ADE9078 datasheet(33/108 Pages) AD

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ADE9078

Data Sheet

Rev. 0 | Page 32 of 107

Using the equations in the Phase Compensation section, it can

be seen that at 60 Hz, the voltage channel delay is 5.4°, as follows:













360

4000

(Degrees)

Delay

Channel

Voltage

This calculation leads to a phase calibration range of −15° to

+5.4° at 60 Hz.

Note that this phase compensation is equivalent to a delay or

advance in time. As the line frequency varies, the applied phase

compensation varies as well according to the phase correction

equation.

Multipoint Gain and Phase Calibration

The ADE9078 allows the current channel gain and phase

compensation to vary as a function of the calculated input

current rms amplitude in xIRMS, which is useful to correct for

the nonlinearities of current transformer sensors to achieve

very high meter accuracy, for example in Class 0.2 meters.

Multipoint Gain and Phase

The current channel gain, xIGAIN, is applied regardless of the

xIRMS input signal level. This gain compensates for the

nominal gain error of the current channel, including the current

transformer and burden resistors. If multipoint gain and phase

compensation is enabled, an additional current gain value is

applied based on the xIRMS value to compensate for the

current transformer gain shift over input signal amplitude. The

current channel datapath is shown in Figure 51.

If multipoint gain and phase compensation is enabled, with

MTEN = 1 in the CONFIG0 register, an additional gain factor,

xIGAIN0 through xIGAIN4, is applied based on the xIRMS

current rms amplitude and the MTTHR_Lx and MTTHR_Hx

The applied current channel phase compensation varies based

on the xIRMS input signal level as well if multipoint gain and

phase compensation is enabled.

GAIN,

PHASE

CORRECTION

MTTHR_L1 ,

MTTHR_H0

MTTHR_H4 =

FULL SCALE

MTTHR_L0

= 0

REGION0

REGION1

REGION2

REGION3

REGION4

MTTHR_L2,

MTTHR_H1

MTTHR_L3,

MTTHR_H2

MTTHR_L4,

MTTHR_H3

xIGAIN4

xPHCAL4

xIGAIN3

xPHCAL3

xIGAIN2

xPHCAL2

xIGAIN1

xPHCAL1

xIGAIN0

xPHCAL0

Figure 50. Multipoint Gain and Phase Calibration

The MTTHR_Lx and MTTHR_Hx registers set up the regions

in which to apply each set of corrections, allowing hysteresis.

The decision of which coefficients to apply is done according to

the following rules:

If xIRMS >MTTHR_H[current_region]

If current_region ≤ 3

Current_region++;

Else If xIRMS < MTTHR_L[current_region]

If current_region ≥ 1

current_region--;

xIGAIN = xIGAIN[current_region];

xPHCAL = xPHCAL[current_region];

xMTREGION = current_region;

For example, if AIRMS goes above MTTHR_H2, the gain and

phase correction is set to AIGAIN3 and APHCAL3,

respectively. Then, if AIRMS goes below MTTHR_L3, the gain

and phase correction is set to AIGAIN2 and APHCAL2.

For proper operation, the value of the registers must be

increasing such that MTTHR_L0 < MTTHR_L1 <

MTTHR_H0 < MTTHR_L2 < MTTHR_H1 < MTTHR_L3 <

MTTHR_H2 < MTTHR_L4 < MTTHR_H3 < MTTHR_H4.

The following example configuration uses two regions, such

that Region 0 is used from 0 A to 20A and Region 1 is used

from 22 A to full scale:

•

MTTHR_L0 = 0

•

MTTHR_L1 = 0x95 9AC1 (20 A for this meter)

•

MTTHR_H0 = 0xA4 90A2 (22 A for this meter)

•

MTTHR_L2 = 0x7FFFFFFFE (maximum positive

threshold − 1)

•

MTTHR_H1 = 0x7FFFFFFFF (maximum positive

threshold)

The xMTREGION registers indicate the current region for each

phase and correspondingly, which xIGAINx and xPHCALx

coefficients are being applied.

Multipoint phase and gain calibration is disabled by default. To

enable it, set the MTEN bit in the CONFIG0 register.

Single-Point Gain and Phase

When multipoint gain and phase calibration is disabled, single-

point gain and phase calibration is allowed.

In this case, the xIGAIN register is applied. No additional current

channel gain is applied based on the xIRMS amplitude.

When multipoint gain and phase calibration is disabled, the

xPHCAL0 phase compensation is always applied regardless of

the xIRMS value.

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