Vaisala WXT520 Guide de l'utilisateur télécharger pdf (Page 154)

User’s Guide ______________________________________________________________________

152 _________________________________________________________________ M210906EN-C

Example (composite data message queries to the sensors 1 and 3 are

assigned as follows):

0R0<cr><lf>

1R0<cr><lf>

2R0<cr><lf>

NMEA 0183 v3.0, Query

The NMEA 0183 query messages do not contain device address

information. Individual query commands can thus not be directed to

different transmitters. Instead, a specific Time Slot method can be used

for receiving data from several transmitters on the bus, just with a single

query command.

To generate different time slots, each WXT520 is given an individual

delay for its query response, by using the RS-485 line delay parameter

aXU,L. This parameter defines the time (in milliseconds) between the

last character of the query and the first character of the response from

WXT520.

Example (a bus with three WXT520s):

WXT520 #1 communication settings:

0XU,A=0,M=Q,C=3,I=0,B=4800,D=8,P=N,S=1,L=25

WXT520 #2 communication settings:

0XU,A=0,M=Q,C=3,I=0,B=4800,D=8,P=N,S=1,L=1000

WXT520 #3 communication settings:

0XU,A=0,M=Q,C=3,I=0,B=4800,D=8,P=N,S=1,L=2000

Now, when the XDR-query command $--WIQ,XDR*2D<cr><lf> is

sent, WXT520 #1 responds after 25 ms, WXT520 #2 after 1000 ms and

WXT520 #3 responds after 2000 ms. The sufficient delays depend on

the maximum number of characters in the response messages and the

baud rate. Note that all the transmitters are assigned with the same

address. Hence the data logger, after sending the query, shall sort out the

response messages on the basis of the individual response times.

To gain even more addressability transducer ID information provided in

the XDR response messages can also be used. If WXT520 address is set

to 0 (aXU,A=0) and all parameters are chosen except Rain peak

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Vaisala WXT520 Guide de l'utilisateur Page 154