Indicating By Microwave Energy The Constituent Proportions Of A Flowing Substance

Abstract

A method and apparatus for indicating the proportions of the constituents of a flowing substance of the type wherein the effective dielectric constant depends upon the constituents, for example, butter, containing water wherein the butter flows along a main section waveguide, whilst microwave energy is propagated along a branch section waveguide through a window and into the main section waveguide. The whole waveguide configuration with the butter in the main section is a resonant microwave structure, and the ratio of the water in the butter is determined from the resonant frequency of the structure.

Description

This invention relates to an apparatus for indicating the ratio of the constituents of a flowing substance.

When, for example, butter is being extracted as a flowing substance, it is important for economic and legal reasons that changes in the water content of the butter be rapidly detected.

High frequency resonant techniques have been proposed to detect the water content of butter utilizing high frequencies in the range 1 to 100 MH.sub.3 to determine the water content of the butter by the capacitance effect of the butter. The butter is passed between the two plates of a capacitor forming part of a resonant circuit. With this proposal it is difficult to achieve a high Q and so the technique lacks sensitivity. Furthermore, at these frequencies the dielectric constant of water is largely dependent upon the electrical conductivity of water and consequently, any results obtained will depend initially on the salt content of the water, because of these factors it is difficult to determine the moisture content of the butter to the desired accuracy.

It has also been proposed to use microwave techniques to measure the water content of butter by measurements of change in attenuation when microwaves are transmitted between two waveguide antennas of the horn type, whilst a flowing sample of the butter is passed between the antennas. This proposal has the disadvantage that both the water and butter are lossy materials and so the changes in attenuation do not indicate the changes in the water content of the butter to the desired accuracy.

It is an object of the invention to provide an apparatus for indicating changes in the constituents of a flowing substance, which apparatus utilizes microwave energy, is relatively inexpensive to manufacture, and is capable of measuring the water content with greater accuracy than would be achieved by known methods.

According to the invention there is provided apparatus for indicating the proportions of the constituents of a flowing substance of the type wherein the effective dielectric constant thereof depends upon said constituents, comprising a main section of waveguide, and a branch section of waveguide attached to said main section to form a waveguide junction therewith, such that when said main section of the junction is filled with the substance the whole configuration becomes a resonant microwave structure, a window sealing the interior of said branch section from the interior of said main section at the junction of said sections, said window allowing a substantially unobstructed passage for microwave energy propagated along said branch section and into said main section, said window also defining with said main section an unobstructed passage along said main section for the passage of said flowing substance therealong as a filling for said main section, a microwave source for generating microwave energy for propagation along said branch section and into said main section, and means for indicating from the resonant frequency of the structure, which is dependent on the effective dielectric constant of the substance, the ratio of the constituents of said flowing substance.

Further, according to the invention there is provided a method of indicating proportions of the constituents of a flowing substance of the type wherein the effective dielectric constant thereof depends upon said constituents, comprising passing said substance as a filling along a main section waveguide, a branch section waveguide being joined to said main section to form a junction therewith, and to provide a microwave structure therewith, exciting at a frequency on the resonant response pattern thereof said microwave structure, with said main section containing butter, to pass microwave energy along said branch section and into said main section, and determining from changes in the resonant frequency of said structure, which is dependent on the dielectric constant of the substance, the ratio of said constituents of said substance.

In the accompanying drawings which illustrate, by way of example, an embodiment of the invention,

FIG. 1 is a perspective view of an apparatus for determining, in terms of resonant frequency changes, the water content of butter as a flowing substance from an extruder.

FIG. 2 is a section along II--II, FIG. 1 of the waveguide assembly.

FIG. 3 is a section along III--III, FIG. 2 of a portion of the branch section waveguide and window, and

FIG. 4 is a perspective view of a fixed frequency microwave energy source and a means for indicating the water content of butter which are for use with the apparatus shown in FIG. 1, in place of the swept frequency source and oscilloscope.

In FIGS. 1 to 3 there is shown a main section of waveguide 1, a branch section of waveguide 2, a coaxial switch 16, a directional coupler 3, an adjustable attenuator 4, a swept frequency source 5, and an oscilloscope 6. A window 7 of methyl methacrylate resin seals the branch section 2 from the main section 1.

The main section 1 comprises a portion of an outlet end 8 of an extrusion chamber which is secured by the screws 9 to the main portion (not shown) of an extrusion chamber of a butter extruder. The main section 1 has an opening 10 which is sealed from the interior of the branch section 2 by a retaining flange 11 and the window 7. The retaining flange 11 is clamped to the main section 1 by screws 12. The window 7 protrudes below the retaining flange 10 to lie flush with the inner surface of the main section 1 to define therewith an unobstructed passage along the main section 1 for the passage of butter therealong as a complete filling for the main section 1. That is, the window 7 provides a continuation of the inner surface of the main section 1 and so does not create any voids in the flow of butter through the main section 1. The butter leaves the main section 1 over a lip 13.

The branch section 2 has a coupling connector 14 mounted in it, and the coupling connector 14 is connected to the coaxial switch 16. The coaxial switch 16, which is mounted on a bracket 17, is connected to the primary line 19 of the directional coupler 3. The coaxial switch 16 is connected to the input 21 of the adjustable attenuator 4. The adjustable attenuator 4 is terminated at 22 by a short circuit. The reverse output 26 is connected to a crystal detector mount 27, which in turn is connected to the `Y` input 28 of the oscilloscope 6. The primary line 19 of the directional coupler 3 is connected to the signal output 20 of the swept frequency source 5. The directional coupler 3 has a forward secondary line 23 connected to a crystal detector mount 24, and the crystal detector mount 24 is connected to the levelling terminal 25 of the swept frequency source 5. The external sweep 29 of the swept frequency source 5 is connected to the `X` input 30 of the oscilloscope 6.

In some instances the secondary line 23, crystal detector mount 24, and levelling terminal 25 may be omitted from the apparatus.

In operation the apparatus is arranged as shown and butter 18 (shown chain dotted in FIG. 2) having approximately the desired water content, is extruded along the main section 1. The main section 1, and the branch section 2, are such that when the main section 1 is completely filled with butter the whole configuration becomes a resonant microwave structure. The effective dielectric constant of the butter, which effects the resonant frequency of the microwave structure, depends upon the dielectric constants of the different constituents of the butter. Assuming that the only variable is variations in the water content of the butter 18, then the effective dielectric constant of the butter 18 will vary according to the water content thereof.

Whilst the butter 18, having approximately the desired water content, is being extruded in this manner, the swept frequency source 5 is used to observe the frequency response of the main section waveguide 1 filled with butter 18, and the window 7. As the swept frequency source 5 sweeps over an appropriate range for the particular apparatus, in this instance 2 to 3 GHz. a series of absorption resonances is observed. The highest Q resonance is selected from the series, and from this a fixed frequency is selected on the steepest portion of the resonance curve, that is, the portion of the resonance curve which forms the smallest angle with the Y-axis. With the swept frequency source 5 set at this fixed frequency butter 18 having the desired water content is extruded along the main waveguide section 1 and the switch 14 is activated to bring the attenuator 4 into the circuit. The attenuator 4 is then adjusted so that the signal indicated on the oscilloscope is in the central position. The attenuator 4 is then switched out of the circuit using the switch 14.

The water content of the butter 18 being extruded is changed to the maximum and minimum tolerable amounts, and the amplitudes on the oscilloscope are noted in both instances. The amplitude signal of response on the oscilloscope 6, is related in an approximately linear manner to the water content of the butter 18.

Once the amplitudes are known for the maximum and minimum tolerable water contents in the butter 18, the apparatus will then continuously indicate the water content of the butter being extruded.

When the apparatus is used to indicate the water content of one substance, such as butter, that is, the apparatus is not required to be adjusted to suit different substances during different production runs, the swept frequency source 5 and the oscilloscope 6 need only be used to determine the fixed frequency. Once the fixed frequency is known the swept frequency source 5 and the oscilloscope 6 may be replaced by the relatively inexpensive apparatus shown in FIG. 4.

Referring to FIG. 4, a fixed frequency source 19 which is modulated at a suitable audio frequency, is shown in the place of the swept frequency source 5 (FIG. 1), and a read out indicator 20, comprising a tuned audio amplifier and readout meter, is shown in the place of the oscilloscope 6 (FIG. 1). The frequency of the fixed frequency source 19 is that which was determined using the swept frequency source 5 and oscilloscope 6 shown in FIG. 1. The tuned audio amplifier of the readout indicator 20 is tuned to the modulation frequency of the fixed frequency source 19.

In operation the readout indicator 20 is graduated in the same manner as the apparatus shown in FIG. 1, for the center position for the desired water content in the butter 18. The read out indicator 20 is then graduated in the same manner as the apparatus shown in FIG. 1 for the maximum and minimum tolerable water contents in the butter 18. The apparatus is then ready for use to indicate the water content in continuously extruding butter 18.

In this patent specification effective dielectric constant is the resultant dielectric constant of the combined or mixed constituents of the substance.

Further, in this patent specification the resonant frequency of the microwave structure is determined by the physical dimensions of the configuration and by the effective dielectric constant of the substance. The resonant frequency will depend largely on the real part of the dielectric constant and the Q will depend largely on the loss factor of the substance and the physical configuration of the microwave structure.

In other embodiments of the invention other configurations of microwave structure may be used, for example, the T-shaped waveguide structure described with reference to FIG. 1 may have a second branch section waveguide disposed on the opposite thereto of the main section waveguide, and the required information for water content could be derived and fed to the indicator from the second branch section. Obviously other configurations of microwave structure may be used.

The apparatus may be used for detecting the ratio of the constituents of many other materials, for example, margarine, cheese, oil, gasoline, natural and synthetic plastic materials, and may also be used with particulate materials such as sugar, grain or powdered substances, provided these materials are dimensionally stable within the main section of the waveguide structure.

Claims

I claim:

1. Apparatus for indicating the proportions of the constituents of a flowing substance of the type wherein the effective dielectric constant thereof depends upon said constituents, comprising a main section waveguide, and a branch section waveguide secured to said main section to form a waveguide junction therewith, such that when said main section is completely filled with the substance the whole configuration becomes a resonant microwave structure, a window sealing the interior of said branch section from the interior of said main section at the junction of said sections, said window allowing a substantially unobstructed passage for microwave energy propagated along said branch section and into said main section, said window also defining with said main section an unobstructed passage along said main section for the passage of said flowing substance therealong as a filling for said main section, a microwave source for generating microwave energy, at a frequency on the steepest portion on the resonance curve of said microwave structure, for propagation along said branch section and into said main section, and means electrically connected to the main section waveguide for indicating from the amplitude of the signal response of the structure, which is dependent on the effective dielectric constant of the substance, the ratio of the constituents of said flowing substance.

2. Apparatus according to claim 1, wherein said main section waveguide is an outlet end of an extrusion chamber for said flowing substance.

3. Apparatus according to claim 1, wherein said window is a methyl methacrylate resin.

4. Apparatus according to claim 1, wherein said branch section waveguide is secured to said main section waveguide to form a waveguide T-junction.

5. Apparatus according to claim 1, wherein said means for indicating the ratio of the constituents comprises a meter, and said meter has a scale graduated in the desired range of ratios of said constituents.

6. Apparatus according to claim 5, wherein an attenuator is provided electrically connecting said branch section waveguide to said means for indicating said resonant frequency as a means of permanent calibration.

7. A method of indicating the proportions of the constituents of a flowing substance of the type wherein the effective dielectric constant thereof depends upon said constituents, comprising passing said substance as a complete filling along a main section waveguide, a branch section waveguide being joined to said main section to form a junction therewith, and to provide a microwave structure therewith when completely filled with the substance, energizing at a frequency on the steepest portion of the resonance curve of said microwave structure, said microwave structure with said main section containing said substance by passing microwave energy along said branch section and into said main section, and determining from the amplitude of the response signal of said structure, which is dependent on the effective dielectric constant of the substance, the ratio of said constituents of said substance.