Campbell cs215 Instruction Manual - page 18
CS215 Temperature and Relative Humidity Probe
The sensor will automatically switch to making measurements
every 11 seconds (±2 second) the first time it receives the aR!
command. It makes the measurements based on its own clock
which is not synchronized to the datalogger clock. This means
measurements made with the aR! command can be up to 11
seconds old. This is not normally an issue for environmental
measurements due to slow rate of change of RH and temperature.
If measurements are requested more frequently than every 11
seconds the aR! option will return repeated values, up until the
point the sensor takes its next measurement. If measurements
are requested at 2 sec or faster, the sensor will increase its
measurement rate to approximately every 5 seconds. The
automatic measurement mode can only be cancelled by powering
down the sensor to reset it.
NOTE
• aMC!, aCC!, aRC!, which are the same as the instructions above but where
the C at the end of the instruction forces a validation for the data received
from the sensor using a checksum. If the checksum is invalid, the logger
will re-request the data up to three times. The checksum validation
increases the measurement time by about 40 milliseconds if there are no
errors. Retries will increase the measurement time in proportion to the
number of retries. Use of the checksum option is only normally necessary
for very long cable runs.
Where in all cases “a” is the address of the sensor and “!” is the command
terminator. These two characters are normally sent implicitly by Campbell
Scientific dataloggers.
7.4.1 Measurements at Slow Scan Rates
If the scan rate of your measurement sequence is slow (several seconds or
more), use the aM! command to read the data from the sensor in the main scan
for CRBasic or main table for Edlog. If the scan rate has to be faster, please
refer to Section 7.4.2, Measurements at Fast Scan Rates.
With Campbell Scientific dataloggers, the aM! command involves just one
program instruction. The datalogger sends the command, waits and then
automatically sends the ‘aD0!’ (get data) command and collects the
measurements from the sensor. The sensor returns two values (temperature in
degrees Celsius and relative humidity as a percentage (0 to 100)).
If your Short Cut version does not include specific support for
the CS215, the generic SDI12 Sensor instruction can be used by
setting the first parameter label to represent temperature and the
second for relative humidity.
NOTE
Example programs for measurement at Slow Scan Rates are shown in the
Example Programs (see Section 7.4.3).
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