Sutron Corporation X-Link Operations & Maintenance Manual, Rev 1.63 5/24/2016 pg. 79
command, changing the sensor’s address from 0 to x, where x is a unique
number or letter of your choice.
7.1.4.5.
SDI-12 Command
When the measurement type is set to
SDI-12
, data is obtained by sending a
command to the SDI-12 sensor. The sensor will reply with the measured data.
The command is set by the user through the
SDI-12 Address
and
SDI-12
Command
fields. For example, if the address is set to 0 and the command is set
to M!, 0M! will be sent to the sensor.
7.1.4.6.
SDI-12 Param
Some sensors will respond with multiple data values. The
SDI-12 Param
designates which of these data values the user is interested in.
The common setup for SDI-12 sensors is to specify the
SDI-12 Address
as 0,
SDI-
12 Command
as M! and the
SDI-12 Param
as 1. This commands SDI-12 device at
address 0 to make a measurement and to take the first value returned. Newer
SDI-12 devices support the following additional commands:
MC
Measure and include CRC in reply
C
Measure concurrent
CC
Measure concurrent and include CRC in reply
R
Read real-time
Some SDI-12 devices can return more than one sensor reading, such as a water
quality probe that returns dissolved oxygen, conductivity, temperature etc.
Some of these devices will return more than one reading when issued a single
measurement command and others require that multiple measurement
commands be given.
In the case of the devices that return more than one reading to a single measure
command, the
SDI-12 Param
specifies which of the sensor readings returned by
the SDI-12 device to use. Setting the parameter to 1 tells X-Link to use the first
value returned from the device; setting parameter to 3 tells X-Link to use the
third value returned from the device.
If more than one parameter needs to be measured, a different measurement
needs to be set up for each parameter. These measurements should have
identical setups, except for the
SDI-12 Param
setting. Be sure to keep the
measurement time and interval the same for these measurements. If you vary
the time and interval, X-Link will end up taking multiple sensor measurements
even though one would have sufficed (thus slowing down the system and using
more power).
In the case of devices which require multiple commands to be issued (e.g. 0M1!
retrieves pressure, 0M2! retrieves temperature) multiple measurements need to
