Vaisala DRYCAP DMT340 SERIES Guide de l'utilisateur télécharger pdf (Page 63)

Chapter 3 _______________________________________________________________ Installation

VAISALA _______________________________________________________________________ 63

Table 6 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

6. If you use RS-485 (or RS-422) to connect just one DMT340 to a

master computer,enable the internal termination of DMT340 by

switching switches 1 and 2 ON. Make sure that the master's end of

the line is also terminated (by using master's internal termination or

with a separate terminator).

If you are connecting many transmitters 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

transmitter without blocking the bus operation.

NOTE

If you use the internal termination of the transmitter at the end of the

RS-485 bus (instead of using separate terminators) removing that

transmitter will block the bus operation.

7. Use the bus type (4-wire/2-wire) to select the selection switch 3.

In 4-wire mode RS-485 master sends data to the DMT340 through

terminals RxA and RxB and receives data from DMT340 through

terminals TxA and TxB.

Figure 42 4-Wire RS-485 Bus

1 2 ... 58 59 60 61 62 63 64 65 66 67 68 ... 168 169

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Vaisala DRYCAP DMT340 SERIES Guide de l'utilisateur Page 63