MAXQ3183 Datasheet, PDF (66/102 Pages) Maxim Integrated Products – Low-Power, Multifunction, Polyphase AFE with Harmonics and Tamper Detect

Low-Power, Multifunction, Polyphase AFE
with Harmonics and Tamper Detect
• 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 I_FS.
• 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 I_FS 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.
I_FS is 102.4A and V_FS 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.
LINE
NEUTRAL
LOAD
LAB
METER
V
Figure 15. Offset Testing Setup
UNIT
UNDER
TEST
V
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