GB2211618A

GB2211618A - High frequency oscillatory circuit for moisture measurement

Info

Publication number: GB2211618A
Application number: GB8829323A
Authority: GB
Inventors: Dierk Schroder; Norbert Hohenstein; Bernd Heck
Original assignee: Koerber AG
Current assignee: Koerber AG
Priority date: 1987-12-19
Filing date: 1988-12-16
Publication date: 1989-07-05
Also published as: CA1333450C; GB2211618B; GB8829323D0; JPH01203958A; DE3743216A1; IT1228037B; IT8822967A0; DE3743216C2; FR2627866A1

Description

1. 2211618 HIGH FREQUENCY OSCILLATORY CMCUIT The invention relates to

improvements in high frequency oscillatory circuits. More particularly, the invention relates to improvements in high frequency oscillatory circuits of the type having a capacitance and an inductance. Still more particularly, the invention relates to improvements in high frequency oscillatory circuits which can be used to monitor the characteristics of at ldast one of.a plurality of materials, such as for ascertaining the mass or concentration of one material which is combined with or admixed to another material, especially for ascertaining the moisture content of the other material (e.g., tobacco, coffee or tea) wherein the moisture is the one material, or for ascertaining the mass of the other material.

It is already known to employ high frequency oscillatory circuits in order to ascertain the moisture content of a flowable material, e.g., to ascertain the percentage of water (first material) in a stream of tobacco particles (second material). Reference may be had, for example, to commonly owned U.S. Pat. No. 3,979,581. The same or similar apparatus can be used to ascertain the mass of the second material independently of the percentage of first material therein. It is important that the desired parameters of the first material be ascertained independently of fluctuations of its percentage in the second material and independently of fluctuations of the mass of second material, or that the desired parameters of the second material be ascertained independently of eventual fluctuations of the percentage of first material therein. A drawback of presently known high frequency oscillatory circuits for use in such apparatus is that they are 2.

1 unduly affected by temperature changes and/or other variables, such as long-range drifts.

The invention is embodied in a high frequency oscillatory circuit which can be used for monitoring the characteristics of at least one of two materials, particularly for ascertaining the mass or concentration of one material which is combined with or admixed to another material. A presently preferred use of the improved circuit is in connection with ascertainment of moisture content of a moist-material (other material), e. g., tobaccoi wherein moisture is the one material, or in connection with ascertainment of the mass of the other material. The circuit comprises an inductance and a capacitance. The capacitance includes a dielectric which is constituted by the materials the characteristics of which are being monitored, and a condenser having a ceramic carrier and electrodes on the carrier. The condenser is preferably a stray field condenser having a flat surface. The electrodes are located at the flat surface.

The electrodes can constitute or resemble combs with prongs. The prongs of one electrode alternate with the prongs of the other electrode. In accordance with a presently preferred embodiment of the condenser, the carrier has a rectangular supporting surface for the electrodes, and such surface has first and second longer sides and first and second shorter sides. one of the electrodes includes first and second webs which extend along the respective (first and second) longer sides of the supporting surface, and first and second sets of prongs. The prongs of the first set extend from the first web toward but short of the second web, and the prongs of the second set extend from the second web ttward but short of the first web. The one electrode can further comprise two additional webs which extend along the first and second shorter sides of the supporting surface and connect the first and second webs to each other. The other electrode preferably comprises a third web which is-disposed between the first and second sets of prongs, a third set of prongs which extend from the third web and alternate with the prongs of the first set, and a fourth set of prongs which extend from the third web and alternate with the prongs of the second set.

4.

Each electrode can include a metallic layer on the carrier, particularly a thin metallic film.

A wear-resistant coating (particularly a thin film of glaze) can be applied over the carrier and the electrodes.

The inductance can comprise a ceramic core and electrically conductive windings which surround the core. The core can include a-cylinder and the windings can constitute remnants of---ametallic envelope which surrounds the core and from which metallic material was removed so as to separate the windings from each other. i.e.# to convert a portion at least of the envelope into a series of discrete windings.

The stray field condenser contacts the dielectric (i.e., the monitored materials) when the circuit is in use, and the circuit preferably further comprises a housing for a signal processing unit and for the core of the inductance. The stray field condenser is preferably applied to an outer side of the housing.

The dielectric can include a moisture-containing organic material, particularly a consumable substance such as tobacco, coffee or tea.

The novel feature which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved high frequency oscillatory circuit itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

5.

FIG. 1 is plan view of a stray field condenser which can be used in the improved high frequency oscillatory circuit;

FIG. 2 is a sectional view as seen in the direction of arrows from the line II-II of FIG. 1. further showing a housing for the condenser, an inductance in the housing, and a signal evaluating circuit in the housing; and FIG. 3 is an enlarged side elevational view of the inducance, with some of the windings omitted.

FIG. 1 shows a stray field condenser 1 (also called open field condenser) which can be used in the improved high frequency oscillatory circuit. The condenser 1 comprises a thin platelike carrier 4 of a ceramic material (this term is intended to embrace genuine ceramics as well as materials (such as quarts) exhibiting similar characteristics. The exposed supporting surfate of the carrier 4 is provided with two electrodes 2 and 3 which preferably constitute metallic layers, most preferably very thin films of metallic material. Such films can be applied in accordance with a technique which is known from the art of applying thick film conductors. A presently preferred ceramic material of the carrier 4 is sintered aluminum oxide (Al 2 0 3) which can be used in pure form or in admixture to a relatively small percentage of other substances-, e.g., silicates. Another material which can be classified as a ceramic (i.e., which can be used for the making of the carrier 4) is hard porcelain. It is important to select a ceramic substance which exhibits a small change of loss angle (tangent delta), dielectric constant and/or elongation (stretching) in response to fluctuations of te4nperature and/or long range drifts.

The electrode 2 includes first and second relatively wide strip-shaped webs 6, 7 which extend along the long sides 8, 9 of the flat rectangular electrode supporting surface of the carrier 4, a first set of relatively narrow prongs 13 which extend from the web 6 toward but short of the web 7, a second set of relatively narrow prongs 13 which extend from the web 7 toward but short of 7.

the web 60 and two additional webs 11 which extend along the short sides 12 of the supporting surface of the carrier 4 and conductively connect the respective ends of the webs 6, 7 to each other. The width of the webs 11 can equal, or can exceed, the width of the webs 6 and 7. The electrode 3 comprises a relatively wide web 16 which is applied to the central region 14 of the supporting surface of the carrier 4 between the two sets of prongs 13 and substantially midway between the webs 6, 7, a set of prongs 17 which extend from one side of the web 16 and alternate with the prongs 13 of the web 6, and a set of prongs 17 which extend from the other side of the web 16 and alternate with the prongs 13 of the web 7. It can be said that the electrodes 2 and 3 include or constitute two combs with prongs or teeth which alternate with each other.

The electrodes 2p 3 are connected with a high-frequency voltgge source, not shown, by conductors 102, 103 (see FIG. 2). The thin films of metallic material which constitute the electrodes 2, 3 can have a thickness of 0.01-0.1 mm.

The supporting surface of the carrier 4 and the electrodes 2, 3 are preferably coated with a relatively thin layer (particularly a very thin film) of wear-resistant material, such as a special glass or another glaze. The thickness of such glaze (which can be transparent or translucenty can be in the range of 0.01-0.1 mm.

The electrodes 2, 3 which are shown in FIG. 1 exhibit the advantage that the capacity of the stray field condenser 1 is highly satisfactory, the same as the extent (height) of the stray field. Moreover, the condenser 1 is not appreciably influenced by temperature changes and/or by long-range drifts.

8.

FIG. 2 shows a portion of a housing 21 having an end wall 22. The platelike carrier 4 of the stray field condenser 1 is bonded or otherwise reliably-affixed to the outer side of the wall 22. When the oscillatory circuit is in use, the carrier 4 and its electrodes 2. 3 are contacted by a flow of materials to he monitored, e.g., by a stream of moisturecontaining tobacco particles, by a stream of whole or comminuted coffee. beans, by a stream of tobacco leaves or by a stream of other consummable organic substances. The thickness of electrodes 2 and 3 is exaggerated in FIG. 2 for the sake of clarity.

A shoulder 23 of the housing 21 supports a plate-like member 24 which is secured to the housing and carries the core (spool body) 26 of an inductance forming part of the improved oscillatory circuit. The details of the inductance are shown in FIG. 3. The core 26 constitutes or includes a cylinder which is preferably made of a ceramic material exhibiting characteristics similar to those of the material of the carrier 4, i.e., the loss angle, dielectric constant and/or elongation of the material of the core 26 should not be unduly affected by fluctuations of temperature and/or long range drifts. The presently preferred material of the core 26 is a sintered ceramic substance.

The surface of the core 26 is metallized. i.e., it is provided with a layer or envelope 27a (preferably a very thin film) of an electrically conductive metallic material. Portions of the envelope 27a are removed (see FIG. 3) so that the cylindrical core 26 is surrounded by discrete windings 27 of very thin metallic material. The windings 27 form a helical strip conductor.

9.

Signals denoting changes of parameters of the oscillatory circuit are transmitted to a signal evaluating and processing unit 28 having an output 29 for transmission of processed signals denoting the mass and/or moisture and/or other characteristics of the material or materials contacting the electrodes 2. 3 while the electrodes are connected to a high-fr equency voltage source via conductors 102, 103. For example, signalsat the output 29 of the evaluating unit 28 can denote the moisture content (first material) of an organic (second) material such as tea, coffee or tobacco. Alternatively, signals at the output 29 can denote the dry mass of the monitored material. The manner in which signals denoting variable parameters of the oscillatory circuit are processed is or can be the same as disclosed in numerous United States and foreign patents and patent applications of the assignee of the present application. Reference may be had, by way of example, to commonly owned U.S. Pats. Nos. 3.979, 581, 3,795,984, 3,320,520, 3,777,258 and 3,950.698 and/or to abandoned United States patent application Serial No. 945,697.

The housing 21 of FIG. 2 can contain and/or carry additional components of apparatus for measuring, evaluating, indicating and/or using information denoting certain characteristics (such as massr moisture content and/or othersY of organic substances.

10.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features thatt from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art andr thereforei such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.

Claims

CLAIM

1. A high frequency oscillatory circuit for monitoring the characteristics of at least one of a plurality of materials, particularly for ascertaining the mass or concentration of one material which is combined with or admixed to another material, especially for ascertaining the moisture content of the other material wherein the moisture is the one material or for ascertaining the mass of the other material, comprising an-inductance and a capacitance, said capacitance including a dielectric constituted by the materials the characteristics of which are being monitored, and a condenser having a ceramic carrier and electrodes on said carrier.

12.

2. The circuit of claim 1, wherein said condenser is a stray field condenser.

3. The circuit of claim 2, wherein said condenser has a flat surface and said electrodes are located at said surface.

4. The circuit of claim 1, wherein said electrodes include combs having prongs and the prongs of one of said electrodes alternate with the prongs of another of said electrodes.

5. The circuit of claim 1, wherein said carrier has a rectangular shape with first and second long sides and first and second short sides. 1 t 13.

6. The circuit of claim 5, wherein one of said electrodes includes first and second webs extending along the respective long sides and first and second sets of prongs. the prongs of said first set extending from said first web toward said second web and the prongs of said second set extending from said second web toward said first web.

7. The circuit of claim 6, wherein another of said electrodes comprises a third web disposed between said first and second sets of prongs, a third set of prongs extending from said third web and alternating with the prongs of said first set, and a fourth set of prongs extending from said third web and alternating with the prongs of said second set.

14.

8. The circuit of claim 1, wherein each of said electrodes includes a metallic layer on said carrier.

9. The circuit of claim 8, wherein said layers are films.

10. The circuit of claim 1, further comprising a wear-resistant coating overlying said carrier and said electrodes.

11. The circuit of claim 10, wherein said coating is a film of glaze.

15.

12. The circuit of claim 1, wherein said inductance comprises a ceramic core and electrically conductive windings surrounding said core.

13. The circuit of claim 12, wherein said core includes a cylinder.

14. The circuit of claim 12, wherein said windings are remnants of a metallic envelope surrounding said core.

16.

15. The circuit of claim 1, wherein said condenser is a stray field condenser which contacts the monitored materials, and further comprising a housing and a signal processing unit in said housing, said housing having an outer side and said condenser being disposed at said outer side, said inductance including a core in said housing.

16. The circuit of claim 1, wherein the dielectric includes a moisturecontaining organic material.

17. The circuit of claim 15, wherein the organic material is a consumable substance.

1 17.

18. The circuit of claim 17, wherein the consumable substance is tobacco.

19. The circuit of claim 17, wherein the consumable substance is tea.

20. The circuit of claim 17, wherein the consumable substance is coffee.

21. A high frequency oscillatory circuit, for monitoring the characteristics of at least one of a plurality of materials, substantially as herein described with reference to the accompanying drawings.

1; Published 1989 at The Patent Office. State House, 66171 li,ghHolburn, Lonlcr;,1r,1R4TP. Further copies mkvbe obtainedfrom The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BRS 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187