MAXQ3180-RAN+ datasheet(44/48 Pages) MAXIM

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the

Voltage Gain Calibration section, and tFR is

the sampling time that depends on the

MAXQ3180 system clock frequency and sam-

pling rate register setting (ADCRATE):

tFR = (ADCRATE + 1) x 8/fSYS

For example, for the default conditions

ADCRATE = 199 and fSYS = 8MHz, then tFR =

200μs = 55.55nh. Using typical example values

IFS = 100A and VFS = 545V, the formula for the

threshold can be transformed into the following:

Typical (THR1 or THR2) = 86,579,669,725/MC

Note: Threshold is a 32-bit register, which

imposes a limitation on the minimal meter con-

stant to avoid overflow.

When the PLSCFG and THR1 (or THR2) regis-

ters are set, the pulse output error can be mea-

sured by tester equipment. That error is usually

expressed as % of the expected power.

3) If choice 2a was made (apparent energy by read-

ing RAM register), then perform step 3.

Calculate expected raw energy value using the

following proportion:

Full_scale voltage x Full_scale_current: pro-

duce FS_raw_pwr = 218/(fLINE x tFR)

V_input_voltage x I_input_current: produce

Expected_raw_pwr

Here, Full_scale_voltage, Full_scale_current, and

tFR are the same as described above, fLINE is the

line frequency of the input voltage, typically 50Hz

or 60Hz.

4) Calculate E_gain coefficient:

a) If output was measured by reading RAM register:

E_gain = [(Expected_raw_pwr/

Measured_raw_pwr) - 1] x 216

b) If output was measured through pulse output

error:

E_gain = (216) x (-Measured_Error%)/

(100% +Measured_Error%)

Note: All intermediate calculations should be

performed with double precision, the last result

rounded to the nearest integer.

Power Linearity Calibration

This calibration compensates for nonlinearity over the

range and requires at least four power measurements

at different loads. To perform the power linearity cali-

bration, all three phase voltages 220V must be applied.

Only one current signal is applied to the phase input

being calibrated. The current sine wave should be in

phase with the corresponding voltage sine wave, i.e.,

power factor 1. Other current inputs should be 0.

1) Clear the Eoff_hi, Gain_lo, and Eoff_lo coefficients

being calibrated to 0x0000.

2) Make power measurements.

a) First power measurement. Apply current input

signal of the RMS value close to IFS/21.5 to the

phase input being calibrated. For example, typ-

ical target value is 100/21.5 = 35.36A, so rea-

sonable input current is 30A or 40A. Measure

average raw apparent energy by reading the

RAM register several times. Denote applied

current as I1 and measured power as P1 for

future reference.

b) Second power measurement. Apply current

input signal of the RMS value close to IFS/24.5

to the phase input being calibrated. For exam-

ple, typical target value is 100/24.5 = 4.42A, so

reasonable input current is 4A or 5A. Measure

average raw apparent energy by reading the

RAM register several times. Denote applied

current as I2 and measured power as P2 for

future reference.

c) Third power measurement. Apply current input

signal of the RMS value close to IFS/26.5 to the

phase input being calibrated. For example, typ-

ical target value is 100/26.5 = 1.10A, so reason-

able input current is 1A. Measure average raw

apparent energy by reading the RAM register

several times. Denote applied current as I3 and

measured power as P3 for future reference.

d) Fourth power measurement. Apply current

input signal of the RMS value close to IFS/29.5

to the phase input being calibrated. For exam-

ple, typical target value is 100/29.5 = 0.14A, so

reasonable input current is 0.1A or 0.2A.

Measure average raw apparent energy by

reading the RAM register several times. Denote

applied current as I4 and measured power as

P4 for future reference.

Low-Power, Multifunction, Polyphase AFE

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