Campbell Scientific Sentek EnviroSCAN EasyAG SDI-12 Manual v 3.4 - Manual (Page 13)

EnviroSMART & EasyAG SDI-12 Probe Manual
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Data Reading
The EnviroSMART and EasyAG SDI-12 probe interfaces accept the Start Measurement command
(aM! or aMn!) and Start Concurrent Measurement command (aC! or aCn!) for obtaining calibrated
values from the probes sensors.
Note: The EnviroSMART and EasyAG SDI-12 probe interfaces do not support the Continuous
Measurement command (aRn!). The probe will respond with its address followed by in
response to this command.
The EnviroSMART and EasyAG SDI-12 probe interface returns sensor values in sensor depth order,
starting at the shallowest depth (i.e. 10 cm). A sensor with a depth of zero (an un-configured sensor)
will not be reported by the SDI-12 probe interface.
As the Start Measurement command (aM! or aMn!) reports how many sensor readings to expect, the
controlling device should issue Send Data commands (aDn!) until it either receives a reply with no data
(a, indicating that the probe abandoned sampling, or that all data has been received), or
until it has received all of specified number of sensor values.
Note: The controlling device may choose not to issue all Send Data commands (aDn!) when retrieving
the data.
Note: The EnviroSMART and EasyAG SDI-12 probe interface currently uses a fixed format of “sign
followed by three digits, followed by the decimal point, followed by four decimal digits” (±nnn.nnnn)
to return readings. This may change in future issues of the EnviroSMART or EasyAG SDI-12 probe
interface firmware (software should not rely on this fixed format).
Note: Valid soil moisture values will always be in the range +000.0000 to +101.0000. Soil moisture data
which would result in values in the range -0.1 to 0.0 will be returned as +000.0000. Any soil moisture
values outside of this range (caused by faulty sensors, incorrect probe installation or configuration) will
be returned as -999.9999. A failed sensor will also return a value of -999.9999.
Data Reading using the Start Measurement Command (aM! or aMn!)
The following table shows the allocation of the Start Measurement commands (aM! or aMn!):
aM! Read Soil Moisture values 1 – 9
aM1! Read Soil Moisture values 10 – 16
aM2! Read Salinity values 1 – 9
aM3! Read Salinity values 10 – 16
Note: Start Measurement commands (aM! or aMn!) above “aM3!” will result in a response of
“a0000”.
Soil Moisture Values (aM! and aM1!)
The Start Measurement command (aM! or aMn!) allows up to nine(9) values to be returned. As it is
possible to have up to sixteen(16) soil moisture values from the EnviroSMART SDI-12 probe
interface, two(2) Start Measurement commands (aM! or aMn!), “aM!” and “aM1!” are required. The
Send Data command (aDn!) may return up to three(3) values.