-inspections/dp/B01HQBRZ9O#Ask

I have taken about 6 - readings with the new meter of the 3 - 21,000volt overhead powerlines that are running about 25' above my yard and am only getting a reading of about 0.01mG.
The largest reading that I am getting is from my static utility meter in which the reading is on average 550.00mG at 1" distance and only 10.00mG at 12" distance. I am not an expert with the inverse square law but these two readings vs their distances seem off. I plan to call my utility company in hopes of getting someone out here with their meter in order to compare my readings with theirs.

Thanks for helping me find a sensitive EMF meter. It sounds more politically correct