EEVblog 1379 - What's all this NPLC Stuff Anyhow? 

I love demoing this trickery to people however I usually take it a bit further and put my feet on a power board or hold a mains cable which capacitively couple huge amounts (for 10 MΩ) of signal onto a bench DMM or oscilloscope (sometimes 50+ V and enough to dimly light an LED), this way you can also demo how grounding yourself almost completely removes the signal and that those capacitively coupled 'ghost' voltages (especially those from isolated switching supplies) aren’t something to be afraid of (but might give you a small tingle).

Dave finds the free energy test leads and still doesn't believe in it

Most people outside of the electronics industry have no idea how big and ubiquitous the electric fields are that surround us all the time. When I was just starting out in electronics design, I was working on a switching power supply, and was measuring the switching frequency which changes with load on a very old (1950 - 1960) scope. I was doing this in the basement of the house where I was living. Depending on the day, I was seeing both the expected switching frequency but also a signal at 1.160 MHz. I chased that 1160 KHz signal for weeks, trying to understand what was going on. Finally 1 day the signal was so big that dominated the measurement to such and extent that it was clear that this signal had some sort of modulation on it. So I ran it through a diode and then into my stereo input, and presto I was listening to a local AM radio station on 1160 KHz. Turns out that the basement dimensions were just the right size to form a resonant cavity, and that AM station would somedays be up to 1.5 Vpp on open leads. Even just moving to an upstairs room would cause the radio signal to be reduced to more normal radio signal level of uV or nV, un-measurable on my ancient scope. Just a little story about how experience is important when designing anything. :-)

Free energy community: "That's free 2Vpp form empty lead! Gonna harvest that"

These little fragments of new knowledge is what I love most about this channel. :)

Fun fact: The integration time adjustment on many meters maxes out at 10 NPLC, and the 100 NPLC setting is just an average of ten 10 NPLC measurements for example. This is because of the 1/f noise in the input amps and integrator which becomes problematic with longer integration times. I think the Keithley 7510 that Dave shows in the video performs best in the 1-5 NPLC range, Keithley might have shown a graph of noise vs NPLC in the manual somewhere, very interesting stuff!

3:30 the stock market uses this as their input for deciding the prices of most stocks lol

These are the videos that both make this channel what it is and underrate it at the same time! But I believe that these will be the videos that people will always come back to in time because the content is so valuable... Great job 👌

Thank you Dave! I have a 5.5 digit HP bench multimeter. I bought it used on eBay and the 1 VDC reading had me concerned. I did a google on the subject and read it was due to the high impedance. I let it go at that. Now watching this great video enlightened me so much deeper on the subject. I had not idea the multimeter was integrating. I never knew about the powerline cycles etc. Now I know, thanks to you. I am now going back through my multimeter manuals to understand how to vary the number of PLCs etc.

That Keithley has an amazing refresh speed, looks like at least 50x a normal multimeter.

I learn something!

Wow Dave your meter looks so much better than the OEM red meter. Looks good in blue.

Thanks for demystifying this.

Committed to memory. As always, thank you Dave

I always thought my meter was at fault since it was a dumpster find. Good to know it's working just fine. Thanks.

wow that was interesting! I never expected such a phenomena to occur!

So, essentially, you’re deliberately abusing the Nyquist Sampling theory - winner, winner, chicken dinner! 🤣

Dave must have found those leads in the Over Unity section on ebay.

Excelent video!! Welcome to the difference between deterministic noise and random noise. Averaging ( low pass filter after sampling depending on implementation ) is mainly designed to kill high freq random noise. A moving average ( different from averaging frames) can cancel out a deterministic noise if the averaging period exactly matches the signal period( to kill a 50hz signal with a Fs of 100KHz you need 2k samples) . However as you said, "Integration" is effectively anti-alliaisng low pass filter before sampling is performed. By increasing the the value of integration you move the role off frequency under 60Hz killing the deterministic noise.

I'm already fall in love this meters

Handy hint. Cheers, Dave.

I miss Bob Pease , what a star he was.

Love the title, RIP the analogue king

Actually, you can google this when you need this info. But Dave's visual presentation and charismatic explanation is always the best way to learn and remember something new! 👍

Thanks Dave good stuff!

Very interesting stuff. I love these videos and find them interesting. Thumbs up :D

Greetings from Caracas Venezuela I just subscribed to your channel, thank you for sharing your knowledge God bless you always!

When a microphone capsule FET input leg is open, I can hear tons of random hiss.

I literally used a 8.5 digit meter the other day, and saw this exact thing! So coincidental!

Thanks for explaining the reason for this, I have Keithley 2000 and 2015 bench meters. The voltages are higher on the 2015, thought it was some coupling from the audio circuits until I got the 2000.

Thanks Dave

Thanks for posting dave i got the same thing in my uni t ut61e

When sampling a signal, you can reject local interference by sampling at a frequency equal to the lowest common multiple of the frequencies to reject, or harmonics of the LCM of the frequencies to reject. EG Sample at 300 SPS to reject both 60 and 50 Hz.

The video title reminds me of Bob Pease series... RIP EE greybeard

I typically leave mine set at 10 NPLC, sometimes I use 100NPLC if I need more accuracy.

A 7.5 digit meter has a continuity beeper and cap range?!?!? Yikes. No transistor test??? Aww...

At first I had no idea what could cause that, but I'm pretty sure it's an alias after you showed us the trend. Great video as always!

Dave have you ever wondered why picked up PowerLine noise is never even close to sinusoidal and rather triangular? Where is the non-linearity? ???

"wiggle, wiggle, wiggle, wiggle, wiggle, yeah: -- LMFAO!!

Good topic! 😁

I loved this episode - fun and enlightening topic. Now.....send me one of those 7.5 digit meters so I can do confirmation tests in my own lab.

damn you deserve that IEEE recognition.

Love the title. Reminiscent of Bob Pease, RIP.

Damn, free energy, ... have to make a circuit to charge my phone 😂

Never forgetting this one....

Sampling high impedance singlas is where this can really come in and bit one. I though sometimes wonder, if 230 +/-20 VAC noticeably worse than 110 +/-10 VAC. Considering that most regions using the lower voltages tends to operate at 60Hz instead of 50Hz, then it should have some stronger capacitive coupling into leads and such, but the reduced voltage should negate that effect by a fair bit more. I guess there isn't an all too major difference for one or the other in the end, and if one is really paranoid, then one would just shield one's main power cables. (And yes, magnetic interference is also an issue, but steel conduit should reduce such. Though, building an anechoic chamber to have a lab inside of is likely the highest degree a voltnut can reach...)

very interesting!

Internally for many DMM aperture time is not always equal NPLC, so saying its a symptom is not quite right. For example settings NPLC100 on 3458A is not same as aperture to same time, as meter internally takes NPLC10 readings and filter them together.

Is it (PLC) based on triggering or timer? And would a multimeter for US market be less precise in a country with 50Hz mains?

Is that sampling video available somewhere? Because I don't see the difference between averaging lots of samples taken at way above nyquist rate and integration as long as they represent the same amount of wall time. At least if we remove numerical precision issues in the averaging.

Try power the bench meter from isolated supply. Can it make any difference?

Is the BM786 integration time in the 50Hz filter in this multimeter set in the firmware or is this a physical integrating RC plus some kind of diode chain? In light of some of the minor issues with the EMF pickup reported regarding the measurement of reasonably large resistance around 660-670kOm would be interesting to know

Could you manually calculate mean of sine of logged data? I think it's some unproper use of mean function in multimeter in case it don't work...

I think this is what my 3478A is doing. I always thought is was going to break at some point. The resistance is pretty far out of spec on lower resistances but it still works. Are these still worth sending off for calibration?

You keep telling you cannot get the same result with short integration times and averaging the samples. But I cannot see why averaging would not work, as long as the sample rate is high enough to avoid aliasing AND the averaging time window is large enough. Assuming you have some large sample rate, as the length of the averaging window approaches infinity, the cutoff frequency of the "effective lowpass filter" should be approaching zero.

Who can kindly share the link to Dave's video on dual-slope ADC sampling? Thx!

How do the high end dmm meter overcome the issue related to noise coupled via the mains supply which is coupled via the mains step down transformer. Even if we have filter capactor at the output stage of the power supply will they still not couple noise on the powersupply lines?

I think I remember from my school years, that this phenomenon has to do with Nyquist theory of signal sampling, that states that if you want to measure a signal of a given frequency, you need to set your aperture to at least twice the frequency of the phenomenon. This NPLC setting is doing exactly opposite: if you don't ever want to see a signal of a given frequency (to exclude it as a noise without having to filter it later using math ) you just set your aperture low enough.

Hey Dave! You should take a look at the Miniware MDP XP portable lab power supply. It can run off a power bank too! It looks like a pretty good gadget worth taking a look at. I'm planning on buying myself one. :)

It's quite unscientific I'm sure, but I hooked a fm car antenna up to my scope and walk around and look at all the stuff it picks up. Holding it up by the microwave produces some interesting stuff as well as sockets, cfl's and so on.

Fascinating stuff...Oh yeah, can you do an impersonation of Ben Heck ?

Do these high end DMMs actually measure incoming mains crossing point to sync the NPLC, or does it rely on an internal clock? Just thinking you could get quite a lot of phase error on the final cycle with high NPLC counts if it's not synced.

So this means that hand-held DMM that don't allow manual setting of 50/60Hz have to be pre-configured for the target region?

Is the PLC just a fixed value or is the up down integration timing actually coming from the power line of the bench plug ... Ie will it track drifts in the power frequencies?

So can you run it on a car battery?

Does the equipament measure it's AC supply frequency to determine if 1PLC is 1/50 or 1/60 second? What if the instrument power cord is being fed by a generator or inverter with a frequency that is not in sync with the "real" all around mains electrical fields?

hey dave, would or could wifi and radio transmissions be the cause? the waveform looks like its repeating the same way a radio wave would

Hello Dave! Big fan! Can you tell me when the 121GW will be back in stock?

I don't understand why post-averaging does nothing. I could write a simple program to do a moving average on those fluctuating voltages shown and it would definitely have an effect. Either the meter's averaging window is very small as to make it useless or I'm missing something.

Nice. Nice. On a related note. I wonder if shielded mains cabling in walls and lighting, and from sockets to equipement, would help with anything to reduce the noise floor further. I know there are mains cable with shield or screen, or even both. There is for example a Swiss company called Gotham Cables that manufacturers some shmick multi-shielded mains cables (about 8CHF/m), I am not exactly sure who is manufacturing these cables for Gotham, but maybe labkable from Chaina. Another similar company is Lappcable, Yarbo, Elecaudio, and Oyaide (some of which are definitively total snake oil and don't come with any datasheets or certifcations, but still are interesting) . They obviously sell these stuff mostly to audiophilic nuts, but maybe there is a bit of merit in using them. Similar cables can be found for industrial applications, most notably motors, servos and steppers, but they usually have weird voltage ratings, and usually way more conductors to be useful for mains. Usually one will then connect the shield and screen to earth close to the source (i.e. socket or distribution board). Another option is to put mains cables in walls and stuff in metal pipes or channels, and ground them. Just an idea for future experiments. In some lab settings it is possibility to use that, for example when building a new lab, then one could put proper trunking, grounded pipes, shielded cables, and shielded cords and outlets, and lighting (there are companies making EMI shielded LED drivers and fixtures, as well shielded incandescend light sources, often to be used in RF testing or testing chambers).

Hi Dave I thought the leads act like a dipole antenna....

Is it fair to say that the difference between PLC integration and simply averaging multiple samples later, is that the samples averaged may not exactly coincide with the mains cycle? Kind of like filming a spinning wheel; only when the frame rate exactly coincides with the rotation speed does the wheel appear to stand still, otherwise regardless of frame rate it will appear to spin one way or the other. The wheel can even appear to slow down and everse direction as the frame rate comes in and out of time with the rotation speed.

I've got a cheap handhelt autoranging multimeter, and it jumps around even much worse than these high end meters. It jumps around in the tens of volts...

When will you be designing a filter? :)

What would be the purpose of having a non-integer PLC setting if it needs to be used always for accurate measurements?

Hi Dave, brymen bm786 is currently sold out on amazon. Is there any plans to resume it's supply in nearest future? I really want to order one. Thanks in advance.

Not mains and crap ...free energy!!

is it picking up radio?

Is the timing for the integration directly coupled to the mains cycles or is it determined by some crystal oscillator? I imagine that this could lead to some kind of discrepancy/error because of oscillator tolerances and drift.

Should that mean then that when using a high end bench meter if they are that sensitive, should the test leads be shielded

I have several top bench meters in my own lab too. In my dreams.

Does not appear to be an issue with the Agilent 34401A 6 1/2 digit meter. I wonder why?

Then what is the use of sub unit PLC?

Dave head not audio synced with vid. Only mentioned because I know you care how your new setup is doing.

+1 for sorting out us newbies & self taught old grey beards.

1:50 Are you sure it's your microphone and not a geiger counter?

My fluke model 322 clamp meter was damaged, please can you send me the diagram, friend, I can't get it anywhere

With the probes tips unconnected the voltage across them could be anything. You need to connect to a known voltage. People usually short them.

At 1 PLC does it actually sample a crap load of samples and then integrate them or does it simply sample once a PLC?

Must be all the 'Free' energy from the ether that you are measuring... LOL

"Joule slope" :-)

How to bug the new guys test bench...

I just keep looking at that Keithley DMM7510 meter, and can’t concentrate on the video….

Using a digital oscilloscope should be another way of demoing intergration

This is all a lot of fun when you are in a plane....

0:00 I bet it's gonna start with "Hi" 0:02 Knew it!

I am not getting how the mains signal is being picked up. Is it just from a 50/60Hz magnetic field coming off of nearby powered-up equipment and transformers? That would explain why twisting the leads greatly decreases the amplitude of the signal on the bench multimeter. But the leads aren't connected to each other. They don't form a loop! How can a magnetic field induce a current without a conductor that loops? I am thinking here of the Maxwell-Faraday equation where EMF is induced by magnetic flux-- but magnetic flux, by definition, is measured through a *closed* loop. Or is it somehow caused by the power supply of the bench meter? Would a battery-powered meter not show this? No, Dave suggests the reason the handheld DMM doesn't show it is because the signal is integrated over a large enough time interval. That suggests it is a real signal that is coming through space and putting charges on the inputs of the instrument, right? What exactly is the physical mechanism that causes the 50/60 Hz signal to end up measured by the bench meter?

se me daño mi pinza amperimetrica fluke modelo 322 por favor me puedes enviar el esquematico amigo no lo consigo en ninguna parte

How does this affect measuring actual signals at 50 or 60Hz?

Nice to see someone using IrfanView