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5.3.2 Influences of Vibration and Pulsations
Generally, Coriolis mass flowmeters can best make measurements with minimal pipeline vibration and
pulsations. In applications where vibration and pulsations are not negligible, take the following measures:
(1) Locate the meter sufficiently away from the sources of vibration and pulsations.
(2) Provide attenuators, such as flexible tubes and chambers. However, if this meter itself is the very source
of transmitting vibration to these elements during its operation, a drift in zeroing may result.
To get around this problem, take necessary countermeasures by, for example, locating such elements of
vibration sufficiently apart from the meter.
(3) Close shutoff valves upstream and downstream of the meter at process flow shutdown. (For the sake of
preventing erratic signal generation at shutoff, be sure to prevent pressure buildup inside from exceeding
the max. allowable pressure of the meter.)
(4) If meters of the same kind are to be installed in the same tubing, locate them sufficiently apart (at least 5
times the face-to-face length across the meter) and secure each meter with sturdy supports.
5.3.3 Prevention of Cavitation
Cavitation can cause a loss of meter accuracy in measurement. Maintain line pressures that will not cause
cavitation upstream and downstream of the meter for this reason. Avoid making such an arrangement as to
open the line to the atmosphere immediately downstream of the meter. Care must be exercised particularly in
handling liquids of low steam pressure.
In practice, recommended minimum back pressure (pressure on the downstream side) of the meter is calcu-
lated by the formula:
Pd＝3ΔP＋1.3Pv
Where Pd : Downstream pressure (MPa [absolute])
ΔP : Pressure loss across the flowmeter (MPa)
Pv : Steam pressure at the temperature during measurement (MPa [absolute])
5.3.4 Prevention of Excessive Flow Rate
CAUTION:
Exceeding the meter's maximum flow rate will not significantly reduce the
meter's long term durability. However, the output will be held at 110% of the
allowable full scale flow rate.
5.3.5 Keeping the Sensor Unit Completely Filled
CAUTION:
The sensor must be filled with the process fluid during measurement.
A partially filled sensor unit results in large errors particularly at zeroing.
5.3.6 Bypass Line
For maintenance and servicing, it is good practice to provide a bypass loop.
Fig. 5.2 Bypass Line
Flow
Direction
Valve Valve
Bypass Line
Valve
ALTImass
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