Measurement Of Moisture Content Of Materials

Abstract

An RF signal field is established through a partially conductive material, such as tobacco having a positive moisture content, and variations in the strength of the field, in response to change in the moisture content, are detected. The probe contacting the material is constructed with three conductive elements, the middle of which is grounded to provide measurements only of the strength of the RF field through the tobacco.

Description

FIELD OF INVENTION

The present invention is directed to the measurement of the moisture content of materials, more particularly to the measurement and monitoring of the moisture content of tobacco.

BACKGROUND TO THE INVENTION

The properties of tobacco vary considerably with the moisture content thereof. These variations affect the quality of cigarettes and, therefore, it is very desirable to maintain the moisture content of tobacco within predetermined limits.

A number of prior art systems have been suggested for the continuous monitoring of tobacco moisture so that adjustments could be made to tobacco having a moisture content outside the predetermined values. None of these prior art systems has been found to be accurate or consistent.

SUMMARY OF INVENTION

In the present invention an RF signal field is established through the tobacco and variations in the strength of the field, in response to changes in the moisture content of the tobacco, are detected.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of one embodiment of the present invention;

FIG. 2 is a schematic representation of the monitoring device shown in FIG. 1;

FIG. 3 is a perspective view of the probe of FIG. 2; and

FIG. 4 is a sectional view of the probe of FIG. 3 in operation.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the drawings, tobacco whose moisture content is to be measured is passed from a source of tobacco 10 by line 12 through a moisture-content monitoring device 14, the tobacco thereafter being passed to a cigarette maker. This embodiment is described with the moisture content of the tobacco prior to passage thereof to the cigarette maker. The monitoring may occur at any other convenient location in the manufacture of the cigarettes, and more than one such monitoring may occur.

The moisture content of the tobacco is monitored continuously by the device 14 and any detected deviation of the moisture content of the tobacco from predetermined limits may be corrected for the tobacco passing to the cigarette maker and for the tobacco in the source.

The monitoring device 14 includes a probe 16 which contacts the tobacco stream 18 as it passes through the monitoring device 14. The probe 16 includes a base block 20 constructed substantially of electrically insulating material of low dielectric constant and having a smooth flat face 22 contacting the tobacco stream 18.

Embedded in the base block 20 are two horizontally spaced-apart substantially parallel electrically conducting elements 24 and 26. The elements 24 and 26 are positioned close to the face 22 and are electrically insulated from each other.

The elements 24 and 26 may be in any convenient form, preferably elongate strips in the manner illustrated. In addition, a third electrically conductive element 28 is embedded in the base block 20, the element 28 being positioned between and substantially parallel to the elements 24 and 26. The element 28 is positioned close to the face 22 and preferably is in the form of an elongate strip, as illustrated, the strips forming the elements 24, 26 and 28 being located in the same plane, the plane being parallel to the face 22.

The element 24 is electrically connected to an oscillator 30 which may be of any convenient construction to provide a highly stabilized RF signal to the element 24.

As the tobacco passes in contact with the probe 16 an RF field is established through the tobacco stream 18 between the elements 24 and 26. The strength of this field depends on the moisture content of the tobacco and will vary in accordance with variations in the moisture content.

The element 26 is electrically connected to an amplifier 32 to amplify the RF signal received at the element 26 to a recordable level. The amplifier may be of any convenient construction.

A recording device, typically a meter 34, is electrically connected to the amplifier 32 whereby the strength of the RF signal field between the elements 24 and 26 may be detected. The meter 34 is suitably calibrated to indicate visually the detected variations and to indicate readings outside predetermined limits.

The RF signal passes between the elements 24 and 26 only through the tobacco. The strength of the field varies with the variations in the moisture content. The amplified variations are detected by the meter 34, which is suitably calibrated. Any detected variations beyond the predetermined limits for the tobacco may then be adjusted accordingly.

While this monitoring system as just described operates satisfactorily over short periods of time, it has been found that on prolonged use a substantially continuous layer of moisture tends to form on the face 22 of the probe 16. The presence of this layer causes the RF signal to pass mainly directly from the element 24 to the element 26 through the layer, thereby rendering ineffective the monitoring of the moisture content with the tobacco.

In accordance with the present invention this is overcome in a particular manner. Thus, the third element 28 is earthed as shown schematically at 36 and this has the effect of interrupting the passage of the field directly between the elements 24 and 26. Thus, even in the presence of a layer of water on the face 22, the only variations in the strength of the RF field measured are those through the tobacco stream 18.

The presence of the earthed element 28 does reduce considerably the overall strength of the RF signal field, indicated schematically by the arrows 38 in FIG. 4, but this reduction in strength may be compensated by the use of a suitably-powered amplifier 32. The presence of the earthed element 28 therefore allows the monitoring device 14 to monitor continuously on a long term basis variation in the conductivity of the tobacco itself, and therefore the moisture content thereof, in the stream 18, irrespective of the accumulation of a very conductive layer of water or other material on the face of the probe 16 in contact with the stream 18.

The probe 16 may be positioned below the stream 18, as illustrated in FIG. 4, or, alternatively, may be positioned in contact with the top surface of the stream. In the latter embodiment, the probe is supported in a floating manner so that it is in contact with the tobacco at all times, irrespective of variations of the thickness of the tobacco layer passing in contact with the probe.

The above-described system, while particularly useful in monitoring the moisture content of tobacco, may be used to monitor the moisture content of any other desired material, such as cereal, dog food, etc.

Modifications are possible within the scope of the present invention.

Claims

1. A measuring device for measuring the moisture content of a material comprising

probe means adapted to contact said material,

said probe means including a block of electrically insulating material of low dielectric constant having a smooth, planar material-engaging surface,

first, second and third elongated strips of conductive material embedded in said block in parallel spaced-apart manner, the plane of location of said first, second and third elongate elements being substantially parallel to said planar material engaging surface,

said third elongate element being located between said first and second elongate elements,

means establishing a highly stabilized RF signal at said first elongate conductive element and means connected to said second elongate conductive element for measuring the strength of the RF signal passing between said first and second elongate conductive elements through material in contact with said material-contacting surface in response to the moisture content of said material, and

means grounding said third elongate conductive element to earth whereby said RF signal passing between said first and second elongate conductive

2. A method of monitoring the moisture content of tobacco which comprises

continuously feeding a stream of tobacco having a finite moisture content from a source thereof through a monitoring zone,

providing in said monitoring zone a probe including a block of electrically insulating material of low dielectric constant having a smooth planar surface in contact with which said tobacco flows,

said probe including first, second and third elongate strips of conductive material embedded in said block in parallel spaced-apart manner, the plane of location of said first, and third elongate elements being substantially parallel to said planar surface, said third elongate element being located between said first and second elongate elements,

continuously providing a highly stabilized RF signal to said first elongate element,

continuously maintaining an RF signal field along a conductive path between said first and second elongate elements,

continuously maintaining said third elongate element grounded to earth to short any conductive path directly between said first and second elongate elements, whereby said field is maintained through said tobacco, and

continuously detecting changes in the strength of said RF signal field through said tobacco in response to changes in the moisture content of said tobacco.