Add mode & Subtract and invert mode on the oscilloscope, Time base variable vernier

[danny davis]

Add mode & Subtract and invert mode on the oscilloscope, Time base variable vernier

The Add mode on the oscilloscope is used when a circuit has multiple channels , so you use the ADD mode to ADD the 2 channels when troubleshooting a circuit that has different channels

But How does the ADD mode help you troubleshoot circuit's that has different channels with the same waveforms or with different waveforms?

When you do you use the Invert mode?

Analog O-scopes on a time base, has a Variable Vernier detent knob, if you click the detent out of calibrate position it puts the time base in a recurrent time base that is not calibrated they say

So what is the time base variable vernier knob used for?

 

[adi0803199]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

The Add mode on the oscilloscope is used when a circuit has multiple channels , so you use the ADD mode to ADD the 2 channels when troubleshooting a circuit that has different channels

But How does the ADD mode help you troubleshoot circuit's that has different channels with the same waveforms or with different waveforms?

When you do you use the Invert mode?

Invert mode is used for subtracting two waveforms from the two channels connected to the oscilloscope (Channel A -Channel B).We first invert Channel B and then press the Add mode in the oscilloscope.We can use the same procedure to subtract channel B from channel A.Variable Time base is used whenever we need to fit in a low frequency signal into the screen of the analog o-scope(Remember the screen size is a constant).

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

Invert mode is used for subtracting two waveforms from the two channels connected to the oscilloscope (Channel A -Channel B)

Yes but why would you want to subtract two waveforms? when would you use this for?

.We first invert Channel B and then press the Add mode in the oscilloscope

.

Yes I know when you want to measure the voltage difference across a component like a DVM meter does

Variable Time base is used whenever we need to fit in a low frequency signal into the screen of the analog o-scope

But you can fit low frequency signals on the o scope screen without using a VAR know

So what is it used for?

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Some O-scopes also have a Delay Time knob for the Time base , what is it used for? for what kind of measurements?

Here is a video on it
http://www.youtube.com/watch?v=8LV5-wgiYGo

 

[adi0803199]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

A simple situation when we use Subtraction is in the circuit containing op-amps or difference amplifier.Here the two inputs are subtracted to give an amplified signal.Generally we don't always get a proper output from the difference amplifier.In order to troubleshoot,we check whether the supply is proper,then we check whether the resistors are of appropriate value and connected properly and finally we check whether the desired input is given to the op-amp. Now suppose ,I have to check the input given to the op-amp,then we use this to check whether we send a required input to the op-amp.

Yes I know when you want to measure the voltage difference across a component like a DVM meter does

DVM can only give you the difference obtained in case of dc signal and it gives a rms value in case of an ac signal,but a random periodic signal,DVM cannot measure in such a case.

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

DVM can only give you the difference obtained in case of dc signal and it gives a rms value in case of an ac signal,but a random periodic signal,DVM cannot measure in such a case.

Yes True, The AC voltage difference

What you mean by the voltage difference of a random periodic signal?

A simple situation when we use Subtraction is in the circuit containing op-amps or difference amplifier.

Yes , but do you use the O-scope Invert and Add mode when troubleshooting Difference amps? and how do you use it to troubleshoot?

When do you use the ADD MODE on the O-scope to troubleshoot? or use it for what?

 

[adi0803199]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

If you know the input that you are giving to each stage in a circuit that you are working with,then the I know the input waveform which is checked using an o-scope not just the values(rms,dc).By a periodic signal,I mean square or triangular wave which has the same rms as that of sine wave,then how do you know what signal you are giving at the input stage?(It can be a sine wave or a triangular wave,you need an oscilloscope to see what the waveform is.)

When do you use the ADD MODE on the O-scope to troubleshoot? or use it for what?

Suppose I need to check whether two signals that are inverted with respect to each other.Typical circuit is that of a Inverting unity gain amplifier.Now a simple way to check that is use the ADD mode in the oscilloscope.

how do you use it to troubleshoot?

See the first post that I have posted.

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

Suppose I need to check whether two signals that are inverted with respect to each other.Typical circuit is that of a Inverting unity gain amplifier.Now a simple way to check that is use the ADD mode in the oscilloscope.

So you put the oscilloscope probes on the Two signals that are on the INPUT pins of the Op-amp , to check if they are inverting? and you use the ADD MODE on the O-scope?

DVM can only give you the difference obtained in case of dc signal and it gives a rms value in case of an ac signal,but a random periodic signal,DVM cannot measure in such a case.

Yes , a DVM meter can also Measure the AC voltage difference and DC voltage difference across a component

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Suppose I need to check whether two signals that are inverted with respect to each other.Typical circuit is that of a Inverting unity gain amplifier.Now a simple way to check that is use the ADD mode in the oscilloscope

The Two signals would Cancel out is they are inverted with respect to each other when you use the ADD mode on the O scope

 

[adi0803199]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

So you put the oscilloscope probes on the Two signals that are on the INPUT pins of the Op-amp , to check if they are inverting? and you use the ADD MODE on the O-scope?

Yes you are right,that how you troubleshoot.

Yes , a DVM meter can also Measure the AC voltage difference and DC voltage difference across a component

But it cannot tell us what kind of signal that you have measured,you just know that it is a periodic signal.Not whether it is a sinusoid or a triangular wave.

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

Do you have any examples of when you use the ADD mode or Invert mode on the O-scope , for testing circuits or using it for troubleshooting?

Do you have any examples of using the external trigger for testing circuits or using it for troubleshooting?

I just need examples to learn from please

 

[chuckey]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

Many CROs with "multiple" channels work by taking CH1 display and showing it on the first time base sweep, then CH2, is given a DC offset and is displayed on the next sweep of the time base. This can go on for many channels. The big danger is that the signals are not time referenced (being on different timebase sweeps), they can be compared for shape and amplitude but if some strict timing is being investigated then the only way is to use the add or subtract. Now on say, ADD, the A input + the B input is shown as CH1, the other channels being as before. The CH1 display will show the exact time relationship between the A and B inputs, but the display will need to be understood, using the attenuator and reducing one input will demonstrate which bit of the waveform belongs to which input.
Both the add and subtract features can be used to check the co-incidence of pulses, edges of pulses, rise times etc.
Frank

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

Both the add and subtract features can be used to check the co-incidence of pulses, edges of pulses, rise times etc

.

Can you explain more about how the add and subtract features are to check the pulses, edges of pulses and rise times?

Can you give examples on these

taking CH1 display and showing it on the first time base sweep, then CH2, is given a DC offset and is displayed on the next sweep of the time base.

So you put the AC signal on Ch1 and the DC offset on Channel2?

Why would you want to do this? i don't get it?

 

[chuckey]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

If you add two square pulses, one delayed compared to the other, the front edge of the addition of them will have a "step" in it, the width of the step will be the delay. Or if you use the subtract, a narrow pulse, the width of the delay will be seen.
NO, the CRO puts a DC offset, so each "line for a channel" appears at a different Y position on the screen.
You want to do this so you can look at different parts of a circuit at the same time, say the input signal to a amp,the output of the amp with a flattened peak (gross distortion), and still have spare channels to investigate different parts of the circuit, say the + and - output of a phase splitter.
Frank

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

If you add two square pulses, one delayed compared to the other, the front edge of the addition of them will have a "step" in it, the width of the step will be the delay

You add two square pulses that has a time delay?

When do you use this , for what kind of circuits , troubleshooting what kind of logic? or testing what kind of logic?

the CRO puts a DC offset, so each "line for a channel" appears at a different Y position on the screen.
You want to do this so you can look at different parts of a circuit at the same time, say the input signal to a amp,the output of the amp with a flattened peak (gross distortion), and still have spare channels to investigate different parts of the circuit, say the + and - output of a phase splitter.

What are you talking about, please explain it more in detail or in another way

Are you saying you ADD the DC offset voltages from different stages you're testing?

Yes each stage or channel will have different DC offset voltages, but why ADD them together?

Any other examples you can use the ADD MODE or Invert function, Subtract mode on the O-scope Please give more examples so I can learn from

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Circuits that you have tested or troubleshoot using the EXT. trigger?

Like I used an Ext trigger for XXXX to troubleshoot this board or to test this board

It's like If I was the Hiring person for a job interview and I asked you in your whole career what did you use the EXT. Trigger on the O-scope for and to do what, and you should say? list them please

It's like If I was the Hiring person for a job interview and I asked you in your whole career what did you use the ADD MODE on the O-scope for and to do what, and you should say? list them please

A lot of job interviews ask me this , so I need to know

 

[chuckey]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

" Are you saying you ADD the DC offset voltages from different stages you're testing? ", Read my words :- "the CRO puts a DC offset, so each "line for a chan....". You would use the external Sync input for looking at TV waveforms. Triggering the CRO time base from some point in the line output circuit.
Frank

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

"the CRO puts a DC offset, so each "line for a chan

Explain more about it, i don't get it

Each Signal would have to have DC offset voltage

What do you mean by CRO? the O-scope

Triggering the CRO time base from some point in the line output circuit

.

What are you talking about, what point in the line output circuit? what are you talking about , explain more

 

[chuckey]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

Given a four channel CRO (Cathode Ray Oscilloscope). On the first time base sweep, the CRT (Cathode Ray Tube), displays what is being put into channel 1 at a position 4 Cm (Centimetres) above the centre of the tube. On the next timebase sweep, the CRT displays what is on channel 2, 2 Cms above the centre of the tube. On the next time base sweep, the CRT displays whats on channel 3, 2 Cms below the centre of the tube. On the fourth sweep, channel four is displayed, 4 Cms below the tube centre. On the next sweep of the timebase, channel 1 is displayed.
The above situation is when each channel is AC coupled with its shift control centred. Moving the channel shift controls or displaying the signals with a DC offset, can be confusing as the relative positions of the channel displays move about, so channels may be wrongly identified.
Any point in the lione output circuit.
Frank

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

Given a four channel CRO (Cathode Ray Oscilloscope). On the first time base sweep, the CRT (Cathode Ray Tube), displays what is being put into channel 1 at a position 4 Cm (Centimetres) above the centre of the tube. On the next timebase sweep, the CRT displays what is on channel 2, 2 Cms above the centre of the tube. On the next time base sweep, the CRT displays whats on channel 3, 2 Cms below the centre of the tube. On the fourth sweep, channel four is displayed, 4 Cms below the tube centre. On the next sweep of the timebase, channel 1 is displayed.

Yes I know how to do this, you just use the channel vertical position knob for each channel

The above situation is when each channel is AC coupled with its shift control centred. Moving the channel shift controls or displaying the signals with a DC offset, can be confusing as the relative positions of the channel displays move about, so channels may be wrongly identified.

So how do you fix this problem? you use the ADD MODE? i don't get it

What is your point what you're trying to make about this O-scope DC offset?

 

[danny davis]

Re: Add mode & Subtract and invert mode on the oscilloscope, Time base variable verni

In My Tektronix manuals for the 2445 , 2221, 2212 models they say in the manual that the ADD mode is used for when you want to ADD a DC offset voltage level on ch1 and add it to ch2 which has an AC waveform without DC offset, you then ADD them together to display an AC waveform riding ontop of an DC offset

When would you use this? to add DC offset levels to an AC waveform or any periodic waveforms? for what reason?