energy meter ICs and dynamic range

Status
Not open for further replies.
I

int1

Newbie level 4
Joined
Apr 4, 2013
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Australia
members.optusnet.com.au
Activity points
1,328
I am trying to understand the specs for energy meter ICs. Microchip, Cirrus and Analog Devices for example have utility meter ICs
that claim 1000:1 dynamic range at 0.1% error.

This means 1000W @ +-0.1W or 1W @+-0.001W
So does that really mean the meter can actually detect between 0.001W to 1000W i.e a dynamic range of 1000000:1.
The Cirrus IC claims 4000:1 0.1% error

That is impossible given the noise performance shown in the datasheets (75~80dB).

https://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en028191
https://www.analog.com/en/analog-to...rgy-measurement/ade7753/products/product.html
https://www.cirrus.com/en/products/cs5490.html
 

That is impossible given the noise performance shown in the datasheets (75~80dB).
Click to expand...
You don't consider the small bandwidth of the energy measurement which is probably in a mHz range,
 

FvM said:
You don't consider the small bandwidth of the energy measurement which is probably in a mHz range,
Click to expand...

The problem is to calculate real power the instantaneous voltage and current must be multiplied and then averaged or low pass filtered.
Any inherent noise in the V or I samples will show up in the average power calculation.

The only way I can see to band limiting is put V and I samples through a kind of comb filter where only the fundamental and harmonics are extracted. But I cannot find any references to an applications doing this. ADC input bandwidths are typically 1kHz to 5kHz range which covers all the important harmonics of 50/60Hz line.
 

Dynamic range in the energy meter specification means current dynamic. Voltage will be nominal mains voltage plus/minus expectable variations. As a result, all current spectral components except a small band around the fundamental will be filtered out when multiplying current and voltage and integrating over full 50/60 Hz periods. Low-pass filtering will further reduce the effective noise bandwidth of instantaneous power measurement to a few Hz. In the energy integral, you finally have mHz noise bandwidth.
 
Reactions: int1

    I

    int1

    Points: 2
    Helpful Answer Positive Rating
Ok I finally got it, the voltage measurement is relatively spectral pure with a very high S/N ratio. The power meter then effectively becomes a product detector or synchronous demodulator. Low filtering the 'mixer' output limits the current channel bandwidth, increasing S/N ratio and achieving the > 120dB range needed.

Adam
 

It is not to detect from .001w but in a 1000W it could be +- 0.1W over 1000W.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…