Chapter 3 _______________________________________________________________ Installation
VAISALA _______________________________________________________________________ 47
7.
If you are connecting several barometers to the same RS-485 bus,
make sure that switches 1 and 2 are OFF and terminate the bus with
separate terminators at both ends. This allows removing any
barometer without blocking the bus operation.
8.
Use the bus type (4-wire/2-wire) to select the selection switch 3.
9.
In 4-wire mode RS-485 master sends data to the PTB330
barometer through terminals RxA and RxB and receives data from
PTB330 barometer through terminals TxA and TxB.
10. When operating in communication mode RS-422, set both
switches 3 and 4 to ON position (4-wire wiring is required for RS-
422 mode).
11. Connect the power and close the cover.
NOTE
If you use the internal termination of the barometer at the end of the
RS-485 bus (instead of using separate terminators) removing that
barometer will block the bus operation.
Table 4
Connecting the Twisted Pair Wires to the Screw
Terminals
Screw terminal
Data line (2-wire RS-485)
Data line (4-wire RS-
485/422)
1
(not connected)
RxB
2
(not connected)
RxA
3
Data pair shield
Data pair shield
4
B
TxB
5
A
TxA
