Oil level detection system for deep fat fryer

A detector configured to indirectly monitor a level of liquid within a container is provided. The detector includes a temperature sensor and a heat producing element proximate to the temperature sensor. A shell is disposed around the temperature sensor and heat producing element, the shell is configured to be disposed within a container and to provide a barrier between liquid disposed within the container and each of the temperature sensor and heat producing element. The heat producing element is configured to transfer heat generated therein to the shell, and the sensor is configured to measure a surface temperature of the heat producing element.

TECHNICAL FIELD

The subject disclosure relates to commercial deep fat fryers or other pieces of restaurant or industrial equipment where a heated liquid is maintained within a normal band. Conventional level detectors, such as floats and the like are known to have various drawbacks.

BRIEF SUMMARY

A first representative embodiment of the disclosure provides a deep fat fryer with a liquid level detection system. The fryer includes a vat suitable to hold a volume of cooking liquid. The vat is in thermal communication with a heat source that is configured to provide heat to the cooking liquid when disposed within the vat. A liquid level detector is disposed within the vat, the liquid level detector comprises a heat producing element and a temperature sensor disposed proximate to the heat producing element and configured to provide a first output signal representative of a surface temperature of the heat producing element.

A second representative embodiment of the disclosure provides a detector configured to indirectly monitor a level of liquid within a container. The detector includes a temperature sensor and a heat producing element proximate to the temperature sensor. A shell is disposed around the temperature sensor and heat producing element. The shell is configured to be disposed within a container and to provide a barrier between liquid disposed within the container and each of the temperature sensor and heat producing element. The heat producing element is configured to transfer heat generated therein to the shell, and the sensor is configured to measure a surface temperature of the heat producing element.

A third representative embodiment of the disclosure provides a method of controlling a level of liquid within a cooking vat. The method includes the steps of providing a vat configured to receive a volume of liquid and providing a liquid level detector within the vat. The liquid level detector comprises a heat producing element and a temperature sensor disposed proximate to the heat producing element and configured to provide a first output signal representative of a surface temperature of the heat producing element. The method further comprises the step of providing a controller that selectively energizes and deenergizes the heat producing element, and receives the first output signal. Further the method includes energizing the heat producing element and deenergizing the heat producing element after the first output signal reaches either a predetermined value or a substantially steady state value. The method then measures the rate of change of the first output signal after the heat producing element is deenergized, compares the measured rate of change of the first output signal with a reference value range, and then determines the presence or absence of liquid proximate to the liquid level detector based upon the comparison between the measured rate of change of the first output signal and the reference value range.

Advantages of the disclosed system will become more apparent to those skilled in the art from the following description of embodiments that have been shown and described by way of illustration. As will be realized, other and different embodiments are contemplated, and the disclosed details are capable of modification in various respects. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.

Turning now toFIGS. 1-6, a cooking liquid level detection system1is provided. The cooking level detection system1includes a liquid level detector that is normally disposed within, or extending into, a container that houses a volume of cooking liquid. In some embodiments, the container may be a vat20that is disposed upon a commercial deep fat fryer10, as shown schematically inFIG. 1. In other embodiments, the liquid level detector may be disposed within other types of containers associated with other cooking appliances (or for that matter other types of machines) where the level of cooking liquid (or other liquid disposed within the container) is normally heated above ambient temperature and is normally preferably maintained above a specific level of the container, or within a specific level range. As will be readily appreciated by one of ordinary skill in the art upon review of the instant specification and drawings, the cooking level detection system is readily utilized with a deep fat fryer where cooking liquid, such as oil, is continuously lost from the vat due to being soaked within the food product being cooked therewithin. Accordingly, the oil level within the cooking vat of conventional fryers must be periodically manually monitored during periods of heavy use and the kitchen operators must often manually fill the cooking vat with fresh oil. The instant cooking level detection system provides for an automatic signal that oil level has dropped below a certain level (which can be set by the manufacturer or positioned by the user), which allows for automatic refilling of the oil into the vat, or for an alarm to the kitchen operator that oil needs to be added to the vat.

For the sake of brevity, the cooking level detection system is discussed below with respect to use with a commercial deep fat fryer10. Examples of other equipment that may benefit from the cooking level detection system disclosed herein are rethermalizers, pasta cookers, and the like, and one of ordinary skill in the art would readily understand any appropriate modifications to the system disclosed herein for application with other equipment that could benefit from this system, with a careful review of the instant specification and figures. The fryer10used with the cooking level detection system may be a conventional fryer (shown schematically inFIG. 1), with a housing12that supports a vat20. The fryer10includes a heater18(either an electrical or gas burner) to continuously or cyclically provide heat to the cooking liquid Z (FIGS. 3, 4, 5) disposed within the vat20. The vat20may receive a basket (not shown) that holds food product within the heated cooking liquid (such as oil) to cook the food, and then can be removed to easily remove the food product from the cooking liquid. The fryer10may have a control panel15that allows for user inputs to control the cooking functions of the fryer10. The control panel15may communicate with a control system110(shown schematically inFIG. 1), discussed below to automatically or manually operate the fryer10for manual or repeated cooking cycles (such as cycle the heater18to maintain cooking liquid Z temperature based upon measured liquid temperature or expected temperature).

As best shown inFIGS. 4-5, the cooking liquid level detection system may include a shell30that supports both a temperature sensor50and a heat producing element40. In some embodiments, the shell30may be formed to extend within the cooking volume within the vat20and may fully enclose both the temperature sensor50and the heat producing element40, such that the cooking liquid Z does not come into direct contact with either the temperature sensor50or the heat producing element40.

In some embodiments, best shown inFIG. 3, the shell30may be disposed at or just above the desired minimum operational cooking liquid level24within the vat20, to allow for a determination that cooking liquid Z is not in contact with the shell30, as calculated by the control system110, discussed below. This position of the shell30just above the desired minimum cooking liquid level within the vat20provides for an opportunity to add cooking liquid to the vat20, either through an automated function as directed by the control system110, discussed below, or through manual action, potentially upon receipt of an audible and/or visual low level alarm initiated by the control system110.

In some embodiments, the shell30may include an insulation block38disposed to thermally isolate the heat producing element40and the temperature sensor50from the ambient through an open end34of the shell (where provided). Embodiments that include an insulation block38are calibrated with the assumption that no heat escapes (or only a certain amount or percentage of heat escapes as understood after experimental testing of the system within a vat20with cooking liquid Z) from the open end34of the shell30. The insulation block38may be formed from one of many conventional materials with relatively low thermal conductivity. Alternatively, in other embodiments, the shell30may not include an insulation layer38, with the control system110, discussed below, calibrated based upon the experimentally determined amount of heat escaping the heat producing element40through the open end34of the shell30. In still other embodiments, both opposite ends (32,34) of the shell30may be sealed (with or without an insulation block38provided proximate to the end (similar to open end34) extending out of the vat20. The shell30may extend into the cooking volume through an aperture in a wall defining the vat20and be fixed to the wall defining the vat20with one or more fasteners37(shown schematically inFIGS. 4-5).

The heat producing element40may be disposed in surface-to-surface contact with an inner surface of the shell30, such that a significant portion of the heat generated by the heat producing element40, when energized by the control system110, passes directly to the shell30through conduction heat transfer. The heat producing element40is preferably a resistance heater, which provides a known amount of heat in response to a known amount of current passing therethrough. Generally, the heat produced by a resistance is equivalent to the amount of current (squared) multiplied by the resistance of the heat producing element40(I2R). Other types of known heaters that fit within a small, enclosed shell30and can be remotely operated based upon an electrical signal may be used instead of or in conjunction with a resistance heater. In some embodiments, the heat producing element40may be an RTD with a known or calibrated heat output.

It is preferable that the heat producing element40be disposed close to or in contact with the closed distal end32of the shell30, to minimize the amount of heat transferred to the shell30that is transferred to the wall defining the vat20by conduction rather than to the cooking liquid Z through convection and conduction with the shell30. One of skill in the art, after a thorough review of this specification, will appreciate the optimal length (or range of lengths) for the shell30extending within the vat20based upon the desire to minimize heat loss from the shell to the vat20through conduction, while also minimizing the distance that the shell30extends within the cooking volume to prevent the shell30from interfering with the basket position, a basket lift mechanism, a filtering mechanism, an oil removal mechanism, or other components that may be associated with or placed within the vat20. The heat producing element40is electrically connected to the control system110with one or more wires82, which provide a path for current between the control system110and the heat producing element40to energize the heat producing element40.

In some embodiments, the type and rating for the heat producing element40is selected such that the heat generated by the heat producing element40is sufficient to establish a steady state temperature similar to a normal temperature of the liquid disposed within the vat20. By way of example, in systems designed for use with a deep fat fryer, the heat producing element40may generate a sufficient amount of heat to maintain its temperature around 325-350 degrees F., which is part of or all of the range of normal oil temperatures in a commercial deep fat fryer.

The temperature sensor50is disposed within the shell30and in close proximity to one or more surfaces of the heat producing element40, such that the temperature sensor50measures the surface temperature of the heat producing element40. In some embodiments, the temperature sensor50is in contact with a surface of the heat producing element40. The temperature sensor50may be an RTD (resistance temperature detector), or other compact electrical temperature detecting device. In some embodiments, the temperature sensor50may be of small size in comparison to the heat producing element40, and the shell30, such that the heat transfer from the heat producing element40to the temperature sensor50is small or negligible in comparison to the heat transfer to the shell30from the heat producing element40. The temperature sensor50may be sized and positioned with respect to the heat producing element40such that the temperature measured by the temperature sensor50is based entirely, or almost entirely, upon the surface temperature of the heat producing element40, and not based upon the temperature of the shell30. In some embodiments, all or portions of the outer surface of the temperature sensor50not in contact with (or proximate to) the heat producing element40may be insulated to minimize the contribution of the sensed temperature by the shell30temperature (or ambient temperature within the shell30).

The temperature sensor50may be electrically connected to the control system110with one or more wires84. In some embodiments, the control system110receives a signal from the temperature sensor50that is proportional to or representative of the sensed surface temperature of the heat producing element40. In some embodiments, the temperature sensor50may send a first signal that is proportional to, or representative of, the sensed surface temperature of the heat producing element40and a second signal that is proportional to or representative of a rate of change of the first signal (i.e. the rate of change of surface temperature). In other embodiments, the control system110may calculate the rate of change of temperature instead of the temperature sensor50.

The control system110, is shown schematically inFIG. 1, and may control the operation of the fryer10(e.g. the cyclic operation of the heater18) to maintain a measured oil temperature within a predetermined band, to time and count cooking cycles, etc. and may additionally control the operation of the cooking liquid level detection system. As mentioned above, the control system110is in communication with both of the heat producing element40(through electrical connection82, shown schematically inFIGS. 4-5) and the temperature sensor50(through electrical connection84, shown schematically inFIGS. 4-5). The control system110selectively provides a signal to energize and deenergize the heat producing element40and may also provide electrical power to operate the heat producing element40. The control system may also provide operational power to and receive a signal from the temperature sensor50proportional to or representative of the surface temperature of the heat producing element40. Alternatively, in some embodiments the heat producing element40may receive electrical power for operation from another source, but receive a signal to control the operation of the heat producing element40from the control system110.

In some embodiments, the control system110follows the steps and performs the determinations depicted inFIG. 6, while in other embodiments the control system110may follow a different routine designed to perform one or more of the steps or functions described herein to use the level detection system disclosed herein.

Initially, or at the start of a new monitoring cycle, the control system110may initialize itself (step210) and may perform one or more operational self-checks (such as power available, signal available, open or shorted temperature sensor50detection, etc.) (step215). Next, in step220the control system110energizes the heat producing element40located within the shell30, while measuring the sensed surface temperature of the heat producing element40as received by the temperature signal from the temperature sensor50(step230). When the surface temperature of the heat producing element40reaches either a temperature setpoint (as stored within a memory source, or in a remote storage location in communication with the control system110), such as a temperature setpoint close to or within the normal cooking liquid temperature range (generally 325-350 F), or when the heating sequence has reached a set time duration, the control system110deenergizes the heat producing element40(step240). As will be understood, the temperature setpoint to secure the heat producing element40(“hot setpoint”) may be a function of the various design and operational parameters of the fryer, such as oil temperature, ambient temperature, among other factors. In one specific embodiment, a temperature within the range of about 330-370 degrees Fahrenheit may be appropriate (inclusive off all temperatures within this range), while in other embodiments, specific values such as 350, 355, 358, 360 degrees Fahrenheit may be appropriate for the hot setpoint. Due to tolerances in the heat output of the heat producing element40and the tolerances and calibration of the sensor, this setpoint may vary within a temperature range.

After the heat producing element40is deenergized, the control system110continues to monitor the surface temperature of the heat producing element40(step250) and additionally calculates the magnitude of the rate of change of surface temperature (step260), or in embodiments where the temperature sensor50is capable of calculating this rate of change, receives a signal proportional to or representative of this rate of change of surface temperature. The control system110continuously compares the magnitude of the rate of change of surface temperature with a reference value, or a reference value range (step270). In some embodiments, the control system110may compare the measured rate of change with a range of possible reference values, instead of a specific reference value due to the range of tolerances of the thermal output of a heat producing element40, as well as tolerances or calibration of the sensor, which could cause the measured temperature and therefor the calculated rate of change to be affected. As can be understood, because the heat producing element40and the shell30are configured for efficient heat transfer therebetween, and rate of heat loss and the change in surface temperature (either due to heat loss from the shell30and heat producing element40, or potential heat gain from the relatively hotter oil) is function of the presence of cooking liquid, or the absence of cooking liquid in contact with the outer surface of the shell30. Because the heat producing element40was originally heated to a temperature close to the normal temperature cooking liquid, there will only be a small amount of heat flow through the shell when the heat producing element40is deenergized when the hot cooking liquid is in contact with the shell30. This results in a very small rate of change in the surface temperature of the heat producing element40, and therefore the control system110is programmed to conclude that there is cooking liquid present at the level of the shell30, and the upper surface X (FIG. 4) of the cooking liquid Z is above the shell30.

In contrast, when there is no hot cooking liquid proximate to, or, in contact with the shell30, the shell30contacts the ambient air that is at room temperature (or at an increased temperature, but significantly less than oil temperature). In this situation there is a large heat flux from the shell30to the ambient (due to the difference in temperature therebetween), and therefore a large heat flux from the heat producing element40to the shell30and ultimately to the ambient. This large heat flux causes the surface temperature of the heat producing element40to decrease rapidly, causing the temperature sensor50to sense a large magnitude of the rate of change of surface temperature (step260). When the magnitude of the rate of change of surface temperature is within a reference value range that is indicative of a significant heat loss from the heat producing element40and shell30(either programmed into the control system110or in communication with the control system110) the control system110makes the determination that the cooking liquid is not in contact with the shell30(step280), and the upper surface X is below the shell30(FIG. 5). As will be appreciated by one of ordinary skill in the art with reference to this disclosure, an appropriate reference value range may be a function of various design parameters of the fryer, such as the geometry of the vat, the normal temperature of the cooking fluid, the expected ambient temperature, the normal level of the shell30within the vat, among other factors.

Accordingly, because the system identifies a low cooking liquid condition, the control system110may provide an audible and/or visual alarm (step290) and may initiate an automatic refill sequence (step300). As shown schematically inFIG. 1, the fryer10and specifically the vat20may be fluidly connected to a source of cooking liquid such as in a holding tank100, which may be either pumped to the vat20or allowed to gravity drain to the vat20. In situations where the control system110automatically directs replacement cooking liquid to the vat20, the control system110may operate a pump103that takes suction from the holding tank100and directs replacement liquid to the vat20, and may open one or more isolation valves105to allow cooking liquid to refill the vat20. Upon completion of the cooking liquid refill cycle (as measured by one or more of elapsed time, change in level of the holding tank100, or by other parameters), the control system110may start the level measurement cycle again (step210). In some embodiments, upon a determination that the liquid level X is below the shell30, the control system110may deenergize the heaters18within the vat20, and reenergize (to return to the normal heating cycle) when liquid level returns to the normal band. In some embodiments, after the liquid refill cycle300, the system initiates a delay (such as a 3-5 minute delay) which allows the system to thermally stabilize before the heat producing element40again performs probe checks (step215) and energizes the probe again (step220).

Alternatively, in situations where the calculated rate of change is outside the reference value range (with a lower magnitude than the reference value range), the control system110continues to monitor the surface temperature of the heat producing element40(repeating step250), calculating the rate of change of surface temperature (repeating step260) and comparing that measured rate of change with the reference value range (step270), collectively step310. The control system110may additionally start a clock with the completion of the first comparison step (270) that continues to run as step310continues to be performed. If the rate of change remains outside the reference value range, the monitoring and comparison step (310) may end after a specific time measured by the clock and the system reverts to the probe checks (step215). If the surface temperature decreases to a low temperature setpoint of the heat producing element40, the system also automatically reverts to the probe checks (step215). Similar to the hot setpoint referenced above, the “cool setpoint” for the measured setpoint may be within a range of temperatures, such as between 200 to 275 degrees Fahrenheit (inclusive of all temperatures therewithin). In some embodiments, the cool setpoint may be 245, 250, 255, or 260 degrees Fahrenheit.