FP-4400 PORTABLE CLAMP-ON ULTRASONIC FLOW METER
ONICON Incorporated 727.447.6140
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SECTION 5.0 COMMON QUESTIONS AND ANSWERS
The pipe vibrates. Will it affect the flow meter?
Common vibration frequencies are far lower than the sonic frequencies used by the transit time flow meter, and will
not normally affect accuracy or performance. However, applications where very weak 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.
The flow meter must be installed in a high noise environment. Will this affect operation?
ONICON’s transit time flow meters are designed to discriminate between environmental noise and the transit time signal.
High noise environments may affect the flow meter’s performance where low signal strength and/or low flow velocities are
being measured. Relocate the sensor in a quieter environment if possible.
Will pipe corrosion affect accuracy of the flow meter?
Yes. Rust, loose paint etc. must be removed from the outside of the pipe to provide a clean mounting position when
installing a transit time transducer. Severe corrosion/oxidation on the inside of the pipe may prevent the transit time
signal from penetrating into the flow. If the pipe cannot be cleaned, a spool piece (PVC recommended) should be installed
for transducer mounting.
What effect do pipe liners have on the flow meter?
Typically, there is little to no effect of a well-bonded liner such as cement, epoxy, or tar inside the pipe. Should there be an
air gap between loose insertion liners and the pipe wall, this will prevent the transit time signal from entering the fluid. An
on-site test is recommended to determine if the application is suitable for a transit time flow meter when an unbonded
liner is possible.
Why is transit time recommended for clean liquids?
The transducers transmit sound across the flow stream in order to measure sound velocity and therefore requires a
fluid medium that does not significantly attenuate the ultrasonic signal as it travels through it. The transit time system
will not function when there is high volume of solids or aeration. As a guideline, ONICON transit time flow meters are
recommended for clean liquids with solids or bubbles content less than 2% by volume. Most applications such as water,
chemicals and oils will meet this minimum requirement. When in doubt, an on-site test is recommended to determine if
the application is suitable for transit time.
Can the transducers be submerged in water?
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 1m depth for 30 minutes without damage. Plastic seal jackets and BNC
connectors on the sensor cables should be filled with coupling compound to provide additional moisture protection for
the BNC connectors.
What is the purpose of the Signal Strength Display?
The primary function of the signal strength display is to assist as feedback when mounting transducers. Signal Strength
can also be a useful diagnostics tool when troubleshooting problems with an installation. A signal strength less than 100%
may indicate a problem with the installation or other issues such as a mis-programmed pipe size, pipe material, fluid type
or temperature, or wrong transducer spacing. A signal strength less than 100% may also simply indicate a lot of aeration,
or deteriorated pipe. Consideration should be made to use a 1 cross installation in such a case.
Does the FP-4400 require periodic recalibration?
FP-4400 calibration does not normally drift over time. ONICON offers a calibration service to verify instrument accuracy.
Please use the contact information on the subsequent pages to set up a RMA.
ISO 9001 or similar quality management systems may require periodic and verifiable recalibration of flow meters. FP-
4400 Flow Meters may be returned to ONICON Measurement for factory calibration and issue of a new NIST traceable
certificate.
Can the internal batteries be replaced?
The built-in rechargeable LiPo battery pack is not user-serviceable. The meter should be returned to ONICON for battery
service. Significant harm could occur to the user or property if the lithium battery is damaged, so do not attempt to
operate the meter outside of our recommendations.