Installation, Wiring,
and Specifications
2–13
Installation, Wiring, and Specifications
System Wiring Strategies
The DL05 Micro PLC is very flexible and will work in many different wiring
configurations. By studying this section before actual installation, you can probably
find the best wiring strategy for your application . This will help to lower system cost,
wiring errors, and avoid safety problems.
PLC circuitry is divided into three main regions separated by isolation boundaries,
shown in the drawing below. Electrical isolation provides safety, so that a fault in one
area does not damage another. A powerline filter will provide isolation between the
power source and the power supply. A transformer in the power supply provides
magnetic isolation between the primary and secondary sides. Opto-couplers
provide optical isolation in Input and Output circuits. This isolates logic circuitry from
the field side, where factory machinery connects. Note that the discrete inputs are
isolated from the discrete outputs, because each is isolated from the logic side.
Isolation boundaries protect the operator interface (and the operator) from power
input faults or field wiring faults. When wiring a PLC, it is extremely important to avoid
making external connections that connect logic side circuits to any other.
CPU
Input
Circuit
Main
Power
Supply
Discrete Inputs
Discrete Outputs
Power
Input
Output
Circuit
Primary Side Secondary, or
Logic side
Field Side
PLC
Programming Device or
Operator Interface
Isolation
Boundary
Isolation
Boundary
Filter
The next figure shows the internal layout of DL05 PLCs, as viewed from the front
panel.
Output CircuitInput Circuit
CPU
2 Comm.
Ports
Main
Power
Supply
To Programming Device
or Operator Interface
8 Discrete
Inputs
Commons Commons
6 Discrete Outputs
Power
Input
PLC
DL05
Filter
PLC Isolation
Boundaries
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