Campbell Hausfeld 4-Channel Current/Voltage SDM-CVO4 - Manual (Page 18)

SDM-CVO4 4-Channel Current/Voltage Output Module
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 Signalling
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 problem is where
the sensor outputs are not within the common-mode voltage that the datalogger
will accept (±2.5 V for the CR10X).
Careful consideration should be made before using an SDM-CVO4 for such a
function. Not only is it a relatively expensive method, but it can also result in a
less accurate method of sensor measurement (compared to when the datalogger
excites the sensors directly) if the precision of the output is critical to the sensor
accuracy.
The reason for this is that direct datalogger excitation is a ratiometric
measurement whereby any drift in the excitation output of the datalogger is
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