Flowserve StarPac 3 - Manual (Page 20)

StarPac Intelligent Control System FCD VLENIM0066-05 04/14
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9.1 Shielding Versus Grounding
All signals to the StarPac 3 unit should be in shielded cables. Shields must be tied to a ground at only one end of the
cable to provide a place for environmental electrical noise to be removed from the cable. A ground wire (unlike a shield)
is attached at both ends to provide a continuous path for electrical conductivity.
9.2 Grounding Screw
The green grounding screw, located by the customer interface terminal block should be used to provide the unit with an
adequate and reliable earth ground reference. This ground should be tied to the same ground as the electrical conduit.
Additionally, the electrical conduit connecting to the unit should be earth grounded at both ends of its run.
WARNING: The green grounding screw must not be used to terminate signal shield wires.
9.3 24 VDC Power
The 24 VDC connection points will work best with shielded twisted pair wire with the shield wire connected only at the
source. The input power is isolated within the unit and may be referenced to whatever level is necessary.
WARNING: The 24 VDC power supply should not be connected to earth ground.
9.4 RS-485 Communications
RS-485 wiring requires the use of a shielded twisted pair cable, which is grounded only at the source and not in the
unit. (For maximum performance, wire should have a characteristic impedance of 120 ohms.) The RS-485 input is fully
isolated, using opto-isolators.
The RS-485 allows only a 7 to 12 V common mode voltage differential between stations. RS-232 to RS-485 converters
are not a grounded connection. PC‘s with internal RS-485 cards, on the other hand, are often grounded. If another
ground communication device is on the network, a fault condition will almost certainly exist due to transient and steady
state differences in ground potential.
9.5 4-20 mA Command Input, Auxiliary Input and Feedback Output
These signals are isolated but shielded twisted pair wire should be used to reduce crosstalk from other signals. The
shield should be connected only at the source.
9.6 Discrete Inputs and Outputs
These signals are isolated, but because they are frequently used to switch high voltage (120 VAC), they should be run in
separate shielded wire paths away from the other StarPac 3 signals.
9.7 RS-232 to RS-485 Converter Connection
When connecting a StarPac 3 unit to a communication device, no shield or ground connections exist. Hence, the 24 VDC
power and RS-485 communication shield drain wires must be connected to a convenient ground near the converter.
STOP!
STOP!