Siemens MJ-X, Руководство по установке

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MJ-X
L
Communications Module
17
Table 7-1 RS-485 Cable Specifications
Characteristic Value Maximum/Typical
Impedance 120 ohms Typical
Capacitance (pF/ft) 35 Maximum
Cable Size 22 AWG Typical
DC Resistance 17 ohms/1000 ft Maximum
Velocity of Propagation 80% Maximum
7.2.2 RS-485 Cable Grounding
Ground the cable shield for all devices on the network. Ground the cable shield at only one end to prevent induced
interference that may result from circulating ground currents. If a cable shield is grounded at both ends, a ground
loop can exist between the components. This ground loop can cause induced interference that results in signal
distortion. If there is a ground potential rise between the connected devices, connect the Signal Return (RTN)
between the communication devices. Figure 7-2 illustrates the preferred field device connection method. See
section 4.3.2 on page 7 for jumper considerations.
Data
GND
RS-485 Twisted-Pair Cable RS-485 Twisted-Pair Cable
Shield attached
at this end only Shield grounded
at other end only
From RTU or other device To next device
MJ-X Communications Module
Figure 7-2 RS-485 Connection
7.2.3 RS-485 Connector
The required connector for connecting to the MJ-X
L
RS-232/485 Communications Module is the Phoenix Contact
Screw Terminal Block MSTBT 2,5/8-ST-5,08 or equivalent. Wire the connector as shown in Figure 7-2. This
connector is supplied with the communications module and is shown in Figure 7-3.
.3"
12 Gauge Wire
Maximum
Phoenix Contact Connector
COMBICON MSTB2,5/8-ST-5,08
Figure 7-3 Screw Terminal Block Connector