EMON Simulation

Submitted by Guest on Thu, 08/09/2011 - 09:01

using a copy of the EMON software in Arduino i wanted to understand better how the calculation works.

a online spreadsheet what simulates a voltage and current signal

and does the same calculations as EMON.

pls look and play ( yellow fields INPUT )

for more changes pls get your own (free) account and copy the spreadsheet to your own workspace,

or just download it to your local PC .

Submitted by kllsamui (not verified) on Sat, 10/09/2011 - 02:36.

i found

1. EMON use a digital high pass filter to shift the signal down to a AC without the OFFSET.

if i just subtract 512 instead of that filter calculation,

i get very close to the same results.

2. EMON use a phase shift calibration called "V shifted"

even both signals ( volt and current ) are "measured" by transformers, there can be a different phase error.

also the time difference (0.187 millis?) between the volt and the currentmeasurement adds to this.

but in the simulation i see following effect:

if there is a noise signal ( example 600Hz, 10% amplitude )

and a setting of PHASECAL of 2.3, there is a amplification of the noise to see in the "V shifted" signal!

not if PHASECAL = 1.

Vshifted_noise

so, i think there is a lowpassfilter required between V filtered and V shifted,

and because a lowpassfilter again has a phase error, the same filter must be applied to the currentsignal too.

But if we want to calculate real power by using harmonics, we should not filter them away,

so a different phase shift algorithm is required. May be instead of the recursive approach use just a sample buffer.

if a 50Hz sinus is read by 53 samples, a array buffer of 14 would allow 90deg phase shift back.

( but only in 6.4deg steps / not very analog )

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