Campbell CR800 Series, Operator'S Manual

Page: 245 / 598

Section 7. Installation
245
Aborting an SDI-12 Measurement Command
A measurement command (
M!
or
C!
) is aborted when any other valid command is
sent to the sensor.
SDI-12 Send Data Command
Send data commands are normally issued automatically by the CR800 after the
aMv! or aCv! measurement commands. In transparent mode through CR800
terminal commands, you need to issue these commands in series. When in
automatic mode, if the expected number of data values are not returned in
response to a aD0! command, the datalogger issues aD1! , aD2! , etc., until all data
are received. In transparent mode, you must do likewise. The limiting
constraint is that the total number of characters that can be returned to a aDv!
command is 35 (75 for aCv! ). If the number of characters exceed the limit, the
remainder of the response are obtained with subsequent
aDv!
commands wherein
v increments with each iteration.
aDv!
Request data from the sensor.
Example Syntax:
aD0!
SDI-12 Continuous Measurement Command (aR0! to aR9!)
Sensors that are continuously monitoring, such as a shaft encoder, do not require
an M command. They can be read directly with the Continuous Measurement
Command ( R0! to R9! ). For example, if the sensor is operating in a continuous
measurement mode, then aR0! will return the current reading of the sensor.
Responses to R commands are formatted like responses to send data ( aDv! )
commands. The main difference is that
R
commands do not require a preceding
M command. The maximum number of characters returned in the <values> part
of the response is 75 .
Each R command is an independent measurement. For example, aR5! need not
be preceded by
aR0!
through
aR4!
. If a sensor is unable to take a continuous
measurement, then it must return its address followed by <CR><LF> (carriage
return and line feed) in response to an R command. If a CRC was requested,
then the <CR><LF> must be preceded by the CRC.
aRv!
Request continuous data from the sensor.
Example Syntax:
aR5!