FR2479978A1 - Electrode assembly for fluid flow measurement - comprises two isolated electrodes between which rotor blades pass, causing variations in resistance - Google Patents

Abstract

The appts. uses a rotor blade which passes adjacent to electrodes to produce periodic variations between the electrodes due to changes in resistance of the fluid. This allows a counter to be calibrated. An axial turbine water counter comprises a tubular body (20) in which a turbine (21) rotates on a shaft (22) held by two supports (23). The supports are mounted on housings (25) of electrically insulating material attached to the body by webs (26). Two isolated electrodes (30,31) are fixed in a housing so that the blades of a rotor (27) pass between them. The electrodes are connected into an electronic measuring circuit to detect the variations in electrical resistance and for subsequent conversion into speed flow measurements.

Description

Pulse emitter flow meter for conductive fluids and application to meter calibration.

The present invention relates to the measurement of flow rate of conductive fluids, and more particularly to a flow meter equipped with an emitter of electrical pulses.

 There are different means for remotely transmitting information on the number of revolutions made by the rotor of a flow meter such as a speed meter for example, these means generally consisting of adding to the meter a rotation sensor which can be of the photoelectric or magnetic type, or even a self-generating device of signals of the electromagnetic type.

The addition of such a rotation sensor involves modifying the measurer to incorporate into the rotor or the moving equipment an additional element intended to cooperate with a fixed element of the rostation detector, the modification being even more significant in the case of '' a self-generator.

The invention relates to a conductive fluid meter whose disadvantages are minimized by taking advantage of the conductivity of the fluid to detect in a simple manner the rotational movements of an electrically insulating rotor.

The meter, according to the invention, in which a rotor with blades of electrically insulating material is mounted to be rotated at a speed depending on the flow rate of the fluid to be measured, is characterized in that it comprises - two isolated electrodes arranged in the vicinity of the passage of the blades
of the rotor and connected in operation to a source of potential
electric so that the rotation of the blades produces va
periodic variations in the electrical resistance of the fluid between the
two electrodes, and
means for detecting and means for counting said variations
resistance periodicals.

A particular application of the invention relates to water meters known as speedometers whose turbine is by construction, according to current technology, most often made of insulating plastic material. The resistivity of the water being of the order of 2 to 3000 Rcm, it suffices to have near the passage of the blades of the turbine of the meter two electrodes passing through the injection box of electrically insulating material, for example if it is a multi-jet counter, for collecting on two wires connected to these electrodes periodic variations in electrical resistance at a frequency proportional to the speed of rotation of the rotor, that is to say to the flow rate. Indeed, the sheet of conductive liquid located between the electrodes has a variable geometry with the relative position of the blades of the insulating turbine. As these blades, the number of N, are regularly distributed on the shaft of the turbine> the electrical resistance R measured between the two electrodes is the same for all the angular positions of the turbine spaced by 2 rI / N. The relative LLR modulation is also independent of the resistivity of the fluid,
R and all the greater as the insulating blades of the turbine more completely mask one electrode with respect to the other. It was thus possible to obtain variations 6 R of the order of 5 to 30% depending on the mode
R of realization adopted.

A circuit for processing the electrical signals collected between the electrodes makes it possible to convert the periodic resistance variations into pulses which can be sent to a distant totalizer while requiring only a very low consumption of the order of a few tens of microamperes, which which gives the possibility of using a long life battery making the meter autonomous.

In the case where the chamber in which the rotor of the measurer rotates is partially metallic, such as for example the housing of a single jet water meter, the electrodes can be mounted on an insulating wall of the chamber, for example on the plate generally made of insulating plastic material closing the chamber, in a location as far as possible from the metallic masses with which the fluid is in contact to avoid the influence of the short circuit created by these metallic masses.

If the space available allows, one can also mount on the rotor shaft of the measurer a small auxiliary rotor made of insulating material with flat blades and provide two electrodes arranged one opposite the other so that the rotor blades auxiliary periodically pass between these electrodes during their rotation.

 It is interesting to note that the modifications to be made to the rotor of the measurer are zero, or unimportant in the case of the auxiliary rotor, and that those to operate on the fixed part of the measurer are limited to the mounting of two isolated electrodes, which can be carried out without difficulty, for example by drilling.

The invention thus allows the realization of a flow meter and a transmitter of its remote indications in a space-saving form, easily adaptable to existing meters and whose low consumption of electrical energy allows, using 'a battery, to make its installation autonomous.

Another application of the invention aims to reduce the duration of calibration of multi-jet water meters in which the first needle of the totalizer rotates at slow speed due to the significant reduction gear inserted between it and the shaft. the meter turbine. By providing for the temporary adaptation, during calibration, of an electrode rotation detector directly on the turbine of the meter, it is possible to reduce the calibration time in a significant ratio.

The invention will be better understood by referring to the description which will follow in relation to the appended drawing which represents, by way of nonlimiting examples, different embodiments in accordance with the invention. In this drawing - fig. 1 represents a mode of application of the invention to a comp
water sprayer of multijet type.

- fig. 2 represents another mode of application of the invention to a
water meter of the axial turbine type.

- fig. 3 is a plan view of the auxiliary rotor of the pre figure
cedent.

- fig. 4 is an example of an electrical signal processing circuit
triques collected across the electrodes.

- fig. 5 shows another mode of application of the invention to a
single jet type water meter.

- figs. 6 and 7 schematically represent the assembly of several
pairs of electrodes in bridge circuits.

- fig. 8 schematically represents an application of the invention
the calibration of a multi-jet counter.

In fig. 1, there is shown schematically in cross section the injection boot 10 of a water meter with multiple jets (shown in broken lines) inside which is mounted a rotor 11 with straight radial blades 12 for turning- around an axis 13. The injection boot 10 is made of insulating plastic material and in the space separating two injection or evacuation channels 14 are mounted on the internal wall two electrodes 15,16, for example of a few tenths of a mm in diameter and at a distance from one another of the order of several mm. These electrodes are connected by insulated wires 17 passing through holes in the box 10 to a processing circuit 18 in the body of the meter, or outside the meter, an exemplary embodiment of which will be given later in FIG. 4.

We see that in the position of the rotor 11 shown in solid lines in the figure where a blade 12 is in the space separating the two electrodes 15,16, this insulating blade introduces an additional resistance on the path through the conductive liquid between these two electrodes, while in the position of the rotor 11 shown in dashed lines, there is a direct conductive path through the liquid between the electrodes.

Thus, by connecting the electrodes to a source of potential included in the circuit 18, relative variations in the resistance at the terminals of these electrodes which occur at the rate of passage of the blades 12 of the rotor 11, that is to say say proportional to the speed of rotation of the rotor and finally representative of the flow of liquid passing through the meter.

Fig. 2 shows another embodiment applicable to an axial turbine water meter and using an auxiliary rotor made of insulating material, the blades of which pass periodically between two electrodes. In this figure, we see in the tubular body 20 of the meter a turbine 21 which can rotate around a shaft 22 coaxial with the body 20 and held by two bearings 23. These bearings are mounted in two fairings made of electrically insulating material 24.25 connected to the body 20 by ribs 26 on either side of the turbine 21. Inside the upstream fairing 24 is fixed for example at the end of the shaft 22 a small auxiliary rotor 27 with flat blades 28 in form of circular sector, for example three in number, as shown in fig. 3 which is a plan view of this rotor 27. Two isolated electrodes 30, 31 are also fixed on the fairing 24 so that the blades 28 of the rotor 27 pass between these two electrodes during the rotation of the rotor 27. As before , the electrodes 30, 31 are connected by insulated wires passing through the body 20 to a processing circuit 32 outside the meter, and detect the resistance variations introduced periodically by the passage of the blades of the rotor 27 between them.

Although this assembly requires the addition of an additional element on the moving element of the counter, it has the advantage of providing greater relative variations in resistance, of the order of 30%, than the assembly of FIG. 1 due to the complete masking of the electrodes relative to each other by the blades of the auxiliary rotor.

If the wall supporting the electrodes is not itself insulating, it is possible to use an electrode-carrying element made of electrically insulating material in the shape of a U, the electrodes facing each other on the respective branches of the U between which the auxiliary rotor passes.

Fig. 4 shows an example of an electrical circuit usable for processing the rotation detection signals collected at the terminals of a pair of electrodes and converting them into counting pulses. This processing circuit 40 is composed of an oscillator 41 providing oscillations for example at a frequency of 1000 Hz, of an operational amplifier 42 in the circuit of which the two electrodes A, B are connected, between which the variable resistance 43 of conductive liquid, of a full-wave rectifier circuit 44 and of an amplification and shaping circuit 45 supplying counting pulses at its output, these circuits 44 and 45 being of usual design and not requiring any special description.

The output of the oscillator 41 is connected to the non-inverting input of the amplifier 42 whose role is to supply an approximately constant current in a feedback circuit comprising the resistor 43. The amplifier 42 includes several feedback links: between its output and its inverting input, a first connection comprises a usual resistance 46, and a second connection comprises, in addition to the resistance 43, preferably due to two capacitors 47, 48 mounted on the side and other of this resistor 43 and intended to stop the DC component which would otherwise pollute the electrodes
A, B and would tend to damage them, as well as another resistance 49. A third counter-reaction link comprising an adjustable resistance 50 and another resistance 51, connects the common terminal to the elements 48, 49 to the non-inverting input of the amplifier 42. All of these feedback links are arranged so that the variable resistance 43 existing between the electrodes A, B in the conductive liquid is traversed by a quasi-constant current. The resistor 50 makes it possible to adjust the gain of the amplification.

There is thus collected at the output of the amplifier 42 a voltage 51 substantially proportional and well representative of the variable resistance 43 between the electrodes A, B, this voltage being modulated on a carrier at 1 kHz supplied by the oscillator 41. The circuit of full wave rectification 44 suppresses the carrier oscillation and produces low frequency oscillations 52 - proportional to the measured rotor speed - which are then converted in circuit 45 into pulses capable of being totalized in a display device, for example with liquid crystals, which can be distant from the circuit 40 and on which the flow rate or the consumption of measured liquid is read. The circuit 40 is advantageously produced in the form of a microcircuit incorporated in the case of the liquid counter considered.

Fig. 5 also shows a variant of the arrangement of the electrodes of FIG. 1 in the case of a single jet counter 60, where the rotor 61 rotates in a metal enclosure 62, but closed by a plate made of insulating material 63. The electrodes 64, 65 are mounted on this plate 63 in a zone not too close to the metallic mass of the enclosure, so that the rotor blades influence the conductive path between the electrodes as in the case of FIG. 1, for example symmetrically with respect to a diametrical plane of the enclosure 62 and at a distance from the axis of rotation of the order of 2/3 of the radius. Electrodes too close to the metal enclosure would no longer be sensitive to resistance variations due to the rotor blades due to the short-circuit path created by this enclosure in their vicinity.

Other embodiments of the invention can also consist of the use of two pairs of electrodes diametrically arranged with respect to the axis of the rotor of the meter under consideration, and alternately masked and unmasked. one opposite the other by the blades of an insulating rotor.

In fig. 6, two pairs of electrodes 71 and 72 are respectively mounted opposite one another on the branches of two stirrup-shaped supports 73,74. The rotor 75, the plane blades of which pass alternately through their rotation between the electrodes of each pair 71, 72 is an insulating rotor of the kind of that of FIG. 3, with an odd number of blades. The resistors between these two pairs of electrodes are connected in the arms of a bridge circuit 76 with two other fixed resistors 77,78 external to the liquid 70, for example a Wheatstone or Kohlrausch bridge, fed on a diagonal by a alternating current source 79, and the rotation detection signals are collected across the other diagonal of the bridge. The resistance of the liquid is then maximum between the pair of masked electrodes while it is minimum between the pair of unmasked electrodes, in this way a modulation depth of the alternating carrier wave is obtained which is substantially double that provided by a pair of electrodes alone.

On the assembly shown in fig. 7, a first pair of electrodes 81, 82 is used, these electrodes preferably being arranged symmetrically on either side of an insulating rotor 83, wedged as previously on the shaft of the measurer, but not nearby immediate blades of this rotor, for example at a distance of about a centimeter.

Each electrode 81.82 is in fact a double electrode, that is to say brought to the same potential, but made up of two point electrodes 811.812 and 821.822 separated by an insulating sheath 84.85 respectively. In the immediate vicinity of the rotor 83, that is to say at a distance of the order of a millimeter, two other electrodes 86, 87 are arranged on either side of the blades of this rotor, for example, but not necessarily , roughly aligned with the electrodes 811, 821 and 812, 822 in the liquid 80. The electrodes 81 and 82 are, as in the previous case, connected to a source of alternating potential 88, and the following resistors, inside the liquid 80.
R1 (fixed) between electrodes 811 and 86
R2 (fixed) between electrodes 822 and 87
R3 (variable) between electrodes 812 and 87
R4 (variable) between the electrodes 821 and 86 constitute a "liquid" resistance bridge whose electrodes 86, 87 form the terminals of the output diagonal. The assembly is such that the bridge is permanently unbalanced. The rotor 83 has in this case an even number of blades so that the variable resistances with the passage of the rotor blades vary in phase.

 It should be noted that if, instead of having the electrodes 86.87 on either side of the rotor 83, they have the same side of this rotor, for example at the upper part, then a rotor with an odd number of blades so that the resistance R4 increases when the resistance R2 decreases, and vice versa.

In both cases, a resistance bridge is obtained in which the "liquid" resistors are always proportional to the resistivity of the liquid, the signal collected at the output is thus much less dependent on the resistivity of the conductive liquid.

Another application of the invention consists in the calibration of water meters with multiple jets, (of the same kind as that of FIG. 1) and in particular of meters with dry totalizer, but of which an important part of the mechanical reduction controlling this totalizer is embedded in the liquid so that the output shaft which attacks the first needle of the totalizer through a cable gland has sufficient torque. As a result, in this type of counter, the first needle rotates at low speed, even at high flow rates, and that the calibration therefore takes a very long time. The use of an electrode rotation detector makes it possible to take the information of the number of revolutions directly on the turbine itself which turns at a speed in a ratio much higher than that of the first needle of the totalizer, and consequently to reduce the duration of calibration of the meter in the same report .

To this end, provision is made, as shown diagrammatically in FIG. 8, to pierce in the injection box 91 of the counter 90 two small additional orifices 92 spaced a few mm apart. (but only one of which is visible in the profile view of FIG. 8) in a plane perpendicular to the axis of the turbine 93 opposite, for example, the outlet pipe 94 of the meter. A rod 95 contains two insulated conductors 96 ending in two metal pins 97 which act as electrodes and which can be introduced into the orifices 92 to detect the rotation of the turbine 93. These conductors 96 pass tightly through a sleeve 98 making it possible to connect the outlet of the counter to the discharge of the liquid by a hose, and are connected to a circuit 90 for processing and counting the electrical signals detected by the electrodes 97.

During calibration, it is therefore easy to introduce the electrodes 97 into their housing 92 through the tubing 94, then mount the sleeve 98 on the tubing 94 and proceed to calibrate the counter by adjusting the screw. - usual needle. Once this operation is complete, the sleeve 98 with the rod 95 and the electrodes 97 are removed, and the counter 90 ready for normal operation under the usual conditions.

Of course, the invention is not limited to only the embodiments which have been described by way of examples. In particular, the electrodes of the same pair are not necessarily arranged in a privileged position symmetrically with respect to a diametral plane or transverse to the axis of the measurer, but can occupy any positions, the passage of the blades of the rotor producing in in all cases a detectable modulation representative of its rotation.

Likewise, the auxiliary rotor can take other forms than that with flat blades indicated in FIG. 3 and may for example be produced in the form of a crenellated cylindrical bell according to the available space existing in the measurer, or any other form of revolution having cutouts (serrations or orifices) regularly distributed to pass between two electrodes.

Claims (11)

1 - Flow meter emitting electrical pulses for fluid electrically conductive in which a material paddle rotor electrically insulating is mounted to be rotated at a speed as a function of the flow rate of the fluid to be measured, characterized  in that it includes  - at least one pair of electrodes arranged on an insulating support  in the vicinity of the passage of the rotor blades and connected, in function operation, to a source of electrical potential such that that the rotation of the blades produces periodic variations  of the electrical resistance of the fluid between the two electro of, and  - means of detection and means of counting said va periodic resistance resistance. 2 - Measurer according to claim 1, comprising a rotor mounted in  an injection boot made of electrically insulating material, risé in that the two electrodes are mounted on the wall in  dull of said injection boot. 3 - Measurer according to claim 1, comprising a mounted rotor  in a metal enclosure closed by a material plate electrically insulating, characterized in that the electrodes are  mounted on said plate. 4 - Measurer according to claim 3, characterized in that the é  electrodes are mounted at a distance sufficiently distant from 1 '  metal enclosure to avoid the influence of the short circuit created  by it. 5 - Measurer according to claim 1, wherein the rotor carries to inside the fluid an auxiliary rotor of electrical material insulating, in the shape of a revolution with cutouts evenly distributed, characterized in that the electrodes are arranged in relation to each other to be periodically  masked and unmasked by the passage of the cutouts of said rotor  auxiliary between them.  6 - Measurer according to claim 5, comprising in a body tu  bular a coaxial rotor mounted between two fairings in material electrically insulating, characterized in that the electrodes are mounted on one of said fairings. 7 - Measurer according to claim 1, characterized in that said  means of detecting resistance variations include the mon tage in series of a generator of a carrier wave7 of an amplifica  operational tor arranged to supply a substantially constant current both on a counter-reaction path in which are connected  said electrodes, a rectification circuit eliminating the wave  carrier, and an amplifier circuit for converting into pulses. 8 - Measurer according to claim 7, characterized in that said  feedback channel includes at least one connected capacitor in series with the electrodes. 9 - Measurer according to claim 5, characterized in that it com carries two pairs of electrodes mounted so that the electro of a pair are masked by the auxiliary rotor when the  electrodes of the other pair are unmasked, and in that said  pairs of electrodes are plugged into a bridge circuit with two auxiliary resistors. 10 - Measurer according to claim 5, characterized in that it com  carries a first pair of double electrodes arranged on the side  and the other at a first distance from the insulating auxiliary rotor and a second pair of electrodes disposed at a second distance from the  rotor smaller than the first distance, the four resistances  fluids between the respective electrodes closest to the two pairs constituting a bridge assembly in which the elect trodes of the second pair are the terminals of the diagonal of sor tie. 11 - Application to the calibration of a jet type liquid meter  multiple comprising a rotor of electrically insulating material  rotating in an injection box made of material electrically insulator, characterized in that the injection box is pierced of two additional orifices opposite one of the pipes of the  counter, these two openings being intended to receive temporary  ment, during calibration, two pins playing the role of electro  connected to detection and counting means to de reduce the flow rate measured by said meter.