ABSTRACT
Initial installation is often so poorly undertaken that many flowmeters never meet manufacturer's stated accuracy. The data supplied by most manufacturers is based on steady flow conditions and installation in long straight pipes both upstream and downstream of the meter. In practice, most meter installations rarely meet these idealised requirements – with bends, elbows, valves, T-junctions, pumps, and other discontinuities all producing disturbances that have an adverse effect on the meter accuracy.
Both swirl and distortion of the flow profile can occur – persisting for distances of up to 100 pipe diameters from a discontinuity whilst in excess of 150 pipe diameters can be required for a fully developed flow profile to form.
Attention must be paid to correct torquing since either over-tightening or under-tightening of the flange bolts can produce leakage and, in some extreme cases, damage.
Another installation issue with regards to EM flowmeters is correct earthing/grounding of the primary head and pipeline by any one of the number of methods. Improper grounding is one of the most frequent causes of problems in installations. If the grounding is not symmetrical, ground-loop currents give rise to interference voltages – producing zero-point shifts.
