Vaisala PTB330 User Manual

Page 46

USER'S GUIDE____________________________________________________________________

44 __________________________________________________________________ M210855EN-D

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 may block the bus operation.

Table 5

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)

RxD0-

2 (not

connected)

RxD1+

Shield/Common Wire

4 D0-

TxD0-

5 D1+

TxD1+

Stub

Termination

Junction box

Twisted pair

120R

Twisted pair

Stub

Baud > 19.2K Stub < 10ft, 3m
Baud > 112K Stub < 1ft, 0.3m

Rx D0-
Rx D1+
Common
Tx D0-
Tx D1+

Switch
Term off
Term off
2/4 wire on
RS422 off

Tx D0-
Tx D1+
Common
Rx D0-
Rx D1+

Switch
Term off
Term off
2/4 wire on
RS422 off

Tx D0-
Tx D1+
Common
Rx D0-
Rx D1+

5
4
3
2
1

RS485-1

Address MM

Address NN

RS485 bus master

5
4
3
2
1

1102-028

Figure 26

4-Wire RS-485 Bus