System and method for determining drain pan fluid level

A fryer drain pan fluid level sensing system includes a fryer frame and a fryer vessel mounted on the fryer frame. A drain pan carrying frame is pivotally affixed at a first carrying frame end to the fryer frame, and a drain pan mounted on the drain pan carrying frame for receiving a fluid, which has a fluid density, from a fryer vessel, such that the fluid in the drain pan has a fluid level and a surface area, together defining a fluid volume. A load sensor supports a second carrying frame end opposite the first carrying frame end and generates a force signal proportionate to a weight of the fluid in the drain pan and the drain pan. A processor receives the force signal from the load sensor and determines the fluid level. The processor may determine the fluid level by calculating a fluid level factor by comparing a first difference between the force signal and an empty drain pan signal to a second difference between a full drain pan signal and the empty drain pan signal and then multiplying the fluid level factor by a predetermined full level. Alternatively, the processor may determine the fluid level by scaling the force signal to determine a weight of the fluid in the drain pan, by dividing the weight by the fluid density to determine the fluid volume, and by dividing the fluid volume by the surface area to determine the fluid level.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to systems and methods for determining the 
level of a fluid in a drain pan and, in particular, to systems and methods 
for determining the level of a fluid in a drain pan using a load sensor. 
2. Description of the Related Art 
Known fryers may include a fryer frame, a fryer vessel mounted on the fryer 
frame, a drain pan for receiving a fluid drained from a fryer vessel, and 
a processor for controlling the operation of the fryer. The fluid may be a 
cooking medium, such as vegetable oil or shortening. It is desirable to 
drain such cooking media from the fryer vessel periodically for 
replacement or filtering. Alternatively, the fluid may be a cleaning 
fluid, such as water or a detergent or a combination thereof, which may be 
used to clean the fryer vessel or other fryer components including a drain 
valve through which fluid is drained to the drain pan or the drain pan 
itself 
Because periodic draining of fluids from the fryer vessel to the drain pan 
is a necessary step in the operation of the fryer, it is important to 
accurately determine the level of any fluid that may be added to or may 
already be in the drain pan. If fluid is already in the drain pan, further 
draining may cause the drain pan to overflow causing fluid to spill onto 
fryer components or onto the floor surrounding the fryer. Such spillage 
may result in damage to components of the fryer or even fire if the 
cooking media or cleaning fluids should come in contact with heater 
elements or electrical circuitry. Exposure of electrical circuitry to 
these fluids poses a particular danger of damage because the spillage may 
result in the short circuiting of electric components. 
Such spillage may create other problems. For example, the spillage of 
cooking media or cleaning fluids may result in employees slipping on the 
spilled fluid. Moreover, such spillage is generally unsanitary and may 
present a medium for the growth of bacteria or fungus in the area 
surrounding the fryer. 
A further consideration with respect to the efficient operation of a fryer 
is that by avoiding such spillage, the fryer may be operated in a more 
cost effective manner. By avoiding spillage, less employee time is spent 
cleaning up such spills, and fryer operating time is not lost due to the 
need to clean the fryer and its surroundings. Further, if a cooking medium 
is to be drained, filtered, and reused; the loss of some portion of the 
cooking medium represents a cost increase due to the replacement costs for 
such lost cooking medium. 
SUMMARY OF THE INVENTION 
A need has arisen for a system and method for measuring the level of fluid 
in a fryer drain pan. It is advantageous to know this level for various 
reasons. For example, fluid should not be drained to the drain pan if the 
drain pan is already full, because spillage may result. It is a feature of 
the invention that the fluid level is measured by converting the force 
resulting from the fluid mass to an electrical signal by means of a load 
sensor, such as a strain-gage load cell. It is an advantage of this 
invention that a relatively uncomplicated, mechanical configuration is 
used to transfer the force from the fluid in the drain pan to the load 
cell. 
In an embodiment of the invention, a fryer drain pan fluid level sensing 
system comprises a fryer frame and a fryer vessel mounted on the fryer 
frame. A drain pan carrying frame is pivotally affixed at a first carrying 
frame end to the fryer frame, and a drain pan is mounted on the drain pan 
carrying frame for receiving a fluid, which has a fluid density, from a 
fryer vessel, such that the fluid in the drain pan has a fluid level and a 
surface area, together defining a fluid volume. A load sensor supports a 
second carrying frame end opposite the first carrying frame end and 
generates a force signal proportionate to a weight of the fluid in the 
drain pan and the drain pan. A processor receives the force signal from 
the load sensor and determines the fluid level. The processor may 
determine the fluid level by calculating a fluid level factor by comparing 
a first difference between the force signal and an empty drain pan signal 
to a second difference between a full drain pan signal and the empty drain 
pan signal and then multiplying the fluid level factor by a predetermined 
full level. Alternatively, the processor may determine the fluid level by 
scaling the force signal to determine a weight of the fluid in the drain 
pan, by dividing the weight by the fluid density to determine the fluid 
volume, and by dividing the fluid volume by the surface area to determine 
the fluid level. 
In another embodiment of the invention, a fryer comprises a fryer frame, a 
fryer vessel mounted on the fryer frame, a drain pan carrying frame 
pivotally affixed at a first carrying frame end to the fryer frame, a 
drain pan mounted on the drain pan carrying frame for receiving a fluid 
from a fryer vessel, and a processor for controlling the fryer. The fluid 
has a density and has a fluid level and a surface area in the drain pan, 
together defining a fluid volume. A load sensor supports a second carrying 
frame end opposite the first carrying frame end and generates a force 
signal proportionate to a weight of the fluid in the drain pan and the 
drain pan. The processor receives the force signal from the load sensor 
and determines the fluid level. Again, the processor may determine the 
fluid level by calculating a fluid level factor by comparing a first 
difference between the force signal and an empty drain pan signal to a 
second difference between a full drain pan signal and the empty drain pan 
signal and then multiplying the fluid level factor by a predetermined full 
level. Alternatively, the processor may determine the fluid level by 
scaling the force signal to determine a weight of the fluid in the drain 
pan, by dividing the weight by the fluid density to determine the fluid 
volume, and by dividing the fluid volume by the surface area to determine 
the fluid level. 
In yet another embodiment, a method for determining a level of a fluid in a 
drain pan of a fryer, such as the fryer described above, comprises the 
steps of measuring a predetermined full level when the drain pan is full 
and the full drain pan signal is generated; generating a force signal 
proportionate to a weight of the fluid in the drain pan and the drain pan; 
calculating a fluid level factor by comparing a first difference between 
the force signal and an empty drain pan signal to a second difference 
between a full drain pan signal and the empty drain pan signal; and 
multiplying the fluid level factor by the predetermined full level. 
In still another embodiment, a method for determining a level of a fluid in 
a drain pan of a fryer, such as the fryer described above, comprises the 
steps of generating a force signal proportionate to a weight of the fluid 
in the drain pan and the drain pan, determining the weight of the fluid by 
scaling the force signal, calculating the fluid volume by dividing the 
fluid weight by the fluid density, and calculating the fluid level by 
dividing the fluid volume by the fluid surface area. 
Other objects, features, and advantages will be apparent to persons skilled 
in the relevant art in view of the following detailed description and the 
accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIG. 1, a drain pan 10 is depicted as having a plurality of 
side walls 16. Further, a pair of opposing side walls aligned with a 
longitudinal axis of pan 10 may be formed or equipped with drain pan 
supporting side lips 14 to engage the longitudinal arms of a drain pan 
carrying frame, as described below. Drain pan 10 also may include a drain 
pan supporting front lip 14 which may engage a carrying frame transverse 
arm, as described below. As may be seen from FIG. 1, drain pan 10 defines 
a maximum depth "D." 
In FIG. 2, a perspective view of a fryer frame, a drain pan carrying frame, 
and a load sensor is shown, according to a first embodiment of the 
invention. A fryer frame 20 may include four vertical frame supports 
20a-d. Moreover, a drain pan carrying frame 22 may including first and 
second longitudinal arms 22a and 22b joined at one end by a transverse arm 
22c to form a substantially U-shaped frame, i.e., drain pan carrying frame 
22. A first carrying frame end 23, which is opposite transverse arm 22c, 
is pivotally affixed to fryer frame 20 at a pair of pivot points 24. 
A load sensor supporting bracket 26 extends between vertical frame supports 
20c and 20d, and is positioned above transverse arm 22c of U-shaped frame 
22. A supporting bracket connection 30, such as a U-shaped bolt, is 
suspended beneath bracket 26. A load sensor 34 is suspended from 
connection 30 by an upper load sensor connection 34. For example, load 
sensor 34 may be an Omega LCCB-100, manufactured by Omega Engineering, 
Inc. of Stamford, Conn. A cable 36 joins a pair of second carrying frame 
connecting points 28 to a lower load sensor connection 38, whereby 
U-shaped frame 22 is suspended beneath load sensor 34, as depicted in FIG. 
3. 
Referring to FIG. 4a, a side view of drain pan 10 mounted on drain pan 
carrying frame 22, a fryer vessel 40 with a drain valve 42 positioned over 
drain pan 10, and load sensor 34, is shown, according to the embodiment of 
the invention depicted in FIGS. 1 and 2. As depicted by FIG. 4a, drain pan 
supporting side lip 12 rests upon an upper surface of second longitudinal 
arm 22b, and drain pan supporting front lip 14 rests on transverse arm 22c 
to support drain pan 10 within U-shaped frame 22. Thus, drain pan side 
walls 16 extend below U-shaped frame 22. Referring further to FIG. 4b, an 
overhead view of drain pan 10 mounted on drain pan carrying frame 22, is 
shown, according to the embodiment of the invention depicted in FIGS. 1 
and 2. In FIG. 1, the angled corners of drain pan 10 are depicted, which 
corners impart a pentagonal shape to the periphery of drain pan 10. As 
demonstrated by FIG. 4b, this pentagonal shape avoids interference between 
drain pan 10 and second carrying frame end connecting points 28, and as 
indicated by the letter "A" and the accompanying arrows, the shape of 
drain pan 10 substantially defines the surface area of a fluid in drain 
pan 10. Moreover, this shape facilitates the insertion and removal of 
drain pan 10 from U-shaped frame 22 at first carrying frame end 23. 
Referring to FIG. 5, a schematic diagram of a system for determining the 
fluid level in a drain pan is depicted, according to the embodiment of the 
invention depicted in FIGS. 1-4. Where appropriate, the same reference 
numerals used in FIGS. 1-4 have been used in FIG. 5 to identify similar 
components. Drain pan 10 rests upon drain pan carrying frame 22, and fryer 
vessel 40 equipped with drain valve 42 is positioned above drain pan 10. 
Drain pan carrying frame 22 is pivotally affixed at first carrying frame 
end 23 by a pivot 24 while second carrying frame end 25 is suspended from 
a load sensor 50 by a connecting arm or cable 51. Drain pan 10 contains a 
fluid 100, and drain pan 10 and fluid 100 exert a downward force on 
carrying frame 22 equal to "F." Given the shape of drain pan 10 and its 
position within carrying frame 22, equal downward forces of about F/2 are 
exerted on pivot 24 and against load sensor 50 through connecting arm or 
cable 51. 
Load sensor 50 transmits a signal "S," e.g., a voltage signal to a signal 
conditioning device 52. For example, "V.sub.F," may equal the voltage 
output of load sensor 50 when drain pan 10 is "full," i.e., when the level 
of a known fluid, such as shortening, in drain pan 10 is at a 
predetermined full level "L.sub.F," such that L.sub.F is less than or 
equal to D; "V.sub.0 " may equal the voltage output of load sensor 50 when 
drain pan 10 is empty; and "V.sub.X " may equal the voltage output of load 
sensor 50 when drain pan 10 is at an unknown level "L.sub.X," such that 
L.sub.X is greater than zero and less than or equal to L.sub.F. 
Consequently, the percentage "full" of drain pan 10 is determined by the 
following equation: 
EQU ((V.sub.X -V.sub.0)/(V.sub.F -V.sub.0)).multidot.100=Percentage of 
L.sub.F.Eq. (1a) 
Referring again to FIG. 5, signal S may be sent to signal conditioning 
device 52, which may include a signal filter 52', such as a lowpass 
filter, and an amplifier 52". Signal S then is sent to an analog/digital 
convertor 53 and then to a processor 54, so that the level of fluid 100 
within drain pan 10 may be determined. The determined level then is sent 
to a display 55, so that a fryer operator may be informed of the fluid 
level. Further, display 55 may include an alarm or warning light to alert 
the operator when the determined level reaches or exceeds a predetermined 
level. In this way, the operator may take action to empty drain pan 10 or 
otherwise prevent spillage. Moreover, processor 54 may automatically 
generate a signal, e.g., a signal sent via drain valve connection 56, to 
close drain valve 42 if the fluid level reaches the predetermined value. 
In this configuration, load sensor 50 effectively supports about one-half 
of the weight "W.sub.FD " of fluid 100 and drain pan 10. Consequently, the 
force F/2 indicated by load sensor 50 is about one-half the total force F 
exerted by fluid 100 and drain pan 10, and F is proportionate to W.sub.FD. 
Processor 54 may include circuitry and process control software which 
supply calibration and scaling to eliminate the force due to drain pan 10. 
Signal S from load sensor 50 then may be scaled to determine the weight of 
the fluid "W.sub.F," i.e., (W.sub.FD .multidot..alpha.)=W.sub.F, where 
.alpha. is a scaling factor, and converted to an equivalent level 
measurement given the surface area A of drain pan 10 and the density 
"d.sub.F " of the known fluid, in accordance with the following equation: 
EQU ((W.sub.FD .multidot..alpha.)/d.sub.F)/A=(W.sub.F /d.sub.F)/A=L.sub.FEq. ( 
2a) 
The system may compensate for fluid density variations resulting from 
changes in fluid temperature if a temperature sensor 57 is employed to 
measure the temperature of the fluid in drain pan 10, and if the volume of 
the fluid based on its weight is adjusted to reflect the fluid's density 
at the measured temperature. Information concerning variations in fluid 
density resulting from temperature changes may be stored in processor 54. 
In addition, drain pan 10 also may contain other components, such as a 
filter pan assembly. The weight of such additional components is fixed, 
and processor 54 may compensates by adjusting the scaling factor. 
In FIG. 6, a perspective view of a fryer frame, a drain pan carrying frame, 
and a load sensor is shown, according to a second embodiment of the 
invention. A fryer frame 20' may include four vertical frame supports 
20a-d'. Moreover, a drain pan carrying frame 22' may including first and 
second longitudinal arms 22a' and 22b' joined at one end by a transverse 
arm 22c' to form a substantially U-shaped frame, i.e., drain pan carrying 
frame 22'. A first carrying frame end 23', which is opposite transverse 
arm 22c', is pivotally affixed to fryer frame 20' at a pair of pivot 
points 24'. 
A load sensor supporting bracket 60 extends between vertical frame supports 
20c' and 20d', and is positioned below transverse arm 22c' of U-shaped 
frame 22'. A load sensor 62 is positioned on supporting bracket 60, such 
that transverse arm 22c' rests upon senor 62. For example, load sensor 62 
may be a Tedea-Huntleigh Model 1040 Series Low Profile Off-Center Load 
Cell, manufactured by Tedea-Huntleigh of Canoga Park, Calif. A sensor arm 
64 supports transverse arm 22c' of U-shaped frame 22', whereby U-shaped 
frame 22 transfers a force to load sensor 62, as depicted in FIG. 7. 
Referring to FIG. 8, a schematic diagram of a system for determining the 
fluid level in a drain pan is depicted, according to the embodiment of the 
invention depicted in FIGS. 6 and 7. Where appropriate, the same reference 
numerals used in FIGS. 6 and 7 have been used in FIG. 8 to identify 
similar components. Drain pan 10' rests upon drain pan carrying frame 22'. 
Drain pan carrying frame 22' is pivotally affixed at first carrying frame 
end 23' by a pivot 24' while second carrying frame end 25' rests upon a 
load sensor 80. Drain pan 10' contains a fluid 100, and drain pan 10' and 
fluid 100 exert a downward force on carrying frame 22' equal to "F." Given 
the shape of drain pan 10' and its position within carrying frame 22', 
equal downward forces of about F/2 are exerted on pivot 24 and upon load 
sensor 80. 
Load sensor 80 transmits a signal "S'," e.g., a voltage signal to a signal 
conditioning device 82. For example, "V.sub.F " may equal the voltage 
output of load sensor 80 when drain pan 10' is "full," i.e., when the 
level of a known fluid, such as shortening, in drain pan 10' is at a 
predetermined full level "L.sub.F," such that L.sub.F is less than or 
equal to D; "V.sub.0 " may equal the voltage output of load sensor 80 when 
drain pan 10' is empty; and "V.sub.X " may equal the voltage output of 
load sensor 50 when drain pan 10' is at an unknown level "L.sub.X," such 
that L.sub.X is greater than zero and less than or equal to L.sub.F. 
Consequently, the percentage "full" of drain pan 10' is determined by the 
following equation: 
EQU ((V.sub.X -V.sub.0)/(V.sub.F -V.sub.0)).multidot.100=Percentage of 
L.sub.F.Eq. (1b) 
Referring again to FIG. 8, signal S' may be sent to signal conditioning 
device 82, which may include a signal filter 82', such as a lowpass 
filter, and an amplifier 82". Signal S' then is sent to an analog/digital 
convertor 84 and then to a processor 86, so that the level of fluid 100 
within drain pan 10' may be determined. The determined level then is sent 
to a display 88, so that a fryer operator may be informed of the fluid 
level. Further, display 88 may include an alarm or warning light to alert 
the operator when the determined level reaches or exceeds a predetermined 
level. In this way, the operator may take action to empty drain pan 10' or 
otherwise prevent spillage. Moreover, processor 86 may automatically 
generate a signal to close a drain valve (not shown) if the fluid level 
reaches the predetermined value. 
In this configuration, load sensor 80 effectively supports about one-half 
of the weight "W.sub.FD " of fluid 100 and drain pan 10'. Consequently, 
the force F/2 indicated by load sensor 80 is about one-half the total 
force F exerted by fluid 100 and drain pan 10, and F is proportionate to 
W.sub.FD. Processor 86 may include circuitry and process control software 
which supply calibration and scaling to eliminate the force due to drain 
pan 10'. Signal S from load sensor 80 then may be scaled to determine the 
weight of the fluid "W.sub.F," i.e., (W.sub.FD .multidot..alpha.)=W.sub.F, 
where .alpha. is a scaling factor, and converted to an equivalent level 
measurement given the surface area A of drain pan 10' and the density 
"d.sub.F " of the known fluid, in accordance with the following equation: 
EQU ((W.sub.FD .multidot..alpha.)/d.sub.F)/A=(W.sub.F /d.sub.F)/A=L.sub.FEq. ( 
2b) 
The system may compensate for fluid density variations resulting from 
changes in fluid temperature if a temperature sensor (not shown) is 
employed to measure the temperature of the fluid in drain pan 10', and if 
the volume of the fluid based on its weight is adjusted to reflect the 
fluid's density at the measured temperature. Information concerning 
variations in fluid density resulting from temperature changes may be 
stored in processor 86. In addition, drain pan 10 also may contain other 
components, such as a filter pan assembly. The weight of such additional 
components is fixed, and processor 86 may compensates by adjusting the 
scaling factor. 
Referring to FIG. 9a, a flow chart of the steps of a first method for 
determining the fluid level in a drain pan of a fryer is depicted. This 
fryer may comprise a fryer frame, a fryer vessel mounted on the fryer 
frame, a drain pan carrying frame pivotally affixed at a first carrying 
frame end to the fryer frame, a drain pan for receiving a fluid from a 
fryer vessel, and a processor for controlling the fryer. The fluid has a 
density, and a fluid level and a surface area in the drain pan together 
define a fluid volume. Further, a load sensor supports a second carrying 
frame end opposite the first carrying frame end. In step 90, a 
predetermined full level is measured when the drain pan is full, and the 
full drain pan signal is generated. In step 91, a force signal is 
generated which is proportionate to a weight of the fluid in the drain pan 
and the drain pan. In step 92, a fluid level factor is calculated by 
comparing a first difference between the force signal and an empty drain 
pan signal to a second difference between a full drain pan signal and the 
empty drain pan signal, and in step 93, the fluid level factor is 
multiplied by the predetermined full level. If, in step 94, the fluid 
level is above a predetermined fluid level, e.g., within a range of about 
5% of the predetermined full level, a signal is sent to close the fryer 
vessel drain valve (step 95), and the fluid level is indicated on a 
display (step 96). If, however, the fluid level is not above a 
predetermined fluid level, the fluid level is indicated on a display (step 
97), and the method returns to step 90. 
Referring to FIG. 9b, a flow chart of the steps of a second method for 
determining the fluid level in a drain pan of a fryer is depicted. This 
fryer may be configured as described above. In step 90', a force signal is 
generated proportionate to a weight of the fluid in the drain pan and the 
drain pan. In step 91', the weight of the fluid is determined by scaling 
the force signal. In step 92', the temperature of the fluid in the drain 
pan is measured, and the fluid density is determined dependent on the 
measured temperature (step 93'). In step 94', the fluid volume then is 
calculated by dividing the weight by the determined fluid density, and in 
step 95', the fluid level is calculated by dividing the fluid volume by 
the fluid's surface area in the drain pan. If, in step 96', the fluid 
level is above a predetermined fluid level, e.g., within a range of about 
5% of the predetermined full level, a signal is sent to close the fryer 
vessel drain valve (step 97'), and the fluid level is indicated on a 
display (step 98'). If, however, the fluid level is not above a 
predetermined fluid level, the fluid level is indicated on a display (step 
99'), and the method returns to step 90'. 
While the invention has been described in connection with preferred 
embodiments, it will be understood by those skilled in the art that other 
variations and modifications of the preferred embodiments described above 
may be made without departing from the scope of the invention. Other 
embodiments will be apparent to those skilled in the art from a 
consideration of the specification or practice of the invention disclosed 
herein. It is intended that the specification and examples be considered 
as exemplary only, with the true scope and spirit of the invention being 
indicated by the following claims