maxq3180-ran Maxim Integrated Products, Inc., maxq3180-ran Datasheet - Page 45

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

Note: All intermediate calculations should be per-
formed with double precision, the last result rounded to
the nearest integer. Eoff_hi, Gain_lo, and Eoff_lo are 16-
bit signed coefficients. If a calculated value exceeds 16
bits, the part cannot be calibrated. In this case, assign
the largest possible value, i.e., 0x7FFF for positive over-
flow or 0x8000 for negative overflow.
This calibration is intended to compensate for phase
angle errors across the range of input loads. The
MAXQ3180 uses four PA_n coefficients to calculate the
compensation phase angle as a 3rd-order polynomial:
Where X is proportional to the logarithm of raw IRMS.
Full calibration of all four coefficients requires at least
four measurements of the phase angle across the
range. However, in most cases, only one coefficient
PA_0 is needed that requires at least one phase angle
measurement.
For input signals, all three phase nominal voltages
220V should be applied. Only one current signal is
applied to the phase input being calibrated. Other cur-
rent inputs should be 0.
This calibration procedure requires measuring the
phase angle error of the meter’s output at the given
current input level I_in. This can be done in two ways:
(I) by reading raw RAM registers, or (II) by measuring
pulse output errors at different power factors.
3) Measure average raw VRMS by reading the RAM
4) Measure average NS by reading the RAM register
5) Calculate coefficient K = [NS/2
6) Calculate Eoff_hi coefficient:
7) Calculate Eoff_lo coefficient:
8) Calculate Gain_lo coefficient (using calculated
PA_0 + (PA_1 x X) + (PA_2 x X
register several times.
several times.
above Eoff_hi, Eoff_lo, and K):
Eoff_hi = [(P2 x I1 - P1 x I2)/(I1 - I2)])/K.
Eoff_lo = [(P4 x I3 - P3 x I4)/(I3 - I4)]/K.
Gain_lo = ({(I3/I1) x (P1 + K x Eoff_hi)/
compensation_phase_angle =
(P3 + K x Eoff_lo)} – 1) x 2
Phase Angle Error Measurement
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________
Phase Angle Calibration
16
2
) + (PA_3 x X
] x [VRMS/2
16
16
3
]/2
)
16
.
Measurement Technique I: Measure Output Phase
Angle Error by Reading RAM Registers
Measurement Technique II: Measure Output Phase
Angle Using Pulse Output
Before the pulse output can be measured, the pulse
configuration registers PLSCFG and THR1 (or THR2)
must be properly configured. The pulse output should
be set to active power. For details on how to set those
registers, see the Power Gain Calibration section.
Phase Angle Calibration Procedure
1) Measure average raw active power by reading the
2) Measure average raw reactive power by reading
3) Calculate output phase angle:
4) Calculate output phase angle error:
1) Apply input signal with power factor 1 (input
2) Apply input signal with power factor 0.5L (input
3) Calculate output phase angle error:
1) Clear PA_0, PA_1, PA_2, PA_3 coefficients being
2) Phase angle error measurement.
RAM registers several times.
the RAM registers several times.
phase angle 0°) to the meter’s inputs. Measure
pulse output error for active power, in percent.
Denote it as Err00 for future reference.
phase angle 60°) to the meter’s inputs. Measure
pulse output error for active power, in percent.
Denote it as Err60 for future reference.
calibrated to 0x0000.
a) Apply current input signal of the RMS value close
b) Measure average raw IRMS by reading the
output_PA_error = output_PA - input_PA
to IFS/2
For example, typical target value is 100/2
35.36A, so reasonable input current is 30A or
40A. Measure the output phase angle error as
described above. Denote applied current as I1
and measured phase angle error expressed in
radians as PAerr1 for future reference.
RAM register several times. Denote this as
I1_raw for future reference.
output_PA = atan(Reactive_raw_pwr/
output_PA_error = atan{(1/sqrt(3)) x
(Err00 – Err60)/(100% + Err00)}
1.5
to the phase input being calibrated.
Active_raw_pwr)
1.5
45
=