90E21 Datasheet, PDF (13/57 Pages) Integrated Device Technology – Single-Phase High-Performance Wide-Span Energy Metering IC

90E21/22/23/24
SINGLE-PHASE HIGH-PERFORMANCE WIDE-SPAN ENERGY METERING IC
3.4 N LINE METERING AND ANTI-TAMPERING
3.4.1 METERING MODE AND L/N LINE CURRENT SAMPLING
GAIN CONFIGURATION
The 90E23 and 90E24 have two current sampling circuits with N line
metering and anti-tampering functions. The MMD1 and MMD0 pins are
used to configure the metering mode. Refer to Table-7.
Table-7 Metering Mode
MMD1 MMD0 Metering Mode
CFx (CF1 or CF2) Output
0
0
Anti-tampering
(larger power)
Mode CFx represents the larger energy
line. Refer to section 3.4.2.
0
1
L Line Mode (fixed L line)
CFx represents L line energy all
the time.
1
0
L+N Mode (applicable for
single-phase three-wire
system)
CFx represents the arithmetic
sum of L line and N line energy
1
1
Flexible Mode (line speci-
fied by the LNSel bit
(MMode, 2BH))
CFx represents
specified line.
energy
of
the
The 90E23 and 90E24 have two current sampling circuits with differ-
ent gain configurations. L line gain can be 1, 4, 8, 16 and 24, and N line
gain can be 1, 2 and 4. The configuration is made by the MMode register
(2BH). Generally L line can be sampled over shunt resistor or CT. N line
can be sampled over CT for isolation consideration. Note that Rogowski
coil is not supported.
3.4.2 ANTI-TAMPERING MODE
Threshold
In anti-tampering mode, the power difference threshold between L
line and N line can be: 1%, 2%,... 12%, 12.5%, 6.25%, 3.125% and
1.5625%, altogether 16 choices. The configuration is made by the
Pthresh[3:0] bits (MMode, 2BH) and the default value is 3.125%. The
threshold is applicable for active energy. The metering line of the reac-
tive energy follows that of the active energy.
Compare Method
In anti-tampering mode, the compare method is as follows:
If current metering line is L line and
N Line Active Power - L Line Active Power _{* 100% > Threshold}
L Line Active Power
N line is switched as the metering line, otherwise L line keeps as the
metering line.
If current metering line is N line and
L Line Active Power - N Line Active Power _{* 100% > Threshold}
N Line Active Power
L line is switched as the metering line, otherwise N line keeps as the
metering line.
This method can achieve hysteresis around the threshold automati-
cally. L line is employed after reset by default.
Special Treatment at Low Power
When power is low, general factors such as the quantization error or
calibration difference between L line and N line might cause the power
difference to be exceeded. To ensure L line and N line to start up nor-
mally, special treatment as follows is adopted:
The line with higher power is selected as the metering line when both
L line and N line power are lower than 8 times of the startup power but
higher than the startup power.
Functional Description
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January 10, 2012