invert and add mode on oscilloscope

[walters]

why it is necessary to invert channel b

What can i use the "invert mode" on the oscillscope for?

My channel B or channel#2 has a invert mode but i don't know what to use it for

example :

1.) If i have a 5 volts peak to peak AC waveform on Channel#1 and a 5 volt peak to peak AC waveform on Channel#2 invert mode = Cancel out to zero volts right?

2.) If i have a 5 volt peak to peak AC waveform on channel#1 and a 2 volt peak to peak AC waveform on Channel#2 invert mode= negative -3 volts

But why would i want to do this?


What does using the INVERT mode or ADD MODE tell a electronic designer or technician ?

I know if you use a the invert mode on channel#2 with the ADD mode is "substracts" channel#1 waveform with channel#2 waveform

Subtration mode= invert mode+ add mode at the same time

When would i use this "subtraction mode" on the oscilloscope? any examples please?

When would i use the ADD mode on the oscilloscope ? any examples please?

When would i use the invert mode on the oscilloscope? any examples please?

 

[barry14]

invert and add

The invert mode on an oscilloscope is generally used in place of a true differential amplifier for observing signals that don't have a common ground. For example, if you want to look at the voltage across a resistor where neither end of the resistor is grounded, just connect Channel A of the oscilloscope to one end of the resistor and Channel B to the other end, and put the oscilloscope in ADD mode with Channel B inverted. Then the display is the difference of channels A and B which is the voltage across the resistor (which is proportional to the current through the resistor so current can be monitored at various points in a circuit without a current probe). The performance of this mode is not as good as a true differential ampifier because the gain and phase matching of Channels A and B is not as good especially at frequencies approaching the bandwidth of the oscilloscope. You can adjust the gain of Channel B using the variable gain control to compensate to some extent for gain differences. Just connect the same signal to both channels and adjust the variable gain for the minimum displayed signal. The ADD mode is mainly for this application of observing signals differentially. However there may be occasions when you want to observe the sum of two signals such as looking at the two out of phase outputs of a class B amplifier stage.

 

[walters]

mode of oscilloscope

Thanks alot Barry for the information

if you want to look at the voltage across a resistor where neither end of the resistor is grounded, just connect Channel A of the oscilloscope to one end of the resistor and Channel B to the other end, and put the oscilloscope in ADD mode with Channel B inverted. Then the display is the difference of channels A and B which is the voltage across the resistor

#1.) Where do i put my oscilloscope channel A and channel B ground probes then? do i leave them hanging in the air? or connect them to ground still?

Added after 14 minutes:

How can i measure the phase difference and phase angle using the ADD and INVERT MODEs?

I read that each division is = to 45 degrees

Using the ADD mode you can see the phase difference ( horizontal distance ) between the reference waveform to the compared waveform

Added after 10 minutes:

Do you know how to do this one

ELIMINATION OF UNDESIRED SIGNAL COMPONENTS
The ADD feature can be conveniently used to cancel out the effect of an undesired signal component that is superimposed on the signal you wish to observe.

Procedure:
1. Apply the signal containing an undesired component to the CH 1 INPUT jacks and the undesired signal to the CH 2 INPUT jack.
2 Set-the vertical MODE to CHOP and SOURCE to CH2 Verify that CH2 represents the unwanted signal, with an inverse polarity. The polarity can be reversed by setting CH2 to INV.
Set the VERTICAL MODE to ADD, SOURCE to VERT. MODE and CH2 VOLTS/DIV and VARIABLE so that the undesired signal component is cancelled as much as possible. The remaining signal should be the signal you wish to observe alone and free of the unwanted signal


HOW CAN YOU CANCEL OUT THE SIGNAL COMPONENT ? please give examples

Because alot of RF and modulation, interlaced, video horizonatal sync, vertical sync are single ended so how would i be able to CANCEL the signal component ?