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Transmitters – Vaisala PTU200 User Manual

Page 57

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A

PPENDIX

A ____________________ O

PTIONAL

RS485/422 INTERFACE OF

PT

U200 TRANSMITTERS

V

AISALA

_________________________________________________________________________ 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 HI

LO

RX/TX

HI
LO

RX/TX

HI
LO

RX/TX

HI
LO

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 .

Example of required software commands:

>seri
9600

E 7 1 F

>seri H

(select half duplex serial operation)

9600

E 7 1 H

>intv 1 s

(select at least 1 second outputting interval)

Output intrv. : 1 s

>addr 7

(select address of the transmitter)