What is the difference between AC and DC signal?

 

AC (Alternating Current) voltage varies with time.
DC (Direct Current) voltage is steady and does not vary with time.

 

AC also reverses direction of current (alternates polarity each cycle).
Max.

 

The meaning of AC and DC depends on the context. Either explanation given above can be applied depending on the context of usage.

1) From a frequency domain perspective, DC is zero frequency, AC is non-zero frequency

2) From a time domain perspective, DC never changes sign. AC has sign reversal.

 

A DC signal, can mean a varying DC level, such as the output from an analogue sensor. For example, the output from a thermo-couple will vary with temperature etc.

 

The meaning of AC and DC depends on the context.

Bingo.

For instance the power coming off a full wave rectifier can be called DC even though it has a huge voltage swing. But the current does not reverse direction.

Pure DC is almost an abstract concept, since any DC source will likely have some noise in it and that noise can be called the AC component. Likewise an AC signal might contain an offset, a DC component.

 

My personal perception and the one I have always adhered to has always been the 'Alternating' refers to the current change in Direction through the conductor.
Max.

 

Here is an example of where AC may or may not change direction.
When analyzing an amplifier circuit, there are two types of analyses, DC and AC.

In DC analysis, one studies the current and voltages of the steady-state conditions, quiescent or non-quiescent.
In AC analysis, one studies the signal amplification. The input and output signals need not change sign.

 

Need to add a distinction between DC and AC coupling for a scope.

DC includes the non-time varying part. AC just shows the time varying part of the signal.

 

My personal perception and the one I have always adhered to has always been the 'Alternating' refers to the current change in Direction through the conductor.

That seems too restrictive.
It means you can't call a varying signal riding on a DC level, such as in an AC amplifier "AC" whereas in practice it is always an AC signal.
To me, if you can see it using the AC coupling on an oscilloscope, it's "AC".

 

To me, if you can see it using the AC coupling on an oscilloscope, it's "AC".

I agree, the AC coupling removes the DC reference point and uses the non-offset trace datum as the zero point where the reversal occurs.
Max.

 

My personal perception and the one I have always adhered to has always been the 'Alternating' refers to the current change in Direction through the conductor.
Max.

That feels right, but the problem is that a varying voltage can very easily be explored to produce an alternating current, for instance with a single capacitor to couple.

 

Thank you all for these guidance