Vaisala PTU200 Series User's Guide download pdf (Page 57)

APPENDIX A ____________________ OPTIONAL RS485/422 INTERFACE OF PTU200 TRANSMITTERS

VAISALA _________________________________________________________________________ 53

APPENDIX A OPTIONAL RS485/422 INTERFACE OF

PTU200 TRANSMITTERS

The two-wire non-isolated half duplex RS 485/422 serial interface is

the recommended way of connecting the PTU200 series transmitters

with other intelligent transmitters.

HOST

COMPUTER

PTB220

...........

RX/TX

120R

33nF

DYNAMIC LINE TERMINATION REQUIRED

IF NO DEVICE AT THE END OF THE BUS

...........

At the ends of the serial bus there must be a PTU200 series

transmitter, a dynamic line adapter (120 ohm resistor in series with a

33 nF capacitor) or a line master. If a branch line is made with a

junction box, the branch should be shorter than 3 meters.

When using PTU200 series transmitters on RS485/422 interface select

half duplex operation, set an address for each transmitter and activate

the POLL/CLOSE mode. The transmitters can then be polled by the

SEND a command or by using the OPEN/POLL commands. The time

interval setting allows to enter a stop (S) command if a continuous

outputting (R) command has been given by mistake (see page 18).

NOTE

1. The sending of PTU200 is controlled with XON/OFF (software

handshaking).

2. The buffer of the transmitter can be cleared with <cr>.

Example of required software commands:

>seri <cr>

9600 E71F

>seri H <cr> (select half duplex serial operation)

9600 E71H

>intv 1 s <cr> (select at least 1 second outputting interval)

Output intrv. : 1 s

>addr 7 <cr> (select address of the transmitter)

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Vaisala PTU200 Series User's Guide Page 57