Campbell Scientific SDM-CVO4 4-Channel Current/Voltage Output Module - Manual (Page 12)

SDM-CVO4 4-Channel Current/Voltage Output Module
SDM-CVO4. Do not connect the screen at both ends of the cable as this may
result in a ground loop being formed.
The output circuitry of the SDM-CVO4 includes protective components to
minimize the chances of damage that can be caused by transients which can be
induced in the signal cable. The protection clamps the transient voltages to
non-damaging levels relative to the ground terminals on each output channel.
If the voltage of that ground point exceeds the datalogger ground potential by
more than approximately 2500 VDC, a secondary level protector will break
down to provide a path for energy to discharge to the datalogger ground. The
likelihood of secondary breakdown can be avoided, if required (perhaps for
safety reasons), by connecting a wire to the output ground terminals of the
SDM-CVO4 to provide a low impedance path to ground. In doing this, though,
there is a risk that you will nullify the effects of the isolation barrier, e.g. if the
ground you connect to is the same ground to which the datalogger is
connected.
You need to carefully study the ground connections of the entire system when
connecting a grounding wire to the output ground terminal, both to avoid
creating a ground loop/referencing problem and also possibly causing a safety
issue.
4.2.4 Output Terminal Connectors
The output connections use normal, 4-way, screw terminal fixings. These can
be unplugged for ease of wiring, if required.
4.3 Output Mode Setting
An internal jumper sets the output mode for each channel of the SDM-CVO4.
The output mode can either be voltage or current mode, as described above. To
change the mode setting, the case must be opened. To do this first disconnect
the device from any source or power, disconnect the output connections (you
can unplug the connectors) and then remove the four larger screws from the
face of the case which has the product name written. Lay the unit on a flat
surface and then, after taking anti-static precautions, lift off the top half of the
case to expose the circuit board.
Then refer to Figure 4-3 below to identify the block of jumpers that control the
output mode. To operate in current mode, the jumper relevant to the channel
concerned must be installed between the two jumper pins, as shown. If
operating in voltage mode, the jumper should not bridge any two pins, but may
be stored, if required, by fitting it to just one of the pins, leaving the other half
unconnected.
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