ABB CL Series Applications Manual page 45

Installation
42
i
Caution!
Analog signals are more sensitive to interference than
digital signals. Consequently, greater care must be taken
when laying and connecting the signal lines.
Incorrect switching states may occur if they are not
connected correctly.
Safety measures with analog signals
Use shielded twisted pair cables to prevent interference
X
with the analog signals.
With short cable lengths, ground the shield at both ends
X
using a large contact area. If the cable length is more than
around 30 m, grounding at both ends can result in
equalisation currents between the two grounding points
and thus in the interference of analog signals. In this case,
only ground the cable at one end.
Do not lay signal cables parallel to power cables.
X
Connect inductive loads to be switched via the logic relay
X
outputs to a separate power feed, or use a suppressor
circuit for motors and valves. If loads such as motors,
solenoid valves or contactors are operated via the same
power feed, switching may give rise to interference on the
analog input signals.
The following four circuits contain examples of applications
for analog value processing.
i
Caution!
Ensure that the reference potential is connected. Connect
the 0 V of the power supply unit for the different setpoint
potentiometers and sensors shown in the examples to the
0 V and neutral conductor terminal (CL-AC1) of the logic
relay power feed. Otherwise incorrect switching states
may occur if they are not connected correctly.
1SVC 440 795 M0100