Campbell Scientific SDM-CD16D 16-Channel Digital Control Port Expansion Module - Manual (Page 7)

SDM-CD16D 16 Channel Digital Control Port Expansion Module
3. Power Considerations
The SDM-CD16D power requirements are large compared to most Campbell
Scientific products when driving significant loads. For many applications an
external power supply, as shown in Figure 3, is recommended to power the
SDM-CD16D.
For some applications it may be convenient to use the datalogger supply to
power the SDM-CD16D, as shown in Figure 3. For long-term applications, the
lead-acid power supply available with Campbell Scientific dataloggers should
be used, allowing the batteries to be float charged. Alkaline batteries are not
recommended for long term applications.
Connection with External Supply
Connection with Datalogger Supply
GND
EXTERNAL
9 TO 18V DC
+ –
SDM-CD16D
DATALOGGER 12V C1
C2
C3
SDM-C1 or C1
SDM-C2 or C2
SDM-C3 or C3 12V
SDM-CD16D DATALOGGER
GND
12V
C1
C2
C3
SDM-C1 or C1
SDM-C2 or C2
SDM-C3 or C3
FIGURE 3. Connection Block Diagrams
If the 21X power supply is used to power the SDM-CD16D, 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 make an external supply for the SDM-CD16D essential. NOTE
3