AUF610 Series Operation Manual
OP610.1.1.5R1ENG
32
Transitional Flow –
Transitional flow is the region of flow when laminar becomes turbulent and vice versa.
Hydraulic characteristics are very hard to predict in this regime. A Reynolds number between-3000 – 8000
usually characterizes it.
Turbulent Flow
- Turbulent flow is the flow regime characterized by chaotic, stochastic property
changes. This includes low momentum diffusion, high momentum convection with rapid variations in
pressure and vector velocity in space and time. A flow with a calculated Reynolds number above 6000
will be turbulent.
Turndown Ratio –
Is the ratio of the maximum to minimum measured process variable between which the
instrument performs to its published specification. Example: If a flow meter has an uncertainty of better
than 2.0% (R) when it measures from 10 USGPM to 150USGPM the actual turndown is 15:1.
APPENDIX II
Understanding Measurement Uncertainty
As we can see from this manual the Ultra Sonic flow Meter can be a very powerful instrument. It can install
on the outside of most pipes and will in most cases, measure the flow inside, sight unseen, with an
uncertainly of better than 2.0 % (R). However, like all instrumentation the resultant reading is only as good
as the configuration data used to set the instrument up and the transducer installation. There are many
potential variables that can negatively impact the integrity of the measurement. Fortunately, with a little
planning and care most outside influences can be mitigated. Further more the instrument has many
troubleshooting features and measurements that allows the user to track down issues that may be
affecting optimum performance.
Pointers to Be Aware of:
•
Accurately determine the pipe dimensions. Is the pipe indeed round? Have assumptions that were
made about the pipe size, diameter and wall thickness correct? Is the pipe perfectly circular? Plastic
pipe has been know to go out of round.
•
Be sure of the pipe material.
•
Be sure of the process. Know the process composition, viscosity and temperature in advance or be
able to determine it at site. Is it what you expected?
•
Observe environmental factors. Hot Sun, vibration in the pipe, flow characteristics, electrical noise.
•
Observe the system dynamics, including the pump, its position and the location of other flow
disturbance inducing obstructions.
•
What is the flow profile? Reynolds Number?
Measurement Uncertainty analysis is both a science and an art, but primarily a science. It consists of two
error components, the random error and the systematic error. The random error is the error inherent to the
basic instrument’s measuring technology. The systematic error is the error added by the installation. As an
example, in perfect conditions, just out of the box, an instrument’s measurement accuracy (measurement
uncertainty) specifications cannot exceed the values listed on the published specification data sheet. If it is
incorrectly installed those values will degrade from the above described optimum situation specification.
Understanding the complete system (including the hydraulics of the process, the flow meter, the receiving
instrument for the flow meter & the customer’s expectations etc.) will go a long way to ensuring a
successful installation.
