Endress+Hauser Promag 53 - Page 47

Promag 53 PROFIBUS-DP/-PA 4 Wiring
Endress+Hauser 47
Setting the terminators
Since mismatches in the impedance result in signal reflections on the line and can thus
lead to communication errors, it is important to terminate the lines properly.
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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 com-
partment.
The terminator switches are located on the I/O board (see Fig. 29).
• For baud rates of up to 1.5 MBaud, terminate the last transmitter on the bus by setting
the terminator switch SW 1 to: ON – ON – ON – ON.
• If the device is to be operated at over 1.5 Mbaud, you can tap the supply voltage for
an external terminator from terminals 24 (GND) and 25 (+5 V) (see Fig. 33).
• If the device is to be operated at a baud rate >1.5 Mbaud, an external terminator is
necessary, e.g. with a 9-pin Sub D cable connector combination, with an integrated
series inductance to compensate for the station's capacitive load and minimise the
resulting line reflections.
Fig. 29: Setting the terminators (PROFIBUS-DP)
A = Factory setting
B = Setting on the last transmitter
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Note:
As a rule, we recommend that an external terminator be used, since a defect in an inter-
nally terminated device can disrupt the entire segment.
F06-53xPBxxx-04-00-xx-xx-002
1
2
O N
34
1
2
O N
34
1
2
O N
34
1
2
O N
34
390 Ω
SW1
220 Ω
390 Ω
+5V
ON
OFF
4 3 2 1
A
SW1
390 Ω
220 Ω
390 Ω
+5V
ON
OFF
4 3 2 1
B