EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Martini on March 26, 2016, 09:19:54 pm
-
Hi,
Fluke is showing rectified AC waveforms in their document about true RMS and I was wondering what it exactly meant.
http://en-us.fluke.com/training/training-library/measurements/electricity/what-is-true-rms.html (http://en-us.fluke.com/training/training-library/measurements/electricity/what-is-true-rms.html)
Someone care to explain to me?
How do you get that AC signal from (I guess) a pure sine wave?
-
Where, exactly, are they showing the rectified sinewave?
The diagram at the top of the page has the caption of "non-sinusoidal", which it is! Possibly due to a phase-controlled unit/module/device.
The other instance, in the table, shows the output of a rectifier that has a significant forward voltage drop, i.e. no, zero output voltage for portions of the sinewave. I guess there is some artistic licence creeping into this diagram since you would not expect to see both positive and negative parts of the cycle as the output of any real-life rectifier circuit.
-
I guess there is some artistic licence creeping into this diagram since you would not expect to see both positive and negative parts of the cycle as the output of any real-life rectifier circuit.
That's what caught my attention. And that's the one they called "single phase diode rectifier"
-
Hi
The "rectifier" stuff is looking at the current on the AC line.
Bob
-
The other instance, in the table, shows the output of a rectifier that has a significant forward voltage drop, i.e. no, zero output voltage for portions of the sinewave. I guess there is some artistic licence creeping into this diagram since you would not expect to see both positive and negative parts of the cycle as the output of any real-life rectifier circuit.
Apparently, some level of liberal artistic rendering is the likely explanation. The "single phase..." diagram is likely meant for the voltage waveform after the plain old single diode rectifying (half bridge), for which all the half waves are on the positive side.
The same can be said for their diagram of 3 phase diode rectifying. It is more likely meant for the waveform after half bridge rectifying 2 of the 3 phase lines, for which all rectified waves should be on the positive side. Though, the flat part depicted in their diagram is a lot longer than it should be (60 degrees) and the middle of the M shaped wave should not reach 0.
-
Hi
The "rectifier" stuff is looking at the current on the AC line.
Oh, that makes sense :)
-
Quote from: uncle_bob on Yesterday at 09:07:31 AM
Hi
The "rectifier" stuff is looking at the current on the AC line.
Oh, that makes sense :)
The AC line current waveform would look like this if you have a full bridge rectifier with very large forward voltage drop.
-
Now I'm lost again.
Why wouldn't it look like this if you had a half bridge rectifier and a DC load?
-
For a half wave rectifier, the conducting phase is between 0 and 180 degrees, or, within the "positive" half of the waveform.
That is, the half waves will only be taken from the same "positive" side. This will show up as positive half waves spaced with flat lines for the voltage after the rectifier, and for the current for both before and after the rectifier (the same current measured at different locations) .
-
You're right, I was confused |O