Sure. Simple one:
Top image, the square wave is 10% higher on average than RMS, but on the other, they match.
Isn't it that a contradiction?
Hello again,
Well, when considering data from different web sites or different charts on any web site we have to know what they are referring too, in exact terms. That's because there are many ways of interpreting the way we measure things and the results of those measurements.
For example, mathematically the average of a sine wave is zero. That's 0v for any sine wave regardless of the amplitude, 1v, 10v, 100v, 1000v, etc. So the mathematical average of a sine wave that has a peak of 1 million volts is zero, but does that do us any good? No, because we know that when we use a sine wave to power something it delivers energy to that thing, and so we'd like a more comprehensive definition of average that we can use to understand power. This means we end up using the average of the absolute value of the sine wave.
Enter the average reading meter. Early meters could read the average of the absolute value of a sine wave which is similar to a full wave rectified sine wave average, but they wanted the meter to read out in volts RMS not volts AVG, so they applied a 'factor' to the meter. This factor would take the reading of the meter and by way of the face scale multiply it by a factor of approximately 1.1107 and since the averate reading meter movement would see a value of about 0.9 for a sine wave with a peak of 1.4142, multiplying 0.9 times 1.11 would result in a reading of very close to 1.000 which is exactly the right value for the actual RMS value of the sine wave.
So we see that AVERAGE reading meter movements use a factor of 1.1107 in order to show the RMS value from the actual value detected which happened to be the AVG value.
Now enter the peak reading meter. The peak of that same sine wave is 1.4142, so to get a reading of 1.0000 we need to multiply that 1.4142 by 0.7071, and so peak reading meters use a different factor which is that 0.7071 which is 1/sqrt(2).
The question now is what happens when we try to measure a square wave with amplitude peak of 1.4142, what do those same meters read.
What happens in the average reading meter is the square wave has an average that is equal to the peak, so it is 1.4142. The RMS value is the same, 1.4142, but when we apply that same factor of 1.11 we get about 1.57 which is 11 percent high. Thus the meter will ready about 11 percent high.
What this means for the two charts is that one is posting the theoretical ACTUAL value, and the other is posting the MEASURED value measured on a meter that has a meter movement that detects the average value.
The results are more clear when we see both waves and their results. In the attachement, we see the two waves in question and various values we get from different operations with those two waves.
The dark blue values are the ACTUAL values, these are the theoretically accurate values that the waves posses. If we had a meter that could measure everything perfectly, these are the values we would measure.
The green values are the meter factors for using the actual values to get to the RMS values.
The red values are the results we get from the meter using the right factor for each type of meter.
The light blue values are the ratios of what the meter calculates (displays) vs what the actual real RMS value is. This represents an error calculation as a ratio. For a ratio of say 1.1/1 that would mean the meter reads 10 percent high.
It is clear that for the square wave using an average reading meter movement we get a reading that is 11 percent too high. Note also that a peak reading meter movement would give us a result that is about 29 percent too low.