GB2169414A

GB2169414A - Density measuring apparatus with electrical display

Info

Publication number: GB2169414A
Application number: GB08600157A
Authority: GB
Inventors: Walter Holzer
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-01-08
Filing date: 1986-01-06
Publication date: 1986-07-09
Also published as: FR2575829A1; DE3500335A1; GB8600157D0; JPS61204541A

Abstract

The density measuring apparatus consists of a measuring vessel (1) filled with fluid (6) to be measured, and in which a float (7) is connected to the free, flexible end of a spring (10) clamped by its other end. The flexure of the spring is recorded by at least one wire strain gauge (11, 12), the electrical signal of which is converted and displayed by a measuring apparatus (15). <IMAGE>

Description

SPECIFICATION Density measuring apparatus with electrical display The invention relates to a density measuring apparatus having a measuring vessel filled with the fluid to be measured, and in which a float is arranged at a free, flexible end of a flexible spring which is firmly clamped by its other end, the positional change of the float in the fluid being recorded and displayable as a measure of the density of the fluid.

A density measuring apparatus of the type described above is known, in which the movement of the float in the fluid is sensed contactlessly via magnetic measuring elements.

Arranged in the float is a permanent magnet which is associated with a follow-up magnet outside the measuring vessel, the follow-up magnet recording the positional change of the permanent magnet in the float. If a fluid substance to be measured fiows through the horizontally arranged measuring vessel, the float, which is completely surrounded by the measuring fluid, is raised until a state of equilibrium exists between the buoyancy, the flexural coefficient of the spring and the weight of the float.

The level adjustment of the float in the measuring vessel thus serves as a measure for the density of the fluid to be measured and is recorded via the follow-up magnet system described above.

However, a disadvantage of the known arrangement is that the follow-up magnet system for recording the positional change of the float operates relatively inaccurately. Moreover, it is difficult with the follow-up magnet system described to obtain an electrical signal which is suitable for continuous signal processing with relatively inexpensive apparatus.

Setting out from the previously mentioned density measuring apparatus, the invention has the object of further developing a density measuring apparatus such that, with substantially improved accuracy of the display, an electrical signal which corresponds to the density of the fluid to be measured can be obtained directly.

To achieve this object, the invention is characterised in that the flexure of the spring is recorded by at least one strain gauge, such as a wire strain gauge, the electrical signal of which is converted and displayed in a measuring apparatus.

An essential feature of the present invention is that at least one wire strain gauge is applied to the spring, which wire strain gauge directly records the flexure of the spring and generates an electrical signal which is suitable for further processing.

Thus, contactless recording of the position of the float is dispensed with and instead the flexure of the spring is used as a measure for the positional change of the float in the fluid to be measured. Thus, the density of the fluid can be displayed directly on an electrical display, which is only possible with the follow-up magnet systems previously mentioned with relatively expensive apparatus.

According to the subject-matter of claim 2, a wire strain gauge is preferably arranged at both the upper side and underside of the spring, and both wire strain gauges are interconnected in a Wheatstone bridge circuit so as to compensate for temperature changes of the fluid to be measured.

Advantages of this Wheatstone bridge circuit are, furthermore, that a zero point correction can be performed, and that digital level values can be set in the electrical measuring apparatus, so that certain control processes can be initiated upon occurrence of density values above or below a predetermined or required density value, values or ranges of the fluid to be measured.

So that the wire strain gauges do not themselves come into contact with the fluid to be measured, according to the subject-matter of claim 3, the wire strain gauges are surrounded by a bellows, sheath or gaiter, which prevents contact between the wire strain gauges and the fluid to be measured.

According to the subject-matter of claim 4, a high sensitivity of the measuring apparatus may be achieved by fixing the float at one end of a connection rod, the other end of which is joined to the free, flexible end of the spring. This ensures that the spring is flexed substantially even with small positional changes of the float.

A particularly simple and operationally reliable fixture may be achieved, in accordance with claim 5, by fixing the firmly mounted or clamped end of the spring in a bush, through which the electrical connections of the wire strain gauges to the measuring apparatus are led.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which the single figure illustrates diagrammatically a possible exemplary embodiment of the invention.

A measuring vessel 1 filled with a fluid 6, for example a liquid, to be measured, has on one side a connection 2-, -via which the fluid flows into the measuring vessel in the direction of the arrow 4, the fluid leaving the measuring vessel 1 in the direction of the arrow 5 at an obliquely opposite position via connection 3. Arranged in the fluid 6 is a float 7, which is movable in the directions of the arrows 17, 18 when there is a change in the density of the fluid 6 to be measured.

The float 7 is connected to one end of a rigid connection rod 8, the opposite end of which is joined at its face to the free, flexible end of a spring 10, such as a leaf or spiral spring, which is clamped by its other end firmly in the inner face of a bush 13, which is fitted tightly in the measuring vessel 1.

When there is a change in the density of the fluid 6, the spring 10 bows or flexes more or less, the connection rod 8 remaining rigid and the float 7 moving in the direction of one or other of the arrows 17 or 18.

The flexure of the spring 10 is recorded by two wire strain gauges 11, 12, one wire strain 'gauge 11 being arranged at the upper side and the second wire strain gauge 12 being arranged at the underside of the spring.

For protection of the wire strain gauges 11, 12 against the effects of the fluid 6, they are surrounded by a bellows 9, one end of which is tightly seated on the bush 13 and on the other end of which is tightly seated on the connection rod 8.

The electrical connections 14 of each wire strain gauge 11, 12 are led out through the face of the bush 13 and lead into a measuring apparatus 15, in which a Wheatstone bridge circuit is arranged, the output signal of which can be displayed directly on a display 16.

With the aid of a zeroing facility, the Wheatstone bridge circuit can be balanced and a limit value transmitter (not shown in detail) initiates follow-up controls when the measured density goes above or below a certain value.

Claims

1. Density measuring apparatus with a measuring vessel filled with a fluid to be measured, and in which a float is connected at or adjacent a free, flexible end of a spring which is secured at or adjacent its other end, the positional changes of the float in the fluid to be measured being recorded and displayable as a measure for the density of the fluid, characterised in that the flexure of the spring is recorded by at least one strain gauge gauge the electrical signal of which is converted and displayed in a measuring apparatus.

2. Density measuring apparatus according to claim 1, characterised in that a wire strain gauge is arranged at or adjacent both the upper side and the underside of the spring, and said wire strain gauges are interconnected in a Wheatstone bridge circuit so as to compensate for temperature changes.

3. Density measuring apparatus according to claim 1 or 2, characterised in that the or each strain gauge is surrounded by a bellows, which prevents contact between the strain gauge and the fluid.

4. Density measuring apparatus according to claim 1, 2 or 3, characterised in that the float is fixed at one end of a connection rod, the other end of which is joined to the free, flexible end of the spring.

5. Density measuring apparatus according to any of claims 1 to 4, characterised in that the spring is a leaf spring or the like, and the firmly clamped or otherwise secured end of the spring is fixed in a bush through which electrical connections of the or each strain gauge to the measuring apparatus are led.

6. A density measuring apparatus substantially as hereinbefore described with reference to the accompanying drawing.