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.
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