58
Note that in this example only three variables of the SQ-X are recorded. The device provides an ex-
tended list of variables that can be read by the data logger. Alternatively, the SQ-X be set to polling
mode and the MRL-7 to request the measurements.
9.3.7
Polling data from an RS-485 device
Various sensing devices perform measurements autonomously and send out the results on request.
The SOMMER IDS-20 Ice detection system is an example of such a device. It detects icing of a surface
with a capacitive transducer and is used, for example, in the wind industry and in aviation to detect ice
loads and icing events. The IDS-20 performs measurements autonomously at an interval of 60 seconds.
The acquired data can be polled with the MRL-7 by wiring the data logger according to
Figure 22: Wiring of IDS-20 ice detection sensor with RS-485 interface
The IDS-20 in this example is configured in
Please note the command
TD
field: this command requests the data from the IDS-20
device and needs to be set in the first variable acquired from the sensor. Additionally,
must be turned on!
Note that in this example only three variables of the IDS-20 are recorded. The device provides an ex-
tended list of variables that can be polled by the data logger.
If a connected sensor requires a command to trigger a measurement and returns the measured data
automatically
needs to be on, but no
TD
command is required.
!
Attention
The response time of different digital sensors varies considerably. Please con-
sult the sensor manual and adjust
9.4
SDI-12
SDI-12 (Serial Data Interface at 1200 Baud) is a serial data communication standard for interfacing
multiple sensors with a single data recorder.
The MRL-7 is equipped with a SDI-12 port on the terminal block X5.
helpful functions to query SDI-12 sensor addresses and to test communication.
9.4.1
Principals
The example below illustrates how the MRL-7 triggers the measurements and requests the results
from three SDI-12 sensors.
