Instruction Manual
Where the SDM-CVO4 is going to be used in applications where the potential
difference between the datalogger and the output terminals exceeds 50 V RMS
AC, 74 VDC then careful consideration has to be taken to ensure safe operation
and compliance with local safety regulations. For such applications Campbell
Scientific does not supply the device as a stand-alone device which will meet all
safety requirements. The SDM-CVO4 is supplied as a component for the user to
install in a system that is, itself, designed to comply with such regulations. The
following guidance is given to help users meet the requirements of such
regulations.
The SDM-CVO4 is designed such that the internal safety barrier meets the
requirements of BS EN 61010-1 (similar to IEC 950). However, the method of
wire connection and earthing facilities prevents the unit being claimed as
compliant with such standards, when supplied as a stand-alone unit.
To meet the safety requirements of most countries, wires carrying hazardous
voltages, terminated in screw terminals must be housed in an enclosure requiring a
tool to open it, and the enclosure must have international symbols on the outside
warning of high voltages. An additional warning label, in the local language, may
be required stating that the source of hazardous voltage must be turned off before
the enclosure is opened.
The exact nature of the enclosure is covered by the standards, but an enclosure
designed to house electrical equipment will usually meet the requirements.
Campbell Scientific's ENC 12/14 or 16/18 enclosures meet these requirements if
fitted with a padlock and with the correct labels on the door.
It is also necessary to ensure that metal parts on the outside of the enclosure that
might come in contact with active high voltage circuits are connected to a safety
ground. The ground lug of Campbell Scientific enclosures is the main issue for the
above enclosures, but this would, in any case, normally be the point of contact to a
good ground point.
Cables that connect to the output of the SDM-CVO4 should have adequate strain
relief at the point of exit from the enclosure, and the cable and any connectors
used should be rated to a high enough voltage and assembled in a safe fashion.
If possible, the external device which is operating at a high voltage relative to
ground should be configured with an earth leakage breaker system to disconnect it
from the voltage source in the event of a breakdown of the insulation in the
system causing a leak to ground.
With a system made to the above requirements the maximum recommended
continuous operating voltage between the datalogger and input is 240 VAC. This
value is derived from the voltage rating of the terminal blocks used and an internal
suppression capacitor (see below).
The unit is designed to withstand a transient flash test of 1500 V RMS AC, for
two seconds. However, you need to be aware of some aspects of the design which
can influence the results of such a test if made.
a)
To help suppress emissions of electromagnetic interference the isolation
barrier is bridged by a 1nF, class ‘Y’ safety capacitor. This 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
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