Campbell Scientific CS215 Temperature and Relative Humidity Probe - Manual (Page 20)

CS215 Temperature and Relative Humidity Probe
8. Operation
8.1 Sensor Measurements
CRBasic instruction SDI12Recorder() measures the CS215 sensor using the
Start Measurement ( aM!), Concurrent Measurement (aC!), or Continuous
Measurement ( aR!) command. In all cases “a” is the address of the sensor and
“!” is the command terminator. The sensor returns two values: temperature in
degrees Celsius and relative humidity as a percentage (0 to 100).
A measurement is initiated with the aM! or aC! command. To these
commands, the sensor responds with the time until the measurement data are
available and the number of values to be returned when one or more
subsequent aD! commands are issued.
When using the aM! command, the datalogger waits the time specified by the
sensor, sends the aD! command, pauses its operation, and waits until either it
receives the data from the sensor or the sensor timeout expires. Because of the
delays this command requires, it is only recommended in measurement scans
of 10 seconds or more.
The aC! command follows the same pattern as the aM! command with the
exception that it does not require the datalogger to pause its operation until the
values are ready. Rather, the datalogger picks up the data with the aD!
command on the next pass through the program. Another measurement request
is then sent so that data are ready on the next scan.
An aR! command switches the sensor to automatically make measurements
and send data every 11 seconds, ±2 seconds, based on the sensor’s internal
clock. If measurements are requested at 2 seconds or faster, the sensor will
increase its measurement rate to approximately every 5 seconds. This
instruction usually takes less than 300 milliseconds to execute. The automatic
measurement mode can only be cancelled by powering down the sensor to reset
it.
See Appendix D, SDI-12 Sensor Support, for additional commands and details
of the SDI-12 protocol.
Only CS215 sensors with serial numbers after E1587 or those with
upgraded firmware support the aR! Command.
8.1.1 Measurements at Fast Scan Rates
8.1.1.1 CRBasic Dataloggers
Using the SlowSequence() function allows the SDI-12 instruction to run as a
background process, causing minimum interference to other measurements that
use the analog hardware. Measuring the sensor in a SlowSequence() section of
the program allows faster programs to run as the main scan.
For the CR5000, use a control port rather than the SDI-12 port to
allow the SDI12recorder instruction to run in the slow sequence.
NOTE
NOTE
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