8
User’s Guide 2018
Electrical Connections
The first rule to be observed is that the flowmeter body and the fluid should be at the same
potential to ensure accurate measurement. Normally the grounding electrode in the flowtube
or the metal pipeline ensures that the potentials are equalised.
Certain installations however, require special consideration:
Unlined metal pipelines (fig a)
In most installations where the flowtube is installed between the flanges of an unlined metal
pipeline, the grounding electrode will be sufficient for accurate measurement.
Where the process fluid has low conductivity, or if there is a possibility of induced currents in
the pipeline, grounding rings and ground connections should be installed.
Plastic or lined pipelines (fig b)
The grounding electrode will ensure accurate measurement on flowmeters up to 150 mm in
size. Above 150 mm, additional precautions may be necessary, such as grounding rings.
NB: Ensure the grounding rings are corrosion-resistant!
Pipelines with cathodic protection (fig c)
Pipelines with electric corrosion protection are generally insulated inside and outside so that
the fluid has no conductive connection to ground. The flowtube must be insulated from the
pipeline.
NB: When installing the flowmeter, ensure that the grounding rings are insulated from
the pipe flanges on both sides of the flowtube. Grounding rings, flowtube and
measuring ground must be interconnected.
Bypass the flowtube and the grounding rings with a conductor of sufficient current carrying
capacity to pass the cathodic protection current with negligible voltage drop.
Customer supplied grounding and connecting cables must have a cross section of 6mm
2
and
be terminated with cable lugs.
SAFMAG Flowmeters require the use of a special cable supplied by FLOWMETRIX SA for
the connections between the meter body and the remote electronics display. Refer to the
connection diagram for details.
Normal electrical and safety practices should be followed when making the electrical
connections.
NB: AC supplies should not be run in the same cable as output signal. Screened
cables should be used for all measurement signals.
