Uncertainty Values for metering devices are always based on the
steady state flow of the single phase homogenous Newtonian fluids
with a meter entrance velocity profile that resembles that which
is obtained in a long straight run of pipe. Departure from these
flow conditions will result in metering errors due to installation
effects. The fluid flow condition at the Flow Meter entrance necessary
for accurate measurement is referred to as the fully developed velocity
flow profile.
ISO 5167 refers to a Fully Developed Velocity Flow Profile as a
state of flow where; the actual fluid velocity flow profile resembles
the fully developed state within 5%, and the swirl angle is within
2 degrees of zero. This requirement is deemed to be acceptable for
all types of metering applications as well (AGA-3, AGA-9, AGA-7),
yet not imposing impossible restrictions on fluid flow conditions
in the pipe.
99% of flow meter applications do NOT exhibit the fully developed
fluid flow state. Piping lengths of up to 150 to 200 internal pipe
diameters are required to create this essential pipe flow condition.
The alternative is to install a CPA 50E Flow Conditioner into the
pipe. This is the most economical and accurate method to create
a fully developed flow profile in the pipe with meter runs lengths
as short as 13 pipe diameters.
