Just remember an EMF reader doesn’t specifically single out AC, it measures any electrical force and that might not be noise. You would, after all expect some current to flow through a cable.
The other important point is at what distance is the force. Most things will give a readingif pressed up against the sensor. But do they drop off with distance? Often just a few cm sees a massive drop off.
This isn’t one of the things I use an EMF meter for. I think it was @Simon-in-Suffolk who suggested it. I use them regularly for mitigating interference in the server room, locating quiet spots for the WiFi router, and vertically over hifi to help understand reasonable shelf distance and stacking order.
And of course checking places people plonk themselves for long periods like the bed, office chair etc. Just remember if pointing to a light source, you may need to insert a card over the sensor to avoid a false positive. The sonsor is somewhat like a solar panel. Light will induce a current. Point it at the sky on a sunny day and see.
I think all / most meters will measure and single out EMF change over time (AC) and detect frequency ranges… some meters will separately measure DC electro magnetic flux… … usually. Some meters provide broadband probes… so detect an aggregate of frequencies between a range , and others have more selectable frequency ranges.
EMF meters can be a great tool for measuring and hunting out RFI… and see if there is actually any measurable unwanted varying EMF (RFI)
I have used a bandscope as an EMF meter before and I can zoom into specific frequencies of EMF and their harmonics from a coupling probe ( a coil )
It was this method I used several years ago when I was hunting out why a small Netgear network switch was causing ‘birdies’ on my NAT03, but a Cisco 2960 wasn’t……
Thanks Simon. I think my update as not very clear. I was trying to convey the need to establish what is “normal” and “desirable” before interpreting readings. You can get a reading easy enough, but whether that is high or unexpected really depends on a control reading.
You can’t really know what numbers are problematic unless you have an acceptable baseline for comparison.
I’ll give a specific example: coming out of my wall in the office I have two mains leads. One’s a powerLine going to a UQ2 and the other just a standard lead going to a mains block for the office equipment. If I take a contact reading from both, the PowerLine reads 350V/m and 190mG, but the standard lead to the mains block reads 350V/m and 27mG. Wow the PL is so much worse on the megnetic reading… or is it? What problem am I attempting to solve and why would I necessarily think any specific number was bad?
Now, if I turn the same test on it’s head and say, “okay, my reading of 350V/m is my baseline, what is the effect of a RF band common mode ferrite choke on the PL?” Then I can measure change. As it turns out, since I moved, I haven’t had time to judiciously apply chokes as I had religiously before so I did this test as I updated this thread. The impact is a very real and reproducible drop of contact electric field from 350V/m to 320V/m.
But what’s missing, and I think needs to be remembered is that in an uncontrolled domestic setting, even in my second more meaningful test, we still don’t have a control baseline to say what is “normal” or “desirable”.
[addendum] Incidentally I measured a low end (much lower end than the PL in terms of cost) Furutech mains cable coming out of a dedicated circuit socket (so two variables have changed, not one) and the reading was 31V/m and 0.0mG. Quite a difference wouldn’t you say. I suppose we can call that reading “desirable”.
Yes the EMF strength falls faster than inverse square law of the distance, and is dependent on the shape and layout of the emanating conductors/leads/piece of equipment etc. This EM field area is what is known as the EMF near field… beyond the near field you then have the transition region or radiative near field and then the far field where the EM field has transitioned to radio waves. There are smooth transitions between these.
The ICNIRP has a fantastic wealth of resources on this including papers of health impacts and considerations. Many governments and standards bodies use some of these findings to define safety standards.
From a scientific and engineering perspective this is a fascinating area as there are still many knowledge gaps on the health impact of EM near fields which require further discovery and investigation… we certainly don’t know it all
I have no idea yet. There are actually 4 variables involved now I think about it. Maybe 5. The really low readings on the Furutech lead include:
An isolated (but not dedicated) earth.
A Furutech socket (I’d not expect that to affect this reading though)
The furutech cable itself.
The dedicated circuit.
And the 5th difference I suppose being that the Furutech is the only thing plugged in on that socket whereas the PowerLine in the office is sharing a two socket outlet with a whole bunch of office gear (though there is an NTT mains noise isolator in line for the office gear).
This has given me something to think about and test. But mucking around on a weekday while I very much have work to do is probably not the time to do it. Seems like a Friday night play activity.
I do also have an oscilloscope with high voltage isolating probes but it’s not rated for RF band. It would pick up 50Hz AC noise quite accurately… As will my Hioki clamp meter. Whether I really want to shred up LAN cables to get at isolated poles or not is another matter I seem to have far to many recreational projects on the go at once.
I seem to have far to many recreational projects on the go at once.