In case of compressible fluids, the ratio of differential pressure divided by upstream pressure should not exceed 0.25 for reduction of error and correction of density. Metering errors caused due to wrong installation of the primary element can become considerable i.e. up to 10%. Following are the possible causes of these errors:
- the condition of the mating pipe sections
- insufficient straight pipe runs
- pressure tap and lead line design errors
In turbulent flow conditions, not more than 10% of the d/p signal could possibly be noise produced by disturbances from valves and fittings. These disturbances can be both up- and downstream of the element, and by the element itself.
To sort out this noise, a damping is provided in d/p cells which prove to be adequate for majority of the applications. Rigorous noise can be diminished by applying two or more pressure taps connected in parallel on both sides of the d/p cell.