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Analog I/O Units Section 7-4
(5) Refer to the following diagram regarding wiring disconnections when volt-
age input is being used.
Example: If analog input device 2 is outputting 5 V and the same power sup-
ply is being used for both devices as shown above, approximately 1/3, or 1.6
V, will be applied to the input for input device 1.
If a wiring disconnection occurs when voltage input is being used, the situa-
tion described below will result. Either separate the power supplies for the
connected devices, or use an isolator for each input.
If the same power supply is being used by the connected devices and a dis-
connection occurs at points A or B in the above diagram, an unwanted circuit
path will occur as shown along the dotted line in the diagram. If that occurs, a
voltage of approximately 1/3 to 1/2 of the output voltage of the other con-
nected device will be generated. If that voltage is generated while the setting
is for 1 to 5 V, open-circuit detection may not be possible. Also, if a disconnec-
tion occurs at point C in the diagram, the negative (-) side will be used in for
both devices and open-circuit detection will not be possible.
This problem will not occur for current inputs even if the same power supply is
used.
Note When external 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 countermeasures
such as those suggested below.
• Turn ON the power supply for the CP1H CPU Unit first, and then turn ON
the power supply for the load after confirming correct operation.
• Turn OFF the power supply for the load before turning OFF the power
supply for the CP1H CPU Unit.
24 VDC
A
CB
Analog
input
device 1
Analog
input
device 2
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