GB1586774A - Apparatus for measuring the flow rate or the speed of a gas stream - Google Patents

Description

(54) APP ARAT U'S' FOR MEAS'UktNG" THE FLOW RATE OR THE SPEED OF A GAS STREAM (71) We, IN,stITtJT NATIONAL DES RA'o-EE'MEN'T's-"'National Instituut Voor Radio-Elementen, en abrégé: "I.R.t.", 11, riie d'Egm ont, Brussèls- Belgium, a Belgian c'dmpa,ny", do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be p'effdrmed, to be particularly described in and by the following statement This invention relates to apparatus for measuring the flow rate or the speed of a gas stream as a function of a sensed electric potential in particular it relates to apparatus in which a pair of tubular electrodes, through which the gas steam passes, are connected to an electric voltage source, said electrode pair forming with a common electrode two electric fields, and in which an ion source is located inside one of the electrodes, the common electrode being connected to a measuring circuit responsive to the potential of said common electrode.

A meter of this kind has been described in Belgian Patent 797,751 filed in the name of the Applicant. In said known meter, the common electrode is comprised of a rod which extends axially through the pair of electrodes which lie in co-axial relationship along the direction of the gas stream with a spacing relative to one another.

A disadvantage of this known apparatus is that a stray electrostatic field is formed between said pair of electrodes.

A more recent proposal by the Applicant in Belgian Patent 841,944, proposes a different geometry for the electrodes which avoids the above-mentioned disadvantages this proposal further allows a low-voltage source to be used in combination with an electronic measuring circuit, substantially reducing the meter size and making it suitable for measuring low gas flow rates in the range of millimeters per second. According to the geometry of said proposal said pair of electrodes lie in concentric relationship, one electrode being longer than the other. However, this proposal tends to disturb the flow of the gas stream, which can lead to inaccurate measurement at low gas flow rates.

Accordingly, the present invention seeks to provide apparatus for measuring the flow rate or speed of a gas steam which mitigates the above-mentioned disadvantages, With this object in mind, the present in invention provides apparatus for measuring the flow rate or speed of a gas stream as a function of a sensed electric potential, comprising a pair of tubular electrodes connected to an electric voltage source, and a tubular common electrode, and through which electrodes the gas steam will pass, said electrode pair being arranged in the direction of the gas stream, one on either side of and spaced from said common electrode, each one of said electrode pair forming an electric field with said common electrode, wherein an ion source is located inside one of the electrodes, and the common electrode is connected to a measuring circuit responsive to the potential of said common electrode.

In a preferred embodiment of the invention, the three electrodes lie in co-axial relationship and they have substantially the same diameter.

In another preferred embodiment of the invention, the ion source is located inside the common electrode.

Other details and features 6f the invention will stand out from the description given below by way of non limitative example and with reference to the accompanying drawing, the single figure of which is a diagrammatic lengthwise cross-section through apparatus for measuring the flow rate of gas stream according to the invention.

The apparatus according to the invention comprises two tube-like electrodes 1, 2 which are connected through lines 3 respectively to ground and the positive pole of a low-voltage source, preferably providing a voltage from 5 to 15 volts.

Between the electrodes 1, 2 is located the common electrode 4, which is also tube-like and connected through a line 5 to an electronic measuring circuit which comprises an operational amplifier 6 and a processing unit 7 for the amplified information.

The three electrodes 1, 4, 2 are thus of tubelike shape and in co-axial relationship.

They are arranged inside a sheath 8 which is made from an insulating material, inside which said electrodes are supported by fastening rings 9. The lines 3, 5 are passed through insulating liners 10.

The ion source which is for instance comprised of a capsule 11, is fastened inside the common electrode 4. Said source is preferably made from that material known as AMERI CIUM which radiates a rays.

The above-described geometry generates two electric fields, one field between electrodes 1, 4 and the other one between electrodes 4, 2. It also forms two ionizing chambers, one chamber inside electrode 1 and the other one inside electrode 2, for the ions generated by the interaction between particles radiated by source 11 and gas atoms which are flowing lengthwise along the inside of the three electrodes in the direction of arrow 12.

The potential at the common electrode 4 is a direct function of the impedances (this term defining the resistance of a circuit to the current flow) of the chambers, which is in turn a function of the speed of the gas stream which moves more or less the ions inside that chamber formed by electrode 1 towards the chamber formed by electrode 2.

Tests have shown that when the meter is connected to a source with a voltage from 5 to 15 volts, the optimum dimensions lie in the following range: length of electrodes 1, 2 = 4 cm length of electrode 4 = 1 cm diameter of electrodes 1, 2, 4 = 1-3 cm -wall thickness of electrodes 1, 2, 4 = 1 mm -spacing between electrodes 1, 4 and 4, 2 = l5cm.

Under such conditions there is obtained a sensitivity of 1 volt per 5 l/h flow rate, this relation being valid (between 1 and 10 l/h, when using a voltage level corresponding to a very low current strength, in the range of a few pA (or ,uA).

It must be understood that the invention is in no way limited to the above embodiments and that many changes can be brought therein without departing from the scope of the invention as defined by the appended claims.

WHAT WE CLAIM IS: 1. Apparatus for measuring the flow rate or the speed of a gas stream as a function of a seized electric potential, comprising a pair of tubular electrodes connected to an electric voltage source, and a tubular common electrode and through which electrodes the gas stream will pass, said electrode pair being arranged in the direction of the gas stream, one on either side of and spaced from said common electrode, each one of said electrode pair forming an electric field with said common electrode, wherein an ion source is located inside one of the electrodes, and the common electrode is connected to a measuring circuit responsive to the potential of said common electrode.

2. Apparatus as claimed in claim 1, in which the ion source lies inside the common electrode.

3. Apparatus claimed in either one of claims 1 and 2, in which the three electrodes lie in co-axial relationship and have substantially the same diameter.

4. Apparatus as claimed in claim 1 or claim 2 in which the length of the common electrode is approximately one-fourth of the legnt of the pair of electrodes.

5. Apparatus as claimed in claim 3, wherein the length of the common electrode is approximately one-fourth of one length of the pair of electrodes.

6. Apparatus as claimed in claim 5, in which the spacing between the common electrode and each one of the pair of electrodes is approximately the diameter of said electrodes.

7. Apparatus as claimed in any one of claims 1 to 6, in which said voltage source is energized by a low-voltage source.

8. Apparatus as claimed in any one of claims 1 to 7, in which said ion source is a source of a rays.

9. Apparatus for measuring the flow rate or speed of a gas stream substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. which said electrodes are supported by fastening rings 9. The lines 3, 5 are passed through insulating liners 10. The ion source which is for instance comprised of a capsule 11, is fastened inside the common electrode 4. Said source is preferably made from that material known as AMERI CIUM which radiates a rays. The above-described geometry generates two electric fields, one field between electrodes 1, 4 and the other one between electrodes 4, 2. It also forms two ionizing chambers, one chamber inside electrode 1 and the other one inside electrode 2, for the ions generated by the interaction between particles radiated by source 11 and gas atoms which are flowing lengthwise along the inside of the three electrodes in the direction of arrow 12. The potential at the common electrode 4 is a direct function of the impedances (this term defining the resistance of a circuit to the current flow) of the chambers, which is in turn a function of the speed of the gas stream which moves more or less the ions inside that chamber formed by electrode 1 towards the chamber formed by electrode 2. Tests have shown that when the meter is connected to a source with a voltage from 5 to 15 volts, the optimum dimensions lie in the following range: length of electrodes 1, 2 = 4 cm length of electrode 4 = 1 cm diameter of electrodes 1, 2, 4 = 1-3 cm -wall thickness of electrodes 1, 2, 4 = 1 mm -spacing between electrodes 1, 4 and 4, 2 = l5cm. Under such conditions there is obtained a sensitivity of 1 volt per 5 l/h flow rate, this relation being valid (between 1 and 10 l/h, when using a voltage level corresponding to a very low current strength, in the range of a few pA (or ,uA). It must be understood that the invention is in no way limited to the above embodiments and that many changes can be brought therein without departing from the scope of the invention as defined by the appended claims. WHAT WE CLAIM IS:

1. Apparatus for measuring the flow rate or the speed of a gas stream as a function of a seized electric potential, comprising a pair of tubular electrodes connected to an electric voltage source, and a tubular common electrode and through which electrodes the gas stream will pass, said electrode pair being arranged in the direction of the gas stream, one on either side of and spaced from said common electrode, each one of said electrode pair forming an electric field with said common electrode, wherein an ion source is located inside one of the electrodes, and the common electrode is connected to a measuring circuit responsive to the potential of said common electrode.

2. Apparatus as claimed in claim 1, in which the ion source lies inside the common electrode.

3. Apparatus claimed in either one of claims 1 and 2, in which the three electrodes lie in co-axial relationship and have substantially the same diameter.

4. Apparatus as claimed in claim 1 or claim 2 in which the length of the common electrode is approximately one-fourth of the legnt of the pair of electrodes.

5. Apparatus as claimed in claim 3, wherein the length of the common electrode is approximately one-fourth of one length of the pair of electrodes.

6. Apparatus as claimed in claim 5, in which the spacing between the common electrode and each one of the pair of electrodes is approximately the diameter of said electrodes.

7. Apparatus as claimed in any one of claims 1 to 6, in which said voltage source is energized by a low-voltage source.

8. Apparatus as claimed in any one of claims 1 to 7, in which said ion source is a source of a rays.

9. Apparatus for measuring the flow rate or speed of a gas stream substantially as hereinbefore described with reference to the accompanying drawings.