Abstract:
An improved level indicator takes advantage of the universal visual impression of typical sight glasses, but without the disadvantages of a physical sight glass protruding from the main body of the reservoir. In addition, other quantities are measured, including two-phase presence in a drainage pipe, temperature of the liquid product measured against either the drain pipe or reservoir, and temporal passage. Each of the measured quantities can result in an individual visual indication, or can thresholded combinationally to provide a combined threshold limit for initiating visual indication. A sealed unit is provided low on a food dispensing reservoir and upstream of a dispensing valve with a sensor in fluid communication with the static pressure in the dispensing valve. Because the sealed unit is in communication with the liquid in the reservoir at the lower position only, several alternatives may be utilized to equate the static pressure with the liquid level in the food service container reservoir.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the field of liquid level sensing, and more particularly to liquid level sensing for non hazardous, non-corrosive materials, and specifically to level indicators used in food service equipment.  
       BACKGROUND OF THE INVENTION  
       [0002]     The standard for level indication equipment has for years been the sight glass. Sight glasses are visible channels, typically tubes, which share part of the volumetric capacity of a vessel and which occupy a level in the visible channel the same as the liquid inside the main vessel. Sight glasses have always had operating limitations that the fittings securing the glass must not leak, that the fittings and glass should be able to be secured tightly enough to withstand the pressure inside the vessel.  
         [0003]     Food service vessels typically utilize large round sight glasses having a lower end connected to open into the bottom and an upper end connected into the top of a main liquid reservoir. The liquid level in the sight glass will match the level in the reservoir as gravity pulls on both liquid columns the same. It is not often realized the rough treatment that such vessels undergo during a typical day of usage. Workers are often not strong enough to supply the strength and acumen necessary to treat a heavy vessel with adequate care. A broken sight glass can result in spillage of contents on carpeting, often creating a coffee stain requiring specialized cleanup. Breakage of sight glasses also poses a danger to nearby occupants. Further, a rising number of incidents have been observed where the glass tubes may be intentionally broken by workers to obtain it for recreational drug use. Sight glasses cannot effectively be protected by the use of cages and screens as they would drive up the equipment and maintenance cost significantly, as well as to obscure the visual determination of liquid level. Cleaning and replacement would also then be a problem as any protector would require specialized cleaning and likely removal as a pre-requisite to replacement.  
         [0004]     Having to provide site glasses along the whole effective height of the reservoir also blocks the ability to further utilize other components with it. Insulation blankets cannot be used efficiently where they are so oversized that they cover over the sight glass and create unrestricted air pockets, while a close fitting insulation blanket cannot fit over the sight glass. Other components which are inhibited by the interruption of an even radial surface include protective sleeves, decorative sleeves, advertising, handling instructions and more.  
         [0005]     Another problem with sight glasses is that they must typically be large to insure that enough liquid is swept through them to prevent any collection of debris which might block the sight glass tube. As such, smaller tubes or small flat plastic channels do not work well. Anything smaller than a large glass tube would likely be able to collect debris and to malfunction.  
         [0006]     Sight indicators are important so that food service can be supplied efficiently and accurately. When food and drink reservoirs go empty, users are inconvenienced and sales are lost. When food workers change out half empty containers for filled ones to prevent outages, unused food product is lost. Likewise, hot or cold food and drink which has become room temperature will continue to inconvenience users and result in lost sales. A half reservoir of cold coffee will not be consumed despite a room full of people thirsty for coffee. In terms of overall economics, food service is primarily a service, and when service suffers, sales will suffer. Accommodation must be made to at least enable high level service providers to provide the high level of service when desired.  
       SUMMARY OF THE INVENTION  
       [0007]     An improved level indicator takes advantage of the universal visual impression of typical sight glasses, but without the disadvantages of a physical sight glass protruding from the main body of the reservoir. An improved level indicator takes advantage of the universal visual impression of typical sight glasses, but without the disadvantages of a physical sight glass protruding from the main body of the reservoir. In addition, other quantities are measured, including two-phase presence in a drainage pipe, temperature of the liquid product measured against either the drain pipe or reservoir, and temporal passage. Each of the measured quantities can result in an individual visual indication, or can thresholded combinationally to provide a combined threshold limit for initiating visual indication.  
         [0008]     A sealed unit is provided low on a food dispensing reservoir and upstream of a dispensing valve with a sensor in fluid communication with the static pressure in the dispensing valve. Because the sealed unit is in communication with the liquid in the reservoir at the lower position only, several alternatives may be utilized to equate the static pressure with the liquid level in the food service container reservoir.  
         [0009]     First, an independent ambient pressure sensor may be utilized. This will enable the unit to distinguish between the exact levels of fullness in Denver, Colo. at a mile high altitude versus Long Beach, Calif. at sea level. Second, a calibration routine may be performed on startup where the sensor recognizes a change in pressure equivalent to a transition from empty to full.  
         [0010]     For example, where a reservoir, for example is filled to a height of one foot, and where water is used, the change in static pressure will be from ambient air pressure to the addition of 62.427 pounds per square foot, or 0.43 pounds per square inch(PSI). At a given temperature at sea level, the pressure is 14.696 PSI. At the same temperature one mile above sea level, the pressure may be 12.096 PSI. Yet the range over which the sensor must measure is 0.43 PSI for a one foot water column height. Higher or shorter main reservoirs  31  should have proportionately more or less resolution. In most commercial coffee containers of the type pictured in  FIG. 1 , a pressure measuring ability range of from about 0-28″ water column resolution is sufficient. Thus, the sensor may be programmed to measure a rapid change in pressure and to take the rapid change on fill up, rather than a measure of an a scalar absolute pressure. Thus, it will measure and give an indication of level based upon the rapid 0.43 PSI difference as its working range between an indication of full and empty.  
         [0011]     Third, it may combine pressure sensing of the ambient air pressure in addition to sensing a pressure change on fill-up. Fourth, the sensor may store and record an average set of maximum and minimum pressure values over time to give a time average pressure range as a time average maximum pressure and a time average minimum pressure.  
         [0012]     The sensor of the invention will also have a range of other sensing and service-out indicators. First, the sensor may include an optional “air gap” optic sensor which can be utilized in conjunction with its small elastomeric pressure tube or with a separate sealed fiber optic tube. A light pulse sent into the product tap pipe will reflectively return if the liquid level in the tap pipe is low enough to create a partially filled channel. A light impulse will be returned to the sensor if the liquid level in the tap pipe is not full, representative of the last eighth of an inch range of liquid flow. This can be used to trigger a special flashing alarm to insure that the food service workers recognize it instantly.  
         [0013]     In addition, other indicators can be employed using the same sensor area just upstream of the drain pipe, as well as contact of the sensor with the main reservoir, including temperature. Minimum acceptable temperature of the product can be programmed. In the alternative, the sensor can be programmed to sense the initial temperature of the reservoir and to give a food service indication when it has changed to a temperature within, say 20° Fahrenheit of room temperature. Coffee, for example would begin at about 190° Fahrenheit, and when the temperature drops to say 110° Fahrenheit, an temperature indicator would light. Likewise, iced tea would begin at about 37° Fahrenheit and would give a temperature problem indication at about 60° Fahrenheit.  
         [0014]     For even more closely managed liquid food service dispensing, a time indicator could also be used. The sensor may trigger automatically on fill by either a temperature trigger, hot or cold, or by a fill pressure trigger. The timer may be set to one time difference for initial introduction of a cold liquid and to a second time difference for initial introduction of a hot liquid, or the time may be programmed. Time indications can be important where the sensor of the invention is used with a heated vessel, and where product spoilage or lack of freshness is keyed more to passage of time than to temperature or usage rate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The invention, its configuration, construction, and operation will be best further described in the following detailed description, taken in conjunction with the accompanying drawings in which:  
         [0016]      FIG. 1  is a perspective view of a food service liquid dispenser having a reservoir mounted above an integral stand and having a front tap and protector with the sensor of the present invention shown exploded from it;  
         [0017]      FIG. 2  is a side sectional view taken along line  2 - 2  of  FIG. 1  and illustrating the connection to the valve and drain pipe, with the pressure tap being above the drain pipe; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     The process and apparatus described herein will in concentrate on the somewhat schematic use of a sensor in conjunction with the drain pipe of a liquid food service container upstream of the valve. Referring to  FIG. 1 , a generic arrangement for a food service liquid dispensing container  11  is shown as having an integrated base stand  13  which supports a vessel  15  above.  
         [0019]     The base has a main “U” shaped support  21  to provide easy clearance for the entry of drinking cups and user access. From the main “U” shaped support  21 , a series of vertical columns  23  attach to a base support  25 .  
         [0020]     A main reservoir  31  has a lid  33  with a small vent hole  35 . An optional bail handle  37  is shaped to accommodate the lid  33  and folds away to enable access to the lid  33 . An upper fitting  39  provides some interruption of the main cylindrical surface of the reservoir  31 . A cylindrical surface  41  is generally only interrupted by a tap  43 . Tap  43  in the alternative, could have emerged from beneath the main cylindrical surface  41 , such as from a point underneath the cylindrical surface  41 . The arrangement of the tap can further free the lower areas of the cylindrical surface  41 .  
         [0021]     Tap  43  may have a flange fitting  45  as an expanded area of material acting a washer to spread its bearing surface onto an expanded area of cylindrical surface  41 , especially where it has an insertion portion extending into the inner reservoir (not shown in  FIG. 1 ) and secured with axial force. The tap  43  being shown is non-integrated into the remainder of the inventive sensor and indicator for familiarity and to demonstrate that the sensor and indicator can be supplied to work with existing components, or it can be supplied along with a tap  43  assembly.  
         [0022]     Tap  43  includes a main horizontally disposed faucet shank, or drainage pipe  47  upstream of a vertical drain  49 . Drain pipes need not be horizontal and may be vertical, but the configuration of  FIG. 1  simply happens to have a horizontal pipe  49 . A vertical pipe below a main reservoir would give a maximum vertical pressure head and would be more accurate in determining the pressure throughout a fuller height of fluid head than a horizontal tap, and particularly a tap  43  which is above the lowermost extent of a liquid level in a reservoir  31 . Continuing away from the cylindrical portion  41 , the horizontally disposed drainage pipe  47  includes a fitting  51  supporting an operating handle  53 . A thin conduit  55  extends from the horizontally disposed drainage pipe  47  from a position upstream of the operation of the valve components within the tap  43 , such that the thin conduit  55  is in fluid communication with the liquid within the main reservoir  31 . Thus, the pressure may drop temporarily when the handle  53  is activated to allow liquid to flow through the vertical drain  49 , but when the tap is shut, the static pressure head upstream of the valve opening will be transmittable along the conduit  55 .  
         [0023]     Further, the orientation and size of conduit  55  can prevent contact of the server media liquid with the transducer. The liquid will compress any air present in the conduit  55  tubing to form a meniscus which will not wet the walls of the conduit  55  beyond the liquid/air interface. This liquid-gas dividing line may move back and forth along the length of the conduit as varying pressure is exerted on the transducer due to changes of liquid level in the reservoir. This will allow the air-liquid interface to move, to compress the air bubble against any transducer to which it is connected, yet isolate the actual transducer from liquid contact. This “air bubble isolation” is assists the long term performance and accuracy of the transducer. This method provides for a pressure reading without a hot or cold media directly contacting the transducer die. Potting, or encasement of all components surrounding the end of the conduit  55  will further prevent leakage and contribute to the operation of this principle.  
         [0024]     To the right and displaced from the tap  43  is an sensor housing  61  having a display area  63 . Display area  63  may utilize LED&#39;s or liquid a liquid crystal display. Sensor housing  61  has a lower inverted “U” shape to help integrate the fit over the main horizontally disposed drainage pipe  47 . Where the sensor housing  61  is rigidly attached directly to the main horizontally disposed drainage pipe  47 , the space between the cylindrical surface  31  and the rear of the sensor housing  61  will be available for adding placards, insulating layers, or other flat materials, including signage.  
         [0025]     The end of thin line  55  is shown free, but will be connected to the rear of the sensor housing  61 , possibly into a potted volume. The additional length of thin line  55  could be provided to enable removal of the sensor housing  61 , especially where removal is necessary to change a battery. In the alternative, a side battery door  65  may be provided. Further, a photo voltaic array  67  may be provided to power the electronic components within the housing  61  either alone or as a supplement to a battery located behind the battery door.  
         [0026]     Referring to  FIG. 2 , a sectional view taken along line  2 - 2  of  FIG. 1 , but with the sensor housing  61  in place, reveals further details of the components assembled into an indicator system  71 . Again, the indicator system  71  can be packaged with or without the associated assembly of the tap  43 . From the left, an internal reservoir  73  contains a liquid  75  shown by periodic interrupted horizontal lines. In this instance, the flange fitting  45  can be seen to include a two sided structure with a matching internal flange portion embracing the effective main reservoir wall  77 . The wall  77  can be made of layers of material which may include a sleeve, applied layers, or insulation layers.  
         [0027]     Liquid  75  is seen to freely exist within the flange fitting  45  and the short length of main horizontally disposed drainage pipe  47  extending beyond the flange fitting  45 . A valve sealing member  81  forms a pressure seal into an internal portion of the main horizontally disposed drainage pipe  47 , just before the vertical drain  49  is accessed. In the tap  43 , fitting  51  houses spring biased (spring mechanism not seen to maintain clarity of the drawing) valve sealing member  81  which is constantly biased to enter the end of the main horizontally disposed drainage pipe  47  to shut off the liquid flow.  
         [0028]     Handle  53  is seen to attached to pivot with respect to valve sealing member  81  and any pivoting of handle  53  will cause the valve sealing member  81  to be withdrawn from sealing contact with the inside of the main horizontally disposed drainage pipe  47  to allow liquid to flow into the vertical drain  49 .  
         [0029]     In normal usage, the tap  43  and its assemblage will remain closed the vast majority of the time. Thus, the thin line  55  will be enabled to register the pressure at the main horizontally disposed drainage pipe  47 , and into a circuit board  85  sensor processing circuit  87 . Sensor processing circuit  87  may be a microprocessor having digital and or analog component circuitry and whose main function is to receive sensor signals and to interpret the sensor signals utilizing an instruction set and to send appropriate information to components in the display area  63 , so that necessary states and indications of necessary actions to be taken can be displayed.  
         [0030]     The location of the end of the thin line  55  should be as low as possible with regard to a bottom floor  89  of the internal reservoir  73  as is possible, so that positive pressure will be present throughout the complete range of liquid  75  level within the internal reservoir  73  as is possible. In an integrated indicator system  71 , the sensor electronics may be located immediately adjacent the main horizontally disposed drainage pipe  47 , preferably below or to the side.  
         [0031]     Also seen within the sensor housing  61  is a battery  91  held between a pair of battery contacts  93 . The battery  91  may be connected to the photocell  67  (connection is not shown) to supplement its power or to recharge it, or to allow battery  91  to act as backup power in dimly lit conditions. A potting line  95  is seen to illustrate that all of the components of the indicator system  71  can be potted, and or formed integrally with the tap  43  which will eliminate the need for fittings, eliminate the possibility of disconnection of the thin line  55 , and eliminate any possibility of external leakage. Only the battery  91  and its battery contacts  93  need be outside the potted area. Further, the circuit board  85  and sensor processing circuit  87  may also be made to be located close to the main horizontally disposed drainage pipe  47  to further reduce the size of the indicator system  71 .  
         [0032]     In terms of temperature, an additional blind bore  101  could be provided in the main horizontally disposed drainage pipe  47  with a temperature sensor  103 , such as a thermocouple connected by a wire set  105  to the circuit board  85  sensor processing circuit  87 . As another example, a thermal sensor  111  can be mounted directly adjacent the main reservoir wall, and connected by a wire set  113  to the circuit board  85  sensor processing circuit  87 . The accuracy of either locating a temperature sensor adjacent the main reservoir  31  or within the main horizontally disposed drainage pipe  47  will depend upon the materials of each of these structures, the degree of insulation and more.  
         [0033]     Further, the thin line  55  can be made of an optical material. In this instance, the sensor processing circuit  87  can periodically generate a light pulse into the thin line  55 . The end of the thin line  55  which terminates at the top of the main horizontally disposed drainage pipe  47  will generate a reflection if the liquid  75  has an air space over it within the main horizontally disposed drainage pipe  47 , to indicate a level approaching a terminally low liquid level. In the alternative, a single, solid fiber optic line  117  can be provided directly into the main horizontally disposed drainage pipe  47  and terminating even with the internal wall of the main horizontally disposed drainage pipe  47  and perhaps polished even with the internal wall.  
         [0034]     Fiber optics can easily work within the main horizontally disposed drainage pipe  47  to essentially detect two phase fluid. Light introduced into a filled tube will reflect only or predominantly at the junction of the fiber and its refractive index, as it passes into the fluid and its refractive index. An additional reflective junction will be present at the surface of the liquid  75  when air is present in pipe  47 . A much greater reflection will occur at the end of the fiber when the tube  47  is partially filled, and a further reflection will occur at the junction of the air and liquid  75  interface within the tube  47 . Thus, any gravitationally induced volume of air in the tube  47  will register a significant reflection in any fiber optic transmission structure regardless of whether it is thin line  55  or solid fiber optic line  117 .  
         [0035]     A similar arrangement could be used where a drainage pipe is vertical, but where a more sensitive change in refractive index is used, or where some mode of reflection or absorption of light against the opposite pipe wall is utilized. A horizontal drainage pipe would function much more efficiently in an indication of complete outage, as there is no level in the main reservoir  31  to hold liquid  75  below such a bottom mounted tap. In this instance, a flashing “out of product” indicator would save users from the temptation to try the operating handle  53  in vain. In the case of the horizontal pipe  47 , and depending upon the depth of the main reservoir  31  below the pope  47 , users might be able or tempted to tilt the container  11  forward to obtain the last bit of liquid  75 . The indications in the display area  63  can discourage this by showing “empty” and possibly help reduce mishaps from attempts at tilting the container  11 . Thus, the indicator system  71  can decrease the incidences of tampering by non-authorized personnel and reduce mishaps.  
         [0036]     In yet another alternative, a pressure cell  121  can be mounted inside the main horizontally disposed drainage pipe  47 , with a transmission wire set  123  leading back to the sensor processing circuit  87 . An internally mounted pressure cell  121  would preferably be self contained, with a surface exposed which is not in the way of flow, and which is somewhat remote from experiencing force. Pressure cell  121  is shown on the bottom of main horizontally disposed drainage pipe  47  but could be located anywhere about its circumference, or indeed anywhere in as close of a proximity as practicable in contact with the lower most liquid  75  to gather the static head pressure efficiently.  
         [0037]     Referring to  FIG. 3 , a closeup view of one embodiment of the display area  63  is seen. A central upper area includes a vertical stack of horizontal bars  131  which individually illuminate to reflect the liquid  75  level within the main reservoir  31 . It is important to have an indicator which can be instantly interpreted by workers of all languages, and this is the case for display area  63 . Vertical stack of horizontal bars  131  may preferably be green in color and indicate either the complete range of fill, or may indicate the top  80 % of fill to indicate to food service workers that the level may be getting low, but should be watched.  
         [0038]     Below the vertical stack of horizontal bars  131  is a second area of diminishing shapes  133 . The shapes  133  may be red in color and indicate a series of levels within the last  20 % of the range of the liquid  75  level within the main reservoir  31 . To the left side of the display area  63  is a first hourglass shaped stack of horizontal bars  135 . The upper set of bars  135  may be green and the lower one or two may be red. As a timer, the bars  133  can indicate the progression of time during which the liquid  75  has been present within the main reservoir  31 .  
         [0039]     A second hourglass shaped stack of horizontal bars  137  is located to the right, and may flash red at different rates to indicate an emergent need to replace the liquid  75 . Where the sensor processing circuit  87  is programmed to cumulate a growing need for replacement of the liquid  75 , the triggering of a second hourglass shaped stack of horizontal bars  137  might occur not based upon just one extreme, such as the falling level of liquid  75  within the main horizontally disposed drainage pipe  47  to the extent that there is an air gap, but perhaps earlier based upon a combination of time and low liquid level.  
         [0040]     For example, second hourglass shaped stack of horizontal bars  137  might trigger a flashing change indication where the temperature was only 80% of the acceptable fall in temperature and where the passage of time was 80% of the critical time passage. This combinational decision to render an change product alarm which is more sensitive than either of the two scalar progressions might also result in a different flashing rate.  
         [0041]     Where the flash rate is proportional to the extremity of measured liquid  75  level and temperature circumstances, food service workers could be instructed to replace the liquid  75  at the slowest rate of flash (quickest circumstances) or to wait until the most rapid rate of flash (for slowest terminal circumstances).told to replace the product at a lesser be adjustable based upon business dictates. For example, in a hotel where a buyer has purchased only a single container of liquid  75 , workers would know to remove the liquid dispensing container  11  at the highest rate of flash. Conversely, where a customer demands only the freshest, hottest product over a given time period, food workers would be alerted to replace the product early in the dispensation cycle, without waiting for outages. This causes a proper increase in sales based upon the quality level demanded. Where high quality product is demanded, the failure in supplying it is a failure in service. As a result, the indicator system  71  helps prevent inadequate service.  
         [0042]     The level of visual indication to the food service worker can be modulated by colors, flashing, increased brightness or other indication. Further, sensor processing circuit  87  may include an on board electromagnetic communications capability to send a signal back to a central station. The signal can include each of the individually measured parameters of time, temperature, level and two-phase bottomed out depletion, or the logic for sending a signal based upon a combinational threshold based upon any number and degree of the time, temperature, level and two-phase bottomed out depletion can be formulated by the sensor processing circuit  87 .  
         [0043]     In such a system in a convention center, for example, a central computer would be receiving signals from a series of food service liquid dispensing containers  11 , typically coffee pots, in the center&#39;s facility. Where certain customers only purchased a single pot, signals from the container  11  would not result in a response. Where another customer had request a high level of service, the computer would detect by radio, a threshold condition and might immediately notify the food service worker by hand-held radio, or by a pager system directing the worker to replace the container  11  immediately.  
         [0044]     Further, in rooms which are busy, and which are of such high priority to have a worker assigned to be present during the event, the central system could be disabled as to that room, relying instead upon a much more immediate visual detection and a much quicker replacement of food product than would be obtainable with distributed information management and control through a computer and paging system.  
         [0045]     It is preferable for all of the components seen in  FIG. 2 , with the exception of the main reservior to be supplied as an integral unit. In the construction of original equipment, assembly time will be significantly reduced by having to merely perform the simple step of inserting the tap  43  and attached sensor housing  61  assembly into the main reservior  31  and forming a fluid tight connection. In terms of retrofit, the provision of a tap  43  and attached sensor housing  61  assembly with the double flange fitting  45  replaced by a unit with a large threaded continuation of fitting  45  and a large nut for engagement of the threaded continuation, would facilitate change out of conventional taps  43  with complete tap and sensor sets in a manner so simple as to enable ordinary user to make the changeout.  
         [0046]     In terms of power management, when the reservoir is empty or has not undergone a change in some time, the display  63  and sensor processing circuit  87  may be programmed to attain a sleep/non-functioning mode, to save battery  91  energy. As the sensor processing circuit  87  detects that the main reservoir  31  has started to become filled and a pressure increase is sensed, the sensor processing circuit  87  will wake up and start to display.  
         [0047]     The sampling rate for the sensor processing circuit  87  may be from 1-30 seconds. This will preclude the display from “jumping” as the server is being filled, and will further save energy. Once the sensor processing circuit  87  detects that a level is stable or not increasing for a period of about two minutes or greater it will start recording time as an indication of product freshness. A center portion or gray bar of the timer indicator in the display area  63  may start flashing to indicate that timing is started. Each horizontal line may be a time increment, such as a 15 minute increment where it is desired that food service workers are able to monitor the temporal progress.  
         [0048]     Once a desired time increment is timed out the upper bar will be empty and the lower one will remain solid. This “hour glass effect” provides and intuitive time display for product freshness in the server. There may be 1-4 timers displayed. As each full timer is times out, about one hour, the next timer will appear on the display. When the server is empty and the transducer senses it will shut off the timers and not display any horizontal bars in the display area  63 .  
         [0049]     If the liquid dispensing container  11  is being pre-heated by filling with liquid (such as to pre-heat with a hot liquid or pre-chill with a cold liquid) and then dumped out it may inadvertently start the level and timer. However once the pre heating or cooling liquid is dumped, and where the sensor processing circuit  87  is so programmed, the liquid dispensing container  11  will reset to zero and wait to start again on another fill cycle.  
         [0050]     The invention has been described with respect to a food service indicator system which replaces a sight glass on liquid dispenser food systems and including temperature and time functions to enable a higher level of food service quality. However, the techniques and structures of the invention can be applied to many similar sets of structures where level indicators, and multiple characteristics are to be taken to account in computing an alert condition, and more particularly where a need to segregate sensor and indicator function in a limited area to enable a greater unobstructed surface of equipment.  
         [0051]     Although the invention has been derived with reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. Therefore, included within the patent warranted hereon are all such changes and modifications as may reasonably and properly be included within the scope of this contribution to the art.