Oscilloscope Earthing / Isolation Challenges - Pt 1

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In this video I demonstrate some of the challenges a common earth through the electrical mains system can pose for oscilloscopes and other test equipment. I show the benefits of a portable / handheld oscilloscope (Siglent SHS810) and one that has isolated inputs (Siglent SHS1102).
(Problems with a function generator and oscilloscope that are both mains earth referenced.)
Thanks to Tester.co.uk for the use of the two Siglent Oscilloscopes:
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In the USA you can buy you Siglent scopes here:
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Thanks to Curt for the Jameco Function Generator Kit (search for product 20685):
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EEVblog #279 - How NOT To Blow Up Your Oscilloscope! :
• EEVblog #279 - How NOT...
ToddFun.com: Isolation Transformer - Tripp Lite IS1000:
• ToddFun.com: Isolation...
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Music clip from KZbin Music Library - Phase Three by Huma-Huma
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[@fieldsofomagh]

Great video,never thought that non isolated channels were troublesome.The 1102 really highlighted the benefits.

[@ToddFun]

Thanks for the shout out and the link to my video. And thanks for this video. I did not know they made isolated probe oscilloscope. That would come in extremely handy.

[@mjlorton]

***** My pleasure Todd.

[@daveys]

Excellent demo of why you’d want to buy a scope with isolated inputs vs a standard scope.

[@superdau]

You said it already (at least mostly), but I repeat it anyway: running your test equipment isolated from mains earth should always be your last resort. Isolate your DUT first. While isolating your scope will allow you to probe anywhere you want in the circuit without the fear of sparks, whatever you clip your ground lead to will come out of the ground clip of the other channels.

[@SeanBZA]

Noise on the blue siglent is from the scope power supply, being injected into the circuit. Try again with it on battery power only, and the noise ( coming down the power lead making it float at around 60VAC or so with HF noise on it as well) should disappear totally. Fix is a better power supply with better isolation and no injected noise, basically a DC supply made from a mains transformer with interwinding shield and with the output not earthed and able to float but with the shield connected to mains earth.

[@mjlorton]

SeanBZA Thanks for that post Sean...follow-up in part 2.

[@PuchMaxi]

It caught me too Martin, not so long ago even! Great video for explaining this. Isolating the device under test or the test equipment sometimes poses a real challenge. I look forward seeing the follow-up vid.

[@niceguy60]

The Siglent SHS1102 is $1,500 the Siglent SHS810 is $500. Buying the Siglent SHS810 and two set of Micsig DP10013 High Voltage Differential Probe for a additional $300 will give the SHS810 the same functionality of the Siglent SHS1102 but at only $800

[@andrewsweet43]

Ok the Siglent oscilloscope weird waveform is probably due to the mains power supply you are using for it. You are actually looking to two 50Hz signals conflicting with each other... The first is coming from your signal generator and the second from the mains. The thing with switching power supplies like the one your portable oscilloscope uses is that most of the times they use some small caps coupling the DC negative output to the mains side... So when looking at AC signals this can cause problems. Try using the same instrument to take the same measurment but only using batteries to she if that's making a difference :)

[@FubarGRblog]

Diodes have some capacitance and some inductance and therfore an unloaded bridge rectifier will oscillate. Usually the problem arises when measuring with a 10x probe because the resistance is too high. Switching to 1x will make the problem disappear. Sometimes simply touching the output of the bridge with your fingers will draw enough current to dampen the oscillations. Here's a related article: www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/electrical/measurearectifier.htm

[@Sinusoidal]

I recall getting caught out on the exact same bridge rectifier problem using a function gen and scope that were both mains earth referenced. One of those things that until you know about can really be a cause of concern, especially due to the possible dangers. Using two channels in differential mode is a good solution without messing about with making a devices ground floating.

[@thingyee1118]

Do Not ! Remove the earth pin to your scope as you can end up with a live chassis. Use a isolation transformer for the DUT or differential probes for the SCOPE.

[@niceguy60]

If you want a portable scope with channel isolation and you don't have the crazy cash flow for either a fluke 190 or 225 than the siglent SHS1102 or siglent SHS1062 are your only cost effective option. I own the siglent SHS810 featured in this video supplemented by a front end isolation module which is substantially cheaper than isolated probes to achieve channel isolation at the extreme cost of a 1MHZ band limit. If I want to use the 100 MHZ band of my scope than I will bulge and buy a isolated probe. My advice if you are a serious hobbyist is to either buy the Siglent models with isolated channels or try to buy a second hand fluke with the feature.

[@OmarMekkawy]

You can use a load resistor ( 1K Ohm ) to solve this problem because there is no current flows in the bridge rectifier due to the high input impedance of oscilloscope.

[@superdau]

Are these 1N4007s? Try adding a load on the output of the bridge rectifier. You've got no current flowing through the diodes, except for the low current that flows into the inputs of the scope. They can't really work as diodes at these low currents, especially 1N4007s.

[@SolidStateWorkshop]

Very true. One of the first things I did when I first got a scope was try to measure the output of a bridge rectifier without any load and I got some realllyyy weird stuff. All sorts of glitches. Added a little load and all the problems went away. Not sure if that's what happened here.

[@gradient8951]

Thank you very much for this information, now I will buy the shs 1102. Nice greetings from Germany

[@zcqw4a1]

This was really helpful info, and I know which Siglent I want to get now. Thank you!

[@muhammadsanibichi6114]

A very good tutorial for students to understand. commendable

[@LenMoret]

Thanks for the heads up, very enlightening!

[@w2aew]

Nice shirt!

[@Todestelzer]

The first thing I bought when I setup my workbench was a isolation transformer and disconnect the earth/ground connection at the outlet from it too.

[@mtoufiq59]

Great explanation

[@lonewolftech]

Thank you for giving me the information I needed! This was a very informative video from an electrical standpoint! Great information! I’ve been looking for a scopemeter that has isolated inputs that doesn’t cost $5k, that one for $1500 is absolutely within my price range. I could not find any info outside of flukes isolated scopemeters :/ I’m quite glad I seen this video.

[@antoniofilipe70]

Hello Mjlorton. I'm the Institute IPRAD director in Portugal (Geobiology Portuguese Institute) and i've interest to by a Siglent unite to mesure Dirty Eletricity. Can you make a vídeo showing a simple process of adjustement and mesurement? Thank you so much and congrats for your very good channel. Have a good week.

[@robertcalkjr.8325]

Nice video, thanks. I was thinking about getting a little function generator kit like yours.

[@michaelboateng5439]

Thanks a bunch! Great Video!!!!

[@qzorn4440]

gee wished they could take 2 single channel portable scopes with bnc probes and sync them together to a laptop and make hobby isolated version... thanks a great video..:)

[@carlosmolina3850]

thanks for the video mj. 500 vs 1500$ scopemeter, the cheapest is 3x the price of the isolated. we can say 3x the lifetime. I don't know if someone here blows their scope 3x. I am using a Chinese scopemeter and it's not earth grounded

[@ThePino154]

legit result following this direction

[@budleyca1]

Very informative, thanks

[@bobbauvian7700]

about the noise, could it be something on and around you LED or florescent lights...etc. start turning thing around you off one at a time that to see if it will go away.

[@brig.4398]

Why doesn't the Signal Generator have an AC transformer inside it so that way it is isolated? That looks like a pretty expensive generator.

[@ivansperanza]

Cheers mate, where can i get a t-shirts like the one you're wearing?

[@FrankieKato149]

Awesome video

[@FranciscoBIdo]

This an old but well-done very precise to the point video. Thank you! I think it's more cost efficient to buy two cheap hand held oscilloscope than one with two isolated channels. Does this make sense to you?

[@vikassudhera923]

Hello sir. I like your all videos sir I want buy isolated oscilloscope not so expensive witch one is best please reply

[@RicardoPenders]

I'm using a full wave bridge rectifier with an isolation transformer but I've connected it differently and I can find any information on the waveform, it would be of great help if you can show that in a video. The transformer I'm using is an audio transformer, it has multiple outputs but the main difference is that is has the center tap which I'm using as the return path because of a too high voltage when I connect it the usual way, normally you just have two output pins that you connect to the bridge rectifier and the output of that is double the frequency of the transformer input, in my case that is 50 Hz input and when rectified I got the 100 Hz which is normal and what you showed in this video. The way I have connected my bridge rectifier is one lead to a "positive" pin of the transformer and the other lead to the center tap, that way I get half the voltage as when connected the usual way not using the center tap but the "negative" pin of the transformer... By positive and negative I mean when you scope the waveform you normally have half of the wave positive and the other half is negative and when rectified it converts the negative part of the wave to positive, that's why you see double the frequency. Now because I don't have an oscilloscope I can't see what's happening with the waveform the way I connected my bridge rectifier, it works no problem but I just cannot find any information online about the waveform anywhere, can you please show that in a video, you'd do me a huge favor. Thanks in advance, Ricardo Penders.

[@InXLsisDeo]

Hello mjlorton, is it possible to do a review of the Siglent SHS806 ? This looks like an interesting product.

[@logikgr]

Awesome, very informative!

[@Dirtyharry70585]

I'm looking at portable hand held, what about the usb only scopes? Wouldn't they also have isolation trouble plus the chance to smoke a laptop?

[@alirezabagheri3979]

thank . very very good

[@tubical71]

I *want* that shirt!!

[@clems6989]

I have always heard "Isolate the DUT. Never the test equipment" of course this does not apply to a portable scope that is isolated by its design. But.......

[@BalticLab]

That's what active probes and differential amplifiers are for... Duh!

[@yaghiyahbrenner8902]

Hey man I just came across your channel cool stuff. +1 subscriber.

[@kalhana1]

For power electronics, we use Yokogawa 16 channel scopes. All isolated channels. But diff probes are useful for normal scopes. Also, if you really wanted to measure across live potentials (using only 1 channel), you could put an isolation TF to power the scope. You'd still have the channel grounds common though. Btw, I'm waiting for more videos from your channel!

[@gahlanaventis]

is fluke 199c scopemeter the 2 channels are isolated from each other like this siglent shs 1002

[@riscy00]

Why they no subtitle support?

[@numex106]

so if i have a 2 channel non-isolated inputs i can't view the input and output signals at the same time?

[@tubical71]

exact! Furthermore you simply short circuit one of the diodes, so you´ll short circuit your power supply as well....

[@niceguy60]

In the application you witnessed in this video no you can't. But if your working on a circuit where the two test points are at the same potential than yes you can use both channels at once.

[@RicardoPenders]

yes you can but you only connect one ground clip from one probe to a common ground and with the second scope probe you only connect signal input... NO GROUND CLIP.

[@dharmaparamanandan9785]

Can u send me the sepciation of UNI T 81B meter?

[@koktelici]

Are they capable of xy plot?

[@jesterraj]

can u review Velleman hps50 scope?

[@mdesm2005]

Use two channels and the math function to get the output of the bridge.

[@mdesm2005]

oops I wrote this before I got to time stamp 18:00 ...

[@Bodragon]

Why do these expensive portable oscilloscopes; and it's not just these Siglent ones specifically, but all of them, why do they use such crappy low resolution displays? I fix tech - PCs, laptops and tablets etc and I replace a lot of broken smartphone screens and a lot of these screens are really cheap. Take the Galaxy J3 for example. It has a 5.0 inch display with a resolution of 720 x 1280 pixels, at a density of around 294 pixels per inch. These screens are going on eBay for about twenty bucks. Seriously, what's going on with these 'scopes?

[@jacquesgilbert2774]

You are correct, the displays with higher resolution are cheap, but that's not the problem. 720x1280 has 6 times as many pixels as 320x480, that means the CPU will take 6 times as long to refresh a screen, and the screen itself may be much slower to refresh and use more power. Scopes are concerned with refresh rates, and portable scopes are concerned with battery life. To keep those the same, the high res screen will call for a bigger, more expensive CPU, more memory, bigger, heavier battery, and so on. The impact on price and performance goes well beyond the $20 display. Yes, phones can be fairly fast, have good battery life, and stay somewhat affordable, but they sell by the millions. Scopes will sell by the thousands at best.

[@tikabass]

I've always felt safer when there is no earth on my bench.