Campbell CS475, Instruction Manual

Page: 26 / 50

CS475, CS476, and CS477 Radar Water Level Sensor
16
The 25616, Adjustment/Display Module , or the terminal emulator in LoggerNet
or
PC400
can be used to enter SDI-12 commands. Appendix C.2 ,
Using
Terminal Emulator and a Datalogger to Send Commands
(p. C-9)
, describes
entering commands using the terminal emulator.
8.2 Sensor Measurement
CRBasic instruction SDI12Recorder() measures the radar sensors using the
Start Measurement ( aM! ) or Concurrent Measurement ( aC! ) command. In all
cases “a” is the address of the sensor and “!” is the command terminator. The
factory-set SDI-12 address is 0. See Appendix C.1.1 , Query/Set the Address
(p.
C-2)
, for instructions on changing the SDI-12 address through the datalogger.
The sensor returns three values: stage measurement (m or ft), distance (m or
ft), and error code (see Section 9 , Diagnostics, Repair, and Maintenance
(p. 16)
).
The stage measurement calculation is based on an initial water stage value,
which is entered using the Set Water Stage Command ( aXSS+nnn.nnn! ). See
Appendix C.1.2 ,
Set Water Stage
(p. C-3)
, for instructions on changing the SDI-
12 address through the datalogger.
A measurement is initiated with the aM! or aC! command. To these
commands, the sensor responds with the time until the measurement data are
available and the number of values to be returned when one or more
subsequent
aD!
commands are issued.
When using the aM! command, the datalogger waits for the time specified by
the sensor, sends the aD! command, pauses its operation, and waits until either
it receives the data from the sensor or the sensor timeout expires. If the
datalogger receives no response, it will send the command a total of three
times, with three retries for each attempt, or until a response is received.
Because of the delays this command requires, it is only recommended in
measurement scans of 10 seconds or more.
The aC! command follows the same pattern as the aM! command with the
exception that it does not require the datalogger to pause its operation until the
values are ready. Rather, the datalogger picks up the data with the aD!
command on the next pass through the program. Another measurement request
is then sent so that data are ready on the next scan. The radar sensor’s output is
measured using a standard SDI-12 instruction to read the data from an SDI-12
sensor.
If using the sensor with other SDI-12 recorders, please refer to your system’s
documentation. Further details of the SDI-12 commands can be found in
Appendix C , SDI-12 Commands/ Changing Settings
(p. C-1)
, and at:
www.sdi-12.org .
9. Diagnostics, Repair, and Maintenance
9.1 Testing Procedure
The testing procedure uses several SDI-12 commands. Detailed
information about these commands are provided in Appendix C ,
SDI-12 Commands/ Changing Settings
(p. C-1)
.
NOTE