ADD mode used for on the Oscilloscope

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DexterMccoy

Joined Feb 19, 2014
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What is the ADD mode used for on the oscilloscope?

What kind of troubleshooting would you use the ADD mode on the oscilloscope for?

What kinds of tests would you use the ADD mode for on the oscilloscope?
 

WBahn

Joined Mar 31, 2012
26,398
What is the ADD mode used for on the oscilloscope?
For adding two signals.

What kind of troubleshooting would you use the ADD mode on the oscilloscope for?
Troubleshooting that would be aided by adding to signals.

What kinds of tests would you use the ADD mode for on the oscilloscope?
Tests that needed signals added together.


Perhaps Billy Mayo could get with you offline and explain things to you.
 

alfacliff

Joined Dec 13, 2013
2,458
It can be used to test whether two signals are timed the same. by adding them, it makes it obvious if they are simultaneous or not. also, you can test delay through a circuit the same way. it also makes it stand out if there is distortion in an amplifier or system.
 

Thread Starter

DexterMccoy

Joined Feb 19, 2014
429
What is the ADD mode used for on the oscilloscope?
For adding two signals.

Quote:
What kind of troubleshooting would you use the ADD mode on the oscilloscope for?
Troubleshooting that would be aided by adding to signals.

Quote:
What kinds of tests would you use the ADD mode for on the oscilloscope?
Tests that needed signals added together.
Yes I know the signals need to be added together
But i need examples of when and how , what kind of circuits would use the ADD mode on the oscilloscope

Do you have any examples of when you have used the ADD mode to add signals together to make a measurement or to do troubleshooting?
 

MrChips

Joined Oct 2, 2009
22,879
Some scopes have ADD function but no SUBTRACT.

If you want to measure the current pulse on the high side of a power supply by monitoring the voltage drop across a series resistor,

connect CH1 probe to one end of the resistor,
connect CH2 probe to the other end of the resistor,
set CH2 to INVERT,
select ADD function.
 

WBahn

Joined Mar 31, 2012
26,398
Yes I know the signals need to be added together
But i need examples of when and how , what kind of circuits would use the ADD mode on the oscilloscope

Do you have any examples of when you have used the ADD mode to add signals together to make a measurement or to do troubleshooting?
I've used the ADD mode lots of times, usually in combination with the inversion mode of one of the channels so as to effectively subtract them. Can you think of any cases where it might be nice to subtract two signals?

Or, if you want to see the common-mode of two signals you add them together.
 

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DexterMccoy

Joined Feb 19, 2014
429
If you want to measure the current pulse on the high side of a power supply by monitoring the voltage drop across a series resistor
Why would you want to measure the "current pulse" of a power supply?

You mean the high frequency pulse for switching power supplies?

Does the series resistor have to be 1 ohm? or can it be any value?

Both O scope ground clips would have to be floating and not used right?
 

Thread Starter

DexterMccoy

Joined Feb 19, 2014
429
've used the ADD mode lots of times, usually in combination with the inversion mode of one of the channels so as to effectively subtract them. Can you think of any cases where it might be nice to subtract two signals?
Can you give examples of when you used them, so i can learn from them please?
 

WBahn

Joined Mar 31, 2012
26,398
Why would you want to measure the "current pulse" of a power supply?

You mean the high frequency pulse for switching power supplies?

Does the series resistor have to be 1 ohm? or can it be any value?

Both O scope ground clips would have to be floating and not used right?
They call them ground clips for a reason. They are not floating to begin with.
 

Thread Starter

DexterMccoy

Joined Feb 19, 2014
429
Yes , but if you use the O scope ground clips while do a differential voltage drop, it will be referenced to ground and you don't want that. You want the ground clips not to be used so there is no reference to ground
 

WBahn

Joined Mar 31, 2012
26,398
Yes , but if you use the O scope ground clips while do a differential voltage drop, it will be referenced to ground and you don't want that. You want the ground clips not to be used so there is no reference to ground
Your scope probes (unless they are specifically differential probes, which tend to be rare and expensive) measure a voltage relative to the scope's ground reference. Which means you want your circuit to be referenced to the scope's ground reference. That's what the scope's ground clips are for. Of course, you need to be aware of what point in your circuit, if any, is otherwise ground referenced and be sure to be consistent with that.
 

WBahn

Joined Mar 31, 2012
26,398
Can you give examples of when you used them, so i can learn from them please?
No. I can't. I haven't done much bench diagnostic work in the last decade or so and I certainly don't recall specific examples of how I made some specific measurement on some specific chip a dozen years ago or so.
 

MrChips

Joined Oct 2, 2009
22,879
Why would you want to measure the "current pulse" of a power supply?

You mean the high frequency pulse for switching power supplies?

Does the series resistor have to be 1 ohm? or can it be any value?

Both O scope ground clips would have to be floating and not used right?
I didn't specify what kind of load the power supply is driving or the type of power supply. This is simply an example of making a current measurement.

The resistor can be of any appropriate value.

The oscilloscope ground clips would be connected to the GROUND of the circuit being tested.
 

ErnieM

Joined Apr 24, 2011
8,108
Why would you want to measure the "current pulse" of a power supply?
It's an example of when you would need such a measurement.

You mean the high frequency pulse for switching power supplies?
Mebby he means that, mebby not. He made an example of a differential signal where the value across an element is measured, not the voltage from one point to ground.

It could be any element in any circuit where you want to watch the voltage directly across something.

Does the series resistor have to be 1 ohm? or can it be any value?
Any. It's an example. It's an imaginary example to illustrate where you would want to make such a measurement.

Both O scope ground clips would have to be floating and not used right?
Nope. Best if both clips go to the ground of the circuit under test, keeps the signals as faithful as they can be that way.

Don't over think this, just remember it and one day when worrying out a problem you'll remember the technique and use it and enjoy troubleshooting bliss.
 
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