Measuring and testing – Volume or rate of flow – System
Patent
1991-12-12
1994-03-08
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
System
G01F 700
Patent
active
052917800
DESCRIPTION:
BRIEF SUMMARY
This invention relates to flow meters of the non-moving part type (NMP) for measuring the flow of fluid in pipes.
It is a problem to provide flow meters of the non-moving part type which can cater for a range of flow rates and properties of fluids which are encountered, for example by the flow of domestic gas through pipes.
A conventional fluidic flow meter normally comprises only one element and difficulty may be experienced in selecting correctly sized meters to cater for large turn downs demanded by some measuring activities, such as domestic gas (400:1) or water (500:1). If the flow meter is small, the sensitivity is good at low flow rates but its pressure drop becomes excessive at high flow rates. However, if the flow meter is large, it is not able to measure low flow rates, but its pressure drop at higher flow rates is acceptable. Additionally, if the calibration of the fluidic-flow meters is non-linear, then the calibration is valid for only one fluid kinematic viscosity. Ideally the calibration is required to be insensitive to fluid kinematic viscosity, but at low flow rates it is normally not.
GB 1 453 587 discloses a flow meter of the kind using a fluidic oscillator which includes feedback loops.
In a flow meter incorporating a single fluidic oscillator, a single vortex shedding meter, or an edge-tone flow meter: ##EQU1##
Ideally, the Strouhal No. is required to be a constant so that the measured frequency relates directly to the flow rate for any given fluid kinematic viscosity.
However, if the Strouhal No. is not constant, that is to say: ##EQU2##
Therefore, with only one fluidic oscillator from which the frequency (f) is measured, it is not possible uniquely to evaluate the flow rate Q unless the kinematic viscosity (.nu.) is known. In a fluid which exhibits variable kinematic viscosity above a certain tolerance range, a single fluidic oscillator is therefore not acceptable.
According to one aspect of our invention a flow meter of the non-moving part type consists solely of first and second flow measuring means having different operating point characteristics, and the flow measuring means are connected together in series.
The flow measuring means may have either different calibration characteristics or they may be of similar geometry but of different sizes.
Since the two flow measuring means have different characteristics we can form two equations from which the flow rate and the kinematic viscosity (.nu.) can be evaluated. As the fluid in both measuring means is the same, Q and .nu. are the same in both measuring means. It follows, therefore that: ##EQU3##
The two measuring means may comprise fluidic oscillators, vortex shedding meters, edge-tone meters, or a combination of any of the three different constructions.
We are also aware of GB-A-2172996 which disclosed a flow meter comprising geometrically identical first and second fluidic elements having jet nozzles of greater and smaller opening areas, respectively, and a by-pass passage communicating with the first fluidic element in parallel with the second fluidic element, the by-pass passage including valve means adapted to open when the flow rate exceeds a predetermined value. Signals from the first fluidic element are utilized for large flow rates, and signals from the second fluidic element for small flow rates.
According to another aspect of our invention in a flow meter of the non-moving part type comprising first and second flow measuring means having different operating point characteristics and which are connected together in series, a third flow measuring means which is larger than either of the first and second measuring means, and which is connected in series with the first and second flow measuring means upstream or downstream therefrom, and a valve controlled passage connected between upstream and downstream ends of the first and second flow measuring means to by-pass the first and second flow measuring means at a given rate of flow, flow rates up to the given rate are calculated by a comparison between the characteristics of t
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patent: 4118780 (1978-10-01), Hirano
patent: 4565098 (1986-01-01), Herzl
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patent: 5005426 (1991-04-01), Lew
Mazharoglu Cetin
Thomas Paul D.
Goldstein Herbert
Kleinke Bernard L.
Potts Jerry R.
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