RMG ERZ2000-NG, Operating Manual

Page: 221 / 454

6 Flow meters
Manual ERZ 2000-NG · EN07 · 2019, May 13th
211
Other manufacturers have, in part, implemented different path arrangements; howev-
er, the further expansion is normally carried out in a similar manner.
The individual mean path speeds are weighted and add up according to the Gauss
quadrature. Multiplication by the pipe cross-section produces the volume flow.
Quality of the installation situation
Ultrasonic meters provide parameters which permit an assessment of the installation
situation. If the values are in the specified ranges, good measuring conditions can be
assumed. If the values are outside of the specified ranges, disturbed flow conditions
could impair the measuring accuracy.
Turbulence
Based on the prevalent flow, particularly the turbulence, characteristic scattering oc-
curs (variance
ߪ
௜
) in determining the individual path speeds (
i
=1..6; number of ultra-
sonic measuring paths) which can permite an evaluation of the installation conditions.
The average turbulence (
Tu
i
) over the ultrasonic measuring path is calculated:
ߪ
௜
ൌ ඩ
ͳ
ܰ െ ͳ
෍൫ݒ
௝ǡ௜
െ ݒlj
௜
൯
ଶ
ே
௝ୀଵ
ר ݅ ൌ ͳǤ Ǥ͸ Ǣ ᩸ ܰ ൌ ʹͲ
ܶݑ
௜
ൌ
ߪ
௜
ȁݒlj
௜
ȁ
Where:
ݒlj
௜
The average speed over time along the ultrasonic measuring path
ݒ
௝ǡ௜
Flow speed along the ultrasonic measuring path
ܰ
= 20; number of measurements for the turbulence calculation
Typical values for very good flow conditions for middle paths are at 2-3 %; the turbu-
lence for outside paths increases to up to 4 %. If these values above 10 %, disturbed
flow conditions could impair the measuring accuracy. The turbulence calculation is
switched off with the lowest speeds.