Campbell cs215 Instruction Manual - page 17
CS215 Temperature and Relative Humidity Probe
• Use low capacitance, low resistance, screened cable (as fitted by Campbell
Scientific). With such cable, distances of several hundred meters to the
sensor are possible.
• Ensure that the power ground cable has low resistance and is connected to
the same ground reference as the datalogger control ports.
• Be aware that “daisy chaining” sensors reduces the maximum cable length
roughly in proportion to the number of sensors connected in parallel.
7.3.2 Power Conservation
The CS215 draws less than 70 µA of current between measurements from its
12 V supply. In most applications this is insignificant compared to the
datalogger and other power uses so the sensor can be permanently connected.
In very low power applications battery power can be conserved by turning the
12 V supply to the CS215 on just before the measurement (allowing a ‘warm-
up’ time of at least 100 ms) and then turning it off afterwards.
This switching can be achieved in different ways depending on the type and
model of your datalogger. If available, the switched 12 V output of the
datalogger can be used.
7.4 Reading the Sensor
The CS215 output is measured using a standard SDI-12 instruction to read the
data from an SDI-12 sensor. For CRBasic dataloggers, the SDI12Recorder()
instruction is used. For Campbell Scientific Edlog dataloggers, Instruction 105
is used. If using the sensor with other SDI-12 recorders, please refer to your
system’s documentation. Further details of the SDI-12 commands can be
found at:
www.sdi-12.org
.
The CS215 complies with a subset of the SDI-12 1.3 instruction set.
Specifically, it supports these SDI-12 commands:
• aM!, initiate measurement (and the subsequent aD0! “get data” command
which is automatically sent by a Campbell Scientific datalogger)
• aC!, initiate concurrent measurement, where the datalogger gets the data
some time later using the aD0! Command (see the datalogger manual for a
more detailed explanation)
• aI!, send identification
• aAb!, change address to b
• ?! query the address of one sensor
CS215 sensors with serial numbers after E1587 also support these additional
SDI-12 commands. (Older sensors can be upgraded to do this but as they need
to be returned to the factory for an upgrade this is not normally economic.)
• aR! (or aR0!), continuous measurements where the sensor will start to
make measurements every 11 seconds automatically and return the most
recent value, without delaying its response to make the measurement (see
note below). This instruction usually takes less than 300 milliseconds to
execute.
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