Flowmetering Faults and Their Causes

With the liberalization of the gas market the demand for reliable and highly precise flowmeter installations rises. Certainly, the measuring accuracies of various measuring installations ascertained on the test bench are already quite remarkable, however, practice shows that the accuracies achieved under field conditions often are considerably lower. The reasons therefore can be categorized into three types considering measuring installations that work according to the active pressure principle (such as orifice plates, nozzles, Venturi tubes). The first category comprises all the causes that lead to a falsification of the pressure within the fluid at the pressure pulsations, respectively. All the influential factors that falsify the active pressure between pressure tappings and differential pressure transducer belong tho the second category (including the volumes within the differential pressure transducer). This group includes errors due to the compensating flows or acoustic resonances within the gauge lines. The third category finally comprises flowrate measurement erros caused by the differential pressure transducer and the follwing equipment.
After a brief explanation of the flowrate measuring via active pressure method the following article elucidates the dominant sources of error per category and documents their shapes of appearance with examples from practice. Further more different ways to avoid or to correct these errors are pointed.