METER TEROS 21 - Connecting the TEROS 21 Sensor

7
COMMAND IMPLEMENTATION
The following tables list the relevant Measurement (M), Continuous (R), and Concurrent (C) commands and
subsequent Data (D) commands when necessary.
MEASUREMENT COMMANDS IMPLEMENTATION
Measurement (M) commands are sent to a single sensor on the SDI-12 bus and require that subsequent Data
(D) commands are sent to that sensor to retrieve the sensor output data before initiating communication with
another sensor on the bus.
Please refer to Table2 and for an explanation of the command sequence and see Table7 for an explanation of
response parameters.
Table2 aM! command sequence
Command Response
This command reports average values when relevant.
aM! atttn
aD0! a-<waterPotential>±<temperature>
NOTE: The measurement and corresponding data commands are intended to be used back to back. After a measurement command is
processed by the sensor, a service request a <CR><LF> is sent from the sensor signaling the measurement is ready. Either wait until ttt
seconds have passed or wait until the service request is received before sending the data commands. See the SDI-12 Specifications v1.3
document for more information.
CONCURRENT MEASUREMENT COMMANDS IMPLEMENTATION
Concurrent (C) measurement commands are typically used with sensors connected to a bus. Concurrent (C)
commands for this sensor deviate from the standard C command implementation. First, send the C command,
wait the specified amount of time detailed in the C command response, and then use D commands to read its
response prior to communicating with another sensor.
Please refer to Table3 for an explanation of the command sequence and see Table7 for an explanation of
response parameters.
Table3 aC! measurement command sequence
Command Response
This command reports average values when relevant.
aC! attnn
aD0! a-<waterPotential>±<temperature>
NOTES: This command does not adhere to the SDI-12 concurrent command requirements. See METER SDI-12 Implementation for more
information.
The measurement and corresponding data commands are intended to be used back to back. After a measurement command is processed
by the sensor, a service request a <CR><LF> is sent from the sensor signaling the measurement is ready. Either wait until ttt seconds have
passed or wait until the service request is received before sending the data commands. See the SDI-12 Specifications v1.3 document for
more information.
CONTINUOUS MEASUREMENT COMMANDS IMPLEMENTATION
Continuous (R) measurement commands trigger a sensor measurement and return the data automatically
after the readings are completed without needing to send a D command.
Please refer to Table4 through Table6 for an explanation of the command sequence and see Table7 for an
explanation of response parameters.
Table4 aR0! measurement command sequence
Command Response
This command reports instantaneous values.
aR0! a-<waterPotential>±<temperature>
NOTE: This command does not adhere to the SDI-12 response timing. See METER SDI-12 Implementation for moreinformation.