# Square waveform or pulse waveforms DC or AC?

Discussion in 'General Electronics Discussion' started by Danny Daviss, Mar 16, 2013.

1. ### Danny Daviss

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Mar 16, 2013
When measuring square waveforms or pulse waveforms , sometimes on the oscilloscope mode I use AC to remove the DC offset, but other times I have to use the DC mode on the oscilloscope to see the square waveform or pulse waveforms, The AC mode doesn't show the square waveform or pulse waveform but other times it does work in the AC mode on the oscilloscope

So I'm confused as how does a tech know if his squarewaveform or pulse is AC or DC?

Is DC offset and DC component the same thing or is there a difference?

Sometimes when I'm using an oscilloscope the pulse train waveform has DC offset , so its 3 volts DC offset with a pulse train waveform riding on top of it, What is this called? when a square waveform, pulse or pulse train signal is riding on top of a DC offset or DC component?

2. ### Harald KappModeratorModerator

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Nov 17, 2011
You should understand the workings of an oscilloscope. Here is a tutorial. Or Google oscilloscope tutorial.

3. ### Danny Daviss

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Mar 16, 2013
When you use the AC mode, the oscilloscope places a capacitor in series with the input. This removes the DC component of the signal.

Yes I know, But in AC mode it just was a blank screen, no square waveform or pulse train at all

ONLY in DC mode, I could view the squarewaveform or pulse train waveform, it has DC offset of 3 volts and a squarewaveform/pulse train riding on top of it

DC is a constant value, no pulse. AC generally refers to alternating between + and -

But it only works in DC mode not AC mode , why is that?

Is the squarewaveform/pulsetrain waveform is DC, alternating between from high to low than its AC or DC?

4. ### BobK

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Jan 5, 2010
Try twiddling with the trigger level knob.

Bob

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Well, it's never DC...

In this situation both mean the same thing.

6. ### Danny Daviss

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Mar 16, 2013
when do u see dc component or when is it doesn't mean the same thing? when do u know its dc component and not dc offset

7. ### Danny Daviss

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Mar 16, 2013
For Op-amps , I see trim pots either on the non inverting or inverting inputs tied with a trim pot to ground and to supply voltage

When you see this , is this biasing, DC offset voltage or DC component?

8. ### davennModerator

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Sep 5, 2009
its setting a reference voltage.
in this situation the op-amp would normally be getting used as a comparator
so it will compare the reference voltage with the voltage present on the other input pin

Dave

9. ### Danny Daviss

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Mar 16, 2013
Yes true

Here is a webpage, scroll down and look at the diagrams because i see these a lot in schematics and is this op amp as a comparator like u said, they call it an " Offset voltage adjustment" which is what?

They have 4 diagrams just scroll down and see these types a lot

Are these op amps comparator's or what when using trim pots like this?

67
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Mar 16, 2013
11. ### Harald KappModeratorModerator

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Nov 17, 2011
We do have a problem with your rather scant if not imprecise descriptions. It could be either of the possibilities you name. Add schematics and reference the parts, voltages and currents you're talking about so we can understand what you mean.
My glass-ball, as Steve's, is broken, too.