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Recently I have come across Energy Meter IC "CS5463". I read the datasheet and it says that the internal registers of the IC stores the Power information as a percentage. My understanding is that I have to multiply the percentage with a number to get the absolute power rather than normalized power. My question is what that number should be?

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  • \$\begingroup\$ With the full-scale value which is probably dependent on external component selection (I think of a user defined current sense resistor which is selected according to the expected current range). \$\endgroup\$ – Arsenal Oct 27 '15 at 8:04
  • \$\begingroup\$ Link to the datasheet and tell us what bits of it you're having trouble with. The information will be in there somewhere. \$\endgroup\$ – Brian Drummond Oct 27 '15 at 11:24
  • \$\begingroup\$ cirrus.com/en/pubs/proDatasheet/CS5463_F3.pdf \$\endgroup\$ – Khurram Oct 27 '15 at 12:16
  • \$\begingroup\$ This is the link to the datasheet. it says on page 16 \$\endgroup\$ – Khurram Oct 27 '15 at 12:20
  • \$\begingroup\$ It says on page 16 under section 5.4 "All measurements are available as a percentage of full scale." I cannot get what full scale is. \$\endgroup\$ – Khurram Oct 27 '15 at 12:22
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Full scale is the maximum value that the register or channel can holdor display.

section 5.1 on page 16 says

The full-scale differential input voltage for the current and voltage channel is 250 mVP.

Current may be sensed eg with an inline shunt rsistor.
By choosing a shunt resistance or other means the current which causes 250 mV peak to occur at the current input is the full scale current.

Voltage may be sensed with a resistive divider.
The input voltage which when applied to the installed resistive divider causes 250 mV peak to occur at the voltage input for is the full scale voltage.

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  • \$\begingroup\$ Yes exactly, using this approach when we read current and voltage registers we can convert the normalized value to the real values but how can we use active power register(which holds normalized value) to calculate power? should I assume that full scale active power and apparent power is V(full scale)*I(full scale)? \$\endgroup\$ – Khurram Oct 28 '15 at 9:58
  • \$\begingroup\$ @Khurram Page 28 on in the data sheet advises on what you'd expect to find in the registers. In each case FS returns a 2's complement value of 1 in a 23 bit register. This is when eg on current Vsense at current input is at max value (which seems to be 60% of abs max to allow overload). PRESUMABLY by applying the various formulae and establishinhg what the derived values are when source values are at maximum (eg power when V & I are max) you'd expect a value of 1.00000 ... in the power register. BUT trying it and seeing what happens seems wise and more liable to give the right answer :-). Alas \$\endgroup\$ – Russell McMahon Oct 28 '15 at 13:48

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