Voltage quality recorder?


i am an electronics hobbyist, and want to develop an system which is an voltage quality recorder, i mean it measures the various voltage disturbances like transients, swells, sags, THD, etc,
I was comfortable in analyzing the concept and with the software too. but for the hardware implementation i am confused of which kind of TI microcontroller or microprocessor is suitable for my project. i will work on the real time calculations and will use FFT in analyzing the voltage.I am planning on dsp processors of C2000 series of TI. But not able to wisely choose them. On what major parameters should i look upon while choosing them. I would be helped if anyone can suggest me which one would precisely be used for this cause.
Any more suggestions on how to proceed with it are welcomed.

Thank you.

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SolidRaven4 years ago
Any microcontroller with sufficient memory will do. Just look at the connectivity you need. A DSP processor might be useful but not strictly necessary. You're not dealing with a high data throughput here. The variations on the power grid are usually rather slow. So keep in mind, you're working at 50 or 60 Hz depending on your location. The harmonics generated are usually rather low in frequency, I wouldn't go looking for them beyond 500 Hz.
Though if you have big loads with switched mode power supplies they can go into the kHz range. Even then, any ADC with 100 kSa/s should be sufficient to monitor most of those. Especially considering your microcontroller operates at a clock of 30 MHz easily these days. Lets just say it's not much problem to store and analyse data coming in at a rate of 10-15 kBps (8-12 bits). At least not if you bother to code a bit efficiently. To store the data you could use a flash card, a 4 gigabyte card should be sufficient to hold the data for a few days.
If you only record the changes it might be able to hold data for several weeks, but that will complicate the algorithms you need and I'm not really sure if you're up for the math to modify the formulas to work with such data easily.

To actually go to the real design problems:
A good anti-aliasing filter is paramount here as power lines tend to pick up a lot of high frequency junk along the way. Especially if you still live in a country where they're not underground yet. And these lines work like giant antennas and run along telephone lines for several kilometres. There's some coupling going on there. So to keep it short, use a low pass filter while keeping nyquist in mind. Don't bother going too high order on it.

Another problem is reliable attenuation. While you'll need a big resistor to avoid drawing too much voltage from the grid you must also remember that larger resistors cause more thermal noise. So be sure to find a good balance. If you're worried about introducing a large load by buffering, use an instrumentation amplifier. The input resistance of such setup will look like an open circuit compared to the normal loads on the grid. 

Electronics and grid voltages, it's not a very good combination. There are several optocouplers that allow linear coupling if you combine them with opamps. A good example is the IL300. The datasheet has the necessary circuit. Again you'll need operational amplifiers for most of these.

And a final bit of advice -assuming you have access to one-; Be sure to analyse your circuit with a network analyser, it can save you a lot of headaches. 

Have fun!
chamunks4 years ago
How about this oscilloscope https://play.google.com/store/apps/details?id=com.nfx.noscpro&hl=en If you already own a droid you're set plus you can get droids for ultra cheap of of any gregslist site out there.
Tejas Narayan (author) 4 years ago
I couldn't find anything like MSP450 from TI, and what i exactly want to build is an separate device for this entire process so that i can check the power purity from the ac mains of my house or anywhere.
please help me out...
typo. try msp430 instead.
iceng4 years ago
You don't specify the first things an engineer needs to know ;
  1. What is the shortest event you wish to record.
  2. What is highest voltage.
  3. What is the lowest voltage.
  4. Is the voltage record logarithmic.
  5. How much time do you want to record.
  6. Does continuous recording with hourly erasing less 10min pre & post event work 4U..
  7. Are you ready for the cost
  8. This has been done before.
  9. What is Power Purity Mean ?
What you want is an oscilloscope. A basic USB oscilloscope should do exactly what you want. You'll be able to record the data on your HDD.
There are power meter chips, which incorporate the MSP450 available from TI, which AFAIK include FFT hardware.