If the flow fluid of some parameters such as pressure, velocity and density change and transformation in a row, explosive changes, we will call the flow pulsation flow.
In almost total in the industrial production of pipe flow is resistance stability, both under the laminar flow turbulence, those conditions there is always the internal and external environment of various kinds of interference from the fluid.
Pulsating flow measurement accuracy of instrumentation effects occur, serious when a measured value distortion, so in the process of industry for the liquid medium flow pulsation of the flow measurement precision influence to attach importance to it.
Embellish of instrument science and technology is engaged in production of turbine flowmeter, * * for many years, has been to the research and development and production of the turbine flowmeter to maintain the original understanding, also accumulated a lot of useful in production practice experience, this paper is to introduce the periodic pulsation flow analysis of the impact of turbine flowmeter measurement precision, the reference for the broad masses of users.
1, the pulsating flow measurement of empty way ripple everywhere at all times, but it is difficult to measure.
Can directly measure pulsating flow is almost no, we only measure the pulse * to parameters, such as amplitude, frequency and waveform, etc. , then elucidated the pulse from these parameters might bring what kind of impact to the instrument output.
Even measure the parameters of the pulse is uncertain to really accurate analysis, basic way is to use a few especially instrument for pipe flow fluid acoustic expound to measure the pulse parameters.
If the production process of the pipeline fluid pulsation frequency is low, also can not meet the pipeline flow meter
s and pressure transmitter has assembly can use frequency limit, from the output of the pressure gauge pointer swing can detect the existence of the pulse.
But to realize pulse of each parameter value need specific measurements.
The research found that pulse related to flow velocity and has nothing to do with the static pressure.
Thus, available measurement qVrms/qV (
QVrms is large volume flow pulsation value;
QV is the average of the volume flow of)
To realize pulse situation.
The following is a measurement qVrms/qV way: (1) measuring pulse amplitude, can assume VRMS/v≈
QVrms/qV, average flow velocity v refers to the tube, VRMS is big pulsating quantity of tube flow velocity.
Can be close to the flow meter in the pipe insert the upstream a thermal anemometer probe (
Hot wire or thermistor)
With an online intends to show the square of the velocity fluctuation quantity machine.
(2) when the flow meters close to the pulse source (
Such as where are smaller than the wavelength of the pulsating quarter)
Pulse amplitude and pulse source.
Can from the volume of a pulse source, such as rotation speed change could estimate the amplitude.
Although this method is not very reasonable, but it does not need to use other instrument.
(3) if the flow meter is a differential pressure meter, to export pulse amplitude, is measured at austerity device of differential pressure pulsation amplitude & Delta;
PPS the results will be used to roughly expect the pulsation amplitude.
This value is along with the change of pulse frequency changes, from the following equation can be launched qVrms/qV big possible values: qVrms/qV≤
PPS type: & Delta;
PRMS is the power of differential pressure pulsation, & Delta;
PPS for the steady state flow measure differential pressure.
Elucidating the flow transmitter output spectrum of primary data, so as to take the pulse conditions.
Assume that pulsating frequency is not far beyond the corresponding range of flow transmitter, so in the spectrum of the output signal, theory by using Fourier spectrum instrument can measure pulse frequency.
2, periodic pulsation flow influence on turbine flowmeter measurement precision of explanation by 2.
A mathematical model of fostering and the dynamic characteristics of turbine flow meter when the pulsation frequency beyond a certain range, the measured value of the turbine flowmeter is bigger mistakes will happen.
Mistakes will have the following several aspects: the origin of * resonance of the rotor blades, gear meshing (
Flexible output of the turbine meter)
And gear, the rotation inertia, the shape of a pulsating flow, shaft friction resistance, etc.
Because the total pulse is composed of sine wave superposition, so that from the exposition of sine pulse impact on the measured value of the turbine flowmeter to elucidate the influence of the periodic pulse situation.
Theory and indicates the action to participate in sinusoidal unchanged to the system, the response under the condition of special riot is similar frequency sinusoidal output, but the amplitude and phase is determined in the specific system dynamic characteristics.
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