Section 7. Installation
SDI-12 Start Measurement Commands
Measurement commands elicite responses in the form:
atttnn
where:
a is the sensor address
ttt is the time (s) until measurement data are available
nn is the number of values to be returned when one or more subsequent D!
commands are issued.
aMv!
Starts a standard measurement. Qualifier v is a variable between 1 and 9. If
supported by the sensor manufacturer, v requests variant data. Variants may
include alternate units (e.g., °C or °F), additional values (e.g., level and
temperature), or a diagnostic of the sensor internal battery.
Syntax:
aMv!
As an example, the response from the command 5M! is:
500410
where:
5 reports the sensor SDI-12 address.
004 indicates the data will be available in 4 seconds.
10 indicates that 10 values will be available.
The command 5M7! elicites a similar response, but the appendage 7 instructs the
sensor to return the voltage of the internal battery.
aC!
Start concurrent measurement. The CR800 requests a measurement, continues
program execution, and picks 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. This command is new with v. 1.2 of the SDI-12 specification.
Syntax:
aC!
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