Isolation of the RIGOL DS1054Z from the mains with three transformers

[eneuro]

Are you a transformer salesperson?

I invest in rare metals such as copper in transformer windings, I don't buy aluminum windings because copper is worth more than crappy plastic probes 

[eneuro]

receives shock of a lifetime from carelessly touching exposed metal on his now high-potential scope 

You don't leave such people at home with electricity in the socket, you just lock the fuse box with a padlock and put nails into the sockets after cutting off the power 

[coppercone2]

the source impedance is all fucked up with a transformer its not a real measurement, the differential probe gives you a realistic measurement. even if it works.

tektronix does not recommend it because
1) its not safe
2) you are measuring some seriously contrived parameters

[JeremyC]

This article promotes TEK's products, so obviously they won't show you how to isolate an oscilloscope with a transformer for <$40, only their "wonderful" inventions useless for me 

You could use 2 x 100X scope probes and A - B math channel in your scope. Most of the 100X probes are rated up to 2000V, you may get them for <$20, below is an example:
https://www.amazon.com/Oscilloscope-Accessory-Voltage-100MHz-Bandwidth/dp/B07F65SZMV/ref=sr_1_4?crid=26HVQFB28J5JY&keywords=100x+oscilloscope+probe&qid=1703915253&sprefix=100x+ocilloscope+probe%2Caps%2C168&sr=8-4

[coppercone2]

also how do you standardize measurements with a isolation transformer? Like tektronix needs to sell a measurement system. That is some chaos. Transformers probobly not even characterized well enough to be used with the kind of measurements and standard tektronix sells/develops. YOu would simply not know if the results are the same without the transformer.

They might make shitty chassis and get a little cheap/greedy but they know what they are doing when it comes to understanding how the electronics works and what makes the measurement accurate. Adding a random impedance between the DUT is not one of those things. Compared to the probe its probobly mostly not usable.

it has a unknown effect on the scope, and an unknown effect on the DUT. You can make guesses but the fact is, its super different then being at line impedance and also not having the RF filtering from the ground caps.

do you really think tektronix is that stupid? they wrote the book on accurate AC/pulse measurements as engineers understand them today. They deal with the top echelons of industry/science. They have spare no expenses government/commercial contracts too (but not for the gear you get). What do you get behind the cutting edge electrical pulse/signal science? most likely a tektronix or tektronix derivative.

And you think tektronix would not sell a cheap isolation transformer if it was any good? the prices lock out tons of market. But its beneath their standards so they cannot realistically sell it. That many unknowns is just considered SHADY measurements in the industry. You are making a fool out of yourself.

if the conditions presented by the isolation transformer were like a parameters the oscilloscope designers had to consider they would be like WTF> !! There would likely be huge design changes to actually make it compatible with some specific transformer and there would still be deviated specifications (all the safety shit aside, assuming it as OK to make it unsafe)

and even then, you put some random bullshit frankenformer made from multiple random ass transformers it would probobly still not be in any kind of spec.

[eneuro]

You could use 2 x 100X scope probes and A - B math channel in your scope. Most of the 100X probes are rated up to 2000V, you may get them for <$20 ...

This might make sense, but these 100X <$20 are suspiciously cheap, compared to the four  PVP3150 passive probes ~40$ which I got when I bought the oscilloscope 

RIGOL PVP3150 Passive Probe:

https://www.testequity.com/product/32272-1-PVP3150

RIGOL PVP3150 Passive Probe, 150 MHz, 1X, 10X, 10 pF, 300 V, CAT2, PVP Series
Rigol PVP3150 1:1/10:1 20/150MHz Passive Oscilloscope Probe
Features and Specifications

Bandwidth: 20/150MHz
Input capacitance: 50 pf / 10 pf
Attenuation ratio 1:1/10:1 (switchable)
Input resistance 1 MΩ / 10 MΩ
Maximum input 150 V RMS CAT II/ 300 V RMS CAT II
Risetime: 17.5 ns at 1X and 2.3 ns at 10X

The Rigol PVP3150 is a 20/150MHz Passive Probe with switchable attenuation of 1x and 10x. Has input voltage 150V at 1x (1 MOhm) and 300V at 10x (10 Mohm). Input capacitance: 50 pf / 10 pf

Brand: RIGOL
Bandwidth: 150 MHz
Attenuation: 1x, 10x
Cable Length: 1.2 m
Series: PVP Series
Capacitance: 10pF
Max Input Voltage: 300 V
Safety Rating: CAT2

I do not need to measure the maximum values of the 230VAC power supply network,  though Max Input Voltage: 300 V of this PVP3150 Passive Probe probably at 10M it's not crazy but still ~325Vmax/10M it is only ~33uA  @ 230VAC mains  

UPDATE:

https://www.salicontech.co.in/product/rigol-pvp3150-150-mhz-passive-probe-with-1x10x/
Manufacturer Specs
Electrical Specifications
...
Input Resistance    1X: 1 MΩ ± 1% @ DC
10X: 10 MΩ ± 1% @ DC
Input Capacitance    1X: 50 pF ± 20 pF
10X: 10 pF ± 5 pF
Max. Rated Input Voltage    1X: 150 VRMS CAT II
10X: 300 VRMS CAT II

It seems that Rigol PVP3150 Passive Probe Max. Rated Input Voltage @10X is 300VRMS so there it is ~424Vpeak  which would be consistent with what is in this guide

ABCs of Probes | MIT https://web.mit.edu/6.101/www/reference/ABCprobes_s.pdf
...
Typically, the maximum voltage for general-purpose passive probes is around 400 to 500 volts (DC + peak AC).
...

[eneuro]

also how do you standardize measurements with a isolation transformer? ...

I don't need any standardization, I just sometimes estimate how much the simulation results of the system differ from the one run after soldering in reality 

[eneuro]

I wonder if there is a amount of transformers you can add to make this stop being stupid

I've tried six, but he hasn't bitten.

If you do not have one 230/230V transformer to isolate the oscilloscope, you need two 230/24V transformers, as in this simulation below, where I am testing a device connected directly to the mains power supply with an oscilloscope isolated from the 230V 50Hz mains supply using T1 230/24V and T2 24/230V 

[johansen]

For like 50$ you can buy 96 AA batteries and run your scope off a battery pack.

anyone tried to measure the capacitance to ground, and compare the waveform of what a high side 370vdc mosfet at 100Khz looks like with a floating scope, compared to a good quality differential probe? (yes, your scope would be floating at 370vdc to ground at 100khz)...

I don't have a differential probe otherwise i would try this myself.

[eneuro]

I don't have a differential probe otherwise i would try this myself.

Measuring differential signal with single ended probe(s) 

https://electronics.stackexchange.com/questions/377132/measuring-differential-signal-with-single-ended-probe

You can use 2 channels on your scope to measure + and - signals with separate probes referenced to ground and then use the "math" function on your scope to subtract the two like everyone else is mentioning here. 
Alternatively, you could use an isolation transformer if you only have 1 channel available on the scope. 

[johansen]

I don't have a differential probe otherwise i would try this myself.

Measuring differential signal with single ended probe(s) 

https://electronics.stackexchange.com/questions/377132/measuring-differential-signal-with-single-ended-probe

You can use 2 channels on your scope to measure + and - signals with separate probes referenced to ground and then use the "math" function on your scope to subtract the two like everyone else is mentioning here. 
Alternatively, you could use an isolation transformer if you only have 1 channel available on the scope. 

I am not trolling. Why are you?

[eneuro]

check also the follow up 1
https://youtu.be/eSZdO_Uca40

Interesting experiments with toroidal transformers 

Electronic system with opto-isolation for detecting the polarization of the 230VAC primary and 24VAC secondary windings of the transformer, ready for soldering on an
80mmx20mm prototype board 

There should now be no problem with cascading several transformers in such a way as to obtain the desired polarization on the secondary winding 

[Spar59]

Just a point here - I will take criticism if someone poiunts out it has alredy been mentioned in this thread or they have technical knowledge to the contrary.

True safety isolation transformers intended for that purpose either use seperate bobbins on an E-I core or else have an inter-winding screen to reduce capacitive coupling and to provide a safety barrier if the inter-winding insulation fails.

While it appears you are determined to do a floating scope arrangement it is something I personally would avoid at all costs if measuring mains voltages on the unit under test, to avoid ground loops when testing a low voltage system, maybe.  A differential probe would be bettter or possibly use 2 channels and the maths function to subtract one input from the other to create a differential measurement with suitably rated single-ended probes which would be cheaper than a dedicated differential probe.

[coromonadalix]

@Spar59

you're absolutely right,  but this thread as derailed a lot from the previouly locked one,  its no longer relevant, lots of stupid ideas and stubborness

you have optically linked probes, differential probes  ... all safe

now  when you have gimmicks for phase detection / polarity  etc  ....   pffffffff   it's because you know zits  ........


you want to try poor solutions while playing with safety,   yeah  go burn yourself ...


wating for the 4 5 6 transformers ideas  pffffffffffff

[eneuro]

you have optically linked probes, differential probes  ... all safe 

I've four RIGOL PVP3150 Passive Probes so it's easy to make one differential probe out of two by connecting the crocodile clips together 

I have PC817 optocouplers and they are sufficient for such simple things @50Hz

Meanwhile, the electronic circuit for transformer polarization tests was sent to the PCB factory 

[eneuro]

I am not trolling.

I am not joking. 

[joeqsmith]

Read OP's original thread.  Looks like the lamp was initially intended to run directly from mains but now wants to isolate the entire system with a separate transformer for the low voltage supply.  Maybe I miss-read.   

Personally, I tend to leave the equipment as is.  Can't think of a time I have ever needed to isolate a scope or other equipment.  Looking at their ZCD and driver for the lamp, I still don't see the need.   I would use a proper probe or isolate the device.  In cases where the device is intended to be directly connected to the mains,  I normally have to pass various EMC tests anyway so we are making our own mains.  I am not going to run it on the actual mains and assume that is good enough to test the products performance.     Again, maybe I am missing something. 

[eneuro]

Again, maybe I am missing something.

Yes, It's not rocket science 
The PCB for testing the polarity of transformers is already in production, and slow fuses (T500mA,T250mA,T2A) have been ordered in the meantime and one circuit will be soldered on a prototype PCB and flooded with an insulator 
PCBWay Factory Tour:

[johansen]

Why does the polarity of the transformer matter?

You already have isolation in the power supply of the oscope.

[tggzzz]

Why does the polarity of the transformer matter?

You already have isolation in the power supply of the oscope.

The smell of "cargo cult engineering" is overpowering.

[tom66]

Whilst everyone argues about whether it is safe or not to float your scope (it's not, but I'm guilty of doing it, so sue me) - you can power a Rigol DS1xxxZ scope off approximately 50V DC placed across the live and neutral terminals.  That is enough for the internal flyback stage on the PSU to function.  It'll pull around 12W in this configuration.  I have a little magic box somewhere that has a boost converter in it that powers my scope from a 12-24V battery or car cigarette lighter.  It cost probably £10 in parts from eBay.  No need to overcomplicate things.

[magic]

I can't even understand what this guy is trying to do at this point.

Last time I thought I knew, I was under impression he is isolating his scope only to connect it to an already isolated device (i.e. the device could be grounded by the scope without smoking anything).

 


... and it doesn't help that the @#$$$% started to upload ant-scale images because somebody "pirated" one and defaced it with alternative suggestions

[eneuro]

No need to overcomplicate things.

You're right, that's why I use transformers for this purpose 

I need to know the polarity of the transformers not only in the case of cascade connection but also a 1:1 transformer, because I can also use it to isolate the tested systems, so I want the output to be the same as the input, not an inverted sine wave of mains 230VAC 

Professionalism means attention to detail. 

[coromonadalix]

No need to overcomplicate things.

Professionalism means attention to detail. 

we talk about "phase" here not polarity     if you where that professional,  you should use the right terms   

you're in phase or out of phase ...             and normally since you don't get the scope grounded   all your gimmick serve nothing

i never had any problems with 1 isolation transformer  loll  if you know  how  to use them   

[eneuro]

you can power a Rigol DS1xxxZ scope off approximately 50V DC placed across the live and neutral terminals.  That is enough for the internal flyback stage on the PSU to function.  It'll pull around 12W in this configuration.

Good to know 
On the label on the back, the minimum frequency range is 44Hz to 400Hz max, so I didn't expected that this oscilloscope could be powered by DC voltage.