MAXQ3180-RAN+ datasheet(45/48 Pages) MAXIM

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3) Measure average raw VRMS by reading the RAM

4) Measure average NS by reading the RAM register

several times.

5) Calculate coefficient K = [NS/216] x [VRMS/216]/216.

6) Calculate Eoff_hi coefficient:

Eoff_hi = [(P2 x I1 - P1 x I2)/(I1 - I2)])/K.

7) Calculate Eoff_lo coefficient:

Eoff_lo = [(P4 x I3 - P3 x I4)/(I3 - I4)]/K.

8) Calculate Gain_lo coefficient (using calculated

above Eoff_hi, Eoff_lo, and K):

Gain_lo = ({(I3/I1) x (P1 + K x Eoff_hi)/

(P3 + K x Eoff_lo)} – 1) x 216

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.

Phase Angle Calibration

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:

compensation_phase_angle =

PA_0 + (PA_1 x X) + (PA_2 x X2) + (PA_3 x X3)

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.

Phase Angle Error Measurement

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.

Measurement Technique I: Measure Output Phase

Angle Error by Reading RAM Registers

1) Measure average raw active power by reading the

RAM registers several times.

2) Measure average raw reactive power by reading

the RAM registers several times.

3) Calculate output phase angle:

output_PA = atan(Reactive_raw_pwr/

Active_raw_pwr)

4) Calculate output phase angle error:

output_PA_error = output_PA - input_PA

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.

1) Apply input signal with power factor 1 (input

phase angle 0

°) to the meter’s inputs. Measure

pulse output error for active power, in percent.

Denote it as Err00 for future reference.

2) Apply input signal with power factor 0.5L (input

phase angle 60

°) to the meter’s inputs. Measure

pulse output error for active power, in percent.

Denote it as Err60 for future reference.

3) Calculate output phase angle error:

output_PA_error = atan{(1/sqrt(3)) x

(Err00 – Err60)/(100% + Err00)}

Phase Angle Calibration Procedure

1) Clear PA_0, PA_1, PA_2, PA_3 coefficients being

calibrated to 0x0000.

2) Phase angle error measurement.

a) Apply current input signal of the RMS value close

to IFS/21.5 to the phase input being calibrated.

For example, typical target value is 100/21.5 =

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.

b) Measure average raw IRMS by reading the

RAM register several times. Denote this as

I1_raw for future reference.

Low-Power, Multifunction, Polyphase AFE

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