GB2312515A - Electromagnetic flowmeters - Google Patents

Abstract

An electromagnetic flow meter 60 capable of measuring the difference or sum in flow between two liquids flowing in separate pipes comprises two conduits 84,86 that are subject to the magnetic field from a pair of coils 66,68. Electrodes 70,72, and 74,76 of the conduits are connected to measuring equipment (not shown) by flexible leads 78, 80, 82, thereby to allow relative rotation of the conduits. By this means, the meter can be calibrated and arranged to provide the difference between or the sum of the two flows therethrough.

Description

IMPROVEMENTS IN OR RELATING TO FLOW METERS Field of the Invention The present invention relates to improvements in or relating to flow meters, and is more particularly concerned with electromagnetic flow meters.

Background of the Invention Electromagnetic flow meters are well known.

In such devices, the flow of a conductive liquid moving at right angles to a magnetic field generates an electric current which is proportional to the velocity of the liquid, the generated current being in a direction which is mutually at right angles to both the magnetic field and the direction of flow of the liquid.

Commercially available flow meters utilise electric current collecting electrodes made of carefully chosen material so that the electrodes are not damaged by the current. Furthermore, the magnetic field is periodically reversed so that polarisation of the electrodes is avoided.

Problem to be solved by the Invention When manufacturing photographic emulsions, the difference between respective flow rates of the silver solution (silver nitrate) and the salt solution (sodium chloride or potassium bromide) need to be accurately known to ensure that the emulsion produced has the correct proportions of these solutions.

Conventional electromagnetic flow meters can be used to provide the flow rate for each of the solutions, the difference between the two measurements being subsequently determined. However, due to the errors in the readings produced by differences in the components of each flow meter, for example, the coils providing the magnetic fields, the difference in readings obtained from the two flow meters may not be sufficiently accurate for use in the manufacture of photographic emulsions.

Floe meters for measuring differential fluid flow rates are disclosed, for example, in GB 2056691A, GB 2003274A, and US 4195515. However, these flow meters lack some versatility.

Summary of the Invention It is therefore an object of the present invention to provide an improved flow meter.

In accordance with one aspect of the present invention, there is provided a flow meter comprising: a magnetic field; two parallel flow paths located in the magnetic field and orthogonal thereto, the flow paths being formed by conduits which have liquids flowing therethrough in opposite directions, each conduit having an electrode pair formed therein which makes contact with the liquid flowing therethrough, each electrode pair being positioned to collect a current generated by the liquid flow through the conduits; support means for supporting the conduits in the magnetic field; and a flexible electrical connection formed between one electrode of each electrode pair of the two conduits which allows relative rotation of one conduit with respect to the other, the other electrode of each electrode pair being connected to provide a current indicative of the net flow through both conduits.

Advantageously, the flexible electrical connection is made between electrodes which are adjacent one another on the two conduits. This means that the difference in flow rates between the two liquids flowing through the conduits can be determined.

The relative rotation of the conduits, which may be of generally cylindrical configuration, will be appreciated to be about their respective elongate axes in order to maintain the orthogonal relationship with the magnetic field. The rotation may be small, for example for use in calibrating the meter so as to eliminate minor differences that may exist in the electrical outputs of the two conduits under identical flow conditions. The rotation, however, may be through substantially 1800, whereby the net flow measured is the sum of, rather than the difference between, the flow rates in the two conduits.

The known differential meters referred to above, whilst providing two flow channels, comprise conduits that are fixed relative to each other and require other means for allowing determination of the sum of the flow rates or calibration.

Advantageous Effect of the Invention A flow meter in accordance with the present -invention overcomes the problems associated with the prior art in that a single flow meter can be used directly to measure a difference in two flow rates.

This substantially reduces errors produced when two flow meters are used to measure two flow rates and the difference between the two flow rates is determined by subtraction of readings from two flow meters, without the need for further calculation.

Furthermore, the flow meter can also conveniently be adapted to measure the sum of the flow rates through the two conduits.

Brief Description of the Drawl gs~ For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which: Figure 1 is a sketch illustrating a simple commercially available prior art electromagnetic flow meter; and Figure 2 is a sectioned view of a flow meter in accordance with the present invention.

Detailed Description of the Invention A conventional simple electromagnetic flow meter 10 is shown in Figure 1. The flow meter 10 comprises a conduit portion 12 through which liquid to be measured (not shown) flows. Coils 14, 16 are located above and below the conduit portion 12 to generate a magnetic field in the flow meter 10.

Electrodes 18, 20 are provided in the conduit portion 12 to collect the electric current produced as the liquid flows through the magnetic field produced by the coils 14, 16 in the flow meter 10. The coils 14, 16 and the electrodes 18, 20 are arranged in pairs opposite one another with the conduit portion 12 between them. The coil pair 14, 16 isalso positioned to be orthogonal to electrode pair 18, 20 as shown in Figure 1.

In the conventional flow meter 10, shown in Figure 1, the direction of the electric current generated between the two electrodes 18, 20 will change direction if the direction of flow of liquid through the conduit portion 12 is reversed, provided the direction of the magnetic field generated by coils 14, 16 is unchanged.

Figure 2 illustrates a flow meter 60 in accordance with the present-invention. The fiowmeter 60 comprises a pair of parallel conduits 62, 64, which define two flow paths, mounted in a magnetic field which is provided by coils 66, 68. The conduits 62, 64 are generally cylindrical and are made of a suitable non-conducting material. The conduits 62, 64 are positioned to be orthogonal to the magnetic field by support means (not shown). Flow of liquid is out of the plane of the paper in conduit 62 and into the plane of the paper in conduit 64 in a similar fashion to that described with reference to Figures 2, 3 and 4 above.

Conduit 62 has a pair of electrodes 70, 72 formed in its wall. Similarly, conduit 64 has a pair of electrodes 74, 76 formed in its wall. Electrode 72 of conduit 62 and electrode 74 of conduit 64 are connected together, by a flexible electrical connection indicated as 78, to form a continuous electrode element. As shown in Figure 2, electrodes 70, 76 provide a current which is the difference between the flow rates in conduits 62, 64, electrodes 70, 76 being connected to an amplifier (not shown) by means of further flexible electrical connections 80, 82 as shown.

The flexible connections 78, 80, 82, however, allow the conduits 62, 64 to be rotated relative to one another about their respective axes 84, 86. For example, as shown conduit 62 is fixed and conduit 64 is rotatable about axis 86 as indicated by arrow 'A'. This relative rotation between the two conduits 62, 64 provides a means of adjusting the sensitivity of the flow meter 60. In some instances, it may be necessary to rotate both conduits 62, 64 about their axes 84, 86 to provide the adjustment in sensitivity.

It will be readily appreciated that any relative rotation between the two conduits 62, 64 should be small if the flow meter 60 is to operate as a differential flow meter. This is because the current generated by the flow of liquid is mutually orthogonal to the flow of the liquid and the magnetic field as described above. Such a small rotation is useful in the calibration of the flow meter.

However, in the flow meter 60, it is possible to rotate one conduit 64, for example, through 1800 so that electrodes 74, 76 switch places relative to that shown in Figure 2. This means that, although the liquid flows through conduit 64 in the same direction, that is, into the plane of the paper, the electric current generated by that flow is opposite in sign to that generated if the electrodes 74, 76 are as shown in Figure 2. In this case, the output from electrodes 70, 76 provides the sum of the flow rates through conduits 62, 64 and not the difference in flow rates.

It will be readily appreciated that a flow meter in accordance with the present invention can be utilised in a flow control system where it is desired to control the flow rate of two liquids in relation to one another, and is not limited to the manufacture of photographic emulsions.

Claims (5)

CLAIMS:

1. A flow meter comprising: means for producing a magnetic field; two parallel flow paths arranged to be located in the magnetic field and orthogonal thereto, the flow paths being formed by conduits which, in use, have liquids flowing therethrough in opposite directions, each conduit having an electrode pair formed therein which makes contact with the liquid flowing therethrough, each electrode pair being positioned to collect a current generated by the liquid flow through the conduits; support means for supporting the conduits in the magnetic field; and a flexible electrical connection formed between one electrode of each electrode pair of the two conduits which allows relative rotation of one conduit with respect to the other, the other electrode of each electrode pair being connected to provide a current indicative of the net flow through both conduits.

2. A flow meter according to claim 1, wherein the flexible electrical connection is made between electrodes which are adjacent one another on the two conduits.

3. A flow meter according to claim 1 or 2, wherein both conduits are rotatable with respect to one another.

4. A flow meter according to any one of the preceding claims, wherein at least one of the conduits is rotatable through substantially 1800.

5. A flow meter substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.