AC circuit (120v single phase) smooth to a10 sec. average voltage sine wave

[David Kimbley]

Hi circuit gurus,

I would like to take a household ac voltage (ie sine wave), and then do 2 things with it.

1) create the 5-10 second average voltage sine wave of it, (not calcuated, actually smoothed) and
2) offset (phase shift) the actual sine wave (not averaged now) coming in by 180 degrees.

These are probably both simple to a person more knowlegable in electronics and circuits than I am.

Please be specific on how exactly these ac currents can be created. Any help would be greatly appreciated.
Let me know if I need to be more specific in my description.

Sincerely, David K

 

[Arouse1973]

Hi David. What do you mean 5 - 10 second average? Please explain what you are doing.
Thanks
Adam

 

[David Kimbley]

Hi Adam, Sorry, after I thought about it, I realized this is not clear. Ok, in this case, by "average" I mean: you take 600 cycles say (10 seconds) add them together, and divide it 600. So that every instant of voltage is like a "smoothed" sine-wave minimizing any irregular spikes/drops which might have occured. Yes, I am NOT looking for the average of the voltage over time (which would be about 0 volts). Or even the positive average (which would be about 120 v -- I think).
Hope this helps...
David

 

[David Kimbley]

David here again...
I also realize my 2nd part is not very clear. It probably should be polar reversed rather than phase shifted.

 

[Arouse1973]

Hi David, who told you the average of a sinewave is 0? No I am not mad......

 

[Arouse1973]

Hi Adam, Sorry, after I thought about it, I realized this is not clear. Ok, in this case, by "average" I mean: you take 600 cycles say (10 seconds) add them together, and divide it 600. So that every instant of voltage is like a "smoothed" sine-wave minimizing any irregular spikes/drops which might have occured. Yes, I am NOT looking for the average of the voltage over time (which would be about 0 volts). Or even the positive average (which would be about 120 v -- I think).
Hope this helps...
David

An integrator will do this for you. A simple diode and RC network. Still not sure what you want to do.
Adam

 

[David Kimbley]

Hi Again Adam, Glad I did not make you mad. But does not the positive alternating voltage potential pretty much equal the negative voltage potential such that when added they are pretty close to zero?
But this question of what the average voltage is, is sort of beside my question. How can a smoothed voltage be acheived in an actual circuit with inductors/capacitors, etc.
and thanks for the prompt reply.
David K

 

[Arouse1973]

Yes your right, but the average of a sinewave is taken over half the period because over a full cycle as you said is zero.
Adam

 

[Arouse1973]

Diode and capacitor, basically a rectifier, but you lose a diode drop. If this is not ok the a absolute value circuit would be used.

 

[David Kimbley]

Hi Adam, Ok, an "Integrator". Is "an Integrator" a well known term for an electronic circuit which will do what I've described? Can a person buy an "integrator" in the local electronics store, or does it have to be built with "A simple diode and RC network". And just to be clear RC means some combination of a resistor and capacitor I think. Sorry, I'm kind of an electronics newbie--probably could tell.

As for what I am trying to do Adam, it is primarily to remove temporary voltage fluxuations in household 120 Vac current. Sort of like a surge protector, but I hope simpler..
David

 

[David Kimbley]

Hi again, Ok, you mentioned a rectifier. But then wouldn't that change it to a DC voltage? I want to keep it AC.

 

[Arouse1973]

Yes it would change it to DC. So you dont want to measure anything then. I think what your after is a mains filter.
Adam

 

[Martaine2005]

Sorry Adam. Could not resist this..

You may require a filter like these. 1st is on-board filter and 2nd wires into plug..

 

[BobK]

I understand what you are trying to do, even if no one else does. But what do you want to do with this smoothed sine wave? Are you going to power something with it, or is it just a low current signal that you want?

Bob

 

[Martaine2005]

even if no one else does.

Politically correct. But aimed at me.
BobK, you are absolutely correct. I have no idea. But suppressing the mains would smooth it and protect against voltage spikes too. At least that is what I have been told. If I am wrong, then I apologise.

On the other hand, if you understand what the OP meant, please share it.

 

[davenn]

On the other hand, if you understand what the OP meant, please share it.

Yeah Bob, please do


Dave

 

[BobK]

As I understand it, he wants to analyze the waveform over many cycles, then produce a waveform that, at each point in the cycle, gives the average voltage at that point in the cycles analyzed.

Bob

 

[hevans1944]

And the way to do this... is not simple! You want to digitize and store a goodly number of samples per cycle in a random access or serial memory device. If this is a real-time application with a running average, you discard the last sample when the next sample comes in. A FILO (first in, last out) buffer with independently addressable write and read data paths in other words. Length of buffer determined by number of samples per cycle and the total number of cycles you want to average. Then, between each sample, you sum all the samples at corresponding positions on the sine-wave input that are in the FILO buffer and divide each of those sums by the number of cycles you have accumulated, writing the results to another FILO buffer. Finally, between samples, you read out this point-averaged data in the second FILO buffer to a digital-to-analog converter. Voila! There is your sine wave again, reconstructed with a running average. You will also need a low-pass filter on the DAC output to filter out the piece-wise step-representation of the sine wave. And you need to do the calculations pretty fast: during the time between successive samples or you won't keep up. Keeping the number of samples per cycle, and the number of cycles, limited to integer powers of two will perhaps simplify the computations. Try to avoid floating-point calculations, although modern processors tear through floating-point number-crunching at warp speed.

Or... you can purchase a UPS (Uninterruptible Power Supply) that generates a clean sine wave from a battery-backed power oscillator and phase-lock it to the incoming power line frequency, which is what I would do if I weren't trying to analyze power line glitches in real time with a really fast multi-core processor. Either approach is a bit pricey, depending or how much you can build versus how much you want to buy off-the-shelf. What is your experience in building high-speed digital electronics with analog front-ends and analog outputs?

You can "invert" a sine wave by applying it to the primary of a 1:1 isolation transformer and then choosing one of the two secondary wires for output, the other secondary wire being your reference for measurement.

As @BobK asked, what are you gonna do with your "smoothed" sine waves? I might consider buying some if they were really smooth and non-fattening.

 

[Arouse1973]

I think I understand what he means now. I suppose it depends on your interpretation of the word smooth. For me to smooth something is to make it flat. Like a smoothing capacitor in a power supply. What the OP wants to do is to produce a clean sine wave from one with distortion (noise). That's how I would say it anyhow.
Thanks
Adam

 

[David Kimbley]

Hi again all,
Wow, thanks for all the interest, and for all your considerations. And yes Bob, you have correctly explained my initial question. And Hevans, thank you,... a LOT of good info there I'm sure, but I am disappointed to hear it is not as simple as I'd hoped.. I'm really trying to keep this as simple as possible.
It seems though, there is a great amount of interest in the overall purpose of this endeavor.
This first "AC averaging" is just step 1. After this is done (however decided), I want to invert the live (realtime) AC, and add the two together (averaged & realtime). --A very small voltage now. Ultimately this summed AC is what I want to measure.
So it'd end up with just the realtime voltage fluctuation. Now you see why I can't use a UPS or clean power-- I want the unclean power-fluxes to measure. The mention above of an integrator made me wonder if I could use a Differentiator--since this is ultimately what I want. But I dont think you can do this with AC, since it's varying all the time.

Any more thoughts, insights, suggestions ??
And thanks again for all your help,

David K