Hi welcome to the Eev blog an Electronics Engineering video blog of interest to anyone involved in electronics design. I'm your host Dave Jones Hi I'm Dave Jones I've got my Tectronics Oscilloscope here and I'm going to show you a rather interesting effect that you may not have seen before or you've heard of, but you may not know that it actually applies to the Humble Oscope probe. I've got my standard Tectronics 200 MHz P2o probe here and let's take a look at this effect. Okay, I've got my TDS 1012 Digital storage oscilloscope here.

the Uh Single Channel I've got it set up to 100 Mt per division, 500 microc time base set to normal trigger and the trigger levels at about 50 MTS or thereabouts. and I've got my probe here set to Uh time 10 position. I've taken off the Uh Ground probe and the Um tip as well because if you put the tip on, you'll notice that we, uh, pick up a fair bit of noise if we do that. So we'll just take that off and watch this.

Look at that. look at that effect. I'm just gently tapping that probe on the desk there and you can see that there is an an actual Uh shock response a stand a pretty standard shock response that is picked up by the probe and you'll notice that this will change a bit depending on the surface I've got. Obviously, if I tap it on the bench here, that's a hard surface so that's generating a lot of Uh G's into the actual probe itself.

Now, if I put it onto the antistatic mat over here, which is spongier, it's a similar kind of response. It's uh, slightly. it's the same frequency response, but uh, the response is a little bit dampened because of the surface we're actually doing it on. Now one of the keys to this is the orientation.

the physical rotation orientation of the probe when it actually strikes the surface like this. Now if if I've got this switch on the other side here, over here, that's the one that's the position that generates the most amount. Now if I just rotate it so that the Um switch is on the top there. So I've rotated at 90, it still does it, but we get a different response and it is dampened.

and if we rotate at 90 again, so we're 180 where we uh, were from before or you'll notice that there's once again very little shock response and we rotate another 90 and we're getting back there. but we have to have the probe around facing the other side to get that effect. And if you're wondering if time 1 or * 10 position makes a difference, well, we'll put it on X 1 here and we'll do it again. There it is.

It really doesn't make much difference at all. And if you're wondering what sort of voltage levels we can get out of this, well, this is 500 m per Division And let's do that, shall we? I Can get that to well over Uh 2 Vols Peak to Peak And we don't have to just tap it on the bench either. We can actually tap it with a screwdriver and use it as a set of drumsticks. Neat.

But as you can see, the response is certainly a fair bit different. And you're wondering what this little waveform here was, which we, uh, picked a glimpse of there. It has nothing to do with this shock response, but I show I thought I'd Show you this anyway cuz it's another rather interesting effect. If you put the probe near the screen like that, you can pick up the uh backlight um signal.

You can pick up the EMC from the backlight on the screen like that. And it's rather interesting that each each oscilloscope will have its own um, uh, specific waveform for the backlight inverter. You're wondering what happens when we short out the probe. Well, I've got some Al foil here as we call it in Australia You guys might call it something different, but let's short that short that probe out like that.

There we go. It's shorted out with some Al oil and let's try it again. We can still get the response, but it's significantly significantly lower amplitude and it is a different response. Once again, we have the orientation the same around like that and as you can see it is it's a it's changed frequency and B it's a it's A It is a different response with uh, multiple Um transitions, uh, negative and positive.

And here's a cleaner response of that: I've turned the voltage level up and as you can see you can see the really sharp drops on this waveform. It is remarkably different. And it's not just the probe either. If we just sit the probe down there and we tap the input compensation circuit like that, Bingo you can get another response.

It's much lower in in amplitude. It's totally different, but it also has a shock response. So what's causing this? Well, it's probably a little bit complex, but what it uh ultimately is likely to come down to are the Uh ceramic capacitors used in these probes. for compensation.

this probe here will have a Um ceramic, uh compensation capacitor in it. um, some probes, this one doesn't but some pros will actually have an adjustment uh pot there as well. so they'll have an adjustable capacitor as well and also in the Um in the probe connector. Over here has a similar sort of circuit.

So I've got my little Dave CAD drawing here of a multi-layer ceramic capacitor and this is how they're constructed. They're actually that's why they call an Mlcc multi-layer ceramic capacitor because they are made up of multiple layers of uh, multiple layers of metal. between the dialectric, um, uh, the dialectric material and they're quite a complex construction. and they are highly.

these ones are highly susceptible to What's called the peo electric effect, and I won't go into detail of what the P Electric effect is, but it it uh is is basically Um. if like a Uh, a shock or vibration sensor will be a similar thing, it'll be a piso electric material like this. like a capacitor. essentially like a capacitor, but it's tuned for uh, you know, a flat response, a flat shock response.

but uh, multi-layer ceramic capacitors can have exactly the same effect. It's not nearly as linear, but it can certainly generate some high voltages, and it works both ways. If you apply a shock or a vibration into the capacitor, it will generate a voltage. But likewise, it will also generate sound output.

If you input a specific frequency at a high enough level, it will actually generate a sound. or what's called sing Um, it's called singing. These Capacitors will actually generate a noise, so it works both ways. Now, the capacitors used in these probes are very low value.

so they're likely in Um N/ Cog capacitor, which is not a multi-layer ceramic capacitor. And they're not supposed to be susceptible to the Poo electric effect, but apparently they are. You would have to go into much more detail to actually dissect these to actually figure out exactly what happened but and what's happening there. but based on the orientation, it's likely to be the internal capacitor.

Now, don't confuse this Peo electric effect with What's called the Tribo electric effect, which typically applies to cables. Now it may be having an effect on this as well. There may be a combined effect, but um I can actually get that if I turn the volts per division down okay to 50 MTS there and I whack this cable on there I can actually get an effect to happen and that's probably the Tribo electric effect. Or maybe it's coupling up through into the probe.

If I hold the probe and dangle it like that and sort of isolate the vibration going up, it's I can still get it, but it's maybe it's uh, actually coupling into the Um the input circuit there. But yeah, I don't know. It's a totally different effect, but it's rather unusual. So there you go.

That's a rather usual effect which you may have to watch out for if you've ever seen. If you ever see like an Impulse response like that, you know it might actually be something to do with the probe and somebody bumped it tapped it during probing or something like that. You might have to be careful. Might be a trap for young players, but give it a go.

It's rather interesting. Try it out with your probe on your scope and see what you get. Catch you later. Hi guys! This is actually my entry for the Mycronic Scope competition uh, which runs until the end of April So if you like this uh video, please go to the site and vote for it and you can actually vote uh once every day up until the end of April from a different uh IP address.

So uh, please get on there and vote for me if you like it and hopefully I can win this thing because now that I'm a, uh, officially an unemployed full-time video blogger I think I need to so really appreciate it guys. Catch you later! Yeah.