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Troubleshooting
7-14
TI545/TI555 System Manual
7.8
Checking RS-485 (Twisted Pair) Cable Installation
To locate problems with RS-485 communication links, use a digital or analog
meter capable of measuring resistance between 0 and 150 ohms.
Measure the line-to-line and line-to-shield resistance as follows:
1.
Remove power from the controller and all bases.
2.
Disconnect the CPU and all RBCs from the cable by removing the 9-pin
D-connector.
3.
Measure the resistance from either isolated wire to the other isolated
wire (line-to-line) and record this value.
4.
Measure the resistance from one line to the shield wire and record this
value.
5.
Measure the resistance from the other line to the shield wire and
record this value.
6.
Compare the values you recorded with those in Table 7-3.
Table 7-3
Cable Resistance
Trunk Cable Type
9860 or 9271
9182
Trunk Cable Type
Min
Max
Min
Max
Line-to-line
52 ohms
70 ohms
63 ohms
87 ohms
Line-to-shield
100K ohms
–
100K ohms
–
Using Digital or
Analog Meter