I have a couple of questions, regarding the ADE7953.

1.- For the RMS value, how many samples are taken?, I mean, which is the value of "N" in the equation 2, page 24?. It is said the measure takes more or less 200 ms at a rate of 6.99 kHz, but I can't understand how translate this rate to a number of samples.

2.- Why the value of Active Power, for resistive load, don't match exactly the value obtained from P = Vrms*Irms, assuming that both current and voltage are pure sine waves? For a load of 80 W light bulb with 110 V, the values are:

Vrms : 110 V.

Irms : 718 mA.

Active Power : 8000 mW

So P = 110*0.718 = 78,98 W = 7898 mW, it is an acceptable error?

Thanks in advance,

Best regards

Hi ricpar124,

1、The samples number is not a constant value, you can see from the data path, there is a low pass filter. The data after ADC have a rate at 6.99 kSPS, the low pass filter has a IIR structure, which owns a feedback loop. If you really want to know what's "N" means, we should call N is the number of the data from begin to the end. For example, if you have got data for one second, N = 1*6.99k, if you have got data for two second, N=2*6.99k. So N equals to the whole number from the data calculation begin to the time data update. The low pass filter will use the whole data from begin to the end. 200ms means that the IIR system need at least 200ms to come to a stable status. So you can't use the data in the 200ms time. You can understand it like that, the data come to the low pass filter at a rate like 6.99 kHz, the data will also come out and update to the register at a rate like 6.99kHz.

2、The value of Active Power don't match exactly the value obtained from P = Vrms*Irms, there are many factors, so we need to do the calibration. For example, the resistor value is not absolutely the ideal value, the signal you put is not as you supposed to be, the voltage signal and current signal have a small phase delay and so on. If the error is acceptable is defined by you, it's depends on your application. Our ADE7953 datasheet show the SPECIFICATIONS of our chip, like Active energy error typical value is 0.1% over the dynamic range of 3000:1 and so on. When you use the chip in your application, the error will change because some factors I mentioned before. You can also get the error information of our chip from TYPICAL PERFORMANCE CHARACTERISTICS section, for your application, the error can be calculated by (7898-8000)/8000*100%= -1.275%. In a word, if the error is acceptable is defined by your application.

Best regards,

Gary