Endress+Hauser PROMAG 33, Operating Manual

Page: 32 / 126

Connecting a Promag 33 to a RS 485 Rackbus
Setting the termination resistors
3
28
20 Data A
Data B
21
22
23
24
25
26
27
1
2
Ground terminal
bus screening
ba0
09y
78
Fig. 32
Electrical connection for the
Rackbus RS 485
Note!
Warning!
Warning!
Warning!
Danger from electrical shock! Switch off power supply before opening the cover from the
electronics area.
The termination switches are on the RS 485 communication board (see Fig. below).
The termination switches can usually be left at the factory setting (all switches = OFF).
•
With the last transmitter on the bus (furthest from the PC), turn on the termination
resistor via the selector switches to: OFF – ON – ON – OFF
•
If a bus initial voltage is to be provided, then position the selector switches to:
ON – ON – ON – ON.
Warning!
•
Danger from electrical shock! Switch off power
supply before opening the transmitter housing.
•
If instruments with Ex approvals are used, please
observe all instructions and regulations of the Ex
supplementary documentation.
1. Loosen the Allen screw of the safety grip
(3mm Allen screw).
2. Unscrew the cover of the terminal compartment.
3. Wire up:
– Terminal 20
→
Data A
– Terminal 21
→
Data B
– Terminal 28
→
ground bus screening
4. Screw the cover up tight again on to the
terminal compartment.
5. Tighten the Allen screw of the safety
grip securely.
Note!
If the bus is grounded at both sides, then
potential equalisation must also be present!
392
Ω
150
Ω
392
Ω
+5V
OFF ON
1
2
3
4
1
2
ON
3
4
1
2
O N
3
4
1
2
O N
3
4
1
2
ON
3
4
b
a009y79
Selector switches
(Factory setting)
Fig. 33
Setting the termination resistors
4 Electrical Connection Promag 33
32 Hauser