Section 2. Installation and Hardware Set-Up
2-3
•
Electrical noise causing possible loss or corruption of serial data.
•
Electrical noise being transferred back to the datalogger causing errors on
analogue measurements.
•
Long term damage in the form of corrosion caused by current flowing along
electro-chemical gradients.
If it is not possible to prevent a ground loop, or if electrical noise is found to be a
problem, it may be necessary to add an opto-isolated interface to the output of
the SDM-SIO4 serial port. Please contact Campbell Scientific for further details.
Even if ground loops can be prevented, the length of cables that can be used for
RS232 signals is limited to a few tens of metres (the exact length depending on
the RS232 driver hardware and the cable used). Short-haul modems can be added
to the SDM-SIO4 to allow cables up to several kilometres to be used and in
addition providing ground isolation (please contact Campbell Scientific for
further details).
2.4 Power-on Tests — the Status LED
When the SDM-SIO4 is powered up or has been reset by the internal watchdog
hardware it flashes the red LED on the front panel in the following way to
indicate status:
Table 3 Status LED Error Codes
No. of Flashes
Description of error/status.
1
SDM-SIO4 is working correctly.
2
SDM-SIO4 EPROM signature failure.
3
SDM-SIO4 internal battery must be replaced.
NOTE 1: The LED flashes for 1 second on and 1 second off. The LED will also
illuminate when the front panel switch is pressed.
NOTE 2: The LED may take up to 4 seconds before it flashes after power up.
