Campbell Scientific SDM-AO4A Four Channel Analog Output Module - Manual (Page 6)

SDM-AO4A Four Channel Analog Output
3. Power Supply
It is often convenient to power the SDM-AO4A from the datalogger power
supply, but when doing so consideration must be given to the SDM-AO4A's
continuous current drain (the current drain is 11 mA in ±5V mode and 21 mA
in 10V mode). The alkaline supply available with the datalogger has 7.5 Amp-
hours and will power one SDM-AO4A for less than one month. This supply is
not recommended for continuous long-term operation. The rechargeable lead
acid option, float charged by an AC supply or solar panel, may be used for
long term operation.
The SDM-AO4A may also be powered from an external 12 Volt supply,
independent from the datalogger supply. The low side of an external 12 Volt
supply should be connected to datalogger ground and not directly earth
grounded.
Slight alterations in ground potential across a 21X terminal strip are created
when the 21X 12 Volt supply is used to power peripherals. Therefore, low
level voltage measurements (e.g., thermocouples, thermopiles, and
radiometers) should be made differentially when powering the SDM-AO4A
with a 21X 12 Volt output.
4. Physical Connections
Figure 1 shows the front panel of the SDM-AO4A. The terminal block on the
left is used for connection to the datalogger and the terminal block on the right
provides the continuous analog output. The two ground ports on the left block
are identical and connected internally.
Table 1 describes the terminal block connections. Multiple SDM-AO4As may
be used by connecting the datalogger side of one SDM-AO4A to the next.
The CABLE5CBL-L or similar cable is used to connect the module to the
datalogger. A 1-ft cable length should be sufficient when both datalogger and
module are housed within an ENC12/14 enclosure; a 2-ft length may be
required if the datalogger and SDM-AO4A are housed at opposite ends of an
ENC16/18 enclosure.
CRBasic dataloggers should use the SDMSpeed instruction if the cable length
is longer than 20 feet (see Section 7.1.2). The maximum recommended cable
length for the CR7 is 600 ft. For other Edlog dataloggers, the maximum
recommended cable length is 20 feet.
Cables connecting the terminals of the datalogger and
SDM device should be as short as possible to minimize the
risk of corruption of the signal and damage from induced
surges. CAUTION
When first powered up, the device is in low-power mode until the first valid
SDM instruction is received. In this mode, outputs are pulled to GND.
The order of connections is critical. ALWAYS CONNECT
GROUND FIRST, followed by 12V and then the Control
Ports. CAUTION
Shielded twisted pair cabling is recommended for wiring the continuous analog
outputs.
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