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Industry PLC System Theory and
Typical Architecture
Comprised of power supplies, CPUs, and multiple analog and digital
I/O modules, a PLC system controls, actuates, and monitors complex
machine variables. The PLC is designed for multiple inputs and outputs
arrangement, extended temperature ranges, immunity to electrical noise,
and resistance to vibration and impact.
A PLC system comprises power supplies, control and communication
modules, and a variety of analog-input, analog-output, digital-input, and
digital-output modules.
Industry PLC System Design Considerations and
Major Challenges
To have an appropriate PLC system design, designers must consider
many different system requirements including accuracy, bandwidth, and
input range.
X
Analog-input types and ranges can be as small as ±10 mV for
TC
(
thermocouple
)
and RTD and as large as ±10 V for actuator
controllers—or 4 mA to 20 mA currents in process-control systems.
X
Analog-output types and ranges typically include ±5 V, ±10 V, 0 V to
5 V, 0 V to 10 V, 4 mA to 20 mA, and 0 mA to 20 mA. Sometimes over-
range capability is required.
X
The resolution and accuracy of the input/output modules, typically
ranging from 12 to 16 bits, with 0.1% accuracy over the industrial
temperature range.
X
Connectivity to a different field BUS.
X
Isolation between the system power module and low power
electronics, between the input and output, between the I/O and central
control unit, and the isolation grade varies from 1 kV to 2.5 kV.
Project Code: APM_PLC_2016
ADI PROGRAMMABLE
LOGIC CONTROLLER
(
PLC
)
SOLUTIONS
X
Analog-input/output and power supply input protection: fault condition
voltage or current and EMC considerations including electrical surge
and fast pulse transient and ESD.
X
Power efficiency, thermal management, and heat dissipation will
become an increasingly important issue for miniaturized devices as
they attempt to reduce board size.
In addition, more channels or nodes need to be placed within the same
space, requiring dense systems. Therefore, the form factor has to be
reduced to accommodate this. This means smaller housings where
power and heat management become a challenge, requiring solutions in
intelligent power management via integrated dynamic power control.
Historically, the large number of high performance discrete components
required to implement these I/O systems resulted in large and expensive
implementations. Recently, advances in integration have allowed system
designers to migrate to smaller, lower power, lower cost solutions, with
performance approaching these larger systems. The challenge moving
forward is to continue to drive the integration of these solutions, while
increasing their performance and diagnostic capabilities.
ADI offers market tailored solutions to aid in the design process. These
solutions feature our industry-leading technologies and offer a range of
design options—from implementation of discrete components to fully
integrated solutions, and everything in between.
Total Solutions from ADI
Leverage ADI’s amplifier, data conversion, signal processing and power
technology and expertise to high resolution, low noise industry PLC systems.
