Hi just a quick blurb video with potential issue with the keysight u 1272 a multimeter here. What One of my viewers Bernhard Roth was measuring using this meter to measure the current on his power supply at like a project or whatever and getting some strange readings on the display and it turns out that it was near to the leads that were used to measure the current. We're near to an RFID reader and you know he played around. Finally narrowed it down using a function generator to a noise pickup and I'll show you this right now.

it's some sort of you know conducted common mode thing. I Anyway, let's have a go see if we can recreate it. So what I've got is the U 1272 I connected to my function Jenny and I have got our five megahertz. The frequency does matter as we'll see in a minute at 10 volts peak-to-peak square wave.

Okay, well touchy-feely and I'm just going to take just the positive terminal here. Here we go and I'm gonna plug this in on the amps range. Okay so well it's Milliamps. it'll switch dance when we plug it into here and look what we get.

the grounds just flapping around in the breeze. We're getting negative 5 amps. a huge reading like that and you take it out and it goes away. you plug in the negative one.

Let's try that and it's not as high, but you still get a reading on there now. There's obviously some sort of conducted noise which is reference to because this output here is mains earth referenced so that you know is there is a whole system here. There's capacitance everywhere going on. Anyway, we won't go into RFI and EMI and all that sort of stuff, but there is some sort of conducted issue there with that meter and if you plug it into the ground terminal, not nearly as much.

Okay, so there is something relative to the common measurement of the you 1272 ice. So there's obviously some sort of conducted common mode issue going on with this meter. So I thought I'd Actually, just first of all, recreate it with exactly the same settings. Try out a whole bunch of different meters that we've got here and give it a bill.

So the first one is the Keysight u 1273 IX This is their art. Waterproof, low-temperature version of this screen is flickering because it has that only display. Let's plug it in and see what we get. Yep, you bet you look at that.

12.1 amps. Exactly the same thing going on there with that one. Not surprising because it's basically and almond practically identical meter to the u 1272. I Accept it.

Hazard the OLED display on the thing. Now let's try the Keysight u 1282 a You've seen this before. This is the rugged meter and well, not nearly as high, but it's still there. Okay, so we getting negative point one amps so it still seems to be an issue with that one, but not nearly as bad as what we're seeing here.

Let's try the Dawson Metric up. It just switched off Thank You Dawson Metro Heat energy. Here we go, no worries whatsoever. We're down on the micro amp range because this has a single jack to do everything.

Not Not A Not an issue, not an issue whatsoever. My Fluke 87, The venerable old Our Fluke 87. Sorry, I'm not getting the best angles and stuff here. Anyway, it's reading bugger all.

Let's go old school with a fluke 27 Here we go. Nope, bugger all on that one too. And it doesn't matter if I do that negative one of course. And the Broman BM 8, 6, 9.

A lot of fans of this meter out there and nope. And once again, it automatically detected that there's a thing plugged in the air jack and everything's hunky-dory So let's go over to the Fluke 17b, shall we? Let's give that a bow. No, absolutely nothing. The Eevblog be M23 Five? nope, nothing.

And the Unity Cheap. Unity UT 61a Absolutely nothing. And just for kicks the keysight. Um, Three, Double four, six, one A.

Yep, that one actually shows something there. So there you go there - 84. But it's micro amps, right? So if we manually switch that to the AM stranger to be Nephal? really. But no, technically that one has an issue as well.

you're plugging the negative one. So obviously reference to Grant to mains Earth in some way, shape or form. They're plug it into the 10 amp jack. Yep, similar sort of thing.

But you know. Yeah, it's not a huge amount. so as you can see, it basically only seems to be the keysight. These particular ones.

these ones, in particular, the U 1270 series meters, is something going on there. Whether or not it's a huge deal, you could say maybe not. But hey, Burner did actually get this problem in a real world scenario measuring our current you know, project Current Frontier from a power supply. So yeah, there's some sort of conducted mode vulnerability there.

But I'll show you something interesting. Let's now try see what happens instead of just plugging it in. Okay, Bingo. Oh, there it is.

Four amps or whatever. If we just hold it near it, then we can get that to happen as well. So it's not just conducted its radiated pickup as well. Sunset.

So what have they not designed? the RFI in immunity? Good enough inside this thing. Um, seems to be that way. It's certainly picking it up. A lot of other meters out there don't have it.

so let's just quickly experiment with some settings. here. We're on a square wave. Of course, let actually change it to a sine wave.

and I Think the harmonics of the square wave are going to be an issue where it invokes peak-to-peak So five megahertz. There's tons of harmonics right up into the RF region. So let's put it on sine wave. And hey, it's still there though.

Okay, so obviously higher harmonics are causing more of an issue here. So I would presume. So let's go back to square wave. So let's go down in frequency and we should actually I I Think this is going to drop as we go down in frequency at a certain point.

Yep, it's going down down I'll have to go across there. Okay, Nine, Nine Hundred, K 400 K it's going down There we go. It's starting to become a whoop. Did it go back up there a little bit? Maybe it's gonna be all sorts of things, but Nine Kilohertz, you know that's not particularly high.

And once again, if we switch to sign I reck'n'd yet, that would go away. Yep. But so obviously the square waves are calling and causing much higher harmonics s so that can really jump up. We can actually get it even higher than that.

Here we go. Yeah there, there seems to be some points, but look, we can go out to like thirty-two amps Wow Negative: thirty-two apps that you've Airy much and if we actually that's plugged into the positive, check if I plug that into the milliamp Jack There we go. If I plug that into the common terminal. There you go.

Same thing but yeah, you plug that into the amps jack and Wow look at that. Thank you very much. And if we just dangle that over there, be better. If we got a coil or something.

we could really couple it in. but once again, where we can we were able to couple in well in what it thinks is a couple of milliamps. But yeah, and of course we're gonna see this change with amplitude as well. So if we go over to our amplitude and then we drop our amplitude, there you go.

One volt peak-to-peak Okay, it's it's becoming much less of an issue. 500 millivolts you know, but still. Yeah, that is interesting. That is definitely our confirmed.

They're nice results that this thing is susceptible certainly to direct conducted. RFI On to the positive: Am sled like this, but Bernard originally saw it when it wasn't being conducted in it was being irradiated in from a nearby RFI Reader: watch this. I'm measuring 1 amp coming from my Rygel power supply here flowed in power supply. No worries whatsoever.

and if I go to plug this in, look, it's already changing. Just this coupling between from this coax into that meter. Enough to what you know. throw it way out of spec.

Wow. I saw I haven't even connected the damn thing up yet. So now if I hook it on, that's going to completely screw that up. Yep and the right guy power supply is still measuring 1 amp there.

But yeah, this thing is completely knackered look and even now, one volt peak-to-peak here more than enough to throw that completely out. And I try that on other meters and it's simply not an issue. It's only on the keysight ones strain and as far as the bench meter, that was a little bit susceptible. Me nothing because as we saw before, it was like micro amps and check it out if we fill up this meter.

Okay, let's put it down here. couple it into this lead yep, causes it causes an issue down there. But let's let's fill her up and look. as we go higher, the current is decreasing.

Wow Wow We're at point two. This is shocking. Yeah, 10 volts peak-to-peak It's pretty severe at 10 megahertz. you know that's but.

jeez, don't get this on any other meter. See absolutely nothing and you'll notice it can change with just coupling of my hand as well. Watch this mmm spooky action at a distance. Look at that.

Oh, it's nothing to do with my ESD mat either. Look, if I actually if I ground myself I've disconnected my mat from Maine's earth. Okay, look so I May and I've been connected this through to the mains earth on my Rygel here. so it's actually connected through and hmm so just still main serf coupling.

and if I connect myself to the mat as well. So got my finger actually under the conductive bottom of that mat. Properties change a little bit. Maybe if here we go lift my fingers.

not now, Not. It's all the same anyway. spooky so It's not picking something up. You know from my ESD mat or anything like that I've had issues like that before actually with like a floating ESD mat when it's not grounded and stuff like that.

but I Love it. The thing that actually concerns me the most here is not really the conducted mode our stuff when we plug that in. okay, it's an issue they need to look into, but the fact that you're just using this meter on the bench, you've got it sitting next to your you know your object is and you switch it on and look. it's the cable.

It's just flapping around in the breeze. and of course if you take it anywhere near it, you're gone. Ski. I mean that's just.

that is nuts. Absolutely nuts. So there you have it. The You 1270 series has an RFI vulnerability.

You remember the good old Fluke 87 GSM phone thing where you used to put a GSM our phone next to it and it would cause it to lock up and reset. It's not as bad as that, but well, actually I'd rather have my metal lock up and reset then. um, just give you dodgy readings like that. So there's some RFI vulnerability.

They're both are conducted and coupled. so I haven't read the spec sheet offhand for this thing. but they most likely have an Let Romania conformity spec for this thing. But yeah, um, keysight.

Please explain. Catch you next time! Hi Welcome to the EEV blog and Electronics Engineering video blog with interest to anyone involved in electronics design. I'm your host Dave Jones hi Why do I have the lab coat on today? Well it's myth-busting time. Got his mobile phone and he put it next to his flute 8075 and it killed it.

It braked it. So yeah I thought I sacrificed my 8075 and tried here cos this is really interesting. Let's see what happened.