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Analog Input Units Section 5-1
Common Power Supply
for Input Devices
If an open-circuit occurs when more than one input device is using the same
power supply, and voltage input is being supplied, the following situation will
occur (this does not apply when current input is being supplied).
If an open-circuit occurs at A in the above diagram, a sneak circuit will be cre-
ated in the direction of the arrow, and even though the circuit is open, a volt-
age will exist. This voltage will be approximately 1/3 to 1/2 of the output of the
input devices in the part of the circuit that is not open. (The same will apply if
an open circuit occurred at B.) With such a voltage present in the circuit, the
open-circuit will not be detected. When voltage input is being supplied, either
set up the input devices so that they are not using the same power supply, or
use isolators for each input.
Converted Data
If the conversion data is a negative number, it is expressed as a two’s comple-
ment. To obtain an absolute value from this two’s complement, the NEG
instruction is useful.
Conversion Time
The conversion data is refreshed every 4 ms for all 4 points.
Power
supply
Input
device
Input
device
Analog Input Unit
Voltage
occurrence
Internal
circuits
−
−
Bit
First word
First word + 1
First word + 2
First word + 3
Input 0 converted data
Input 1 converted data
Input 2 converted data
Input 3 converted data
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