Hi. Just a very quick follow-up video to my previous one on the P Electric effect or microphonic effect of multi-layer ceramic capacitors on the front end of oscilloscopes inside the PCB and how that a tap on the top of the case can transfer a shock either a low lowish frequency one like that or a high frequency one like that with a little Uh tap through the PCB through all the mechanical couplings into the Uh capacitors, which are generally microphonic, you can get one that are more immune to the microphonic effect. Mder and others make various Uh caps. Anyway, almost every Uh oscilloscope on the market suffers this effect from somewhat.

but I Thought it was quite ironic that if I um, tap the scope and tap the screen on a touchcreen thing that it would couple through and uh, rightly so a lot of people said, hey, that's not a realistic scenario cuz the inputs are unloaded and fair enough so let's take a very quick look at this. Now, typically the multi-layer ceramic capacitor the culprit inside the front end here is generally going to be on the input side of the input buffer. Um, so if it was on the other side of, say, the Jfet amplifier in there, for example, then that would be a low impedance output and the relatively High impedance Uh Mlcc capacitor and the low Uh amplitude signal levels we're talking about here. If you load it down with any significant impedance, it's just going to swamp it out and you're not going to see any impulse at all and I'll be able to demonstrate this in a second.

So a lot of people said, hey, you know it. The effect vanishes if you plug in an actual probe in a real world scenario. Okay, well, let's take a look at that. um, which it does, by the way.

And yes, if you turn on 50 ohms. So let's actually go in here like this and we can I'll actually demo that I Forgot all about the Uh 50 Ohms. Where's here? No, this thing doesn't have a 50 Ohm. Doesn't this thing have a 50 Ohm input? No, it doesn't But if we whack a 50 input Terminator on there, then it completely vanishes.

You won't see anything there. Um, at all. I don't have one handy. Do I No.

Anyway, I'll be able to demo that in a Uh second. So what we're going to do is uh, I'm going to plug in the actual Uh probe which comes with the Rtb Uh 24 scope and this is a problem across virtually All Digital Scopes We'll have a look at the Roden Schwarz I Thought it was quite ironic, just that you know you can tap a touch screen and it comes through. So let's plug in that. it's the RT Zp3.

It's a switchable probe. so let's plug that in. and let's actually short out the input like this and let's turn it to times One mode, shall we? Okay, so basically we are shorting that input, just directly shorting that input. And sure enough, um.

I'm triggering off a different channel here. Number three. You can tell it's color coded actually, so which is quite a nice feature. Um, and so I'm triggering off Channel 3.

All the other channels are getting the impulse through the PCB, but you notice that channel One is just fine and dandy cuzz. We're shorting the input, so that shows that the offending capacitor inside this is on the front side of the input buffer. Um, because we're loading it down with the impedance, the impedance of that's going to be quite High The impedance of this is zero. Um, well, you know it's at the end of the line.

Anyway, Transmission line. We won't get into that details, but let's have a look. What happens if we switch it to X 10. I've still got it shorted.

Okay, but in the Times 10 mode, we've got a Emeg resistor in there. Okay, so let's see if it's still a problem here. And yes, it is. Okay, Yes, it's reduced in amplitude because you've got the Nmeg resistor.

Um, plus the cable capacitance. You know, Well, the transmission line. Let's anyway, right? You've got the 9 Mega resistor in here. Um, effectively across the uh, forming an impedance load, across the the offending capacity inside.

Here, it's loading it down so it's dampening the effect. but it's still not zero. Okay, it's still not zero and you can actually get it. Um, if you touch on the screen.

okay, even still touching on the screen. Granted, you've got to do it quite, you know, viciously. but you can see that it's still couples through so it doesn't get rid of it completely, even with a completely shorted load with X 10. But granted, if you're doing low signal level measurements, you're generally using a low impedance.

Source Anyway, with a X 1 probe, you wouldn't be using a Time 10, so you know there's fair enough Merit to that. but there are cases where you're measuring: High Impedance low low signal amplitude level loads I Used to Uh sources I Used to do this with hydrophones, for example, in Uh, the seismic industry as an example, our photo diodes. Another example, there's various examples of high high output impedance High Impedance low amplitude level um, uh sources so you know it is possible I Just wanted to show that it still actually does come through. Yes, it is greatly diminished, but you can see that it does actually couple through.

It's only because like it's the trigger point I'm trying to, you know, trying to get there. but you can see, you know I'm not even putting a huge amount of force onto that, it seems to. but see, even like even little gentle Taps Like that depending on how how you trigger it, you know you do get a little bit a little bit of something in there. But yes, it essentially vanishes.

So not saying that this is a big that, there's a big problem with this scope or any other scope with this effect. CU In most practical cases, yes, it's going to be diminished or go away completely in a real probing situation. but not always. So there's always that one.

You know that one pain in the ass case. you're going to get where you know you could get an Impulse a little impulse in there. If you're getting low signal level measurements, you got high res mode you're doing. You know, like you, you're trying to see down in the noise.

I Just want to show that it's still actually possible to do that with a shorted probe input. And by the way, um I showed this in the previous video. Uh, and I've done a whole separate video on this a long, long time ago. There are also multi-layer ceramic capacitors inside these.

They're either times 10 probes. either have them in here at the base or they have them inside the probe here. and uh, Daniel from Keite. Actually just did a video where he was tapping the probe like this on the top causing an input and an impulse.

And yes, that impulse is coming from the probe so you can see the amplitude. there is absolutely Mass Oh, absolutely massive right? that? look at that. That's okay. What? What? What do we got there? That's uh, 50 MTS per division because the capacitor inside that probe is causing that so you don't want that is an order of magnitude worse the ones inside here cuz they're more directly coupled either inside here or inside here, right? So look, you can see that I'm still getting stuff coupled through cuz that's coming through low.

Let's go back down. Okay, there we go. That one that one there even though it doesn't do it when you short it out. So if I tap on there right, there's nothing.

But if I tap it on the actual case of that which has the ceramic microphonic capacitor in there, you can see that it's causing that impulse. So just be aware. I've done a separate video a long time ago on that effect, that probe effect and that's probably more important than you know, tapping on the case or anything like that. So I hope you found that interesting.

You just wanted to show that technically it's still possible so all mean, like, by all means, don't avoid buying this because you think you know this is still you know, going to be like a major problem in every Everyday Use it's not I just want to show in some cases of high impedance uh loads. um, High impedance sources that it can be an issue and if you're uh, doing 50 ohm input termination I'll forget it. You're never going to uh see this issue at all because those multi ceramic capacitors are quite, uh, effectively, a high impedance. um Source or effectively a P Electric element.

They're a H, they're a, you know, they're a hydrophone. that kind of Sim same thing that I used to work on basically back in the day. And they, if you're working on a high impedance source with X One probe, it can be a problem so doesn't vanish completely anyway. hope you found that interesting.

Catch you next time.