Arrangement for flow measurement

Details Arrangement for flow measurement Arrangement for flow measurement

1989-11-29

1993-07-06

Goldstein, Herbert

Measuring and testing

Volume or rate of flow

Mass flow by imparting angular or transverse momentum to the...

73198, G01F 184

Patent

active

052243877

DESCRIPTION:

BRIEF SUMMARY
The invention relates to an arrangement for flow measurement.
Mass flow measuring arrangements are known which operate by means of a tube through which the fluid to be measured flows and which is set into resonant oscillation, the mass flowing through being calculated from phase shifts within this tube. The measuring inaccuracies of these arrangements become undesirably great when a heterogeneous two-phase mixture flows through the metering tube. If the measuring arrangement is installed in a line through which various fluids are pumped and if the line is in each case purged with a gas between these fluids, heterogeneous zones occur at the beginning and at the end of each fluid metering in which zones this fluid is mixed together with a part of the purge gas.
The invention has the object of minimizing the measuring inaccuracies during the time in which a heterogenerous two-phase mixture flows through the metering tube.
This object is achieved in accordance with the characterizing clause of a main claim.
Advantageous developments of the invention are described in the subclaims.
During the time in which a recognizable false measurement is provided by the mass flow measuring instrument, the measuring error is to be reduced by analyzing an artificially generated signal instead of the faulty measurement signal.
In the text which follows, an illustrative embodiment of an arrangement for mass flow measurement according to the invention is described and explained with reference to the drawings, in which:
FIG. 1 shows a basic diagram of a system in which the arrangement for mass flow measurement is used,
FIG. 2 shows a measurement signal at the starting time of a metering,
FIG. 3 shows the measurement signal from FIG. 2 at the end of the metering,
FIG. 4 shows a basic circuit diagram of the error correction circuit within the arrangement for mass flow measurement,
FIG. 5 shows a comparison of the signal output by the measuring instrument with the signal received by the counter, during the starting time of a metering and
FIG. 6 shows a comparison as in FIG. 5 but at the end of the same metering.
In FIG. 1, B identifies a container which can be supplied with various raw materials R1, R2, R3 via a line L. Between the feed lines for the raw materials and the container B an arrangement for mass flow measurement M is provided. Apart from the raw materials,R the container B can also be supplied with purge gas G via line L. This purging occurs after each metering during which a particular raw material R is pumped into the container B. The extent of each metering or purging, respectively, is determined by opening and closing valves V1, V2, V3 for the raw materials and Vg for the purge gas.
The measuring instrument Mg within the arrangement for mass flow measurement M exhibits an output signal in the form of pulses, the frequency of which changes with the mass flow through the measuring instrument. In this arrangement, frequency increases with mass.
During the beginning of a metering, initially only the purge gas is present in the metering tube of the arrangement for mass flow measurement. Subsequently, when the raw material R flows through the metering tube, a heterogeneous two-phase mixture of purge gas and raw material is present for a particular time in the metering tube and during this time, the pulses emitted by the measuring instrument do not correspond to the actual mass flow. This can be clearly seen from FIG. 2: at the beginning of the metering, that is to say of the pumping process for the raw material R, the measuring signals have a very high frequency and thus indicate a flow of a great amount of mass, whereas the signal later settles at a value which characterizes a lower mass flow. At the beginning of the metering, however, the mass flow cannot yet be as great as later since, especially at the beginning, the raw material R does not yet fully flow through the line and the metering tube because there is still purge gas in these lines.
At the beginning of metering, the high-frequency measurement signals partly re

REFERENCES:
patent: 3425274 (1969-02-01), Clement et al.
patent: 4192184 (1980-03-01), Cox et al.
patent: 4911006 (1990-03-01), Hargarten et al.

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