4 OPERATION
22
VA FLOWMETERS
www.krohne.com 09/2022 - 4000419908 - AD VA Mech Ex Gb-Db R08 en
4.3.2 Charging non-conductive external parts by cleaning
Area limits are taken into consideration with respect to the chargeability of non-conductive
external parts under atmospheric conditions.
Devices of type VA40 for which it can be expected that combustible electrostatic charging will
occur
due to cleaning are marked with a warning label:
A cleaning cloth moistened with water, for example, should be use to clean surfaces that could
be lo
aded with a charge.
4.3.3 Process dependent charging
In variable area flowmeters, it is possible under field conditions for charge separation to occur in
the measuring tube due to the transport of non-conductive fluids and/or when the flow comes
into contact with non-conductive built-ins (e.g. liners, floats).
For all metal devices, the measuring tube and the welded on process connections form a shield
(Fara
day cage) from which the electrical field cannot escape.
In glass devices, it is basically possible for the electrostatic field generated inside the measuring
tube
to "punch through" to the outside of the device. For that reason, variable area flowmeters
need to be permanently grounded by the operator via the process connections in order to allow
discharge of electrostatic charges.
The operator is also responsible for continuing the complete grounding of the process line.
If grounding cannot be made via the process connections (plastic process connections or
undef
ined connections), the measuring device should be connected to the described ground
potential via the connection to ground. This connection only ensures the electrostatic grounding
of the device and does not meet the requirements for equipotential bonding.
CAUTION!
Attention! Risk of electrostatic charge! Do not rub!
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