ADE9078ACPZ datasheet(42/108 Pages) AD

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Data Sheet

ADE9078

Rev. 0 | Page 41 of 107

If VARACC = 0, the total and fundamental reactive energy

accumulation is signed. The MSB of the AVARHR_HI register

indicates whether the energy is negative or positive.

Other accumulation modes offered include positive only

accumulation mode with VARACC = 10, and negative only

accumulation mode where only negative reactive energy is

accumulated with VARACC = 11.

No Load Detection

No load detection prevents energy accumulation due to noise,

when the input currents are below a given meter start current.

To determine if a no load condition is present, the ADE9078

evaluates if the accumulated energy is below a user defined

threshold over a user defined time period. This no load

detection is done on a per phase and per energy basis.

The NOLOAD_TMR bits in the EP_CFG register determine

whether to evaluate the no load condition over 64 samples to

4096 samples (64/4 kSPS = 16 ms to 1.024 sec) by writing to the

NOLOAD_TMR bits as described in Table 19. No load detection is

enabled by default, over the minimum time of 64/4 kSPS = 16 ms.

No load detection is disabled when the NOLOAD_TMR[2:0] bits

in the EP_CFG register = 111b.

Table 19. No Load Condition Evaluation Time

NOLOAD_TMR

Samples to

Evaluate in No

Load Condition

TimeThat No Load

Detection Is Evaluated

(ms)

128

256

512

128

1024

256

2048

512

4096

1024

No load disabled

The user defined no load thresholds are written into the

ACT_NL_LVL, REACT_NL_LVL, and APP_NL_LVL registers.

The ACT_NL_LVL register sets the no load threshold for the

total active energy. Correspondingly the REACT_NL_LVL

reactive energy whereas the APP_NL_LVL sets the no load

threshold for total apparent energy.

The no load thresholds are calculated according to the following

equation:













SCALE

FULL

xWATT

LVL

xNL

where:

xWATT_FULL_SCALE is the nominal xWATT value with full-

scale inputs, 20,823,646. Note that xVAR and VA have the same

scaling so the same value can be used for all three thresholds.

X is the desired no load input power level. For example, to set

the no load threshold to zero out energy below 50,000 from full

scale, X = 50,000.

Thus, for a 50,000:1 no load threshold level, xNL_LVL is

0x6804.

654

000

20,823,646













LVL

xNL

When a phase is in no load, every fDSP = 4 kSPS, zero energy is

accumulated into the energy registers and CF accumulation.

Note that the x_ACC registers are not affected by no load

detection. Even when in no load, any power calculated in the

respective xWATT, xVAR, and xVA registers is accumulated

into the corresponding x_ACC register every fDSP = 4 kSPS.

No Load Indications

The PHNOLOAD register indicates whether each phase of

energy is in no load. For example, Bit 2 through Bit 0 in the

PHNOLOAD register indicate whether Phase A total apparent

energy, reactive energy, and active energy are in phase on Bit 2

through Bit 0, respectively. If a bit is set, it indicates that the phase

energy is in no load—if it is clear, the phase is not in no load.

The user can enable an interrupt to occur when the no load

status of one of the per phase energy changes, either going into

or out of no load. There is an interrupt enable bit for each type

of energy. Set the RFNOLOAD, VANLOAD, RNLOAD, and

ANLOAD bits in the STATUS1 register to enable an interrupt

on IRQ1 when one or more phases of fundamental VAR, total

VA, total VAR, and total active power no load changes status.

There is also an option to indicate the no load status on

the EVENT pin (see the Interrupts/Events section for more

information).

Figure 62 shows what happens when the xWATT, low-pass

filtered active power value goes above the user configured, no

load threshold and then back down below it again. The same

concept applies to all of the energy values (total and

fundamental VAR, total VA) with the corresponding

REACT_NL_LVL and APP_NL_LVL no load thresholds.

LOW-PASS

FILTERED

ACTIVE POWER (xWATT)

ACTIVE ENERGY

NO LOAD THRESHOLD

(ACT_NL_LVL)

NO LOAD ACCUMULATION INTERVAL IS

SET IN NOLOAD_TMR

ACTIVE ENERGY

NO LOAD ACCUMULATOR

NO LOAD INDICATION

ANOLOAD)

ACTIVE ENERGY,

xWATTHR

Figure 62. No Load Detection and Indication

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