3-1
Section
Analog I/O Units
190
Note
1. Use shielded twisted-pair cables, but do not connect the shield.
2. When an input is not being used, short the + and – terminals.
3. Separate wiring from power lines (AC power supply lines, high-voltage
lines, etc.)
4. When there is noise in the power supply line, install a noise filter on the input
section and the Power Supply Unit.
Reference Information
Consider the following information on open input circuits when using voltage in-
puts.
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 detection function will not
operate. Also, if there is an open circuit at C, the open-circuit detection function
will not operate because the negative sides are the same.
Analog
input
device 1
Analog
input
device 2
24 VDC
A
B
C
For example, if analog input device 2 is outputting 5 V and the same power sup-
ply is being used as shown above, about 1/3, or 1.6 V, will be applied at the input
for input device 1.
To eliminate the above problem, either use separate power supplies, or install an
isolator at each input. This problem will not occur for current inputs even if the
same power supply is used.
Note
When power is supplied (when setting the range code), or when there is a power
interruption, pulse-form analog output of up to 1 ms may be generated.
If this causes problems with operation, take countermeasure such as those sug-
gested below.
•
Turn ON the power supply for the CPU Unit first, and then turn ON the power
supply for the load after confirming correct operation.