Technical and instalation
manual FLOW 38 Batch Page 17 (of 49) COMAC CAL
s.r.o.
Earthing rings
Using for a plastic pipeline or in case of metallic pipelines with internal plastic lining turned up or
pulled out to the front faces of the pipeline flanges. Conductive earthing rings of stainless steel create
conductive connection with the measured substance. Usually, potential equalization is carried out by
means of the reference earthing electrode in the measuring tube. In exceptional cases, the equalizing
currents may run through the reference electrode based on the device earthing conception. This may
lead to deterioration of the sensor, e.g. by electrochemical disintegration of the electrodes. In such
cases, it is necessary to use the earthing rings for potential equalization. This holds true for two-phase
or two-component flows in which the medium is blended badly or its components cannot be blended.
In general it can be said that using the earthing rings is always the protection against stray currents and
the warranty of correct measurement at the same time.
The flow sensor is provided with the earthing screw of stainless steel for the earthing cable supplied
with the mounting accessories. Then this cable must be conductively connected with the earthing rings.
The earthing rings are not part of our standard package and must be ordered separately. Chemical
durability of the material must correspond with the liquid to be measured; it is usually made of the
same material as the sensor electrodes. While mounting, it is necessary to insert seals in both sides of
the earthing ring and take care that no part extends to the internal profile of the sensor (whirling and
turbulence of the medium).
Electrodes
The electrode material must be selected according to chemical resistance to the liquid to be measured.
The purity of the electrodes may have an influence on measurement accuracy, their heavy foulness
may cause even the interruption of the measuring function (isolation from the liquid). It is not necessary
to clean the electrodes right after delivery before their installation in the pipeline. If the electrodes
indicate signs of foulness, clean them with a soft cloth or use a chemical cleaning agent. Mind
damaging to the lining! During routine operation, in case of a great majority of liquids, it is not
necessary to clean the flow meter for the entire operation period of the flow sensor; self-cleaning by
flow of the liquid is sufficient (recommended velocity is over 2 m/sec).
PTFE, PFA and ETFE lining
Meters with PTFE lining are equipped with protective covers to prevent the sealing surfaces from
damaging during transportation or storage and from changing the shape (due to elastic memory of
the PTFE material, it is restraightened to the tube). Protective covers may be removed only right
before the installation. If these covers are removed due to a check, it is necessary to replace them
immediately.
Carry out the installation at the lowest point of the pipeline to avoid the occurrence of vacuum. Never
detach and damage the rim of the PTFE lining turned up to the of flow sensor faces. Remove the covers
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