runs. It is advisable to check the difference in ground potential with some caution before
connecting any wires, to ensure the potential differences are reasonably small and
excessive current will not flow between the two ground wires. There is a current limiting
resistor fitted in the RG line in the SDM-SIO2R, but this will not be adequate in the event of
a serious ground fault, for example, the ground references being 240 V apart due to faulty
AC wiring. If a large potential difference is found, please seek the advice of a qualified
electrician before continuing with the installation
l
CAUTION: The power ground connection should be made with large gauge wire, (for
example, 16 AWG or 1.5 mm
2
) to provide a low impedance path to ground allowing full
protection from static and electrical transients.
l
CAUTION: The SDM-SIO2R is considered to be a component of a measurement system
that is installed in an enclosure and wired in accordance with this manual. Due to space
considerations, full details of the maximum ratings of the connections are not given on the
device. Instead the user should study this manual, and in particular
(p. 6), to determine the maximum voltages that are applicable to any terminal before
starting an installation.
3. Initial inspection
Upon receipt of the SDM-SIO2R, inspect the packaging and contents for damage. File damage
claims with the shipping company. Contact Campbell Scientific to facilitate repair or replacement.
4. Overview
The SDM-SIO2R expands the number of serial ports on a Campbell Scientific data logger. It can
be used as a means of collecting data from digital sensors and/or to send commands to sensors
and devices. It can also be used to send data to remote display devices.
The SDM-SIO2R will accept serial data and store it in its buffer allowing remote equipment to
transmit large amounts of data without needing to stop other processes in the data logger whilst
the data is received.
The SDM-SIO2R connects to the data logger via three digital lines using a proprietary protocol
called SDM. It connects to the remote serial device using a standard serial interface that can be
set to RS-232, RS-485, or RS-422 signal levels.
SDM-SIO2R Serial Input/Output Module with Switched Sensor Power
2
