Flowserve Valtek StarPac 1 Intelligent Control Systems - Manual (Page 2)

41-2 Flowserve Corporation, Valtek Control Products, Tel. USA 801 489 8611
one of the isolation points fail. Therefore, care must be
taken to ensure the RS-485 cable is wired correctly.
The RS-485 allows only a 7 to 12V common mode
voltage differential between stations. Flowserve's
Valtek RS-232 to RS-485 converter is not a grounded
connection. PCs with internal RS-485 cards, on the
other hand, are often grounded. If another ground
communication device is on the network, a fault condi-
tion will almost certainly exist due to transient and
steady state differences in ground potential.
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.
4 - 20 mA I/P Output
This signal is not isolated from the StarPac internal
system ground and will provide a fault path if the I/P or
connecting wires become grounded. Shielded twisted
pair wire should be used with the shield connected in I/P.
Discrete Inputs and Outputs
These signals are isolated, but because they are fre-
quently used to switch high voltage (120VAC), they
should be run in separate shielded wire paths away
from the other StarPac signals.
AIB and RS-232 to RS-485 Converter Connection
When connecting a StarPac system to a communica-
tion device, no shield or ground connections exist.
Hence, the 24VDC power and RS-485 communication
shield drain wires must be connected to a convenient
ground near the AIB or converter.
Figure 1: Shielded Wire Diagram
Wiring and Grounding Guidelines
This section will help achieve a maximum 'noise-free'
environment and performance with a StarPac unit.
Shielding Versus Grounding
All signals to the StarPac system 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 elec-
trical 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.
Grounding Screw
The green grounding screw by the user interface termi-
nal 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 StarPac unit should be earth grounded
at both ends of its run. The green grounding screw
must not be used to terminate signal shield wires.
24VDC Power
The 24VDC connection points will work best with
shielded twisted pair wire with the shield wire con-
nected only at the source. The input power is isolated
within the StarPac system and may be referenced to
whatever level is necessary. The 24VDC power sup-
ply should not be connected to earth ground.
RS-485 Communication
RS-485 wiring requires the use of a shielded twisted
pair cable, which is grounded only at the source and not
in the StarPac unit. (For maximum performance, wire
should have a characteristic impedance of 120 ohms.)
These signals are referenced to the StarPac internal
system ground; hence this is the main fault path should
Valtek StarPac
Valtek StarPac