Influence Of Vibration And Pulsation; Prevention Of Cavitation; Prevention Of Excessive Flows; Prevention Of Gas Mixed Flows - Oval ALTI mass CA00A Instructions Manual

L -- 740 -- 28 -- E

6.4.2 Influence of vibration and pulsation

Generally, Coriolis mass flowmeters can best perform in measurements with least pipeline vibration and
pulsation. In applications where vibration and pulsation are not negligible, the following considerations
must be taken into account:
(1) Locate the meter sufficiently away from the sources of vibration and pulsation.
(2) Provide attenuators, such as flexible tubes and chambers. However, if these elements are caused to
vibrate by the drive of the flowmeter, take measure such as keeping these elements away from the
flowmeter to avoid zero shifts.
(3) Close shutoff valves upstream and downstream of the meter at process flow shutdown. (This is
to prevent erratic signal generation at shutoff. Bear in mind, however, 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 pipeline, locate them sufficiently apart (at
least five times the face-to-face dimension of the meter).

6.4.3 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 high steam pressure.
In practice, recommended minimum backpressure (downstream pressure) of the meter is calculated by
the formula:
where Pd: Downstream pressure (MPa [absolute])
ΔP: Pressure loss across the flowmeter (MPa)
Pv: Steam pressure of the liquid at the temperature of measurement (MPa [absolute])

6.4.4 Prevention of excessive flows

CAUTION: Exceeding the meter's maximum flowrate will not significantly reduce the
meter's long term durability. Bear in mind, however, that the output will be
clamped at 110% of the allowable full scale flowrate.

6.4.5 Prevention of gas mixed flows

Slug flows (gases exist in the process liquid) are generally not measurable at a high degree of accuracy.
It also causes erratic pulse generation at shutdown of the flow.
This transmitter is capable of detecting gas mixed flows. On finding the result of densitometer
measurement exceeding 0.3 to 2g/mL (default setting for liquid measurement), the meter interprets it as a
slug flow and reduces the instant flowrate to zero, interrupting the flow output.
For gas measurement, default setting is 0 to 10g/L so that gas mixed flow detection function is disabled.
For details about setting and operation of the gas mixed flow detection function, see 9.17 Gas Mixed Flow
Alarm.

6.4.6 Keeping the sensor filled with process liquid

CAUTION: The sensor must be filled with the process fluid during measurement.
A partially filled meter results in large errors particularly at zeroing.
[Reference]
For models CA100 to CA250 installed on the horizontal pipeline, it is difficult to wash away air bubbles in
the flow tube at flow rates below 10% of Max. service flow rate (water used as the metered fluid). In such
cases, run the fluid at flow rate greater than 10% of Max. service flow rate first, then adjust the flow rate
to the required rate.
Even with the flow rate greater than 10% of Max. service flow rate, it will take approx. 40 seconds to
completely fill the flow tube from its empty state (water used as the metered fluid).
Expansion of the process fluid due to freezing may damage the measuring pipe. Take measures to
prevent process fluid from freezing.

Pd = 3ΔP + 1.3Pv