Campbell Scientific SDM-CD8S 8 Channel Solid State DC Control Module - Manual (Page 9)

SDM-CD8S 8 Channel Solid State DC Control Module
If the datalogger lead acid supply is used, the current available from the wall
charger limits the continuous output current.
If the 21X power supply is used to power the SDM-CD8S Load Power, all low
level analog measurements (thermocouples, pyranometers, thermopiles, etc.)
must be made differentially. This is a result of slight ground potentials created
along the 21X analog terminal strip when the 12 V supply is used to power
peripherals. This limitation reduces the number of available analog input
channels and may mandate an external supply for the SDM-CD8S.
4. Installation
• The SDM-CD8S must be installed in an enclosure that provides a
pollution degree 2 environment (normally, only nonconductive pollution.
However, a temporary conductivity caused by condensation may be
expected). All Campbell Scientific enclosures meet this requirement.
• Use copper conductors only.
Cables connecting the terminals of the datalogger and
SDM device should be kept as short as possible to
minimize the risk of corruption of the signals and damage
from induced surges. Where long cable runs (>3 m) are
unavoidable and the cables run outside, some extra
protection may be required for the SDM control terminals.
Please contact Campbell Scientific for further advice.
When connecting wires to the SDM signal terminals,
please ensure they are at ground potential before making
the connection, e.g. by touching them to the earth terminal. CAUTION
For datalogger connections, see Table 1.
Multiple SDM-CD8Ss may be wired in parallel by connecting the datalogger
side of one SDM-CD8S to the next. In most installations the total length of the
cables connecting the SDM-CD8S and other SDM peripherals should not
exceed 20 feet.
Total cable lengths in excess of 20 feet may adversely influence
communication performance. (For CR7 dataloggers, the total cable length
should not exceed 600 feet.)
4.1 Wiring
4.1.1 SDM-CD8S Power and Control Connections
Refer to Figure 2 and Table 1 for SDM-CD8S operating power and control
connections to the datalogger.
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