US3365936A - Moisture indicating means and method - Google Patents

Description

Jan. 1968 1.. w. HUBIN E AL 3,365,936

MOISTURE INDICATING MEANS AND METHOD Filed July 10, 1964 F ig.6.

Fig.7.

INVENTORS LORRIN W. HUBIN 8 TIMER EVERETT K MENTZER I /W F I g.8 r eirATTORNE I United States Patent 3,365,936 MOISTURE INDICATING MEANS AND METHOD Lorrin W. Hubin, 1055 Waugh Drive, Hubbard, Ohio 44425, and Everett K. Mentzer, 1053 sequoya Drive, Youngstown, Ohio 44514 Filed July 10, 1964, Ser. No. 381,644 7 Claims. (Cl. 73-73) The present invention relates generally to sensing and indicating devices, and more particularly to a novel and improved means and method for sensing the presence or absence of moisture in ceramic and the like structures.

Many applications exist wherein it becomes imperative to determine the quantity or absence of moisture in certain materials. Important among these applications is the determination or indication of the precise time when certain materials have been completely dried in kilns, drying ovens, furnaces, or the like, in order to reduce the costs of the drying process and to prevent damage to the materials being so processed.

A serious problem exists in the determination of moisture content in materials in high temperature environments, inasmuch as the sensing means thus employed is either rendered inaccurate by the ambient temperature, or the sensing means conducts heat into the material to produce localized drying effects and spurious indications of moisture content. Moreover, in certain forms of sensing means, the sensor itself generates localized heating effects, which though small, become significant when the sensing means is operated during relatively long periods of certain drying cycles.

Accordingly, an object of the invention is the provision of a novel and efficient sensing means and method for indicating moisture content, which alleviate the aforementioned difficulties.

Another object is the provision of novel sensing means for indicating moisture content of a given material, which means is arranged so as to minimize the conduction of heat therethrough into the material from a high temperature environment.

A further object of the invention is the provision of a means and method for minimizing the local generation of heat through prolonged operation of certain forms of moisture sensing devices, as during drying operations.

Still another object of the invention is the provision of a moisture sensing device having means associated there with for indicating the exact moment when a material being dried becomes substantially or acceptably moisturefree.

An additional object of the invention is the provision of a novel and efficient circuit arrangement for operating the moisture sensing means disclosed herein and for providing visible indicia determinative of moisture content or lack thereof in a given material during its drying cycle.

These and other objects of the invention are accomplished in accordance with an illustrative embodiment of the invention, wherein a sensory probe for moisture indicating purposes is pressed into the material being dried, if a soft porous structure, or is otherwise fitted into a closely fitting recess therefor in the material. The probe includes a pair of fiat metallic electrodes electrically separated but physically retained and preferably supported by a fiat insulative member inserted therebetween. The electrodes are each provided with a unique configuration "ice which minimizes the transfer of heat *therealong when the probe and the material are placed in a high temperature environment such as a drying furnace, or the like.

The sensory probe is arranged to operate under the effect of electrolytic action when moisture is present in the material, which of course, requires the application of electric potential and the attendant generation of electrolytic currents when the material is not moisture-free. In one embodiment of the invention, a circuit arrangement is associated with the sensory probe for pulsing the application of potential to the probe to avoid continuous generation of electrolytic currents and localized heating which would otherwise prematurely dry the material in the area of the probe. The flow of pulsed current through the probe can then be measured for a periodic indication of quantitative moisture content until the material is completely dried. At such time the end-point or termination of the drying cycle is indicated by the circuit arrangement through the energization of suitable indicia, as: occasioned, in this example, by the absence of current flowing through the probe.

The foregoing and other objects, features and advantages of the invention are elaborated upon during the forthcoming detailed description of the invention, when taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a front elevational view, partly sectioned, of one form of moisture-sensing probe arranged in accordance with the invention;

FIG. 2 is a cross-sectional view of the probe of FIG. 1 taken along reference line II-II thereof;

FIG. 3 is a cross-sectional view of the probe of FIG. 1 taken along reference line III-III thereof;

FIG. 4 is a longitudinally sectioned view of the probe of FIG. 1 taken along reference line IV-IV thereof;

FIGS. 5 and 6 are top and front elevational views respectively of another form of probe arranged in accordance with the invention;

FIG. 7 is an illustration of another embodiment of the sensing probe of the invention; and

FIG. 8 is a schematic circuit diagram of one form of supply and indication circuit arranged in accordance with the invention for supplying a pulsed potential to a sensing device or other load device, for indicating moisture content quantitatively, and for providing an indication of moisture-freedom or zero current flow in the sensing or other load device.

Referring now with more specificity to FIGS. 1 to 4 of the drawings, the illustrative embodiment of the moisturesensing probe shown therein comprises an electrically insulative holder 10, which is further arranged for supporting in spaced, insulated relation a pair of flat electrodes 12 and 14. The holder 10, which can be fabricated from a suitable plastic or reinforced plastic material, is formed with a central web portion 16 and thickened lateral edge portions 18. A pair of opposed grooves 20 are provided respectively in the thickened portions 18 adjacent each side of the web portion 15. Each pair of opposed grooves is disposed and dimensioned to receive respectively the lateral edges of one of the electrodes 12 or 14 in sufficiently tight-fitting engagement to afford physical support therefor.

The probe thus formed is inserted into a moisture-retaining material denoted generally by the reference character 22. In an exemplary application of the invention, the material 22 is a shaped mass of dolomite, sawdust and a binder comprising sodium silicate. Such material is used, for example, in the steel industry for covering crucibles to prevent too rapid cooling of the melt and to promote release of gases from the melt. In this respect, it is essential that the porous dolomite structure be absolutely dry to avoid deleterious interference with the release of such gases and the possibility of explosion due to the formation of steam.

The dolomite or other moisture-bearing material can be dried in a kiln or drying oven or the like, and one or more of the probes of the invention can be inserted into the moisture-bearing material while in the kiln or oven to monitor the moisture content of the material during the desired drying cycle. In this manner, the precise residence time in the kiln or oven can be determined so as to avoid over or under drying of the material. When the moisture-bearing material is so placed, it is apparent that the metallic electrodes 12 and 14 of the probe will readily conduct heat from the hot oven into that part of the moisture-bearing material immediately surrounding the probe and effect an accelerated drying condition, which will cause the probe to yield a spurious indication of dryness.

In order substantially to eliminate such spurious results and to render the probe useful in a high temperature environment, each of the electrodes 12 or 14 is provided with a central necked-down or reduced portion 24, which reduces the flow of heat to the lower or active electrode portions 26 to a negligibly minimal amount. The electro- 'lytic currents, then, are substantially limited to passage between the lower or active portions 26 of the electrodes 12 and 14, at least during the latter drydng stages in the kiln or oven.

The upper portions 28 of the electrodes 12 and 14 are of substantially the same shape as the lower, active portions 26 thereof to afford symmetry to each electrode and permit insertion of either end first into the moisturebearing material. Although the upper portions 28 can be eliminated, or replaced by upward extensions (not shown) of the reduced portions 24, provision of the similarly shaped upper portions 28 and lower active portions 26 is desirable to eliminate operator error in positioning the probe in the material. After the probe is inserted into the material to the desired depth, conductors 30 and 32 are afiixed to the upper protruding ends (FIGS. 3 and 4) of the electrodes 12 and 14, respectively. The conductors can be connected to a suitable source of potential, or to the pulsed power supply circuit presently to be described in connection with FIG. 8.

In FIGS. 5 and 6 an alternative form of moisture-sensing probe is illustrated. The latter probe is similar to that described above, except that electrodes 12' and 14' are adhesively attached or otherwise secured to a fiat insulating support member 34. In this embodiment the latter member is not formed with the grooved edge portions 18 of FIGS. 14.

In FIG. 7, an embodiment of the invention is shown which does not require a necked-down intermediate portion to prevent localized heating at the test area. It again comprises an insulating board 35 having electrodes glued or otherwise secured to its opposite sides, only one of such electrodes 37 being shown in FIG. 7. In this case, each electrode comprises a thin foil of aluminum or other suitable metal having a thickness on the order of about 0.002 inch. Aluminum foil, such as that sold for household use in wrapping foods, will suifice. Preferably the binder for holding the foil to the insulating board is sodium silicate. Alternatively, an aluminum-coated adhesive tape may be employed. In either case, the gage of the foil is such that it will not conduct enough heat down into the body being dried to produce deleterious effects.

Referring now to FIG. 8 of the drawings, a pulsed supply circuit is shown and arranged in accordance with the invention for use with the aforesaid probe. The circuit includes a pair of supply busses 40 and 42 connected to a source of potential via terminals 41 and 43. One of the conductors, conductor 40 for example, includes a seriesconnected, manually operated, on-oif switch 44. Con nected in series across the busses 40 and 42 are a push button-type starting switch 46 and a start and run relay coil R1. When the start button 46 is released, the relay coil R1 is locked in by a parallel path including its own contacts R11, a normally closed, pushbutton-type stop switch 48, and normally closed relay contacts R4-1 (con trolled by relay coil R4 described below). At the same time, relay contacts R12 are closed by coil R1 to en ergize both the primary winding 50 of transformer and a relay coil R2, the function of which is described hereinafter. The energization of the primary winding 50 can be indicated by a pilot lamp 54, if desired.

The secondary winding 56 of transformer 52 is connected to the electrodes 12 and 14 of the probe described above through conductors 30 and 32. As was explained, application of potential to the electrodes 12 and 14 is pulsed to avoid the deleterious effects of localized drying, which would otherwise occur if the electrolytic currents through the moist material 22 were continuous.

The pulsed potential is effected by a suitably cammed timer switch 58 having an appropriately shaped rise and dwell configuration (not shown) to conform to the aforementioned or other desired pulsation schedule. The timer switch 58, which is operated by timer motor 60, is connected in series with pulsing relay coil R3 across the sup ply busses 40 and 42. When energized by the timer switch 58, the relay coil R3 opens its normally closed contacts R3-1 which are connected in shorting relation across the secondary winding 56. When so opened, the shorting eon= tacts R3-1 permit the secondary winding to deliver a pulse to the electrodes 12 and 14. If desired, the flow of electrolytic current between the electrodes 12 and 14 can be indicated by a sensitive ammeter 62, or the like. The ameter 62 can be calibrated to indicate the moisture content in suitable units.

As will be understood, it is desired to furnish visual indica, such as indicator lamp 64, which is energized only when the desired degree of drying is obtained. In this ex ample, the aforementioned supply circuit is further ar ranged to energize the indicator lamp 64 only when the material 22 is completely dry.

In'furtherance of this purpose, the indicator lamp 64 is connected across the supply busses 40 and 42 in series with relay contacts R4-2 which are closed upon energization of indicator relay coil R4. The relay coil R4 is of the slow dropout variety and is energized by timer switch 58 upon closing of normally closed relay contacts R2-1 connected in series with the relay coil R4. When there is moisture in the material 22, however, the contacts R21 are held open by the aforementioned holding relay coil R2, which is energized with current flowing through secondary winding 56. Thus, relay coil R2 remains energized as long as moisture remains in the material 22 and the resultant electrolytic currents impose a secondary load upon the primary winding 50 when the shorting relay contacts R3-1 are opened.

Energization of the indicator relay coil R4 also closes its contacts R43 to lock in the relay coil R4. The contacts R43 are connected serially to the stop button 48 in a parallel path relative to the timer switch 58 and relay contacts R2-1. The thus energized relay coil R4 also opens its normally closed contacts R41 to deenergize the starting and running relay coil R1, which deenergizes the transformer 52. The indicator lamp 64, then, remains on until the stop button 4-8 is actuated to deenergize the indicator relay R4.

To recapitulate the operation of the invention, the electrodes 12 and 14 are first inserted into the material to be dried and the start button 46 depressed with the onofl? switch 44 closed. This action energizes relay coil R1 which is held energized through its now-closed contacts R1-1 and the contacts R4-1 of relay R4. Energization of relay coil R1 also closes its contacts R1-2, thereby energizing pilot lamp 54, the primary winding 50 of transformer 52 and relay coil R2. Current now flows between the electrodes 12 and 14, assuming that the material contains moisture. At the same time, the timer 60 periodically closes contacts 58, thereby periodically energizing relay R3. When relay R3 is deenergized, contacts R3-1 are closed, thereby shorting the secondary winding 56 of the transformer 52. However, when contacts R3-1 are open, current flows between the electrodes 12 and 14, assuming that moisture is present in the material.

When the material being dried is completely free of moisture, and assuming that relay contacts R3-1 are open, no current will flow between the electrodes 12 and 14 and no current will flow in the secondary winding 56 of transformer 52. Consequently, a back E.M.F. will be developed in the primary winding 50 which will oppose the potential between busses 40 and 42. As a result, the current through relay coil R2 is reduced, causing it to drop out, thereby closing contacts R2-1. When contacts R2-1 close, the relay coil R4 becomes energized when contacts 58 close, thereby opening contacts R41 and closing contacts R4-2 and R43. Opening of contacts R41 deenergizes relay coil R1, whereupon contacts R1-2 open to deenergize the primary winding 50 and pilot lamp 54. At the same time, closure of contacts R4-2 energizes indicator lamp 64 to indicate that the material is dry; and contacts R4-3 hold relay coil R4 energized until the stop pushbutton 48 is depressed. When pushbutton 48 is depressed, relay coil R4 become deenergized and the system is again ready for a moisture-sensing operation.

From the foregoing, it will be apparent that novel and efficient forms of a moisture-sensing probe and supply circuit therefor have been disclosed herein. Inasmuch as the descriptive materials herein are exemplary and not limitative of the invention, it will be apparent that numerous modifications of the invention will occur to those skilled in the art without departing from the spirit and scope of the invention. Moreover, it will be obvious that certain features of the invention can be employed with out corresponding use of other features.

We claim as our invention:

1. A moisture-sensing probe for use in a high temperature environment, said probe comprising a pair of elongated generally planar electrode members, an elongated generally flat insulative member interposed between said electrode members, said insulative member having supporting means disposed along its lateral edges and supportingly engaging the adjacent lateral edges respectively of said electrode member, means ttor connecting said members to a source of electric potential, said members each having a reduced portion between said connecting means and an active portion of said electrode to minimize transfer of heat to said active portion.

2. A moisture-sensing probe for use in a high temperature environment, said probe comprising a pair of elongated generally flat electrode members, an elongated generally flat insulative member interposed between said electrode members and secured thereto, said electrode members each having an active electrode portion adjacent each end thereof and a reduced portion extending therebetween to minimize transfer of heat between said active portions, and means coupled to an end of each of said electrode members for connecting said electrode members to a source of electric potential.

3. A moisture-sensing probe for use in a high temperature environment, said probe comprising a pair of elongated generally flat electrode members, an elongated generally flat insulative member interposed between said electrode members and supportingly secured thereto, said electrode members each having an active electrode portion adjacent each end thereof and a reduced portion extending therebetween to minimize transfer of heat between said active portions, the active electrode portions of each electrode member being shaped and disposed on one above the other so that either end of the probe can be inserted, and means coupled to an end of each of said electrode members for connecting said electrode members to a source of electric potential.

4. A moisture-sensing probe for use in a high temperature environment, said probe comprising a pair of elongated generally planar electrode members, an elongated generally fiat insulative member interposed between said electrode members, said insulating member having thickened lateral edge portions extending along its length, each of said thickened edge portions having a pair oi grooves disposed therein on opposite sides respectively of the flat surface of said insulative member for support;- ingly engaging the adjacent lateral edges respectively of said electrode members, means for connecting said members to a source of electric potential, said members each having a reduced portion between said connecting means and an active portion of said electrode to minimize transfer of heat to said active portion.

5. A moisture-sensing probe for use in a high temperature environment, said probe comprising a pair of elongated generally planar electrode members, an elongated generally flat insulative member interposed between said electrode members, said insulative member having thickened lateral edge portions extending along its length, each of said thickened edge portions having a pair of grooves disposed therein on opposite sides respectively of. the flat surface of said insulative member for supportingly engaging the adjacent lateral edges respectively of said electrode members, said electrode members each having an active electrode portion adjacent each end thereof and a reduced portion extending therebetween tominimize transfer of heat between said active portions, the active electrode portions of each electrode member being shaped and disposed on one above the other so that either end of the probe can be inserted, and means coupled to an end of each of said electrode members for connecting said electrode members to a source of electric potential.

6. The combination, with kiln means for drying to essentially complete dryness a metallurgical hot top, of apparatus for determining when said hot top is completely dry during drying of said hot top, comprising a pair of electrodes adapted to be inserted Within said hot top when the hot top contains moisture, means for intermittently energizing said electrodes with an electrical potential at an energization repetition rate which is independent of the amount of moisture in said hot top to minimize the drying effect of currents induced in the hot top between said spaced electrodes, and means connected to said electrodes for indicating essentially complete dryness of said hot top when current no longer flows through the hot top between said electrodes upon application of said electrical potential thereto.

7. The combination, with kiln means for drying to essentially complete dryness a metallurgical hot top, of apparatus for determining essentially complete dryness of said hot top during drying thereof, comprising a pair of electrodes adapted for insertion Within said hot top when the hot top contains moisture, means for intermittently energizing said electrodes with an electrical potential at an essentially fixed energization repetition rate during dry of the hot top to minimize the drying eifect of currents induced in the hot top between said spaced electrodes, and means connected to said electrodes for indicating essentially complete dryness of said hot top when current no longer flows through the hot top between said electrodes upon application of said electrical potential thereto.

References Cited UNITED STATES PATENTS Ives 7373 Kott 7373 Dember 73-3365 Higgins 324- 65 8 Bouyoucos 7373 Kaplan 32465 Peltola 73362 Booth 73-17 RICHARD C. QUEISSER, Primary Examiner.

JAMES J. GILL, Examiner.

JAMES WILLIAMSON, Assistant Examiner.

Claims (1)

1. 6. THE COMBINATION, WITH KILN MEANS FOR DRYING TO ESSENTIALLY COMPLETE DRYNESS A METALLURGICAL HOT TOP, OF APPARATUS FOR DETERMINING WHEN SAID HOT TOP IS COMPLETELY DRY DURING DRYING OF SAID HOT TOP, COMPRISING A PAIR OF ELECTRODES ADAPTED TO BE INSERTED WITHIN SAID HOT TOP WHEN THE HOT TOP CONTAINS MOISTURE, MEANS FOR INTERMITTENTLY ENERGIZING SAID ELECTRODES WITH AN ELECTRICAL POTENTIAL AT AN ENERGIZATION REPETITION RATE WHICH IS INDEPENDENT OF THE AMOUNT OF MOISTURE IN SAID HOT TOP TO MINIMIZE THE DRYING EFFECT OF CURRENTS INDUCED IN THE HOT TOP BETWEEN SAID SPACED ELECTRODES, AND MEANS CONNECTED TO SAID ELECTRODES FOR INDICATING ESSENTIALLY COMPLETE DRYNESS OF SAID HOT TOP WHEN CURRENT NO LONGER FLOWS THROUGH THE HOT TOP BETWEEN SAID ELECTRODES UPON APPLICATION OF SAID ELECTRICAL POTENTIAL THERETO.

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