Section 7. Installation
177
Serial number = 101
Start Measurement Commands (aM! & aC!)
A measurement is initiated with M! or C! commands. The response to each
command has the form atttnn, where
• a = sensor address
• ttt = time, in seconds, until measurement data are available
• nn = the number of values to be returned when one or more subsequent D!
commands are issued.
Start Measurement Command (aMv!)
Qualifier v is a variable between 1 and 9. If supported by the sensor
manufacturer, v requests variant data. Variants may include:
• alternate units (for example, °C or °F)
• additional values (e.g., level and temperature)
• diagnostic of the sensor’s internal battery
Example:
Command:5M!
Response:500410(atttnn,indicatesaddress5,datareadyin4seconds,
willreport10values).
Example:
Command:5M7!
Response:500201(atttnnindicatesaddress5,datareadyin2seco
nds,
willreport1value).v=7instructsthesensortoreturnthevoltageofits
internalbattery.
Start Concurrent Measurement Command (aC!)
Concurrent measurement allows the CR800 to request a measurement, continue
program execution, and pick up the requested data on the next pass through the
program. A measurement request is then sent again so data are ready on the next
scan. The datalogger scan rate should be set such that the resulting skew between
time of measurement and time of data collection does not compromise data
integrity.
Note This command is new to Version 1.2 or higher of the SDI-12 Specification.
Older sensors, older loggers, or new sensors that do not meet v1.2 specifications
will likely not support this command
Aborting a Measurement Command
A measurement command (M! or C!) is aborted when any other valid command is
sent to the sensor.
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