ade7518 Analog Devices, Inc., ade7518 Datasheet - Page 60

• Manufacturer Part Number: ade7518
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc, And Lcd Driver
• Manufacturer: Analog Devices, Inc.

ADE7518
Apparent Energy Pulse Output
All ADE7518 circuitry has a pulse output whose frequency is
proportional to apparent power (see the Energy-to-Frequency
Conversion section). This pulse frequency output uses the
calibrated signal after VAGAIN. This output can also be used
to output a pulse whose frequency is proportional to I
The pulse output is active low and should preferably be connected
to an LED, as shown in Figure 66.
Line Apparent Energy Accumulation
The ADE7518 is designed with a special apparent energy
accumulation mode that simplifies the calibration process.
By using the on-chip zero-crossing detection, the ADE7518
accumulates the apparent power signal in the LVAHR register
for an integral number of half cycles, as shown in Figure 64. Line
apparent energy accumulation mode is always active.
The number of half-line cycles is specified in the LINCYC regis-
ter, which is an unsigned 16-bit register. The ADE7518 can
accumulate apparent power for up to 65,535 combined half
cycles. Because the apparent power is integrated on the same
integral number of line cycles as the line active register and
reactive energy register, these values can easily be compared.
The energies are calculated more accurately because of this
precise timing control, and provide all the information needed
for reactive power and power factor calculation.
At the end of an energy calibration cycle, the CYCEND flag
in the Interrupt Status 3 SFR (MIRQSTH, 0xDE) is set. If the
CYCEND enable bit in the Interrupt Enable 3 SFR (MIRQENH,
0xDB) is enabled, the 8052 core has a pending ADE interrupt.
As for LWATTHR, when a new half-line cycle is written
in the LINCYC register, the LVAHR register is reset and a new
accumulation starts at the next zero crossing. The number of
half-line cycles is then counted until LINCYC is reached.
This implementation provides a valid measurement at the first
CYCEND interrupt after writing to the LINCYC register. The
line apparent energy accumulation uses the same signal path as
the apparent energy accumulation. The LSB size of these two
registers is equivalent.
VOLTAGE CHANNEL
FROM
ADC
LPF1
APPARENT POWER
ZERO-CROSSING
DETECTION
Figure 64. Line Cycle Apparent Energy Accumulation
or I
rms
rms
.
VADIV[7:0]
%
Rev. 0 | Page 60 of 128
LINCYC[15:0]
CALIBR ATION
CONTROL
+
+
Apparent Power No Load Detection
The ADE7518 includes a no load threshold feature on the
apparent power that eliminates any creep effects in the meter.
The ADE7518 accomplishes this by not accumulating energy if
the multiplier output is below the no load threshold. When the
apparent power is below the no load threshold, the VANOLOAD
flag in the Interrupt Status 1 SFR (MIRQSTL, 0xDC) is set.
If the VANOLOAD bit is set in the Interrupt Enable 1 SFR
(MIRQENL, 0xD9), the 8052 core has a pending ADE interrupt.
The ADE interrupt stays active until the APNOLOAD status bit
is cleared (see the Energy Measurement Interrupts section).
The no load threshold level is selectable by setting the
VANOLOAD bits in the NLMODE register (0x0E). Setting
these bits to 0b00 disables the no load detection, and setting
them to 0b01, 0b10, or 0b11 sets the no load detection threshold
to 0.030%, 0.015%, and 0.0075% of the full-scale output fre-
quency of the multiplier, respectively.
This no load threshold can also be applied to the I
output when selected. In this case, the level of no load threshold
is the same as for the apparent energy.
AMPERE-HOUR ACCUMULATION
In a tampering situation where no voltage is available to the
energy meter, the ADE7518 is capable of accumulating the
ampere-hour instead of apparent power into VAHR, RVAHR, and
LVAHR. When Bit 3 (VARMSCFCON) of the MODE2 register
(0x0C) is set, VAHR, RVAHR, LVAHR, and the input for the
digital-to-frequency converter accumulate I
apparent power. All the signal processing and calibration
registers available for apparent power and energy accumulation
remain the same when ampere-hour accumulation is selected.
However, the scaling difference between I
power requires independent values for gain calibration in the
VAGAIN, VADIV, CFxNUM, and CFxDEN registers.
48
23
LVAHR[23:0]
0
LVAHR REGISTER IS
UPDATED EVERY LINCYC
ZERO CROSSING WITH THE
TOTAL APPARENT ENERGY
DURING THAT DURATION
0
rms
rms
and apparent
instead of
rms
pulse