Installation,
Wiring,
and
Specifications
2--19
Installation, Wiring, and Specifications
DL105 PLC User Manual, 3rd Edition
In order for a PLC I/O circuit to operate,
current must enter at one terminal and exit
at another. This means at least two
terminals are associated with every I/O
point. In the figure to the right, the Input or
Output terminal is the
main path
for the
current. One additional terminal must
provide the
return path
to the power
supply.
+
--
I/O
Circuit
PLC
(I/O Point)
Return Path
Field
Device
Main Path
If we had unlimited space and budget for
I/O terminals, then every I/O point could
have two dedicated terminals just as the
figure above shows. However, providing
this level of flexibility is not practical or
even necessary for most applications. So,
most Input or Output point groups on
PLCs share the return path among two or
more I/O points. The figure to the right
shows a group (or
bank
) of 4 input points
which share a common return path. In this
way, the four inputs require only five
terminals instead of eight.
+
--
Input
Sensing
PLC
Input 4
Common
Input 3
Input 2
Input 1
Note: In the circuit above, the current in the common path is 4 times any channel’s
input current when all inputs are energized. This is especially important in output
circuits, where heavier gauge wire is sometimes necessary on commons.
Most DL105 input and output circuits are
grouped into banks that share a common
return path. The best indication of I/O
common grouping is on the wiring label.
The I/O common grouping bar, labeled at
the right, occurs in the section of wiring
label below it. It indicates X0, X1, X2, and
X3 share the common terminal located
between X1 and X2.
I/O Common Grouping Bar
The following complete label shows two banks of four inputs and one bank of two.
The following label for relay outputs shows four banks of two output points each.
The last label below for DC outputs has no common grouping bar. In this unique
case, all eight outputs share the same electrical common. The common is available
on three terminals, so there is a physical place to connect each point’s common wire.
I/O “Common”
Terminal Concepts
Содержание DL105
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Страница 308: ...1B DL105 Error Codes In This Appendix Error Code Table...
Страница 314: ...1C Instruction Execution Times In This Appendix Introduction Instruction Execution Times...
Страница 324: ...1D Special Relays In This Appendix DL105 PLC Special Relays...
Страница 327: ...1E PLC Memory In This Appendix DL105 PLC Memory...
Страница 329: ...1F European Union Directives CE In This Appendix European Union EU Directives Basic EMC Installation Guidelines...
