Range of ADE7978 with ADE7932

Hi,

as far as i have understood from searching maximum post on energy meter forum and your product there are only few ics which measure harmonics distortion, one series is ADE7978 with ADE7932/ADE7933/ADE7923 and another is ADE7880. Is it correct

1- Can you please let me know the difference between these series except isolation?

2- I want to measure single phase 50Hz 90V-440V, 0.01A-10A AC with 0.5% accuracy, is it possible to do that if yes with what accuracy level? and with which series?

I know i need to  step down the voltage into desired range of IC input and need to use shunt / CT for current measurement.

3- at multiple location it is said the dynamic range of 500:1 or 1000:1. what does it mean exactly. say for example in my case, should i calculate the Dynamic range = 440V / 90V = 4.9 (in my case for voltage). or it will be

Dynamic range = (Vmax X 100) / (2 X accuracy x Vmin) = 500 (in my case for voltage).

4- Will it get total harmonic distortion of voltage and current separately or i will get harmonic distortion separately say upto 63? and in second case from where i will found it?

5- Is it possible to measure DC with high ripple with any of these IC?

6- why i can't use the shunt for measuring current with ADE7880?

Sorry, i know that i have put many question in single post, but it was just to save TAT.

Thanks in advance.

with regards,

Ankush

  • Hi Ankush,

    That is correct, in the current ADE family it is the ADE7978 and the ADE7880 which measure THD.

    1. The largest difference is isolation, because there is isolation between all 3 phases, it is possible to use a shunt to measure the current on each phase while for the ADE7880 a CT or rogowski coil needs to be used to measure the current. The other main difference is that the ADE7880 offers a full harmonic engine inside the part which gives information about specific harmonics. This means the harmonic distortion of individual harmonics can be measured.
    2. For the voltage range you mention of 90-440V and current range of 0.01-10A, you can expect an energy accuracy of 0.2% over a dynamic range of 2000:1. Then for the RMS measurement, you can expect VRMS accuracy of 0.1% and IRMS accuracy of 0.25% over a dynamic range of 500:1. Let me explain dynamic range a little, when we say dynamic range in terms of the RMS, this means that for the range of full scale input (+/-500mV Peak) down to 500 times smaller (+/-1mV Peak) you can expect the RMS to be accurate to 0.1% and 0.25% for voltage and current respectively. Then when talking about energy, this means that with a constant voltage and the current from full scale to 2000 times smaller than full scale the error will typically be 0.2%. With the voltage range of about 5:1 and a current range of about 1000:1, you should expect to be in that performance range as long as the current sensor and voltage divider are chosen to maximize the range.
    3. See explanation in 2.
    4. The ADE7978 and ADE7880 both offer a THD measurement for the current channel (ITHD) and a separate one for the voltage channel (VTHD). Then the ADE7880 offers extra harmonic measurements including Harmonic Distortion of individual harmonics out to the 63rd harmonic.
    5. DC measurement is possible but it is with degraded performance since the High Pass Filter inside the part needs to be disabled. Are you looking to measure both AC and DC? The Application Note: http://www.analog.com/media/en/technical-documentation/application-notes/AN-1304.pdf , explains the expected performance of our parts with a DC measurement. The biggest issue is the variation in offset.
    6. This depends, if 3 phases at different potentials are being measured then a shunt can not be used because then the phases would be shorted together with the ADE7880. If the current measurements are on the same potential then it could be possible although the 7880 was not designed with a shunt in mind and therefore the gain on the current channels is smaller than on the ADE7933 for example.

    Let me know if you have any other questions.

    Regards,

    Dlath

  • Hi Dlath,

    thanks for your reply. i got answers of my all query except point 2. For measuring the current range from 10mA-10A with 0.5% accuracy, DR will come to 50000. which seems not possible into this.

    Let me know if i am at mistaken.

    i am calculating dynamic range by

    Dynamic range = (Imax X 100) / (2 X accuracy x Imin).

    with regards,

    Ankush Agrawal

  • Hello Ankush,

    We specify in the ADE7880 datasheet 2000:1  0.2% active energy, so if you use a CT and select a burden to make your full-scale 353mv RMS at 10 amps and you go down to 10ma that is 1000:1 so the energy performance will be <0.2%. Now if you set your burden to 50% dynamic range for transients your 10ma range would now be 2000:1 effective dynamic range with 10A at 2:1 at 2000:1 your energies would still be < 0.2%.  Now at 2000:1 to achieve 0.2% the effective energy dynamic range is 2000 / 0.2%  or 1E6:1 for energies. This measurement will have noise so the longer you accumulate the more repeatable the measurement. As a note when using CF the averaging is automatic. The ADE7880 will output a CF period 1000 times longer at 10ma than the pulse at 10 amps.

    This example will work for the RMS dynamic ranges.

    Does this help?

    Dave Smith

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