# Oscilloscope - Why do I need to use ground as reference to take accurate measurement?

Discussion in 'Homework Help' started by exidez, Oct 2, 2008.

1. ### exidez Thread Starter Member

Aug 22, 2008
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I have always been told when measuring a voltage across a component in a circuit that I must have the ground clip connected to a zero reference point. This means I have to rearrange the circuit so that the component i am measuring is the last component closest to ground.
Why is this? why can i not just measure the voltage like DC (straight across the component)?

I am only guessing, but is this so it can tell how many degrees out of phase it is?
If I were to measure across a component like DC, what implications would that give?

Thanks

2. ### veritas Active Member

Feb 7, 2008
167
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For many oscilloscopes, each probe has a common ground, so if you have one probe grounded and another with its ground clip connected to another potential, you will be shorting that part of the circuit.

*edit* I know that doesn't completely answer the question, but it's one aspect of it.

Apr 5, 2008
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4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
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I don't understand how you came to the understanding that you would have to rearrange components in order to measure voltage/waveforms with an o'scope.

Using a ground (or circuit common) reference simply means that all your measurements are made relative to a common point. The clip ties to common, the probes sees the signal/voltage relative to that reference point. You do the same thing with a meter (and get better resolution on voltages).

5. ### exidez Thread Starter Member

Aug 22, 2008
26
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I think that actually answers the question. We are taking measurements with reference to the input voltage so we know how many degrees out of phase it is. if i measure a component in the middle of the circuit i will be sc'ing the components from that point onwards. This means the phase and voltage will be different.
This is why we were told the rearrange the circuit all the time.
Thanks, that helped a lot