US 2692972 A
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Oct. '26, 1954 K. EDGERTON ET AL 2,692,972
HIGH-FREQUENCY MOISTURE REGISTER WITH BUTTON-TYPE ELECTRODE Filed April 19, 1951 4415527- 6. foac'lera'zv" Marv/1v 4. Ma. flew 6? INVENTOR.
iatented Get. 26, 1954 HIGH-FREQUENCY WITH BUTTON Albert K. Edgerton,
MOISTURE REGISTER TYPE ELECTRODE Roscoe, and Marvin L. osemead, Calif.
Application April 19, 1951, Serial No. 221,901
3 Claims. 1
This invention relates generally to moisture register systems, and more particularly to high frequency moisture register systems having electrodes for applying high frequency electric fields to substances to be moisture tested.
For an understanding of prior systems of the general type with which the present invention is concerned, reference may be directed to Patent No. 2,231,035 issued February 11, 1941, to Robert L. Stephens and James P. Dallas. The method consists in subjecting the material to be tested to the influence of a high frequency electric field put out by a test electrode unit, thereby causing a change in the electrical state of the electrical moisture register circuit which energizes the electrode unit, which change may for instance be read on an indicating instrument, or utilized to effect a control operation, etc. In accordance with a preferred type of moisture register circuit, disclosed in the aforesaid Patent No. 2,231,025, the system operates or reads in terms of the power absorbed from the electric held of the test electrode unit by the power absorbing factors, e. g., moisture content, in the material placed in said field. It should be stated, however, that while the electrodes may be operated in conjunction with test or control equipment on a power absorption principle, no limitation thereto is to be implied, since the electrodes of the present invention are adapted for use of moisture register circuit, such as those operating on the dielectric constant or frequency change principle.
Previously known electrode units or the general class to which the invention appertains are disclosed in Patent Nos. 2,123,812 and 2,219,497 to Robert L. Stephens and James P. Dallas. Such electrodes are of a co-planar type, i. e., they comprise two or more electrode elements in a common plane, so as to be capable of placement flush against a surface of material to be subjected to test. The electric field between electrode elements of opposite polarity projects or arches beyond the common plane of the electrode elements and so penetrates the material on test. Previously known electrode units of this class, such as disclosed in the above-mentioned patents, are well adapted for measurement of moisture content in a body of material having a flat face to which the electrodes can be applied, particularly if such surface be reasonably smooth. Thus, such electrodes have in some instances comprised a pair or set of flat co-planar plates of some substantial area, which can readily be applied flat against such a surface. It is somein various other types times desired, however, to make a moisture test on a material that does not present a flat or smooth surface. For instance, the material may be a piece of rough lumber, or a textile sample, and electrode units of the type hereinbefore mentioned are not suitable for application thereto.
It is accordingly a primary object of the present invention to provide a moisture register system including an electrode unit of the class mentioned which is adapted for application to surfaces departing from smooth, fiat planes, as for example, rough lumber, textiles, pebble grain plaster walls, etc.
Previously known electrodes of this general class have suifered from the fact that the read ing obtained depends, among other things, upon the pressure with which the electrode is exerted against the material to be tested. A further object is accordingly the provision of an electrode unit of the class mentioned which has provision for eliminating the variability factor owing to different degrees of pressure application against the material.
Also, in some prior electrodes of this class, certain variable capacity effects are introduced during operation, causing erratic results. A further object of the invention is accordingly the provision of such an electrode unit whereby variable capacity elfects within the electrode structure itself are avoided.
The invention will be best understood from the following detailed description of one present illustrative embodiment thereof, reference for this purpose being had to the accompanying drawings, in which:
Figure l is a sectional view taken through the electrode unit, being a section taken on line 22 of Figure 2;
Figure 2 is a rear face unit; and
Figure 3 is a front face view thereof.
In the drawings, numeral HI designates generally a disk-shaped base, formed of any suitable insulation material, such as a synthetic resin plastic, or the like. Secured to the back of this disk H], as by screws H, is a rear cover disk 12, also formed of insulation material. This assembly may be carried or supported in any suitable or convenient way, not necessary to illustrate here. It may for example form the nose of an instrument carrying the electronic moisture measurement circuit, but these structural details form no part of the invention and are not necessary to illustrate herein.
Extending through disk view of the electrode 10 is a centrally located aperture l3, and a plurality of apertures M arranged in a circle around aperture l3, there being eight of the apertures M in the present in stance. Disk I2 has, correspondingly, a contrally located aperture l5, and a plurality of apertures it alined with the apertures I4. The apertures l5 and I6 are of a reduced diameter as compared with apertures l3 and 14, for a purpose which will presently appear. Disposed in the axially alined apertures 13 and I5 is a cylindrical pin 18, of slightly less diameter than aperture l5, so as to fit with suificient looseness in aperture I5 as to be capable of some wobble, and on the outer end of this pin I8 is an electrically conductive electrode disk 20. The rearward end of pin [8 carries a snap ring 2! adapted to engage against the rear face of disk H to limit the separation of disk with reference to the front face of disk II], as shown in Figure 1, and
an electrically conductive coil spring 22 surrounding pin l8 and acting between disk 20 and disk 12 yieldingly urges the pin l8 and electrode disk 20 away from the disk i6. Similarly, apertures l4 and it have disposed therein pins 22,
loosely fitted in apertures l6, and carrying at their outer ends smaller electrically conductive electrode disks the rearward ends of pins 22 carrying snap rings 24 which limit projection of .the pins 22 and electrode disks 23 from the front face of the device.
Electrically conductive spring 26 surrounding pins 22 yieldingly urges the electrode disks 23 and pins 22 to the illustrated position of extension.
Formed on the front face of the disk Hi are a plurality of spacing lugs 30, of greater thickness, 1
or dimensional projection from the front face of disk [8, than the thickness of the electrode disks 2!! and 23, so that when the electrode device is applied to a sample of material, the disks 2!) and 23 may recede to a position where their outer face is co-planar with the forward face of the lugs 30, but with a spacing distance remaining between the inner surface of said disks 20 and 23 and the forward face of disk it. This clearance space so preserved between the disks 20 and 23 and the front face of the disk It assures the preservation of a substantial air gap between said disks 2c and 23 and the insulation disk ID. If this air gap were to be eliminated, the dielectric substance of the insulation disk I!) would strongly affect the electric field between the back surfaces of the central electrode disk 20 and the back surface of the electrode disks 23, giving materially increased capacity effects which would throw oir very materially the accuracy of the results obtained by the moisture measurement instrument connected to the electrode. Also, it will be seen that the final resting position of the disks 20 and 23 will be independent of the pressure with which the electrode device is pressed down against the material to be tested. The degree of pressural application of the disks 20 and 23 to the material on test will therefore depend entirely upon the spring pressure exerted by springs 22 and 26 in the retracted (dotted line) position of the disks and not upon the degree of pressure with which the unit as a whole is applied to the material.
The springs 22 and 26 ar soldered to the rearward faces of the electrode disks 2:) and 23, respectively, and the other ends of these springs are extended somewhat tangentially, for example, as indicated at 33 in Figure 2, and to these extensions are connected the electrical conductors which lead to the electric moisture measurement circuit. As here indicated, an electrically conductive loop 34 is connected to the several springs 26, and has extending therefrom a conductor 35 extended outwardly through disk 12 and connected to lead 35 going to moisture measurement instrument M. In a similar manner, there is connected to spring 22 a conductor 31, which extends outwardly through disk I2, and is connected to lead 38 going to measurement circuit M. It will be seen that this measurement circuit may be similar to that referred to in the aforementioned Patent No. 2,231,035. It is usually and preferably of a high frequency type, and it functions to create a high frequency field between the electrode elements to which it is connected.
In operation, the electrode unit is applied directly to the surface of the material to be tested, for example a piece of rough lumber, or the like. The spacer ribs 3d engage directly against the material to be tested, while the electrode disks 20 are forced rearwardly, against their extension springs, to the positions illustrated in dotted lines. In such position, the degree of pressure exerted by the electrode disks against the material is governed exclusively by the extension springs, and is independent of the degree of pressure with which the electrode unit is forced against the material. Also, in this position, the electrode disks remain substantially spaced from the electrode disk l9, and hence there is preserved an adequate air gap between the rear faces of the several disks, so that the capacity of the unit is not materially influenced by the proximity of the insulation disk IS. The spacer may well be designed to provide for an air gap for this purpose of say 1 or even larger.
It will be seen that the central disk 20 comprises one element of an electric condenser, and the peripheral disks Z3, taken as a group, comprise the other element of the condenser. An electric field arches forwardly from the unit between the disk 20 and each of the disks 23, and this field penetrates the material to which the unit has been applied, the material on test thus, ineifect, coming into the field of the condenser and influencing its dielectric and power loss characteristics. These characteristics are reflected and read in the circuit of the moisture measurement circuit M. It will be clear that in such a device, back capacity effects between the rearward faces of the disks 23 should remain substantially constant. and this has been achieved through making provision for maintaining the disks 2i! and 23 at an adequate clearance space from the disk Hi. It will be seen also that the geometry of the electrode configuration is such that the cylindrical pins l8 and 22 moving through the insulation disks [9 and I2 will not affect the capacity of the unit.
The invention has been disclosed in a present preferred embodiment, but it will be understood that various changes in design, structure and arrangement may be made without departing from the spirit and scope of the invention.
1. An electrode unit for a high frequency moisture measurement system, comprising: an insulation wall structure comprisin an assembly of forward and rearward insulation walls secured to one another, a plurality of pairs of alined apertures through said walls, the apertures in the forward wall being of greater diameter than the apertures in the rearward wall, pins extending through said pairs of apertures, said pins having a loose fit in the smaller apertures in said rearward wall, electrode disks on the forward ends of said pins, forwardly of said forward wall, coil springs encircling said pins within the larger apertures in the forward wall, said springs acting between said electrode disks and the inner face of said rearward wall, stop means on the rearward ends of the pins engageable with the rearward wall to limit extension of the pins and disks from the forward wall, and spacer means projecting forwardly from the forward wall a distance greater than the thickness of said electrode disks.
2. For use with a high frequency moisture measurement circuit adapted to energize opposed capacitor electrodes to create a dielectric field therebetween, an electrode unit comprising an insulation wall structure having apertures therein, electrically conductive electrode supporting means working in said apertures, laterally extended capacitor electrodes on said supporting means forwardly of said wall structure, resilient means for extending said capacitor electrodes forwardly from said wall structure, the dimensions between the edges of said laterally extended capacitor electrodes bein substantially less than the dimensions between corresponding electrode supporting means, whereby when said capacitor electrodes are energized by said high frequency circuit, the resulting dielectric field will exist primarily between said capacitor electrodes and will be materially weaker between the corresponding electrode supporting means, said capacitor electrodes being retractable against said resilient means toward the forward face of said insulation wall structure to a position in which portions of said wall structure are in the dielectric circuit between the back surfaces of adjacent capacitor electrodes, thereby tending to form condensers providing substantial leakage paths for dielectric flux, and spacer means on said insulation wall structure projecting forwardly from said wall structure and having forward surfaces engageable with the surface of a sample of material to be tested, said capacitor electrodes having a.
thickness dimension measured parallel to the direction of their extension movement that is less than the ditance between the plane defined by said surfaces of said spacer means and the surface of said wall structure in back of said capacitor electrodes, whereby an air gap is preserved between said capacitor electrodes and the surface of the insulation wall structure when the capacitor electrodes are retracted into positions with their outer faces coinciding with said plane of said spacer means, which air gap reduces said dielectric leakage flux to a negligible value.
3. An electrode unit for a high frequency moisture measurement system, comprising: an insulation wall structure, apertures through said wall structure, pins loosely fitted in said apertures reciprocable through said wall structure, electrode disks on the forward ends of said pins forwardly of said wall structure adapted for application to the surface of a sample and capable of a limited wobble as they are applied to the sample by virtue of said loose fit of said pins in said wall structure, spring means for extending said pins and disks forwardly from said wall structure, stop means for limiting the forward extension of said pins and disks, and spacer means on the forward face of said wall structure engageable with the sample of material to be tested, said spacer means pro- J'ecting forwardly from said wall structure a distance greater than the thickness of said disks, whereby to limit the retraction of said disks when said wall structure is applied to the sample to a position wherein an air gap is retained between the rearward faces of the disks and the forward face of the wall structure.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,895,643 Putnam Jan. 31, 1933 2,123,812 Stevens et al July 12, 1938 2,476,943 Brady July 19, 1949 2,502,059 Muzzey Mar. 28, 1950 2,544,673 Haber Mar. 13, 1951