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Analog Input Units Section 7-2
For example, if analog input device 2 is outputting 5 V and the same power
supply is being used as shown above, about 1/3, or 1.6 V, will be applied at
the input for input device 1.
Consider the following information on open input circuits when using voltage
inputs. Either use separate power supplies, or install an isolator at each input.
If the same power supply is used as shown in the following diagram and an
open circuit occurs at point A or B, an unwanted current flow will occur as
shown by the dotted lines in the diagram, creating a voltage at the other input
of about 1/3 to 1/2. If the 1 to 5-V range is being used, the open-circuit detec-
tion function will not operate. Also, if there is an open circuit at C, the open-cir-
cuit detection function will not operate because the negative sides are the
same.
Allocating I/O Words Four input words and two output words are allocated from the next words fol-
lowing the last I/O words allocated to the CPU Unit or an existing Expansion
Unit or Expansion I/O Unit.
Writing Set Data Write the settings for input use, averaging use, and range codes for words n+1
and n+2. When the set data is transferred from the CPU Unit to the Analog I/O
Unit, the A/D conversion will be started.
A
CB
Analog
input
device
1
Analog
input
device
2
24 VDC
3. Creating the Ladder Program
Words (m+1) to (m+4)
Analog Input Unit
Words (n+1), (n+2)
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