MAXQ3183-RAN+ datasheet(66/102 Pages) MAXIM

66 / 102 page

Low-Power, Multifunction, Polyphase AFE

with Harmonics and Tamper Detect

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• Divide the applied value (in meter unit) by the value

read from the MAXQ3183. The result should be a

value between 0 and 2. If the value falls outside of

this range, you have probably miscalculated IFS.

• Multiply the calculated value by 214. The result is the

gain value to be programmed into A.I_GAIN. Ensure

the most significant bit is 0.

When the gain value is programmed, wait for approxi-

mately 2 to 3 seconds, then reread the RMS value from

A.IRMS. Check that the measured value is correct by

comparing A.IRMS against the applied current in meter

unit.

Current Calibration Example

Assume IFS is 102.4A and the meter has a base current

of 10A and a maximum current of 60A.

• The meter is calibrated at the base current of 10A.

• Convert the applied current to meter units. This cal-

culation gives 10 x 224/102.4 = 1,638,400 =

0x00190000.

• Read the A.IRMS register. You read 0x0017DC85.

This is 1,563,781 decimal.

• Divide the applied current by the current read from the

meter. The result is 1,638,400/1,563,781 = 1.0477.

• Multiply by 214 x 1.0477 = 17,166 = 0x430E. Write

this value to the A.I_GAIN register.

Calibrating Phase Offset

For this calibration step, it is necessary to have a power

factor meter, capable of measuring phase angle, con-

nected in the same circuit as the MAXQ3183 meter.

Note that calibration can be performed at any precision

power factor setting. We use a pure resistive load (PF =

1.0) load to illustrate the procedure.

• Apply a resistive load to the meter; the current drawn

by the load should correspond to the base current of

your meter.

• Record the phase angle and direction (capacitive or

inductive) reported on the power factor meter.

• Read and record the real and reactive energy from

the X.ACT and X.REA registers. Divide the reactive

energy by the real energy. This is the tangent of the

power-phase angle.

• Read the X.REA register. If the high-order bit is set,

the power factor reported in the above step is capac-

itive. If the high-order bit is clear, the power factor

reported in the above step is inductive.

• Now determine the correction factor: treating capaci-

tive values as negative and inductive values as posi-

tive, subtract the angle read from the MAXQ3183

from the angle read from the reference meter. The

result is the compensation angle.

• Multiply the compensation angle (in radians) by

65,536. This is the value to write into X.PA0.

If I1THR and I2THR are left at their default values

(0x0000), then the value in X.PA0 is applied to the full

measurement range. Alternatively, you could write the

same value into X.PA0, X.PA1, and X.PA2. Then the

same compensation is applied through the whole mea-

surement range regardless of the I1THR and I2THR set-

tings. If desired, calibrate for the phase angle at up to

three different current levels to compensate for nonlin-

earity in the current sensor. See the

Advanced

Operation section for more information.

Phase Offset Calibration Example

Assume the meter is a 10/60 meter; that is, the base

current is 10A and the maximum rated current is 60A.

IFS is 102.4A and VFS is 558.1V. The test point is 10A

and 240V.

• Connect the MAXQ3183-based meter under test in

series with a lab grade reference meter. See the con-

figuration below.

• Apply power to the meter and apply a load of 10A

resistive.

• Verify that the I1THR, I2THR, A.PA0, A.PA1, and

A.PA2 registers contain zero.

• Read the power factor on the reference meter. You

read 1.5° capacitive. This is not unusual. The load

might not be truly resistive or reactance in the test

configuration could be reflected in the measurement.

• Read the real energy from register A.ACT (0x1D0).

You read 0x2865D6 (2,646,510 meter units).

• Read the reactive energy from register A.REA

(0x1D4). You read 0xFFFFA5C0 (-23,104 meter

units).

• Divide the reactive by the active power: -23,104/

2,646,510 = -0.009.

LAB

METER

UNIT

UNDER

TEST

LOAD

LINE

NEUTRAL

Figure 15. Offset Testing Setup

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