Vaisala HMP240 - Manual (Page 95)

HMP240
M210300en Appendix 2: RS 485/422 serial port module
93
2. OPERATION
The HMP240 transmitter can either be given an address or operated without an
address. Both single and dual loop wiring with half duplex connection can be
used. No address is needed when only one HMP240 transmitter is used; when
several transmitters are connected to the same line, each transmitter must be
given an address in the initial configuration.
A single transmitter can get its operating voltage from the master or it can
have its own (floating) power supply.
The serial line structure is a parallel interfaced chain (daisy chain). At the end
of the serial line there must be an HMP240 transmitter, dynamic line adapter
(120 ohm resistor in series with a 33 nF capacitor) or line master. If a branch
line is made with a junction box, the branch should be shorter than 3 meters.
When connecting the device, follow the instructions given in the figure in
Chapter 1.
TX HI
TX LO
TWISTED PAIR WIRING
-
HOST COMPUTER
DUAL LOOP WIRING
TWISTED PAIR WIRING
HOST COMPUTER
RX LO
RX HI
TX HI
TX LO
RX LO
RX HI
TX HI
TX LO
RX LO
RX HI
TX HI
TX LO
RX LO
RX HI
TX HI
TX LO RX LO
RX HI
120R
33 nF
TX HI
TX LO
RX LO
RX HI
120R
33 nF
120R
33 nF
NOTE: DYNAMIC LINE TERMINATION
REQUIRED IF NO DEVICE
AT THE END OF THE BUS.
NOTE: DYNAMIC LINE TERMINATION
REQUIRED IF NO DEVICE
AT THE END OF THE BUS.
HMP243 transmitters
1 to n pieces
HMP243 transmitters
1 to n pieces
SINGLE LOOP WIRING