Flowmeter with a variable constriction

Measuring and testing – Volume or rate of flow – Proportional

Patent

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Details

7386152, 7386158, 73 3, G01F 100, G01F 500

Patent

active

055548059

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a flowmeter which is adapted to enable the total fluid flow through a conduit to be measured, this conduit being referred to hereinafter as the main conduit.
The invention can also be applied to measure the prevailing rate of flow, although for the sake of simplicity, the flowmeter will be described herebelow with reference solely to its alternative function of measuring the total fluid flow.
The invention is a further development of a flowmeter which utilizes a flowmeter constriction arranged or inserted in a section of the main conduit, a measuring conduit which extends parallel with the main conduit section and is connected across the constriction, wherein a subflow is caused to pass through the measuring conduit in response to the pressure difference across the constriction caused by the rate of flow in the main conduit section, a subflow meter connected in the measuring conduit, and an electric signal converter with associated correction unit constructed to convert a signal delivered by the subflow meter to a proportional signal which corresponds to the total flow through the main conduit and which is applied to a flow registering or flow presenting means.
It will be understood that with flowmeters of this kind, the flow measured in a measuring conduit will always have a given primary relationship with the total flow through the main conduit and a given secondary relationship with the flow passing through the flowmeter of which said conduit section forms part. This first, primary relationship is the relationship significant to the present invention.


BACKGROUND ART

Flowmeters of the aforedescribed kind are known to the art and can be referred to as "by-pass flowmeters", since a determined part of the momentary total flow through the main conduit is caused to pass through the measuring conduit and the volume of this flow is proportional to the total flow through the main conduit. These known flowmeters include a larger or smaller fixed throttling orifice in the main conduit section, and the measuring conduit, or branch pipe, connected in parallel across the constriction includes a flowmeter which delivers a signal corresponding to the flow (or rate of flow) through the measuring conduit.
For the sake of simplification, this signal is exemplified in the following description as one pulse per unit of volume passing through the measuring conduit.
A measured frequency multiplied by the volume unit can then be considered proportional to the by-pass flow or the percentage of flow through the subflow meter and therewith, with a chosen constant, also proportional to the total flow through the main conduit.
The pressure difference occurring across the throttle will increase with increasing flow through the throughflow area of the throttle and therewith drive the by-pass flow through the measuring conduit and the measuring device and through the main conduit section of the flowmeter.
It is known that a maximized, accepted pressure difference and flow rate in the measuring conduit and through the subflow meter is applicable to a maximum total flow through the main conduit.
It is also known to use the same by-pass meter for different measuring ranges, by appropriately dimensioning the cross-section of the main conduit and the size of the throttle in accordance with a chosen measuring range.
Among other things, it is necessary to afford each flowmeter with the largest possible measuring range or dynamics, as will be explained more precisely in the following.
In the case of a by-pass meter of the type intended here and described in some detail in the aforegoing, it is known that when the resistance coefficient of the throttle and the measuring conduit together with the by-pass meter are equal and the flow is turbulent, the ratio of the flow through the throttle to the flow through the measuring conduit will be constant, and that the signal delivered by the flowmeter in the measuring conduit will be proportional to the sum of both flows.
The British Patent Specifica

REFERENCES:
patent: 3252324 (1966-05-01), Steele
patent: 3554031 (1971-01-01), Turner
patent: 4459860 (1984-07-01), Walters
patent: 4461173 (1984-07-01), Olin
patent: 4524616 (1985-06-01), Drexel et al.
patent: 5333496 (1994-08-01), Fenelon

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