Timeline for RMS of a complex waveform
Current License: CC BY-SA 3.0
19 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Feb 9, 2017 at 8:52 | vote | accept | Vedanshu | ||
| Jan 21, 2017 at 18:11 | comment | added | Vedanshu | Let us continue this discussion in chat. | |
| Jan 21, 2017 at 18:03 | comment | added | Andy aka | Think about this a bit. What if the sine window was from 89 to 91 degrees - the sine value is pretty much 1 in this area but if you focussed on 179 to 181 degrees the value is pretty much zero. You are misapplying the formula. The formula assumes that for time period d1, the waveform in d1 repeats for ever hence it's RMS value is totally represented by the waveform in d1. You are missapplying the formula because the partial sinewave has to repeat from 180 degrees onwards and you are not assuming this. You cannot solve your problem with this method. | |
| Jan 21, 2017 at 17:59 | comment | added | Vedanshu | sine wave here is periodic with period 360 degree. | |
| Jan 21, 2017 at 17:58 | comment | added | Andy aka | What you are assuming is like saying that the RMS value of part of a sinewave is exactly the same as any other part of that sinewave and that is incorrect. | |
| Jan 21, 2017 at 17:57 | comment | added | Vedanshu | sine wave conducts from 54 to 180 and repeated after 360 hence the duty cycle was 126/360. | |
| Jan 21, 2017 at 17:55 | comment | added | Andy aka | Hey hold on a minute, you are applying the formula inappropriately. You have to apply it as if the sinewave between 54 degrees and 180 was repeated from 180 onwards. You are assuming a full sinewave from zero to 360 degrees and this breaks the rule of the formula. | |
| Jan 21, 2017 at 17:51 | comment | added | Vedanshu | yes you are right, it is zero for the rest. | |
| Jan 21, 2017 at 17:50 | comment | added | Andy aka | Well I agree with your numbers now but I'm assuming that the waveform is zero for the rest of the time (65%). Maybe the answer you were told is incorrect? | |
| Jan 21, 2017 at 17:45 | comment | added | Vedanshu | Yes you are right, the conduction time was 126 degrees from 54 to 180 degrees, so the duty cycle is (180-54)/360 = 126/360 =0.35 | |
| Jan 21, 2017 at 17:40 | comment | added | Andy aka | What happened to the 54 degrees that you mentioned i.e. 126-54 = 72 which, as a duty cycle is 0.2 for a full sinewave of 360 degrees. Also, for the other 288 degrees what happens to the waveform? You are not being very clear. | |
| Jan 21, 2017 at 17:37 | comment | added | Vedanshu | rms of the sine is \$(\text{peak value})/\sqrt{2}\$ so in the final calculation of rms where we have to square its value, I replaced it with \$ (\text{peak value})^2/2\$ and 0.35 is the duty cycle 126/360 = 0.35 | |
| Jan 21, 2017 at 17:32 | comment | added | Andy aka | I don't understand the numbers in your calculation, like, where does the 0.35 come from? Ditto the 0.5? Also what is T given that the partial duration of the sinewave is 0.2 x 360 degrees? | |
| Jan 21, 2017 at 17:07 | comment | added | Vedanshu | Okay, I'm putting my calculation in the question above. | |
| Jan 21, 2017 at 17:03 | history | edited | Andy aka | CC BY-SA 3.0 |
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| Jan 21, 2017 at 17:01 | comment | added | Andy aka | It is valid as far as I'm concerned - maybe you made some rounding error? | |
| Jan 21, 2017 at 17:00 | comment | added | Vedanshu | So, is it valid for sinusoidal and any other non-linear functions also ? Because on calculation I was getting wrong answer(small error). | |
| Jan 21, 2017 at 17:00 | history | edited | Andy aka | CC BY-SA 3.0 |
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| Jan 21, 2017 at 16:54 | history | answered | Andy aka | CC BY-SA 3.0 |