Campbell SDM-SIO4, Instruction Manual

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Section 2. Installation and Hardware Set-Up
2-3
lightning protection is recommended on all lines connected to the serial ports
(contact Campbell Scientific for further details).
The possibility of ground loops being set up between the datalogger and the
remote RS232 device via the serial cable should also be considered. Ground
loops formed by secondary return earth paths can lead to various problems
including:
•
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 meters (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 kilometers 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 2-2. 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.