MAXQ3180-RAN+ datasheet(43/48 Pages) MAXIM

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connected together to result in zero current. Note: All

intermediate calculations should be performed with

double precision, and the last result rounded to the

nearest integer.

1) Clear I_gain coefficient that is being calibrated to

0x0000.

2) Measure average raw IRMS by reading the RAM

3) Calculate expected raw RMS value using the fol-

lowing proportion:

Full_scale_current: produces FS_raw_rms = 230

I_input_current: produces Expected_raw_rms

Here, Full_scale_current is the input current that is

transformed into 1VRMS at the input pins. That

Full_scale_current value depends on the transduc-

er chosen for meter design. For example, if current

sensor is a transformer 10A to 5mA with 20

Ω load

resistor, then Full_scale_current = 100A, because

it is transformed to 50mA x 20

Ω = 1V.

4) Calculate I_gain coefficient:

I_gain = [Expected_raw_rms/

Measured_raw_rms) - 1] x 216

Voltage Gain Calibration

To perform the voltage gain calibration, all three phase

voltages 220V should be applied. Current inputs should

be zero. Note: All intermediate calculations should be

performed with double precision, the last result round-

ed to the nearest integer.

1) Clear V_gain coefficient being calibrated to

0x0000.

2) Measure average raw VRMS by reading the RAM

3) Calculate expected raw RMS value using the fol-

lowing proportion:

Full_scale_voltage: produces FS_raw_rms = 230

V_input_voltage: produces Expected_raw_rms

Here, Full_scale_voltage is the input voltage that is

transformed into 1VRMS at the input pins. That

Full_scale_voltage value depends on the trans-

ducer chosen for meter design. For example, if

voltage sensor is a divider with a 544:1 resistor

ratio, then Full_scale_voltage = 545V, because it is

transformed to 1V.

4) Calculate V_gain coefficient:

V_gain = [(Expected_raw_rms/

Measured_raw_rms) - 1] x 216

Power Gain Calibration

To perform the power gain calibration, all three phase

voltages 220V must be applied. Only one current signal

of max amplitude (IMAX) 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 zero.

1) Clear the E_gain coefficient being calibrated to

0x0000.

2) Measure the power output of the meter. This can

be done in two ways: (a) by reading raw RAM reg-

isters from the MAXQ3180, or (b) by measuring

pulse output error. The following procedure

depends on the way of measuring power output.

a) Measure average raw apparent energy by

reading the RAM register several times.

b) Pulse output error is typically measured by the

tester equipment. The pulse output parameters

in the MAXQ3180 must be properly configured

before pulse output error can be measured.

The PLSCFG register should be set to output

apparent energy of one phase being calibrat-

ed. That setting is:

If measuring pulse 1 output on the CFP pin:

PLSCFG = 0x0021 for phase A

PLSCFG = 0x0022 for phase B

PLSCFG = 0x0024 for phase C

If measuring pulse 2 output on the CFQ pin:

PLSCFG = 0x2100 for phase A

PLSCFG = 0x2200 for phase B

PLSCFG = 0x2400 for phase C

c) Then, the corresponding pulse threshold regis-

ter should be set to the proper value; that is,

THR1 register if measure pulse 1 output on the

CFP pin, or THR2 register if measure pulse 2

output on the CFQ pin. The value for the thresh-

old register defines the pulse output rate and

should match the rate expected by tester

equipment. The tester typically expresses pulse

output rate as a meter constant (MC) indicating

the number of pulses per kWh. The proper

threshold value is then calculated as:

(THR1 or THR2) = 218 x 103/(MC x IFS x VFS x tFR)

In this formula IFS is the Full_scale_current

described in the

Current Gain Calibration sec-

tion, VFS is the Full_scale_voltage described in

Low-Power, Multifunction, Polyphase AFE

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