Common Questions And Answers - GF UD2100 Betriebsanleitung

UD2100 Ultrasonic Doppler Flow Meter
7.3

Common questions and answers

Question
The pipe vibrates. Will it affect the flow
meter?
The flow meter must be installed in a high
noise environment. Will this affect opera-
tion?
Will pipe corrosion affect accuracy of the
flow meter?
What effect do pipe liners have on the flow
meter?
Why is Doppler only recommended for
liquids containing suspended solids or
gases?
Can the sensor be submerged in water?
What is the purpose of the Signal Strength
Display?
Can I change the length of the sensor
cable?
32
Answer
Common vibration frequencies are far lower than the sonic frequencies used by
the GF flow meter, and will not normally affect accuracy or performance. However,
applications where very weak Doppler signal is present (when sensitivity is
adjusted to maximum and signal strength is low), accuracy may be affected by pipe
vibration, or the flow meter may show readings under no-flow conditions. Attempt
to relocate the sensor on a pipe section where vibration is reduced, or arrange pipe
mounting brackets to reduce vibration at the sensor mounting location.
GF doppler flow meters are designed to discriminate between environmental noise
and the Doppler signal. High noise environments may affect the flow meter's
performance where low signal strength and/or low flow velocities are being
measured.
Yes. Rust, loose paint etc. must be removed from the outside of the pipe to provide
a clean mounting position when installing a Doppler sensor. Severe corrosion/
oxidation on the inside of the pipe may prevent the Doppler signal from penetrating
into the flow. If the pipe cannot be cleaned, a spool piece (PVC recommended)
should be installed for sensor mounting.
The air gap between loose insertion liners and the pipe wall prevent the Doppler
signal from entering the flow. Better results can be expected with bonded liners
such as cement, epoxy or tar, however an on site test is recommended to deter-
mine if the application is suitable for a Doppler flow meter.
The Doppler sensor transmits sound into the flow stream which must be reflected
back to the sensor to indicate flow velocity. Gas bubbles or suspended solids act as
reflectors for the Doppler signal. As a guideline, GF doppler flow meters are
recommended for liquids containing solids or bubbles with a minimum size of 100
microns and a minimum concentration of 75 ppm. Most applications (except
potable, distilled or deionized water) will meet this minimum requirement.
Yes, for short periods of time or by accident, but it is not recommended for
continuous operation. The sensor is constructed to withstand submersion to 10 psi
without damage, but external liquid moving in contact with the sensor can be
interpreted as flow and cause false readings.
Doppler signals of very low strength are not accepted or processed by the instru-
ment. This feature assists in rejection of environmental noise and vibration. Use
the display to evaluate signal strength in your application. Strong signals will
increase in percentage to a maximum of 100% or greater.
Yes. GF doppler flow meter's design allow cable lengths up to 500 ft (152 m) with
no loss of signal strength. Extended cable should be installed in rigid or flexible
conduit for mechanical protection. Use only GF shielded coaxial pair cable. Cable
junctions should be made through a terminal block and housed in a watertight
metal junction box. BNC coaxial connectors (TV cable type) are not recommended
for cable splices.
Operating Instructions