maxq3180-ran Maxim Integrated Products, Inc., maxq3180-ran Datasheet - Page 43

• Manufacturer Part Number: maxq3180-ran
• Description: Low-power, Multifunction, Polyphase Afe
• Manufacturer: Maxim Integrated Products, Inc.

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.
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 I_gain coefficient that is being calibrated to
2) Measure average raw IRMS by reading the RAM
3) Calculate expected raw RMS value using the fol-
4) Calculate I_gain coefficient:
1) Clear V_gain coefficient being calibrated to
2) Measure average raw VRMS by reading the RAM
3) Calculate expected raw RMS value using the fol-
4) Calculate V_gain coefficient:
0x0000.
register several times.
lowing proportion:
Here, Full_scale_current is the input current that is
transformed into 1V
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 20Ω load
resistor, then Full_scale_current = 100A, because
it is transformed to 50mA x 20Ω = 1V.
0x0000.
register several times.
lowing proportion:
Here, Full_scale_voltage is the input voltage that is
transformed into 1V
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.
Full_scale_current: produces FS_raw_rms = 2
I_input_current: produces Expected_raw_rms
Full_scale_voltage: produces FS_raw_rms = 2
V_input_voltage: produces Expected_raw_rms
V_gain = [(Expected_raw_rms/
Measured_raw_rms) - 1] x 2
Measured_raw_rms) - 1] x 2
I_gain = [Expected_raw_rms/
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________
Voltage Gain Calibration
RMS
RMS
at the input pins. That
at the input pins. That
16
16
30
30
To perform the power gain calibration, all three phase
voltages 220V must be applied. Only one current signal
of max amplitude (I
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
2) Measure the power output of the meter. This can
0x0000.
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
b) Pulse output error is typically measured by the
c) Then, the corresponding pulse threshold regis-
reading the RAM register several times.
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
or
If measuring pulse 2 output on the CFQ pin:
PLSCFG = 0x2100 for phase A
PLSCFG = 0x2200 for phase B
PLSCFG = 0x2400 for phase C
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:
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
(THR1 or THR2) = 2
MAX
) is applied to the phase input
Power Gain Calibration
18
x 10
3
/(MC x IFS x VFS x t
FR
43
)