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3.1.3 Signal Processing Module
The signal processing and communication module (SPM) incorporates a signal processing
circuit and a communication control circuit. Figure 3.1.3.1 shows the block diagram.
The signal processing circuit consists of an analog filter, multiplexer, analog to digital (A/D)
converter, main processing unit (MPU) and memories (RAM and ROM), and executes all kinds
of processing including protection, measurement, recording and display.
The SPM contains a lithium-ion battery, which should be removed at the end-of-life of the
product. The nominal backup time of a lithium-ion battery is one year after the shipment from
the factory.
The analog filter performs low-pass filtering for the corresponding current and voltage signals.
The A/D converter has a resolution of 16 bits and samples input signals at sampling frequencies
of 2400Hz (at 50Hz) and 2880Hz (at 60Hz).
The MPU carries out operations for the measuring elements and scheme logic operations for
protection, recording, displaying and signal transmission control.
The SPM can be provided with Optical interface or Ethernet LAN interface for serial
communication system.
Figure 3.1.3.1 Signal Processing Module
Analog filter
Other
modules
A/D
converter
MPU
Analog filter
Analog filter
Multiplexer
Analog
input
RAM ROM
Optical I/F
(
O
p
tion
)
Link with Serial
communication
system
Ethernet LAN
I/F
(
O
p
tion
)