Greyline TTFM 6.1, User Manual

Page: 58 / 79

Page 58
TTFM 6.1 Transit Time Flow Meter
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 Greyline flow meter,
and will not normally affect accuracy or performance. However, applications where very weak Transit
Time 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?
Greyline 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 sensor. 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 sensor mounting.
What effect do pipe liners have on the flow meter?
The air gap between loose insertion liners and the pipe wall prevent the Transit Time 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 determine if the application is suitable for a Transit Time
flow meter.
Why is Transit Time recommended for clean liquids?
The Transit Time sensor transmits sound across the flow stream in order to measure the time it takes to
arrive at the other sensor, and therefore requires a fluid medium that is relatively transparent to the
acoustic signal. The Transit Time system will not function when there is high volume of solids or
aeration. As a guideline, Greyline Transit Time flow meters are recommended for clean liquids with
solids or bubbles content less than 2% by volume.
Can the sensor 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 10 psi (0.7 Bar) without damage provided the
protective rubber boot is filled with Super Lube®.