Endress+Hauser Proline t-mass 65, Руководство по эксплуатации

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Proline t-mass 65 PROFIBUS DP/PA Operation
Hauser 45
5.6.3 Configuring the terminating resistors
!
Note!
It is important to terminate the RS485 line correctly at the start and end of the bus segment since
impedance mismatch results in reflections on the line which can cause faulty data transfer.
#
Warning!
Risk of electric shock. Exposed components carry dangerous voltages.
Make sure that the power supply is switched off before you remove the cover of the electronics
compartment.
• For baudrates up to 1.5 MBaud, the termination is set via the terminating switch SW 1 for the
last transmitter on the bus: ON – ON – ON – ON.
• The measuring device is operated with a baudrate >1.5 MBaud:
Due to the capacitive load of the device and the line reflection generated as a result, make sure
that external termination is used.
The miniature switch for termination is located on the I/O board (see Figure):
a0005408
Fig. 32: Set terminating resistors (for baud rates < 1.5 MBaud)
A = Factory setting
B = Setting at the last transmitter
!
Note!
It is generally recommended to use external termination since if a device that is terminated
internally is defect, this can result in the failure of the entire segment.
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4 W
E
N
O
1
2
3
4 W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4 W
E
N
O
1
2
3
4
W
E
N
O
1
2
3
4
W
E
N
O
390
W
+5V
A
3
4
1
2
OFF ON
220
W
390
W
SW 1
390
W
+5V
B
3
4
1
2
OFF ON
220
W
390
W
SW 1