CA1135970A - Attitude compensating indicator - Google Patents

Abstract

TITLE

ATTITUDE COMPENSATING INDICATOR

INVENTORS

Samuel RUBEN
Philip T. KALKER

ABSTRACT
There has been a long existing need for an acurate indicator assembly to monitor, for example, a level of liquid in a container such as a fuel tank, steam boiler or the like, when the same is subject to continuous motion when in use. Thus, disclosed is an indicator which comprises an attitude compensating sensor comprising at least one variable resistor assembly disposed adjacent to the bottom container. The resistor assembly comprises weight responsive variable resistors located in the fluid connection with the bottom of a fluid container and may be conviently located in the support structure of the container and in communication with the movable wall near the lower end of the container. The housing defines a passage-way which makes contact with external ambient air by connection to a opening provided in a wall of the container where the sensor itself comprises a paired resistors which are directly electrically connected to an electronic current responsive meter that is calibrated to indicated the liquid content.

Description

~L~3Si9~() BACKGROUND OF THE INVENTION
This invention relates to indicating apparatus and par-ticularly to electrically operated indicating apparatus respon-sive to changes in electric current.
The use of electrically responsive indicating apparatus to measure certain physical conditions, such as temperature, pressure and liquid level is well known. Further, many of the indicating apparatus have employed devices which measure the change in the particular physical state as a Function of elec-trical resistance, with the results of the measurement appro-priately displayed on an ammeter. Indicator assemblies employing the measurement of resistance are found in U.S. Patent No. 1,285,145 to Harrington et al., U.S. Patent No. 1,705,158 to McCoy, U.S.
Patent No. 2,004,421 to Smulski, U.S. Pa-tent No. 2,333,406 to Ballard, U.S. Patent No. 2,339,021 to Lingel, U.S. Patent No.

2,883,623 to Hastings et al., U.S. Patent No. 2,985,019 to Colvin, U.S. Patent Nos. 3,013,233 and 3,013,234 to~ourns, U.S. Patent No. 3,247,716 to Ranke, U.S. Patent No. 3,630,087 to Ogden et al., U.S. Patent No. 3,638,481 to Wilner, and U.S. Patent No. 3,640,134 to Hop.
The majority of the above listed patents are generally related to the measurement of a physical state as a Function of resistance. Certain of the patents, including the patents to Bourns, Ranke and Colvin, attempt to measure differences in pres-sure to arrive at a pressure ratio by the employment of paired resistance elements or transducers appropriately linked. Ogden et al. and Hop attempt to balance separate pressure readings to arrive at a mean value.
The prior art represented above also discloses a wide variety of transducer elements, ranging from the coiled struc- `
tures known as Bourdon tubes, and including bellows-type re-sistors, piezoresistive elements, as well as simple mechanical ~359~0 linkage between a floa-t member and a rheostat arm. All of the indicator assemblies d-iscussecl above possess certain deficien-cies in that they are in most instances complicated devices that are costly to manufacture and maintain, or in the alterna-tive are simple devices less expensive to manufacture however in-accurate in performance.
A need has long existed for an accurate indicator assembly to monitor, for example, a level o-f liquid fuel in a container such as a fuel tank, steam boiler or the like, which is subject to motion in use. Specifically, in the instance of marine vessels and aircraft, the fuel tanks are necessarily subjected to constant changes in attitude from the horizontal which ren-ders the accurate metering of the fuel level extremely difficult.
Attempts to adapt the transducers shbwn in the prior art have resulted in complicated, cumbersome assemblies which were gen-erally unreliable and costly. Thus, for example, the device disclosed in the patent to Hop comprises a particularly complex assembly attempting to derive accurate measurement through a measurement of pressure differentials at various points in the fluid container, which pressure differentials are then fed into a summing and dividing circuit which is designed to arrive at a mean value. A need thus exists for a simple, space-saving and accurate indicator assembly.
SUM~lARY OF THE INVENTION
In accorclance with the present invention, an indicator is disclosed for measuring the liquid content of a container, which comprises an attitude compensating sensor comprising at least one variable resistor assembly disposed adjacent the bottom of the container. In the instance where two or more resistor assemblies are emp~loyed, the resistor assemblies are located at opposite ends of the container and are electrically connected to each other in series.

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The resistor assemblies comprise weight responsive variable resistors loca-ted in Fluid connection with the bottom of a fluid container and, in one embodiment, may be located within the container and supported within a housing and in com-munication with a movable wall near its lower end. The housing also defines a pssageway which makes contact with the external ambient air by connection to an opening provided in a wall of the container. In one embodiment, the resistors employed in -the invention may be of the compression type, anJ the housings are in registry with openings located in the top wall of the con-tainer.
The sensor comprising the paired resistors is directly electrically connected to an electric current-responsive meter which is calibrated to indicate liquid content. Electric power may be provided to the indicator by connection to an appropriate voltage supply, such as a storage battery or the like. The exact construction of the current-responsive meter useful in : the present indicator may vary, and, in one embodiment, may include a meter adapted to compensate for variations in the output of the voltage supply.
Accordingly, it is a principal object of the present invention to provide a liquid content indicator as aforesaid which provides constant level indication unaffected by changes in the attitude of the container.
It is a yet further object of the present invention to provide a liquid content indicator as aforesaid wherein said liquid content is measured as a function of electrical resistance.
It is a yet further object of the present invention to provide a liquid content indicator as aforesaid which is of simple, unobtrusive construction and insulation and offers con-sistent accuracy in operation.
Other objects and advantages will become apparent to ..

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those skilled in the art from a review o-f the ensuing descrip-tion which proceeds with reference -to the following accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a fragmentary schematic side sectional view illustrating a resis-tor comprising one embodiment of the present invention D
Figure 2 is a Fragmentary side sectional view illus-trating a specific resistor construction comprising an alternate embodiment of the present invention.
Figure 3 is a schematic side sectional view illustrat-ing the sensor of Figure 2 electrically connected and located in a liquid container.
Figure 4 is a schematic side sectional view illustrat-ing an alternate sensor.
I)ETAILED DESCRIPTION OF THE INVENTION
The'indicator of the present invention comprises an attitude correcting sensor comprising at least one variable resistor assembly disposed within a liquid container and adjacent its bottom. A first embodiment of the invention is illustrated in Figure 1 wherein a liquid container 2 shown in fragmentary fashion is fitted with a variable resistor assembly 4. Re-; sistor assembly 4 comprises a housing 6 mounted within container 2 by fluid-tight attachment to side wall 9. Housing 6 extends ~, from side wall 9 into proximity with bottom wall 10 of container 2, where it defines a chamber 12 which provides support for a weight responsive, variable resistor 14. Chamber 12 comprises an upper wall 16 which is connected to a neck 18 which extends into - , fluid-tight contact with wall 9~ Neck 18 provides an air passage-way which mates with an axially aligned opening 20 provided in side wall 9 and thereby places the interior of housing 6 in fluid contact with the ambient atmosphere outside container 2. The ,:~

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placement of the internal environment o-F housing 6 in registry with the external ambient serves, among other things, to allow the resistors 14 to compensate themselves for any changes of atmospheric pressure exerted upon the contained liquid that may take place. This particular feature is especially valuable in the instance where the indicator of the present invention is installed in the fuel tank of an airplane.
The present invention includes the provision of housing 6 in fluid-tight connection with any of the walls of container 2, so long as the above functions of support and contact of housing 6 with the external ambient are possible. The construction shown in Figure 1 is therefore intended to be illustrative of one embodiment, as further embodiments are shown in Figures 2, 3 and ~, to be discussed in detail later on.
~lousing 6 comprises at least one movable wall respon-sive to changes in liquid weight, and situated ;n communication ;
with the weight responsive variable resistor mounted therein.
Referring further to Figure 1, housing 6 defines a movable wall communicating with variable resistor 1~, comprising lower wall 22, which is situated in substantial alignment with bottom 10 of container 2. As noted, lower wall 22 is adapted to move in response to the changes in the weight of liquid occurring as a function of variations of liquicl levelO Thus, for example, an increase in the level of liquid 24 exerts greater weight and ;-~
pressure against lower wall 22 which forces lower wall 22 upward~
and toward upper wall 16.
In the illustration of Figure 1, variable resistor 1 is schematically depicted and comprises a conventional wire wound resistance element 26 along which a sliding conductor 28 is de-signed to travel. Accordingly, when lower wall 22 moves toward upper wall 16, conductor 28 moves along element 26 to cause a decrease in the resistance, and a corresponding increase in the ;

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current output issu-ing from resistor 14.
In the embodimen-t illustrated in Figure 1, the move-ment of lower wall 22 is facilitated by the provision of movable side wall 30, which is adapted For lateral movement. Side wall 30 is preferably prepared from a flexible, resilient material and may, as illustrated, assume a bellows-type configuration to accommodate the movement oF lower wall 22.
Resistor 1~ is shown in Figure 1 as mounted between upper wall 16 and lower wall 22, whereby the movement of lower wall 22 causes a change in the resistance output. Upper wall 16 remains stationary, as does neck 18, and therefore the resistor 14 is preferably mounted adjacent these stationary structures, in addition to i-ts contact with the movable wall, to facilitate the occurrence of the changes in resistance. Thus, as will be noted with reference to Figure 2 below, the resistor of the present invention may be mounted in attachment to the neck, as well as the upper wall of the housing. In this regard, the integral diameter of neck 18 is not critical, however, neck 18 may have a diameter less than that of chamber 12.
The sensor of the present invention may be constructed from a variety of materials sufficiently resistant to pressure and inert to the liquid environment, particularly in the instance where the liquid is a hydrocarbon fuel. Thus, the housing, in-cluding the neck and the stationary portions of the chamber may be constructed from a wide variety of pressure and corrosion re- ~ ;
sistant metals, such as stainless steel and the like. The portions of the chamber requiring resilience and flexibility may be con-structed from materials selected from the group consisting of thin gauge metals exhibiting acceptable bencl strength, such as beryllium-copper alloys~ employed in thicknesses of up to about two mils; certain resinous materials comprising silicon polymers including polysiloxanes; and certain organic resinous materials including polyolefins such as polyethylene and polypropylene.
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Further discussion of materials useful in accordance with the construction of the present invention will proceed with refer-ence to specific embodiments later on.
As noted above, the present indicator comprises a sensor including at least two variable resistor assemblies which may be located within a liquid container adjacent its bottom and at opposite ends thereof, adapted to compensate for changes in the attitude of the container with respect to the hor;zontal so that the accurate measurement of the level of liquid within the container will not be adversely aFfected. In this regard, the preceding discussion has dealt generally with one construction of a resistor assembly useful with the present invention, and the following description will relate to a resistor assembly somewhat variant therewith.
. Referring now to Figure 2, a resistor assembly in accord-ance with a ~urther embodiment of the present invention employs a variable resistor known as a "compression type" resistor. The compression type resistor functions by the variation of contact resistance between materials which have negative pressure re-:20 sistance coefficients or which function by the compression oFa mixture of powder or flake of a conductive material with an insulating material, whereby compression, in effect, increases the electrical pathways provided by the resistor mixture. A par-ticular resistor functioning as a "compression type" resistor useful in accordance with the present invention is disclosed in ;
U.S. Patent No. 2,375,178, issued May 1, 19~5, entitled "VARIABLE
ELECTRICAL RESISTER", and invented by Samuel Ruben. The resistor material disclosed in Ruben comprises a fibrous inorganic mat such as a glass mat or the like which has been impregnated with a resistor materlal, such as colloidal graphite, platinum, nickel or the like, after which the impregnated mat is heated to bond the resistor material firmly thereto. The exact resistance values .. ~,.. ~ .

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exhibited by the resulting resistor ma-terial can be controlled by varying the amount of impregnant employed. Further details respecting the process and opera-tion of the resistor of Ruben will not be enumerated herein as they are not believed material to the present invention, and the artisan is accordingly re-ferred to the patent therefor.
Referring now to Figure 2, a liquid container 32 is fragmentarily illustrated and a variable resistor assembly 34 is shown disposed therein. Resistor assembly 34, like resistor assembly 4 in Figure l, comprises a housing 36, a chamber 38 disposed adjacent the bottom wall 40 of container 32, and a neck 42 attachecl to chamber 38. In this embodiment, neck 42 extends upwardly and into contact with top wall 44 of container 32.
Neck 42 1s further modified by the addition thereto of a mounting plate 46, which may be detachably mounted to top wall 44 as illustrated, by the use of an appropriate fluid-tight gasket 48 and bulkhead screw assembl1es 50. Thus, neck 42 cooperates with mounting plate 46 to define an opening 52 which permits the air passageway defined by neck 42 to register with the ambient atmosphere lying outside container 32, as set forth in the discus sion of Figure l, above. The construction of neck 42 simplifies the installation of resistor assembly 34, as container 32 need only be provided with a hole having a diameter slightly greater than the diameter of chamber 38. Appropriate attachment holes may then be drilled and the bulkhead fittings affixed thereto, so that resistor assembly and appropriate gasket 48 need only be lowered into position and firmly fastened by the attachment of the screws as shown.
~- Referring further to Figure 2, neck 42 is illustrated as detachably attached to chamber 38 by the provision of a threaded collar annularly disposed about neck 42, which is adaDted to enage complementary threads provided within an opening :.

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defined in upper wall 56. Chamber 38 is locked into position ; by the provision of a lock nut 58 and interstitial washer 60 and gasket 62 which assure the maintenance of a fluid-tight connection.
In the embodiment of Figure 2, both upper wall 56 and side wall 64 of chamber 38 are sta-tionary. Side wall 64 is preferably cylindrical and thus defines a circular opening for the reception of a movable lower wall 66. The inside edge of side wall 64 is chamfered at its lower end to deFine a circum-ferential ledge 68. The outside edge of side wall 64 justannularly displaced from ledge 68 is threaded to receive a circu-lar internally threaded lock nut 70 which cooperates with ledge 68 to retain the peripheral edge of lower wall 66. Additionally, a circumferential gasket 72 may be provided to embrace the peripheral edge of lower wall 66 to assure a fluid-tight seal between lower wall 66 and side wall 64. Though the foregoing ~ -construction is illustrated and described, it is to be understood that the present invention is not limited thereto but includes other constructions accomplishing the same purpose of providing -a fluid-tight connection between respective walls.
Referring further to Figure 2, re~istor assembly 34 is provided with a weight responsive, variable resistor 74 `
mounted within chamber 38 in communication with movable lower wall 66. Resistor 74 is compression responsive, and lower wall 66 is prepared from a flexible material capable of oscillatory movement to exert compressive force on resistor 74 to cause a variation in its current output. Lower wall 66 is disposed in generally parallel relation to bottom wall 40, and moves in re-sponse to force imposed by the weight of contained liquid 76.
Resistor 74 is fixedly mounted within chamber 38 by attachment to an extension of neck 42, adjacent upper wall 56. The pro-vision of neck 42 in this construction simplifies the assembly o-f resistor 74, as well as that of chamber 38, as described earlier.
As noted earlier, resis-tor 74 is d compression type resistor which employs at least one mat of resistive material-impregnated glass fibers prepared in accordance with the '178 patent. In the present illustration7 resistor 74 comprises paired mats 78 and 80 which are disposed in electrically insu-lated coplanar relation to each other and in contact with lower wall 66. Mats 78 and 80 are separated along their adjacent peripheral edges by the provision of a flexible insula-tor strip 82 and are mounted respectively, on individual support plates 84 and 86, which are likewise disposed in electrically insulated coplanar relation. Electrical insulation is provided by insu-lator strip 82 which extends between the peripheral edges of plates 84 and 86, and an appropriate insulator sheet 88 which extends over the upper surfaces of both support plates. Support plates 84 and 86 are in turn attached to a base plate 90 which, as illustrated, is likewise electrically conductive. Support plates 84 and 86 are thus provided with rod-like a-ttachment pegs or screws 92 and 94, which are adapted to seat within appropriate holes provided in base pla-te 9~ As shown in Figure 2, support plate 86 is electrically insulated from base plate 90 by the provision of a continuation of insulator sheet 88 into the opening provided in base plate 90 for the reception of attachment screw 94.
Base plate 90 comprises an essentially planar structure which further includes resistor mounting means 96, comprising a bracket-like extension disposed in perpendicular relation to base plate 90 for attachment to neck 42 in any conventional manner such as that illustrated herein~
In operation, resistor assembly 34 is surrounded with liquid 76 which impinges on lower wall 66 and causes lower wall ~`

1~35~170 66 to deflect in the direction of resis-tor 74. In this embodi-ment, lower wall 66 completes the circui-t between mats 78 and 80 and therefore is prepared from an electrically conductive material, such as beryllium-copper alloy. ~s employed, the thickness of lower wall 66 is preferably between about 1.5 and 2 mils. Further, it is preferably in accordance with the present invention -that the motion of the glass fibers contained in mats 78 and 80 be damped somewhat by the impregnation of the mats with a viscid dielectric fluid such as machine oil, mineral oil and -the like.
In this manner, the resistance ou-tput of resistor 74 ls more uniform.
Referriny now to Figure 3, the indicator of -the pres-ent invention is illustrated schematically in its entirety.
Thus, container 32 is illustrated provided with a sensor com-prising paired variable resistor assemblies 34 located at oppo-site ends of the container and electrically connected to each other in series by the provision of connecting wire 98. In accordance with this invention, wire 98 passes between resistor assemblies 34 and travels through the passageways defined by respective necks 42. In general, electrical connect;on may be achieved by direct provision of connecting wires such as wire 98, as illustrated in Figure 1, or by association of part of the resistor with a conductive member of the assembly, such as, for example, neck 42 and mounting plate 46 as illustrated in Figure 2.
;; Electric current issuing from the last in series of resistor assemblies 3~ travels directly to an electric current responsive meter 100 which is adapted to register and depict the liquid content as a function of the total resistance developed by resistor assemblies 34. As noted, the selection of a particu- -lar electric current responsive meter is not critical, as the sensing assembly of the present invention provides a constant -, ~"

~L3~ 70 total resis-tance ou-tput -to the meter at a particular liquid level which is already correc-ted for variations in attitude from the horizontal posi-tion of container 32. Thus, any me-ter cap-able of being appropriately calibra-ted to convert variations in electrical resistance into corresponding liquid levels -is oper-able.
In accordance with a particular embocliment, meter 100 may include means for compcnsating its readings for variations in the output of the voltage source. Such a meter struc-ture is well known in the art and is illustrated in U.S. Patent No.
2,004,421, issued June 11, 1935, entitled "INDICATING APPARATUS", by Theodore J, Smulski. The Smulski meter includes paired coils so arranged as ko place the voltage source, comprising a battery, in parallel relation to one coil thereof.
The indicator of the present invention further includes a source of voltage, which may be of either alternating or direct current, and in a preferred embodiment illustrated herein, may comprise direct current derived from a storage battery, such as battery 102 schematically represented in Figure 3.
A further embodiment of the present indicator is shown in.Figure 4, wherein the sensor comprises welght-responsive resistors 104 and 106, controlled by weight-sensitive elements 108 and 110, all disposed external to contalner 112, but in fluid communication therewith. Elements 108 and 100 may comprise Bourdon tube gauges. A Bourdon tube gauge is essentially a metal tube having a flattened oval section that is bent to a curve, the free end 114 being closed and the fixed end open to the pressure exerted by the liquid medium under measurement. This ` :-pressure tends to straighten the bent tube, and its consequent measurement is communicated by means of a linkage 116, a toothed sector 118 and a pinion 120, to the axis of a needle or pointer 122, comprising a rheostat arm that moves along a rheostat 124 .t , .. .. .
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to vary the output of the resistor. Resistor 106 is identical in construction to resistor 104 and operates in the same manner The employment of Bourdon tubes as the weight-respon-sive elements results in an indicator that is unaffected by variations in atmospheric pressure, as the Bourdon tubes re-spond only to the specific gravity of the liquid within container 112. Similar advantages are available when alternate weight-sensitive elements, such as aneroid bellows, not illustrated specifically herein, are substituted for the externally mounted Bourdon tubes, discussed above.
Ihe present indicator therefore contemplates a variety of transducers, placed both within and outside of the liquid container, to provide an accurate measurement of liquid level.
The sensor is so disposed with respect to the liquid container that the displacement of the container from the hori-zontal attitude, ~ith its consequential shifting of the contained liquid to one side thereof, will cause a decrease in the weight and pressure exerted on the resistor assembly located in the area of reduced liquid level, along with the corresponding de- ~ -crease in current flow. ~t the same time, the increased liquid level residing in the opposite side of the container will apply greater weight and pressure to the other resistor assembly which will result in a corresponding increase in current flow, such that the total current flow issuing from the sensor, com-prislng the individual current outputs of the respective reslstor assemblies will be the same as if the liquid were evenly dis-tributed in a container maintained in the horizontal position.
Thus, the indicator of the present invention compensates for attitude change and provides a constant liquid level reading for a particular liquid content.
In addition, as the liquid content is reduced, the total current output of the respective resistor assemblies will decrease ~:~3~i9~UI

proportionately so that the meter will accurately reflect the change in liquid content ol- the container. Also, the provision of the passageways and the registry of the respective resistor assemblies with the external ambient atmosphere enables the present indicator to automatically adjust for changes in atmos-pheric pressure, such as may be encountered in the ins-tance where the indicator of the present invention is installed in a fuel tank employed in aircraft, The indicator of the present invention finds wide utility and, particularly, is suited for installation in such liquid containers as fuel tanks for au-tomobiles and aircraft, and the s-team boilers of ships, which are all subject to motion and frequent variation in attitude. Also, the resistor assem-blies may be employed singly in containers, particularly in the instance of the resistor assembly of Figure 2.

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Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An indicator for measuring the liquid content of a container comprising:

(a) an attitude compensating sensor comprising at least one variable resistor assembly, said resistor assembly comprising a housing mounted entirely within said container and in proximity with the bottom thereof, said housing defining at least one movable wall capable of movement in response to changes in liquid; and, (b) a weight-responsive variable resistor connected to said movable wall, wherein the movement of said movable wall will cause a change in the electric current output of said resistor and the total resistance of said sensor remains constant for a particular level of liquid content.

2. An indicator for measuring the liquid content of a container comprising:
(a) an attitude compensating sensor comprising at least one variable-resistor assembly, said resistor assembly comprising a housing mounted entirely within said container attached to one wall thereof, and extending into proximity with the bottom of said container, said housing defining at least one movable wall capable of movement in response to changes in liquid weight;

(b) a weight-responsive variable resistor mounted within said housing in communication with said movable wall;
(c) wherein the movement of said movable wall will cause a change in the electric current output of said resistor and the total resistance of said sensor remains; constant for a particular level of liquid content.

3. The indicator of claim 2 wherein said housing comprises a chamber located near the bottom of said container and a neck extending from said chamber into attachment with said container wall, and said resistor is mounted within said chamber.

4. The indicator of claim 3 wherein said neck defines an air passageway and said container wall defines an opening aligned with said passageway, whereby said housing is in fluid contact with the ambient atmosphere outside said container.

5. The indicator of claim 2 wherein said housing is attached to the top wall of said container.

6. The indicator of claim 4 wherein the diameter of said neck is less than the diameter of said chamber.

7. The indicator of claim 3 wherein said chamber comprises an upper wall attached to said neck, and a movable lower wall located in substantial alignment with the bottom of said container, said lower wall adapted to move in response to the changes in said liquid weight.

8. The indicator of claim 7 wherein said resistor is mounted adjacent said upper wall and in contact with said lower wall.

9. The indicator of claim 8 wherein said resistor comprises a compression-type resistor and said lower wall is electrically conductive.

10. The indicator of claim 9 wherein said resistor comprises at least one resistance element, said resistance element comprising at least one compressible glass fiber mat having a coating of a resistor material permanently bonded thereto, said resistor material selected from the group consisting of colloidal graphite, platinum and nickel.

11. The indicator of claim 9 wherein said resistor comprises paired mats disposed in coplanar relation in contact with said lower wall, said mats peripherally separated by a flexible electric insulator, wherein electrical current passes through said resistor by traveling between said mats across said lower wall.

12. The indicator of claim 11 wherein each of said mats is attached to a corresponding support plate, said support plates are electrically insulated from each other and disposed in coplanar relation, and a unitary base plate is provided which is adapted to retain said support plates and includes means for mounting said resistor adjacent said upper wall of said chamber.

13. The indicator of claim 12 wherein said base plate, and said support plates are electrically conductive, and said base plate is electrically connected to one of said support plates, and electrically insulated from the other, (M&Co.File 163-4-1)