Vaisala HMP228 - Manual (Page 96)

HMP228
Appendix 5: Digital current loop module
M210282en-A
90
2. OPERATION
The HMP228 transmitters 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 HMP228 transmitter is used;
when several transmitters are connected to the same line, each transmitter
must be given an address in the initial configuration.
A current loop must get its operating voltage from the master or it can have its
own (floating) power supply capable of supplying 15...40 V and 20...30 mA.
Unregulated AC/DC adapter can be used, if the current is limited to 20 mA at
least by a serial resistor.
Note.The host computer can restrict the loop supply voltage that can be used;
see computer specifications.
The serial line structure is a serial interfaced chain (daisy chain). At one end
of the serial line there must be a HMP228 transmitter and at the other end a
line master. A branch line can be made with a junction box.
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.
HMP228
transmitters
1 to n pieces
HMP228
transmitters
1 to n pieces
SINGLE LOOP WIRING