Campbell CR850, Operator'S Manual, Page: 181 / 566

Section 7. Installation
181
SDI12Recorder (Temp(3),1,2,"M!",1.0,0)
SDI12Recorder (Temp(4),1,3,"M!",1.0,0)
NextScan
EndSequence
EndProg
However, problems 2 and 3 still are not resolved. These can be resolved by using
the concurrent measurement command,
C! . All measurements will be made at
about the same time and execution time will be about 95 seconds, well within the
5-minute scan rate requirement, as follows:
Public BatteryVolt
Public Temp(4)
BeginProg
Scan (5,Sec,0,0)
'Non-SDI-12 measurements here
NextScan
SlowSequence
Scan (5,Min,0,0)
SDI12Recorder (Temp(1),1,0,"C!",1.0,0)
SDI12Recorder (Temp(2),1,1,"C!",1.0,0)
SDI12Recorder (Temp(3),1,2,"C!",1.0,0)
SDI12Recorder (Temp(4),1,3,"C!",1.0,0)
NextScan
EndProg
A new problem introduced by the C! command, however, is that it causes high
power usage by the CR800. This application has a very tight power budget.
Since the
C! command reissues a measurement request immediately after
receiving data, the sensors will be in a high power state continuously. To remedy
this problem, measurements need to be started with
C! command, but stopped
short of receiving the next measurement command (hard-coded part of the C!
routine) after their data are polled. The SDI12Recorder() instruction C command
(not C! ) provides this functionality as shown in CRBasic example Using Alternate
Concurrent Command (aC)
(p. 182).
A modification of this program can also be
used to allow near-simultaneous measurement of SDI-12 sensors without
requesting additional measurements, such as may be needed in an event-driven
measurement.
Note When only one SDI-12 sensor is attached, that is, multiple sensor
measurements do not need to start concurrently, another reliable method for
making SDI-12 measurements without affecting the main scan is to use the
CRBasic
SlowSequence instruction and the SDI-12 M! command. The main
scan will continue to run during the
ttt
time returned by the SDI-12 sensor. The
trick is to synchronize the returned SDI-12 values with the main scan.