Microchip Technology ARD00342 User Manual
MCP3901 and PIC18F65J90 Energy Meter Reference Design
DS51968A-page 16
© 2012 Microchip Technology Inc.
2.2
INPUT AND ANALOG FRONT END
The MCP3901 and PIC18F65J90 and Energy Meter Reference Design comes
populated with components designed for 220V line voltage. At the bottom of the main
board are the high voltage line and neutral connections. There are four connections
that are made from the PCB to the meter casing. They are labeled LINE, NEUTRAL,
SHUNT1, and SHUNT2. The shunt sits on the high or line side of a two-wire system
and the meter employs a hot or “live” ground. The wires going into the shunt to
SHUNT1 and SHUNT2 should be twisted together. The wires going into the LINE and
NEUTRAL side of the meter should be twisted together, and also kept away from the
SHUNT1 and SHUNT2 wires if possible.
populated with components designed for 220V line voltage. At the bottom of the main
board are the high voltage line and neutral connections. There are four connections
that are made from the PCB to the meter casing. They are labeled LINE, NEUTRAL,
SHUNT1, and SHUNT2. The shunt sits on the high or line side of a two-wire system
and the meter employs a hot or “live” ground. The wires going into the shunt to
SHUNT1 and SHUNT2 should be twisted together. The wires going into the LINE and
NEUTRAL side of the meter should be twisted together, and also kept away from the
SHUNT1 and SHUNT2 wires if possible.
The neutral side of the two-wire system goes into a resistor divider on the voltage
channel input. Anti-aliasing low-pass filters will be included on both differential
channels. The voltage channel uses two 332 k
channel input. Anti-aliasing low-pass filters will be included on both differential
channels. The voltage channel uses two 332 k
Ω resistors to achieve a divider ratio of
664:1. For a line voltage of 230 V
RMS
, the channel 1 input signal size will be
490 mV
PEAK
.
FIGURE 2-4:
Analog Input Circuitry.
68 nF
1.0 k
Ω
68 nF
1.0 k
Ω
68 nF
0
Ω
332 k
Ω 332 kΩ
1.0 k
Ω
68 nF
1.0 k
Ω
MCP3901
CH0+
CH0-
CH1+
CH1+
NEUTRAL
Note:
FB = ferrite beads. Ferrite beads have an impedance of the
specified value at 100 MHz.
specified value at 100 MHz.
10-step optional
ladder
LINE_SHUNT1
LINE_SHUNT2
150 FB (Note)
150 FB (Note)
resistor
Shunt
(external to
PCB part of
meter case)
PCB part of
meter case)