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Oscilloscope EXT. INPUT , source Channel#2

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If a circuit is triggered by an event, input voltage or current, my manager said I have to use a storage o-scope because the circuit is triggered by an event is this true cant use a non- storage scope?

Totally would depend on the circuit in question. What the circuit does, what waveforms you want to observe, the timing involved and other variables. Billy, we have discussed this line of questions. You can't just say "a circuit" without a description of what it does and what the end user wishes to measure. Yes, in some cases a DSO or general storage scope is a better choice for an application but that can't be said without knowing the application in detail. You choose the instrument based upon what you want to measure.

Ron
 
Since the channels aren't isolated, is this dangerous apply a mains 115vac 400hz mains wall line into the channel?

Could be a real problem if the line and neutral are reversed and what the neutral or ground of the 400 Hz. power shares with any other ground or neutral. OK, take the ground lug on your scopes power cord. With the scope unplugged measure the resistance between that ground lug on the mains plug and the outer shells of the scope In/Out BNC connectors. Let me know what resistances you measure. What is the ground reference for your 400 Hz. power?

Ron
 
Should I use an isolation transformer to be safe?

the 115vac 400hz comes from a 3 phase main

Absolutely. I strongly suggest that whenever possible.

Also I am glad you mention the 3 phase mains. Typically three phase mains power regardless of frequency comes in two flavors (configurations) as you have Wye and Delta. I have worked extensively with both but mostly 480 Volt 3 Phase Delta. I don't know what you have but I suggest you get real familiar with 3 phase power. , make sure you understand it. Note that in 3 phase delta there is NO neutral, power is phase to phase. This is where very bad things can happen with a scope that has common ground on the In/Out connectors. I commonly used 4 channel scopes but also using special differential input modules on my scope channels. My guess is you are involved with Laboratory / Production Test type 3 phase supplies that convert 120 or 240 VAC 60 Hz. to 3 phase 120 Volt 400 Hz. power like aircraft type power. Just start getting real friendly with three phase power common configurations like Wye and Delta before trying to monitor this power with a scope.

Ron
 
My Manager just said to me , if you have a 3 phase main output, how do you know which wall outlet is phase A , which wall outlet is phase B, which wall outlet is phase C ?

How do you find out which Phase is which? A, B or C ?

My guess is you are involved with Laboratory / Production Test type 3 phase supplies that convert 120 or 240 VAC 60 Hz. to 3 phase 120 Volt 400 Hz

I'm not sure if they step it up from a 120vac at 60hz , I would have to ask them that

I commonly used 4 channel scopes but also using special differential input modules on my scope channels.

They do have one O-scope that has isolated 4 channels

But what are these differential input modules for oscilloscopes?
 
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?
 
My Manager just said to me , if you have a 3 phase main output, how do you know which wall outlet is phase A , which wall outlet is phase B, which wall outlet is phase C ?

How do you find out which Phase is which? A, B or C ?
Why do you think it is important to know which phase a wall plug is feed from? I can't think of any single phase load that it would matter to. And any multiphase load will have all of it's feed wires in the same connector.

But what are these differential input modules for oscilloscopes?

There are a few out there. you can start with google. But here are some: **broken link removed**

Please note: Differential is not isolated. A transformer will give you differential measurement and isolation.
 
Why do you think it is important to know? I can't think of any single phase load that it would matter to. And any multiphase load will have all of it's feed wires in the same connector.

My manger said that not all phases have the same voltage amplitude, because each one is being loaded down differently in the building

Also My manager had to use an isolation transformer between Phase A and Phase B because it of loading problems

He had a power supply with an isolation transformer to keep it Seperate from the Test Fixture because it was loading down one of the phases

My Manager said that when you put your DVM fluke meter to the main wall output how to you know if it's phase A,B or C?

I'm guessing you can't be plugging in different test equipment using the same phase or different phases, or it will cause loading problems or other problems?


differential input modules for oscilloscopes?

So these differential input modules let you measure Floating voltages? and what else?

If you put 4 of them of 4 seprarate channels on the 0 scope, does this make your 0-scope have 4 isolate channels?
 
Before I forget **broken link removed**. They can run around $2,000 each. Not quite cheapies. :)

My Manager just said to me , if you have a 3 phase main output, how do you know which wall outlet is phase A , which wall outlet is phase B, which wall outlet is phase C ?

Generally I never think of 3 phase power as being distributed around a room in outlets. However, it matters not. To better define the phase relationship it works well if you tell me Wye or Delta? L1 leads L2 by 120 degrees, L2 leads L3 by 120 degrees and L3 leads L1 by 120 degrees. As long as the phase rotation is correct it matters not which is L1, L2 or L3. Take a 3 phase motor wired L1, L2 and L3 and it runs CW. Now reverse any two of the three phases and it runs CCW.

OK, the scope is powered off 120 VAC 60 Hz mains power. So what? You are I assume troubleshooting a 400 Hz board. How many scope channels are you using? If you re using just a single channel let the scope trigger off the channel you are using. I don't know what you are doing exactly.

Ron
 
If you re using just a single channel let the scope trigger off the channel you are using.

How do you do this?

My O scope is plugged into the 120vac 60hz, I won't let me SYNC up to the 120VAC 400hz , to make measurements on AC waveforms , they look like free running waveforms because the oscilloscope is not SYNCed up to the 120vac 400hz

The waveforms on the circuit board when probing around will be Free running not SYNCED because the of the o-scope is not synced up to the 120vac 400hz main lines

What is this called to do this to the O-scope?
 
My manger said that not all phases have the same voltage amplitude, because each one is being loaded down differently in the building

Then someones engineering for load balancing sucks! Load balancing is a prime consideration in any 3 phase distribution be it 60 Hz or 400 Hz. Good power distribution from the sub or point of origin monitors the loads by phase constantly.

Finally and again is this 3 phase delta or wye?

Ron
 
My O scope is plugged into the 120vac 60hz, I won't let me SYNC up to the 120VAC 400hz , to make measurements on AC waveforms , they look like free running waveforms because the oscilloscope is not SYNCed up to the 120vac 400hz

If it is free running then it isn't triggered.

Run a signal into channel 1. Tell the scope to auto trigger off channel 1. The fact the scope is powered from 120 VAC 60 Hz. means nothing unless Line trigger is selected.

Ron
 
Then someones engineering for load balancing sucks! Load balancing is a prime consideration in any 3 phase distribution be it 60 Hz or 400 Hz. Good power distribution from the sub or point of origin monitors the loads by phase constantly.

What can make the load balancing suck on a 3 phase distribution?

Cause we do have to use Isolation transformers from power supplies, test fixtures, etc. because of loading problems

I thought using the isolation transformers was for ground problems not loading problems right?

Finally and again is this 3 phase delta or wye?

I have no idea, I will ask tho?

What makes the difference? is Delta have different loading problems than a WYE?
 
If it is free running then it isn't triggered.

Yes in auto triggered is it free running

IT's NOT FREE RUNNING when I sync the O scope up to the 120vac 400hz main lines

Run a signal into channel 1. Tell the scope to auto trigger off channel 1. The fact the scope is powered from 120 VAC 60 Hz. means nothing unless Line trigger is selected.

The Waveforms are FREE RUNNING when you do that
 
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 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.

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.

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.

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.

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

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

No it does not! The only time that would apply is if the scope is setup for Line Triggering where the scope uses its line frequency for the trigger source. Assuming Internal triggering the scope can trigger from any source you select. You have things like SOURCE and MODE for triggering. Again, you are not understanding how triggering on a scope works or how to apply it.

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

There is no different main line frequency. There is only one mains line frequency and that is the scope's mains power line frequency. You really need to work on your terminology. The scope triggers from a SOURCE, the user determines the source.

All scope triggering needs a source.

YES! The trigger source!

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

Depends on the scope.

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

Again, it depends on the scope as well as the signal, there is no ne size fits all.

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

Do you mean to power the scope? I have no clue what you mean with that statement.
 
My Manager said that when you put your DVM fluke meter to the main wall output how to you know if it's phase A,B or C?
I'm guessing you can't be plugging in different test equipment using the same phase or different phases, or it will cause loading problems or other problems?

Get enough wire to reach from the outlet that you want to test back to the breaker panel. If that outlet is wired to Phase B (L2), there will be zero volts to Phase B in the breaker panel. There will be 115v from the wire to Phases A & C.

If you know which breaker that circuit is on, you can test it at the panel.
Can you use a Fox & Hound tool for this?
Isn’t there a tool that injects a signal to identify breakers?
 
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Thanks for the help on this

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

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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