US2693575A - Moisture determining device for materials - Google Patents

Description

1954 K. M. GREENWOOD ETAL 2,693,575

MOISTURE DETERMINING DEVICE FOR MATERIALS Filed Dec. 1, 1951 2 Sheets-Shae: l

'9?! 37 sex FIG. 2

32 /N VEN TOR5 Namath M. Grzenwcvd Edward W. l ldzcrdll,

1954 K. M. GREENWOOD ETAL 2,693,575

MOISTURE DETERMINING DEVICE FOR MATERIALS Filed Dec. 1, 1951 2 Sheets-Sheet 2 VEN TOFPS I Hanna 23h M. Greenwood,

Edward M Mdzcrdll United States Patent MOISTURE DETERMINING DEVICE FOR MATERIALS Kenneth M. Greenwood, St. Vital, Manitoba, and Edward W. Mazerall, St. Boniface, Manitoba, Canada, assiguors to Halross Instruments Corporation Limited, Winnipeg, Manitoba, Canada Application December 1, 1951, Serial No. 259,342 2 Claims. (Cl. 324-61) This invention relates to new and useful improvements in devices for determining the moisture content of a wide variety of material such as grain, meals, macerated ma terials, and other comminuted materials organic and inorganic, an object of this invention being to provide a device of the character herewithin described whereby the relative moisture content of a sample of the material being tested can be obtained rapidly by relatively unskilled labour and furthermore, eliminates the necessity for full laboratory facilities.

A further object of this invention in conjunction with the foregoing object is to provide a device of the character herewithin described which can be used at the storage location of the materials being tested and can be operated either by dry batteries or by the line supply electricity.

Still another object of this invention is to provide a device of the character herewithin described in which the moisture content of the sample of the material being tested can be obtained extremely rapidly and at the same time to a very high degree of accuracy, a comparison of laboratory and field tests showing a standard estimate of error of less than A of 1%.

A yet further object of this invention is to provide a device of the character herewithin described which, by contrast to the standard method of heating a weighed sample of the material and thus driving out the moisture, does not destroy or injure the sample being tested.

Another object of this invention is to provide a device of the character herewithin described whereby the usual false readings given by dielectric types of moisture determination instruments due to surface moisture on the sample are eliminated by the use of a relatively high frequency current in the neighborhood of between 18 to 20 megacycles as compared with the conventional usual operating frequency of between 50 cycles and 1 megacycle.

A still further object of this invention is to provide a device of the character herewithin described which includes means incorporated in the test cell to compensate for the increase of dielectric constant of the material being tested normally encountered due to the packing effect of the material in the test cell.

A further object of this invention is to provide a device of the character herewithin described which includes means whereby the instrument can be calibrated rapidly before using.

A still further object of this invention is to provide a device of the character herewithin described whereby the accuracy of the instrument can be checked at any time rapidly and easily.

Yet another object of this invention is to provide a device of the character herewithin described which is readily transportable from place to place and can be set up and be ready for use within a few minutes.

A still further object of this invention is to provide a device of the character herewithin described which includes means whereby the even loading of the sample into the cell is ensure Still another object of this invention is to provide a device of the character herewithin described which is relatively economical in manufacture, accurate in re sults, and otherwise, well suited for the purpose for which it is designed.

, With the foregoing objects in view, and such other objects and advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention consists essentially in the arrangement and construction of parts all as hereinafter more particularly described, reference being had to the accompanying drawings in which:

Figure l is a perspective view of the device with the test cell in position.

Figure 2 is a schematic view of the circuit of the device.

Figure 3 is a perspective exploded view of the test cell per se.

Figure 4 is a vertical section taken through the loading funnel used to load the test cell.

Figure 5 is a top plan view of the loading funnel.

In the drawings like characters of reference indicate corresponding parts in the different figures.

It is well known that the knowledge of the moisture content of many products of a granular or macerated nature either organic or inorganic is required for many purposes. As an example, it will be appreciated that, in the case of wheat or other grains, milling cannot be carried out unless the moisture content is below a certain figure. Furthermore, storage becomes difiicult as well as the marketing of the material unless the buyer knows the percentage weight of moisture contained in the material.

As a general rule, it has been established that, for many materials, the percentage moisture content should lie within certain limits to facilitate marketing, grading, processing and storage.

Many methods have been developed to enable a determination of the moisture content of a given material to be obtained, the earliest of which is still used as an accurate standard. This method comprises the heating of a weighed sample of the material thus driving off the moisture whereupon the moisture determination can be made by a comparison of the weight of the material before and after the moisture has been driven 03.

Unfortunately, although this method is highly accurate, it is extremely lengthy and requires a relatively high degree of precision in both apparatus and technique. Furthermore, this method requires laboratory facilities in order that it may be made accurately.

In order that a determination may be made of the moisture content of any given material away from laboratories, various methods and apparatus have been devised to measure a characteristic of the material electrically, which may be correlated with the moisture content. The two main characteristics which have been found to correlate closely with the moisture content are the electrical resistance of the material or inversely, the conductivity of the material, and the dielectric constant thereof.

The electrical resistance of the material is measured by crushing the sample of the material between electrodes connected to a resistance measuring device. However, it has been found that with this method, conditions other than the total moisture content may effect the resistance. The principal condition which effects the resistance is the surface moisture which may be present upon a sample of the material which will register a lower resistance and hence a higher moisture content is actually present within the sample itself.

The present device utilizes the measurement of the dielectric constant of the material and comprises what might be termed the substitution method. In this method, the sample cell is part of a resonant circuit which is first balanced with the sample cell empty. The material is then added to the cell, thus increasing its capacitance and the circuit is then rebalanced by means of a calibrated standard condenser and the change in capacity, as indicated by this condenser, and a suitable indicator, is then correlated to the moisture content. However, several factors may give rise to erroneous results using this principle and it has been found that some of these factors include the manner in which the material is added to the cell due to variations in packing, and also, as in the foregoing resistance method, surface moisture on the materials has the effect of leading to false readings.

In this instrument, as will hereinafter be described, both the efiect of the packing of the material in the cell has been minimized as well as the error due to surface moisture.

Proceeding now to describe the invention in detail, it will be seen upon reference to Figure 1 of the accompanying drawings that it consists of a test cell collectively designated 1 connected to what is defined as a comparative capacitance unit collectively designated 2. Reference to Figure 3 of the accompanying drawings will show the details of construction of the test cell 1 and it will be seen that it consists of a cylindrical container 3 being open at the upper end 4 thereof and closed by means of a base plate 5 which is detachably secured to the base of the cylinder by screws or the like (not illustrated) passing through the wall of the cylinder and an upstanding annular shoulder 6 formed upon the base plate 5.

The aforementioned outer container 3 constitutes one of the electrodes of this test cell and is connected to the unit 2 by means of a hanger '7 extending from the side of the cylinder 3, said hanger ing prongs 8 which engage after to be described.

The central electrode 9 of the test cell comprises an inverted truncated conical portion 10 surmounted by a material dispersal cap 11 which ensures that material poured into the cell is distributed evenly around the central electrode.

This electrode is secured concentrically within the cylindrical container 3 upon an insulating disc 12 spanning the container in spaced relationship above the end cap 5. A bolt 13 passes through a connector 14, through the disc 12, and is screw-thrcadably engageable within the base 15 of the central electrode 9 thus maintaining the central electrode in equal spaced relationship to the Walls of the cylinder 3. A plastic sleeve 16 surrounds the central electrode and prevents the possibility of a direct connection between electrodes should the material being tested act as a high resistance conductor. Furthermore, due to the concentration of field at the central electrode in such a concentric arrangement, the sleeve serves to prevent small portions of the sample, which might differ from the main body of the sample, from having a disproportionate effect on the whole.

Means are provided to eliminate the increased effective the unit in a manner hereindielectric constant of the material when loaded into the cell which is caused it the matenal packs and becomes more dense at the lower ends thereof. In this embodiment, this has been minimized by forming the main portion 10 of the central electrode in the inverted truncated cone as hereinbefore described, thereby giving an increased distance between the central electrode and the walls of the outer container at the base thereof, this distance gradually decreasing towards the upper ends of the two electrodes.

The aforementioned connector 14 extends from the base of the central electrode to a coaxial terminal 17 also provided on the wall of the outer container 3 immediately below the aforementioned hanger 7 and this, together with the hanger '7 enables the test cell 1 to be connected and disconnected from the unit 2 as desired. The coaxial terminal connects the cell electrically to the unit 2.

In order further to minimize errors due to uneven packing of the material within the test cell, a loading funnel is provided which ensures constant loading of various samples of material at a standard rate thus tending to standardize any packing which may occur within the cell. This funnel, designated 18, is shown in detail in Figures 4 and 5 and comprises an open-ended cylinder 19 having a collapsible trap mechanism 2i) spanning the cylinder medially along the length thereof. This trap mechanism 20 includes a pair of semi-circular plates 21 and 22 hinged around a hinge pin 23 which spans the cylinder 19 diametrically. The pin or spindle 23 is provided with an operating button 24 and is capable of limited and shiftable movement across the diameter of the cylinder, a spring 25 normally maintaining the spindle in the position shown in Figure 4.

The opposite end 25 of the spindle or pin 23 is provided with a small cross-bar 27 which, in turn, carries a pair of support pins 28 extending inwardly through apertures formed within the wall of the cylinder 19 and reference to Figure 5 will show that with the pin extending through the wall, the traps 2i and 22 rest thereon thus effectively sealing the upper half of the cylinder from the lower half so that a measured quantity of grain can be deposited within the upper half of the cylinder and. levelled by gentle shaking thereof. v However, as soon as the plunger 24 is pushed inwardly against spring 25, the pins 28 withdraw from the wall of the cylinder thus permitting the traps 21 and 22 to swing downwardly in a substantially vertical position including a pair of outstandshown in Figure 4 thus depositing the grain downwardly through the lower half of the cylinder and into the test cell upon which the cylinder has been placed prior to loading.

It will be observed that a pair of projections 29 extend inwardly from the walls of the cylinder and that the two traps 21 and 22 rest thereagainst when in the position shown in Figure 4. These projections are provided to ensure that the traps are always slightly offset from the vertical plane thus ensuring that they will drop and take up the position in Figure 5 when the loading funnel is reversed for further use.

In conclusion, it will be appreciated that the loading funnel is used in alternate positions, reversal of the'funnel as shown in Figure 4 causing the traps 21 and 22 to take up the position as shown in Figure 5. The electronic unit 2 associated with the test cell 1 takes the form of a comparative capacitance unit the schematic wiring diagram of which is shown in detail in Figure 2. The circuit comprises a pair of oscillators 30 and 3t) linked by a coupling circuit which include a germanium diode 31 and a milliammeter 32. Power is supplied to the circuit by means of the two batteries 33 and 34, the former supplying the A+ current to the filaments and the latter, the 13+ current as indicated, a multiple switch 35 being provided to switch the circuit on and off as required.

The resonant circuit of the oscillator 39 includes an inductance 36 and the frequency of this oscillator is fixed. The resonant circuit of the other oscillator 30' includes an inductance 36 and four capacitances, condensers 37, 33 and 39, and the cell 1 which is shown schematically in the wiring diagram of Figure 2. Condenser 39 is calibrated variable standard condenser operated by knob 40 in Figure l, the calibration showing by means of the dial 41 on the face of the instrument. Condenser 38 is the trimming condenser and is operated by knob 42 on the opposite side of the instrument to knob 43. Condenser 37 is a fixed standard condenser having an associated switch 43 and a resistor 44 in circuit therewith of such a value as to make the condenser 37 the equivalent in both dielectric constant and loss factor to a standard sample of grain having a given moisture content placed in the cell. In this example, the sample has been arbitrarily set at grams having 15% moisture, the grain being wheat.

Proceeding now to describe the operation of the invention, the empty cell 1 is first connected to the side of the unit 2 by means of the hanger 7 and coaxial terminal 17, it being understood that the latter connects the cell electronically to the resonant circuit of the oscillator 30' as signified in Figure 2. The aforementioned prongs 8 of the hanger 7 engage within slots 45 provided in oifstanding lugs 46 situated at the left-hand side of the instrument as shown in Figure l.

The main switch 35 is then moved to the on position thus connecting the batteries 33 and 34 to the circuit. In this connection, although batteries have been shown as a source of power in this embodiment, it will be appreciated that, if desired, a power pack may be supplied so that the unit may be connected to the main source of electrical supply normallypresent in most places where the device Is to be used.

The switch 43 is then closed thus bringing into the circuit the calibrating condenser 37 and its resistor 44, and, in th1s connection, in Figure 1, this position is indicated by the letters CAL and numbered 43'. The calibrated variable condenser 39 is then turned until a predetermined dial reading shows under the hair-line at 41, this position being a calibrating position and being marked on the dial of this condenser. Trimming condenser 38 1s now ad usted by means of knob 42 until there is a minimum flow of current in the coupling circuit between oscillators 30 and 30, this minimum flow being shown on the meter 32. For convenience, an arrow 32' is provided on the dial of the meter with the head directed towards the left thereof with relation to Figure 1, this arrow indicatmgthe direction that the needle of the meter should move in order to indicate the minimum current flow.

When this minimum flow is obtained, the instrument is calibrated ready for use and the switch 43 is opened thus taking the standard condenser 37 out of the circuit. In this connection, the letters OP are shown on the face of the instrument and represents operate as contrasted to calibrate.

A sample of the grain or material to be tested is then carefully weighed as specified on charts supplied with the instrument, which has been calibrated in the range from 40 F. to 104 F. It is important that the temperature of the sample be ascertained prior to the tests being taken and this can be done by any standard method.

This weighed sample is now placed within the pouring funnel 18, the traps 21 and 22 spanning the diameter thereof as illustrated in Figure 5 of the accompanying drawings. This pouring funnel is then placed above the test cell whereupon the plunger 24 is moved inwardly thus releasing the traps 21 and 22 and permitting the sample to descend into the test cell 1, the dispersing cap 11 causing the material to flow evenly around the central electrode 9, thus providing a constant loading method which will give a similar degree of packing irrespective of the number of times that the sample is tested. The potlirling funnel 18 should then be removed from the test eel It will be seen that the sample of the material now loaded within the test cell effects the circuit capacity of the oscillator 30 thus detuning same causing a current to flow in the coupling circuit. Therefore, power will be transferred from one oscillator to another in an effort to keep the two locked in frequency and, in this connection, it should be noted that a change in the circuit capacity of oscillator 30 of as little as 0.01 ,u tf, will cause a change in the circulating current as indicated by the meter. In order to bring the tuning of the oscillator 30' into alignment with that of oscillator 30, the variable calibrated condenser 39 is rotated by means of knob 40 until once again there is a minimum current flow within the coupling circuit as indicated by the meter 32. In other words, the needle of this meter should be as far to the left of the dial as possible (with reference to Figure 1).

The reading of the calibrated condenser is then compared to a chart prepared for the material being tested whereupon the percentage moisture can be read from the chart. In this connection it will be appreciated that charts are provided for any material being tested, these charts being prepared by the correlation of many determinations of moisture by laboratory methods.

Means are provided to check the over-all accuracy of the instrument at any time thus enabling the operator to ensure that the readings taken are accurate determinations of the moisture present in the material being tested. This procedure entails calibrating the instrument as hereinabove described and then weighing out two separate samples of a given material, one sample being approximately three times the weight of the other sample. For the purpose of this application, hard spring wheat of grade 1 or 2, and having a moisture content somewhat less than is used, the two weights being 150 grams and 50 grams.

The 150 grams of wheat are then loaded within the test cell 1 and the dial reading on the calibrated variable condenser 39 is taken for the minimum current flow within the coupling circuit.

This sample is then removed and the 50 gram sample loaded within the cell whereupon the switch 43 is closed thus cutting in the condenser 37. The dial reading on the variable condenser 39 is again taken for the minimum current flow within the coupling circuit and after these two readings have been repeated several times an average is taken of both sets of readings which are then compared tg a l:est graph in order to determine the accuracy of the c ec In conclusion, it should be stressed that the frequency used in this instrument is between 18 and 20 megacycles as compared With a usual frequency of less than one megacycle thus reducing to a minimum false determinations of the moisture content of material normally arising due to surface moisture being present on the grains or particles thereof.

Since various modifications can be made in our invention as hereinabove described, and many apparently widely different embodiments of same made Within the spirit and scope of the claims Without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.

What we claim as our invention is:

1. A test cell for use with a unit for the determination of the relative moisture content of a mass of grain, macerated or comminuted material, said cell comprising in combination an outer container constituting one electrode of said cell, a concentrically disposed central electrode insulated from said container, and means to counteract the increase of dielectric constant of said material due to the packing thereof in said cell, said means comprising the provision of a greater space between said central electrode and said outer container at the base thereof than at the upper ends thereof.

2. A test cell for use with a unit for the determination of the relative moisture content of a mass of grain, macerated or comminuted material, said cell comprising in combination an outer container constituting one electrode of said cell, a concentrically disposed central electrode insulated from said container, and means to counteract the increase of dielectric constant of said material due to the packing thereof in said cell, said means including a cylindrical outer container, said central electrode including a main portion and a material dispersing cap superimposed upon said main portion, said main portion taking the form of an inverted truncated cone whereby the distance between said central electrode and said container at the base thereof is greater than the distance between said central electrode and said container at the upper ends thereof.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,890,545 Limbrick Dec. 13, 1932 2,251,641 Stein Aug. 5, 1941 2,266,114 Bartlett Dec. 16, 1941 2,266,316 Martin et al. Dec. 16, 1941 2,422,742 Odessey June 24, 1947 2,542,928 Kimball et al. Feb. 20, 1951 2,544,012 Edelman Mar. 6, 1951 2,576,772 Bernet et al. Nov. 27, 1951 FOREIGN PATENTS Number Country Date 524,510 Germany May 8, 1931

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