# Question about dynamic range and error range calculation of IRMS and VRMS

Question asked by ghsung on May 24, 2018
Latest reply on Jun 12, 2018 by Gary.Kang.AnalogDevices

Hi, I'm developing energy meter using ADE9000 and want to calculate dynamic range and error range of IRMS and VRMS.
I wonder the calculation below is right or not.

The system parameters I used are
CT ratio = 2500: 1
Rb = 10 ohm
voltage divider R1 = 990k ohm
voltage divider R2 = 1k ohm

The maximum current value is 0.707 * CT ratio / Rb = 0.707 * 2500/10 = 176.75A, and the maximum voltage value is 0.707 * (R1 + R2) / R2 = 0.707 * 991/1 = 700.637V.

A formula for the dynamic range of current would be [{I (Nominal) * Burden Resistor} / CT Turns Ratio] / Smallest signal measurable.
Does the dynamic range depend on the load that I want to measure?

For example, when measuring with a 2 kW (220V, 9.09A) load, the dynamic range will be [9.09 * 10/2500] /35.35 uV = 36.36 mV / 0.03535 mV = 1028.571 (about 1000:1) but in the case of a 10kW(220V, 45.45A) load, the dynamic range is [45.45 * 10/2500] / 35.35 uV = 5142.857 (about 5000: 1). Am I right?
(35.35uV is the fixed smallest signal value on the ADE9000)

And also I wonder that the error range of 0.1% when a dynamic range is over 1000:1 means ±0.05% of measurement value or ± 0.1%.
(For example measured current value is 9A and accuracy is ±0.05%, Is the error range 9±0.0045A?)