Cutler-Hammer D320 PLC, Руководство пользователя

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Chapter 4: Installation and Wiring
35
AC Sensor
The following diagrams show the input device in connection with an AC sensor.
1. Contact Type
2. SSR/Triac Type
2-Wire Sensor
When using a 2-wire type photoelectric switch or a proximity sensor, the sensor may draw such a low
level of current that the input may not be turned off due to the effect of leakage current. To avoid this
leakage current, connect the bridge resistance as shown in the below figure.
Example: D320DIM1624D—12 to 24 VDC type input module (Off voltage 2.5 V, input impedance
3 k
Ω
)
If the Off voltage of the input is 2.5 V, set R so that the voltage between the input terminal is below
2.5 V. Input impedance is 3 k
Ω
. The leakage current I for a given sensor will be provided by the
manufacturer of the sensor. Using the specification for the sensor, R can be calculated from the
following equations:
I
×
3R/(3 + R)
≤
2.5
R
≤
7.5/(3I – 2.5)(k
Ω
)
I = Leakage current of the sensor
R = Bridge resistance value
AC Input Module
Input
Terminal
COM
Terminal
AC Input Module
Input
Terminal
COM
Terminal
I
n
t
e
r
n
a
l
C
i
r
c
u
i
t
Bridge
Resistance
DC Input Module
Input
Terminal
COM
Terminal
R