Communication in SDI-12 mode
42 Snow depth sensor SHM 31, V2.1
10. Communication in SDI-12 mode
Communication in SDI-12 mode corresponds to the:
‘SDI-12: A Serial-Digital Interface Standard for Microprocessor-Bas
ed
S
ensors – Version 1.3 – January 12, 2009’. SDI-12 v1.4 is also supported as of firmware version
v16. The SHM 31-UMB can be operated in Bus mode with other SDI-12 sensors on an SDI master
(logger).
10.1. Connector pin assignment
In SDI-12 mode, the following is used:
• SDI-12 signal line (yellow)
• SDI-12 ground of line V_IN- / SDI-12_GND (white)
Also see the table SHM 31 connector pin assignment, page 17.
10.2. Settings for using SDI-12
Since the interface settings according to the SDI standard differ from the UMB sensors’ settings,
the corresponding parameters must be set with the help of ConfigTool.NET or using the UMB-
ASCII 2.0 protocol.
The following parameter settings must be made (the ASCII 2.0 commands are listed in brackets):
Baud rate: 1200 (BAU=96)
RS485 parity: 7E1 (PRY=2)
Protocol mode: SDI-12 (PRT=3)
Reset: (RST)
After setting the parameters, the sensor must be restarted (reset or power off / on).
The measured data can be transferred in either metric or in US units. This setting can also be
made using UMB or SDI-12. An ASCII 2.0 command is not available for this.
10.
3. Exiting SDI mode
If the SHM 31-UMB is operated in SDI-12 mode, access with ConfigTool.NET is no longer possible
during ongoing operation due to the different interface settings.
One option is to exit SDI-12 mode over the RS232 interface with ASCII commands and to
reconfigure the interface to UMB protocol.
To be able to access the RS485 interface directly again, the interface is operated in standard UMB
mode (19200 8N1) for the first 5 seconds after switch-on or after a reset. The UMB device ID is
switched to 200 for this period of time. This also makes devices with unknown IDs accessible. If
a valid UMB query is received within these 5 s, the device remains in UMB mode for the configured
switching time so that the configuration can be edited:
• Connect the PC to the SHM 31 sensor using an RS485 converter
• Launch ConfigTool.NET and create SHM 31-UMB with ID 200 and activate at least
one
s
ensor. Start the measurement with a 1 sec sampling rate
• Trigger a device reset (operating voltage off / on)
• When the SHM 31-UMB responds, the measurement can be ended; the interface is now
open for configurati
on
Note: The 5 seconds of UMB communication are available from sensor start. Taking this
operating system start into account, the device is ready for SDI-12 queries after approx.
7 – 7.5 sec. This time specification only refers to cold starts. Otherwise, the device responds
within the response times required by the standard.
To Next Page
Loading...
Need help?
General
