Go Down

Topic: Seeedstudio current sensor TA12 (Read 1 time) previous topic - next topic

MarkT

If you sample at 1kHz, say, and square and then average the samples you get the mean-square - take the square root to get RMS.

If you just take the peak value then there are two problems:
1)  you assume the waveform is sinusoidal - typically this won't be the case, since most loads are not linear (only heaters and tungsten lighting are linear really).  Also the voltage may not be very sinusoidal (it should be but all the non-linear devices tend to affect it).
2) If the load fluctuates the peak value will consistently read high.

So it matters if accurate current measurement is your goal, but not if you just need a ballpark reading or want to detect changes.

To be accurate you still have to calibrate the TA12 and ideally measure the negative half-cycles too...
[ I won't respond to messages, use the forum please ]

Constantin

I'd check out the work over at the open energy monitor project - see http://openenergymonitor.org/emon/

They have done all the heavy lifting as far as sampling data directly from AC lines is concerned - i.e. putting on an external DC bias to keep all the voltages inside a measurable range for the Arduino, processing the bias back out in software later, calculating power, etc. All that and documented circuits to keep your Analog pins working.

I'd go over the stuff there before going any further, the examples they have listed and the two AC power theory pages are excellent primers.

Go Up