Commissioning
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4
Commissioning
This chapter describes the commissioning of the RS-485-based bus system.
4.1
Electrical Testing of Connections
Make sure that the terminators have been properly fitted to the fieldbus and service bus.
Testing physical connection right to the end of the segment
1. Disconnect the bus connector from the master.
2. Deactivate the terminator on the bus connector (bus start).
3. Measure the voltage at the bus connector between A and B.
A voltage of U = 220
Ω
/ (220
Ω
+ 2 * 390
Ω
) * 5 V = 1.1 V must be present between A
and B. This voltage is the result of the field-side terminator.
If the 1.1 V voltage is not present, there is either no terminator connected at the end, the
cable is faulty, or there is no terminating voltage at the FB remote I/O unit.
4. Measure the current at the bus connector between A and B.
It must be possible to measure a current of I = 5 V / (2 * 390
Ω
)
≈
6.4 mA between A and
B.
If the current is significantly higher, by a factor of 2 or more, the bus is terminated using more
than one terminator.
If the current is I
≈
0 mA, then either there is no terminator present, the cable is faulty, or
there is no terminating voltage. In this case, there should be a resistance of 220
Ω
between
A and B.
Should neither current nor resistance be present, the terminator is missing at the end of the
bus or the cable is faulty.
5. Activate the terminator on the bus connector for the master.
6. Plug the bus connector back into the master.
Danger!
Explosion hazard
When taking measurements in explosion-hazardous areas, there is an explosion hazard from
sparks forming.
Use suitable measuring equipment or ensure there is no potentially explosive atmosphere.
Note!
Perform the measurements from the control room.
