ade7953 Analog Devices, Inc., ade7953 Datasheet - Page 39

• Manufacturer Part Number: ade7953
• Description: Single Phase, Multifunction Metering Ic With Neutral Current Measurement Ade7953
• Manufacturer: Analog Devices, Inc.

NO-LOAD DETECTION
The ADE7953 includes a no-load detection feature that eliminates
“meter creep. ” Meter creep is defined as excess energy that is
accumulated by the meter when there is no load attached. The
ADE7953 warns of this condition and stops energy accumula-
tion if the energy falls below a programmable threshold. The
ADE7953 includes a no-load feature on the active, reactive, and
apparent energy measurements. This allows a true no-load
condition to be detected and also prevents creep in purely
resistive, inductive, or capacitive load conditions. The no-load
feature is enabled by default.
SETTING THE NO-LOAD THRESHOLDS
Three separate 24-/32-bit registers are available to set the
no-load threshold on the active, reactive, and apparent
energies: AP_NOLOAD (Address 0x203 and Address 0x303),
VAR_NOLOAD (Address 0x204 and Address 0x304), and
VA_NOLOAD (Address 0x205 and Address 0x305). The active,
reactive, and apparent energy no-load thresholds are completely
independent and, therefore, all three thresholds are required.
The no-load thresholds for all three measurements can be set
based on Equation 39.
where:
X is AP, VAR, or VA.
Y is the required threshold amplitude with reference to
full-scale energy (for example 20,000:1).
As shown in Equation 39, the no-load threshold can be config-
ured based on the required level with respect to full scale. For
example, if a no-load threshold of 10,000:1 of the full-scale
current channel is required and the voltage channel is set up to
operate at ±250 mV (50% of full scale), then a value of 20,000 is
required for Y. A default value of 58,393 (decimal) is programmed
into the AP_NOLOAD and VAR_NOLOAD registers, setting
the initial no-load threshold to approximately 10,000:1. The
VA_NOLOAD register has a default value of 0x00.
The no-load thresholds AP_NOLOAD, VAR_NOLOAD, and
VA_NOLOAD must be written before enabling the no-load
feature. The no-load feature is enabled using the DISNOLOAD
register (Address 0x001). If the threshold requires modification,
disable the no-load detection, modify the threshold, and then
reenable the feature using the DISNOLOAD register.
Although separate no-load interrupts are available for Current
Channel A and Current Channel B (phase and neutral current),
the same no-load level is used for both. For example, if the
VAR_NOLOAD level is set to 0.05% of full scale, this value is
the reactive power no-load threshold used for both Current
Channel A (phase) and Current Channel B (neutral).
X_NOLOAD
=
65
,
536
−
1
Y
4 .
(39)
Rev. 0 | Page 39 of 68
ACTIVE ENERGY NO-LOAD DETECTION
Active energy no-load detection can be used in conjunction with
reactive energy no-load detection to establish a “true” no-load
feature. If both the active and reactive energy fall below the
no-load threshold, there is no resistive, inductive, or capacitive
load. The active energy no-load feature can also be used to
prevent creep of the active energy when there is an inductive
or capacitive load present.
If the active energy on either Current Channel A (phase)
or Current Channel B (neutral) falls below the programmed
threshold, the active energy on that channel ceases to accumu-
late in the AENERGYA and AENERGYB registers, respectively.
If either the CF1 or CF2 pin is programmed to output active
energy, the CF output is disabled and held high (see the Energy-
to-Frequency Conversion section). If enabled, the active reverse
power indication ( REVP ) holds its current state while in the no-
load condition (see the
Channel A active energy no-load condition is indicated by the
AP_NOLOADA bit (Bit 6) in the IRQSTATA register (Address
0x22D and Address 0x32D). The Current Channel B active energy
no-load condition is indicated by the AP_NOLOADB bit (Bit 6)
in the IRQSTATB register (Address 0x230 and Address 0x330).
Current Channel A and Current Channel B are independent
and, therefore, a no-load condition on Current Channel A
affects only the energy accumulation, CF output, and reverse
power of Current Channel A, and vice versa.
The active energy no-load feature is enabled by default and can
be disabled by setting Bit 0 in the DISNOLOAD register
(Address 0x001) to 1.
Active Energy No-Load Interrupt
Two interrupts are associated with the active energy no-load
feature: one for Current Channel A (phase) and one for Current
Channel B (neutral). If enabled, these interrupts are triggered
when the active energy falls below the programmed threshold.
The Current Channel A active energy no-load interrupt can be
enabled by setting the AP_NOLOADA bit (Bit 6) in the IRQENA
register (Address 0x22C and Address 0x32C). When this bit is set,
an active energy no-load event on Current Channel A causes
the IRQ pin (Pin 22) to fall to 0 (see the
(Voltage Channel and Current Channel A)
The Current Channel B active energy no-load interrupt can be
enabled by setting the AP_NOLOADB bit (Bit 6) in the IRQENB
register (Address 0x22F and Address 0x32F). When this bit is set,
an active energy no-load event on Current Channel B triggers
the IRQ alternative output (see the
section).
Reverse Power
Current Channel B Interrupts
section). The Current
Primary Interrupts
section).
ADE7953