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SDM-SW8A Switch Closure Input Module
TABLE 2. SDM-SW8A to SDM-SW8A Connections
SDM-SW8A
SDM-SW8A that’s connected to
a CR10(X), CR800, CR850,
CR1000, CR23X, CR3000,
CR5000, or CR7
SDM-SW8A that’s
connected to a 21X
+12 12 V +12
C3 C3 C3
C2 C2 C2
C1 IN C1 IN C1 IN
C1 OUT not used (see Note 2) C1 OUT (see Note 3)
Notes:
(1) If using an auxiliary power supply, instead of connecting the datalogger’s
12 V or +12 terminal to the SW8A, connect the power supply’s positive “+”
wire to the SW8A’s +12 terminal. The power supply’s ground “-” wire
connects to the SW8A’s
terminal along with the wire that connects to the
datalogger’s G or
terminal.
(2) When using a CR10(X), CR800, CR850, CR1000, CR23X, CR3000, or
CR7, a jumper wire is used to connect the C1 IN to the C1 OUT. SDM-
SW8As shipped after March 1, 2006, include this jumper.
(3) If you’re using a 21X and the SDM-SW8A was shipped after March 1,
2006, remove the jumper connecting C1 IN to C1 OUT.
3. Power Supply Considerations
Due to the 3 mA continuous and 6 mA active current drain, an auxiliary 12
VDC power supply is recommended for powering the SW8A in remote, long
term applications.
For some applications it may be convenient to use the datalogger supply to
power the SW8A. For long term applications where AC power is available, or
where a solar panel can be used for recharging, the lead acid power supply
available with Campbell Scientific, Inc. dataloggers could be used. For short
term applications only, the alkaline power supply available with Campbell
Scientific, Inc. dataloggers could be used to power the SW8A.
If the 21X power supply is used to power the SW8A, all low level analog
measurements (thermocouples, pyranometers, thermopiles, etc.) must be made
differentially. This results from 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 SW8A.
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