Campbell Hausfeld 4-Channel Current/Voltage SDM-CVO4 - Manual (Page 14)

SDM-CVO4 4-Channel Current/Voltage Output Module
4.2.3 Shield and Ground Connections
It is generally advisable to used shielded (screened) cable when connecting the
output to any remote system to reduce the chances of noise pickup. The shield
will only be effective if it is connected to a good ground reference point.
As a result of the isolation barrier in the SDM-CVO4, the ground terminals
associated with the output connector of each channel cannot be considered as good
ground reference points. Therefore it is advisable to make the connection of the
screen to a good ground point at the remote system rather than the
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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