XLINK 500/100 Operations & Maintenance Manual page # 82
SDI-12 Param
Most SDI-12 sensors will respond to the measure command with multiple data values. The
SDI-12
Param
designates which of these data values the user is interested in.
Setting the parameter to 1 tells the station to use the first value returned from the sensor;
setting parameter to 3 tells the station to use the third value returned from the sensor.
If you want to record (and transmit) more than one parameter from a single SDI-12 sensor, 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 and the station will make a single
measurement to provide the data for both. If you vary the time and interval, the station 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 be set up. It does not
matter if these measurements are scheduled for the same time, as the station will have to issue
multiple commands to the sensors.
When multiple measurements of type SDI-12 are scheduled to go at the same time, the station
orders the measurement commands so that concurrent measurements are commanded first.
Non-concurrent measurements occur while waiting for concurrent results. Also, the station is
able to recognize when two different measurement schedules rely on data from a single
measurement command (e.g., measurement 1 commands 0M! and expects parameter 1 while
measurement 2 commands the same and expects parameter 2, both scheduled at the same
time). In such cases, the station outputs the measurement command only once.
Warmup
If this number is not zero, then the Switched Power line (terminal #8, SWD+12V) and VREF
(terminals #25 and #21) will be turned on for warmup seconds prior to talking to the SDI-12
sensor. The line will be kept on until the measurement completes.
You may use SWD#1 12V instead of SDI-12 Power to supply power to the SDI-12 sensor as long as
the sensor does not require to be powered on all the time. Some sensors (such as the Sutron
SDR) need to be powered on all the time and will not work correctly if powered from the
Switched Power line.
If you power the sensor via Switched Power, you must setup the Warmup to at
least one second!
Why use Switched Power instead of SDI-12 Power? To reduce power consumption of the SDI-12
sensor. SDI-12 Power is turned on all the time, while Switched Power is only turned on during
the measurement if Warmup is not zero.
Please note that using LinkComm's Send SDI-12 Command window will NOT turn on Switched
Power. However, doing a Live/Forced measurement will.
SDI-12 Command Utility
The SDI-12 command utility dialog is used to send SDI-12 commands to sensors. It can also be
used to quickly find what sensors are connected to the SDI-12 bus.
