Author Topic: Fluke's single phase diode rectifier  (Read 1208 times)

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Offline Martini

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Fluke's single phase diode rectifier
« on: March 27, 2016, 08:19:54 am »
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


Someone care to explain to me?
How do you get that AC signal from (I guess) a pure sine wave?
 

Offline Andy Watson

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Re: Fluke's single phase diode rectifier
« Reply #1 on: March 27, 2016, 08:44:25 am »
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.
« Last Edit: March 27, 2016, 08:49:39 am by Andy Watson »
 

Offline Martini

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Re: Fluke's single phase diode rectifier
« Reply #2 on: March 27, 2016, 09:04:03 am »
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"
 

Offline uncle_bob

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Re: Fluke's single phase diode rectifier
« Reply #3 on: March 27, 2016, 09:07:31 am »
Hi

The "rectifier" stuff is looking at the current on the AC line.

Bob
 

Offline onlooker

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Re: Fluke's single phase diode rectifier
« Reply #4 on: March 27, 2016, 01:16:17 pm »
Quote
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.
 

Offline Martini

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Re: Fluke's single phase diode rectifier
« Reply #5 on: March 28, 2016, 09:35:45 pm »
Hi

The "rectifier" stuff is looking at the current on the AC line.
Oh, that makes sense :)
 

Offline onlooker

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Re: Fluke's single phase diode rectifier
« Reply #6 on: March 28, 2016, 11:53:03 pm »
Quote
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.
 

Offline Martini

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Re: Fluke's single phase diode rectifier
« Reply #7 on: March 29, 2016, 01:18:23 am »
Now I'm lost again.
Why wouldn't it look like this if you had a half bridge rectifier and a DC load?
 

Offline onlooker

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Re: Fluke's single phase diode rectifier
« Reply #8 on: March 29, 2016, 01:35:43 pm »
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) .
« Last Edit: March 29, 2016, 01:57:11 pm by onlooker »
 

Offline Martini

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Re: Fluke's single phase diode rectifier
« Reply #9 on: March 30, 2016, 02:23:21 am »
You're right, I was confused |O
 


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