Oscilloscope EXT. INPUT , source Channel#2

Using a DUAL TRACE SCOPE, You would put One into channel-1 and the other into channal-2
This will allow you to see the Phases, Relative to each other.

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No , I had to use channel#1 as the AC output which has a polarity switch to go from 0 to 180 degrees
Channel#2 I had to put 115vac 400hz and on the O-scope set it to SOURCE on channel 2

This allowed me to view the AC waveform at either 0 or 180 degrees

I used the Channel#2 as a SOURCE REFERENCE

Can't I put 115VAC on the EXT. INPUT on the O-scope and use this as a SOURCE REFERENCE ?

I'm just not sure if i can put an AC waveform input on the EXT INPUT on the O-scope and how much voltage can I put into it?

If you do not read the maximum ratings spec's for the 'scope then you will probably destroy it with too much voltage.

What have you guys done in the past or in general when using Channel#2 to be the reference and having channel#1 Source to channel#2?

What have you guys done in the past or in general when using the EXT input? using reference waveforms or what kind of references


I'm new to using the O-scope like this, using the EXT input and using Channel#2 as a reference and Sourcing channel#1 to Channel#2

Can you help me with some examples on how to use it

When I Said Channal-2, That was for a DUAL TRACE SCOPE.
This has Nothing to do with a "EXT INPUT"

Danny, Sorry I Give up on your Posts.
You need to take some ELectronic Courses.

chemelec said:

Danny, Sorry I Give up on your Posts.
You need to take some ELectronic Courses.

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Hi Gary,
I feel the same way.
Remember "Walters"? Danny is him and on another website forum today he posts the same questions but calls himself "Billy Mayo".

I'm not here to start problems, I'm here to learn and if someone wants to answer my questions that is up to them , you don't have to it's a free world

If you feel that way about me, just PM me , don't say it in my threads please

The Unit or circuit board I'm testing doesn't plug into the wall 120VAC at 60hz, it uses 115VAC at 400hz to be powered , the power supply won't work with 120VAC at 60hz only at 115VAC at 400hz , that's why the O-scope is displaying free running waveforms

That's why I need the oscilloscope to SYNC up to a 115VAC at 400hz not at 120VAC at 60hz

I'm not measuring a phase angle , it's about SYNC the O-scope up to a different AC LINE

What is this called that I'm am doing? it's about Syncing not measuring phase angles of two different waveforms

You do not know how to operate your oscilloscope. Read its owners manual.

The Problem I was having with my O-scope was that my O-scope plugs into a 120VAC at 60hz.

But the circuit boards I'm testing are at 120vac at 400hz.

So I have to TRIGGER my O-scope to the 120vac at 400hz line mains

In order for me to do that, I have to use one of my O-scope channels which will have the 120vac at 400hz line mains as the reference and have my other channels be SOURCED to the 120vac at 400hz

What is this called what I am doing to the O-scope?

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My Manager said you use the EXT input jack for:
1.) A circuit's Clock or Phase loop lock signal can go to the EXT input jack
2.) Function Generators clock output can go to the EXT input jack
3.) Sync the O-scope to the Main lines at a difference frequency

If your scope has an EXT input for triggering, then go ahead and use it. If the scope trigger selector has a "AC line" option, you cannot use it because, as you said, it is only for triggering with 60 Hz. If you need to trigger to the same 400 Hz that is powering the boards under test, then connect whatever signal you have that is synchronous with that 400 Hz power to the EXT input and select "EXT Trigger" in your trigger selector. If the only signal you can find that is synchronous with that 400 Hz is the actual 120-volt power itself, check your scope's EXT input voltage rating to make sure the 120 volts is not too high. If it is you will have to reduce the voltage with a transformer or something.

I think a bigger problem is safety when working with power like this. If you are scoping signals that are tied to the 400 Hz power supply, you should make sure the chassis of your scope is grounded so that a ground lead from your scope doesn't make your entire scope "hot" with 400 Hz power. You should have a thorough understanding of what is grounded and what is floating before attempting any such measurements.

If the scope trigger selector has a "AC line" option, you cannot use it because, as you said, it is only for triggering with 60 Hz.

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Any reason why the O-scope can trigger , because of why? the waveforms are Free running when they aren't in SYNC with the 400hz

The O-scope and the circuit board under test have to MATCH the same MAIN Lines that you plug into the wall?

If you need to trigger to the same 400 Hz that is powering the boards under test, then connect whatever signal you have that is synchronous with that 400 Hz power to the EXT input and select "EXT Trigger" in your trigger selector.

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Yes I did this and it works, but what is this Called when you SYNC the o scope to a different main line frequency? because it's not sync to 60hz it's sync to 400hz

If the only signal you can find that is synchronous with that 400 Hz is the actual 120-volt power itself, check your scope's EXT input voltage rating to make sure the 120 volts is not too high. If it is you will have to reduce the voltage with a transformer or something.

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True you do have to use a AC Step down ratio transformer

I think a bigger problem is safety when working with power like this. If you are scoping signals that are tied to the 400 Hz power supply, you should make sure the chassis of your scope is grounded so that a ground lead from your scope doesn't make your entire scope "hot" with 400 Hz power.

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Yes what is a good AC isolation transformers for O-scopes?

Would I need an AC 115v 400hz Isolation transformer? for my O scope?

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My Manager said you use the EXT input jack for:
1.) A circuit's Clock or Phase loop lock signal can go to the EXT input jack
2.) Function Generators clock output can go to the EXT input jack
3.) Sync the O-scope to the Main lines at a difference frequency

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Can you add any others that you can use the EXT INPUT JACK FOR?

danny davis said:

Any reason why the O-scope can trigger , because of why? the waveforms are Free running when they aren't in SYNC with the 400hz

The O-scope and the circuit board under test have to MATCH the same MAIN Lines that you plug into the wall?

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I don't understand you.

Yes I did this and it works, but what is this Called when you SYNC the o scope to a different main line frequency? because it's not sync to 60hz it's sync to 400hz

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it is called external sync.

Yes what is a good AC isolation transformers for O-scopes?
Would I need an AC 115v 400hz Isolation transformer? for my O scope?

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if you are going to start floating your scope and scoping high voltage signals, knowing as little as you do, I don't want to encourage you and get you electrocuted. You need someone standing next to you who understands what is going on to keep you safe. In the meantime, confine your measurements to low voltage circuits.

why do u have to use the external sync to 400hz to do the measurements why can't i keep it at 60hz? why does the o-scope have to be sync to 400hz?

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What else can I use the External INPUT for on the oscilloscope? what have you used the external input on the oscilloscope for?

danny davis said:

why do u have to use the external sync to 400hz to do the measurements why can't i keep it at 60hz? why does the o-scope have to be sync to 400hz?

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That depends on what you want to see with the scope.

What else can I use the External INPUT for on the oscilloscope? what have you used the external input on the oscilloscope for?

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Usually the EXT input is for triggering only. It cannot be displayed like another trace.

why do u have to use the external sync to 400hz to do the measurements why can't i keep it at 60hz? why does the o-scope have to be sync to 400hz?
That depends on what you want to see with the scope.

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What does it depend on? any reason why it has to be synced up to 400hz to do measurements?

What else can I use the External INPUT for on the oscilloscope? what have you used the external input on the oscilloscope for?
Usually the EXT input is for triggering only. It cannot be displayed like another trace.

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Yes I know that, but what can you use to as a signal to go to the EXT input?

My Manager said you use the EXT input jack for:
1.) A circuit's Clock or Phase loop lock signal can go to the EXT input jack
2.) Function Generators clock output can go to the EXT input jack
3.) Sync the O-scope to the Main lines at a difference frequency

4.) What else can I use ?

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The scope triggers from a SOURCE, the user determines the source.

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Ok when the Scope is triggered from a SOURCE at 60hz and I probe on the circuit board, the waveforms are Free Running.

When the Scope is triggered from a SOURCE at 400hz and I probe on the circuit board , the waveforms are STABLE not free running

Why is that? and why do I have to trigger a SOURCE at 400hz ? I doesn't it the scope work at 60hz? I don't get it

Can you please explain why the scope doesn't work when you trigger a Source it at 60hz but it works at 400hz?

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Yes it has nothing to do with eachother

At work there is 2 different wall main line outputs

You either plug equipment into a 120VAC at 60hz
Or you plug equipment in to the wall at 115VAC at 400hz

Two different line main frequencys

danny davis said:

What does it depend on? any reason why it has to be synced up to 400hz to do measurements?

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Only you know what sort of measurements you want to make, so I have no idea if it has to be synced up to 400Hz or not.

Yes I know that, but what can you use to as a signal to go to the EXT input?

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If you are trying to sync up to the 400 Hz in the boards under test, then I guess you want to sync to either the 400 Hz line voltage itself or some signal that is synchronous with that 400 Hz. Not knowing what is in the circuit you are testing, there is no way I can tell what other signals there may be that are synchronous with the 400 Hz in the board. The reason I suggest some other signal and not the 400 Hz line itself is that the line 400 Hz might have to high a voltage for your EXT input, but maybe you have another signal handy that is synchronous with the 400 Hz and is only 5 volts. That would be much safer. But if you have to, you can always reduce the 400 Hz voltage with a resistive voltage divider or transformer to get a 5-volt signal that is acceptable to the EXT input.

2.) Function Generators clock output can go to the EXT input jack

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This is fine if the Function Generator is actually generating the same 400 Hz that is powering the 400 Hz line to the board under test. But if it is just some other 400 Hz that is not related to the 400 Hz on the board, it will not do any good, and the trigger will still appear free-running.

3.) Sync the O-scope to the Main lines at a difference frequency

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You keep talking about the 400 Hz as if it were a main. It might be a main to the board under test, but it is not a main to the scope. It is just another external signal. The only "main" that the scope knows about is the 60Hz main, so it is best not to confuse the issue by call the 400 Hz power a "main".

Ok when the Scope is triggered from a SOURCE at 60hz and I probe on the circuit board, the waveforms are Free Running.

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Of course. Because the signals you are probing have nothing to do with the 60Hz main.

When the Scope is triggered from a SOURCE at 400hz and I probe on the circuit board , the waveforms are STABLE not free running

Why is that?

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Because that is what it means for the source and the trigger to be synchronous.

and why do I have to trigger a SOURCE at 400hz ?

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I suppose it because you want to look at signals that are periodic with a period that is related to that 400 Hz.

I doesn't it the scope work at 60hz? I don't get it

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That depends on what you want the scope to do. It does "work" at 60 Hz, but apparently it is not doing what you want it to do. Since I also don't know what you want it to do, I cannot help you there.

At work there is 2 different wall main line outputs

You either plug equipment into a 120VAC at 60hz
Or you plug equipment in to the wall at 115VAC at 400hz

Two different line main frequencys

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OK, now I see why you like to call them both "mains".

Before you go any further, find out for sure if the 400 Hz main and the 60 Hz main at your work are single phase mains that have one leg tied to ground. I know that a typical 120-volt main in the USA consists of a neutral leg that is connected to ground somewhere and a hot leg that is 120-volts with respect to that neutral. But I don't know about your 400-volt feed. It might be the same sort of thing, or it might be a floating power feed from a transformer. Until you find out for sure which it is at your work, you cannot safely connect the 400 Hz main to the EXT of the scope.

I suppose it because you want to look at signals that are periodic with a period that is related to that 400 Hz.

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Yes I do,

The Periodic or time period at 400hz is different than a time period at 60hz

The SYNC frequency ( external signal ) is like a clock right?

The Time and frequency of the signal can be different than the SYNC frequency ( external signal )?

The Waveform is superimposed on top of the sync frequency ( external signal ) ?

Before you go any further, find out for sure if the 400 Hz main and the 60 Hz main at your work are single phase mains that have one leg tied to ground. I know that a typical 120-volt main in the USA consists of a neutral leg that is connected to ground somewhere and a hot leg that is 120-volts with respect to that neutral. But I don't know about your 400-volt feed. It might be the same sort of thing, or it might be a floating power feed from a transformer. Until you find out for sure which it is at your work, you cannot safely connect the 400 Hz main to the EXT of the scope.

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Ok this I will have to try to find out at work if they know the answer, but the 115VAC at 400hz is a 3 phase , I don't know if it's delta or WYE

The 115VAC at 400hz goes to a AC ratio step down transformer that outputs 26 VAC at 400hz , this goes to Gyros motors & Syncro motors

This is fine if the Function Generator is actually generating the same 400 Hz that is powering the 400 Hz line to the board under test. But if it is just some other 400 Hz that is not related to the 400 Hz on the board, it will not do any good, and the trigger will still appear free-running.

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The function generators output is 400hz , it's the same frequency why won't it work? i don't get it?

danny davis said:

The SYNC frequency ( external signal ) is like a clock right?

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Yes.

The Time and frequency of the signal can be different than the SYNC frequency ( external signal )?

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Yes, it can be different, but then the signal will appear to be free-running on the scope.

The Waveform is superimposed on top of the sync frequency ( external signal ) ?

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No, superimposed is the wrong word. That makes it sound like the signal and the sync are added together, which is not what happens in a scope.

Ok this I will have to try to find out at work if they know the answer, but the 115VAC at 400hz is a 3 phase , I don't know if it's delta or WYE

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It does not matter if it is a delta or a WYE. All that matters is that it is referenced to ground and not floating.

The 115VAC at 400hz goes to a AC ratio step down transformer that outputs 26 VAC at 400hz , this goes to Gyros motors & Syncro motors

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That is interesting. That means perhaps the board under test is floating with respect to ground. It also means that the 26-volt 400Hz might be a good way to get your EXT sync, since it is a lower and safer voltage, once you find out how to reference the board to ground.

The function generators output is 400hz , it's the same frequency why won't it work? i don't get it?

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It will not work as your EXT sync because no function generator frequency is perfect. It says 400Hz, but really it might be 399.99 Hz. And your "400 Hz" main might actually be 400.01 Hz. If you use the function generator as your EXT sync, the signals from the 400 Hz line might drift very slowly through the display. It would be free running, but it would run by very slowly. Maybe that is OK for you. Maybe you don't mind seeing the display drift slowly, depending on what sort of measurements you are trying to make. If you are trying to make precise phase measurements, the drifting display would make that impossible. But if you only want to see the shape of the Channel 1 signal, maybe a slow drift would not be a problem and you could use the signal generator as your EXT sync. I have done things like that when a true sync signal was not available.

Thanks for the help on this , I really need this info

What's the difference between a 1Khz waveform sync to a 60hz external signal VS a 1Khz waveform sync to a 400hz external signal?

Is the time period different? phase angle different? or what is different about the two?

It's the same frequency at 1Khz waveform , the only difference is the Sync frequency ( external signal )

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What's the difference between triggering and Sourcing?

Sourcing is the synchronization , the O scope is defaulted at 60hz, the horizontal bean circuit is going across the display at 60hz

If I brought you a circuit board and had 10 outputs waveforms and I didn't tell you what the line or sync frequency was , how would you know what to SYNC , SOURCE, TRIGGER the O -scope to?

You would first measure the frequency/time of the waveform? but how would you find out what the SYNC frequency is?

Since the O-scope is defaulted at 60hz, all the waveforms would be Free Running because you don't know what the waveforms are SYNC to.

How would you find out what the signals that are periodic with a period that is related to that SYNC frequency? the frequency/time of the waveform is not the Sync frequency

The Sync frequency is an external signal

How would you find out the external signals frequency without me tell you what is it?

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The SYNC frequency ( external signal ) is like a clock right? YES

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What would you call it a clock or what would you call it since it's not really a clock? what is the right name for it?

The Waveform is superimposed on top of the sync frequency ( external signal ) ?
No, superimposed is the wrong word. That makes it sound like the signal and the sync are added together, which is not what happens in a scope.

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True, Since the waveform is no superimposed, what would it be called?

Ok this I will have to try to find out at work if they know the answer, but the 115VAC at 400hz is a 3 phase , I don't know if it's delta or WYE
It does not matter if it is a delta or a WYE.

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All that matters is that it is referenced to ground and not floating.

Why does it matter if the circuit is reference to ground or floating? what would it change?

The 115VAC at 400hz goes to a AC ratio step down transformer that outputs 26 VAC at 400hz , this goes to Gyros motors & Syncro motors
That is interesting. That means perhaps the board under test is floating with respect to ground. It also means that the 26-volt 400Hz might be a good way to get your EXT sync, since it is a lower and safer voltage, once you find out how to reference the board to ground.

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TRUE , the secondary side is floating , so you can't use this as a reference because it's floating right?

danny davis said:

What's the difference between a 1Khz waveform sync to a 60hz external signal VS a 1Khz waveform sync to a 400hz external signal?

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How the scope behaves depends not only on what sync is selected (60Hz or 500Hz) but also on the sweep rate selection and on the trigger type (AUTO or NORMAL). All I can say in general is that when 60Hz is selected, the sweep will be triggered 60 times per second and if 400 Hz is selected, the sweep will be triggered 400 times per second.

It's the same frequency at 1Khz waveform , the only difference is the Sync frequency ( external signal )

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Yes, it is the same waveform, but it looks different when each sweep of the scope display starts at a different point in the 1kHz waveform. That gives the display the free-running appearance.

What's the difference between triggering and Sourcing?

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Sourcing is the synchronization , the O scope is defaulted at 60hz, the horizontal bean circuit is going across the display at 60hz[/quote]
Well, I've never heard the word "sourcing" used in that way before. But if that is what you mean, then it sounds the same as triggering. But I should point out that the scope does not default to 60Hz triggered sweep. It is just that for convenience, they make scopes that have AC Main and one of the trigger sources, since it is often the case that the circuit your are scoping has waveforms that are synchronized with the AC power supply. Other than that, the selection of 60Hz through the AC Main selection is just like any other external trigger source.

If I brought you a circuit board and had 10 outputs waveforms and I didn't tell you what the line or sync frequency was , how would you know what to SYNC , SOURCE, TRIGGER the O -scope to?

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I might start by studying the schematic of that board to see if I could figure out what those waveforms are supposed to represent. If the schematic was not available, I might start from my knowledge of what function this circuit board is supposed to perform. If I didn't even know what the board was supposed to do, then I would probably give up.
[/quote]How would you find out what the signals that are periodic with a period that is related to that SYNC frequency? the frequency/time of the waveform is not the Sync frequency[/quote]
Trial and error. I would try various sweep rates and various sync sources until something made sense.

How would you find out the external signals frequency without me tell you what is it?

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Instead of any EXT sync selection, I would select Internal so as to use the waveform I am displaying as its own sync source. Then I would try various sweep rates until I could see one cycle of the signal displayed. Then I could estimate the frequency from the measured period on that display.

What would you call it a clock or what would you call it since it's not really a clock? what is the right name for it?

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I might call it a clock, or a sync signal. But what difference does it make what I call it?

True, Since the waveform is no superimposed, what would it be called?

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I would call it a waveform that is displayed with an external sync.

Why does it matter if the circuit is reference to ground or floating? what would it change?

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Ah, a very good question. It matters because when you connect a signal to scope, that signal must be referenced to the ground of the scope. This is true whether the signal is a display channel or an EXT sync input. If the signal itself is floating with respect to ground, you are going to have to connect the ground of the scope to whatever point in the circuit the signal is referenced form. For example, the 26-volt isolation transformer you spoke of has two wires coming out. If you want to connect the scope to one of those wires, then the ground of the scope has to be connected to the other wire. If that other wire was actually 200 volts above ground, then your scope (if it is not a grounded scope) will now have its chassis ground elevated to 200 volts above ground, so that if you touch it, and some part of you is grounded, you will be electrocuted. Or, if the scope is grounded, then connecting the ground of the scope to that 200 volt reference will short out that 200 volts, possibly destroying some circuitry, or at least blowing a fuse. On the other hand, if the output of the isolation transformer is truly floating, then it can be pushed around to any voltage you like (including ground) and it will not complain. You need to find out ahead of time which of these scenarios is the case and respond accordingly. It takes a thorough understanding of circuit board you are testing to answer this question. There are some empirical tests, like trying to gently force a voltage onto a point in the circuit that might be floating and seeing how much current that point draws from your "forcing". However it is much better if you just know what is going on without having to test it empirically.

TRUE , the secondary side is floating , so you can't use this as a reference because it's floating right?

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Not necessarily. If it is truly floating, then it can be tied to ground without any problems. And then you can connect it to the scope. There are also battery operated scopes that are very well suited to scoping floating circuits, because the scope floats with the circuit.