Campbell Scientific SDM-CVO4 4-Channel Current/Voltage Output Module - Manual (Page 16)

SDM-CVO4 4-Channel Current/Voltage Output Module
is rated to withstand a 2700V, 2 second flash test, but will fail if
exposed to voltages in excess of 240 V RMS for long periods.
b) To provide protection from transients and static for this capacitor and
the opto-isolation component that bridges the barrier, there is a spark
gap across the barrier that has a 2500 VDC nominal breakdown
voltage. If this device is at the low end of its tolerance band (±10%),
combined with the normal tolerance of flash test devices, then the
spark gap could fire during a 1500 VAC flash test, which may cause
an indication of failure. Testing at a slightly lower voltage will
confirm whether there is a true fault or not.
If you have any doubts about the safety of your installation please first seek
advice from your local safety advisor and then Campbell Scientific if you
require further technical details.
To ensure safe and correct operation, the SDM-CVO4
must be installed where there is no risk of water ingress or
condensation. CAUTION
5. General Principles of Use
5.1 Voltage or Current Signaling
Where the SDM-CVO4 is being used to retransmit measured values from
sensors to remote displays or measurement systems, the datalogger program
would normally follow the process of taking measurements and writing the
measured values into input locations using the same principles as given in the
manuals for those sensors.
The measured values would then be scaled using the processing instructions of
the datalogger, using either Instructions 37 and 34 or Instruction 53 (if
available in your datalogger). Prior to scaling, or during the scaling
calculations, the values relating to the four channels of the SDM-CVO4 will
normally be written into four new sequential input locations, both to match the
required inputs for Instruction 103 and also to preserve the original
measurement values for other purposes.
Instruction 103 would then be executed at the same rate as the measurements
have been made, to transmit the settings to the SDM-CVO4 and cause the
outputs to be updated at the same rate. As the required output levels are held in
a digital form in the SDM-CVO4, there is little advantage in sending data more
frequently – the only benefit being that it would recover more quickly in the
event of a loss of power.
5.2 Providing Excitation Supplies to Sensors
As mentioned in the introduction to this manual, one application for this device
is to provide an excitation to a sensor or sensors that are to be measured by the
datalogger. This may be considered where a sensor requires a precise voltage
or current excitation which cannot be provided by the datalogger itself, or
perhaps where exciting the sensor from the datalogger or its power supply
would cause a common-mode measurement problem. An example of the latter
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