12 |
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Special Notes Regarding Profiling Probes of 4 or More Segments
GPLP Lite Profiling probes with more than three segments have special requirements for com-
municating. Internally, these probes consist of several circuit boards daisy chained together: A
four-segment probe has two daisy chained 2-segment boards. A six-segment probe has two
daisy chained 3-segment boards. The first board ordinarily handles all normal communications,
particularly handling of all basic SDI-12 commands.
When necessary, there is a specific mechanism and requirements for sending commands di-
rectly to attached daisy chained boards and some special cautions must also be employed. In
particular:
•
Power to daisy chained boards is normally off and must be specifically turned on first
with the
aXSA!
command. A start up delay of at least 150 ms must occur after this
command before sending any further commands to the daisy chained board.
•
All measurement commands automatically turn off power to daisy chained boards to en-
sure the sensor returns to low power state, so if additional commands are to be sent af-
ter a measurement the aXSA! command must be resent to turn power back on.
Commands to a daisy chained board are embedded in the following special extended command
format:
aXn
command
!
where n is the position in the daisy chain. “1” is for the first attached board (segments 3 and 4
in a 4-segment probe), 2 is for the second attached board (usually only with 8-segment probes)
etc. The
command
can be any valid SDI- 12 command, including extended commands. Each
board in the chain includes its address in the response. For example, to get the ID string for the
first attached board (when the main sensor has address 0) send the command
0X1I!
The re-
sponse will be
something like “0013
RIOTTECHGPLPT 0
27SN……”
Note that all subordinate/attached boards in a probe have a default address of 0, and this ad-
dress must NEVER be changed!
If you send the address change (aX0Ab!) command to an inter-
nally daisy chained board, this will render that board and all subsequent boards unresponsive
and inoperative.
Extended SDI-12 Command List
Command
Meaning
Response
aXSc!
aA ON<CR><LF> for c=A
aOFF<CR><LF> for c=0
Enable power to daisy chained
board (GPLP-4, 5, 6 or 8)
aXM!
aMode: n<CR><LF>
read the current mode setting
aXMn!
aMode: n<CR><LF>
write the new mode setting to
n
aXCn!
aCoeff(n): cccccccc<CR><LF> read the coefficient n setting