TECHNICAL FIELD
The subject matter described herein, in general, relates to sensors and in particular, relates to a sensor for measuring level of a liquid in a container.
BACKGROUND
Liquid level sensors are widely used in various applications Ibr detecting the level of liquids. For example, liquid level sensors are employed to detect the level of chemicals in a tank, water stored in a reservoir, and the like. Furthermore, in mechanical devices such as gearbox, crankcase of an engine etc. where constant lubrication of components is necessary for sale operation of the device, it is beneficial to indicate to a user, the level of lubricant present in the lubricant reservoir. "Therefore. information regarding the level of the liquid available in a reser\'oir or a storage device enables a user to maintain requisite quantity of the liquid.
Various liquid level sensors that work on different principles is known in the art. Conventionally, liquid level sensors use float type switches that involve moving parts and are subjected to wear and tear. More recently liquid level sensors employ electrical or electronic elements such as resistors, capacitors, inductors, etc., to determine the level of a liquid. One or more property of these electronic or electrical elements changes directly or indirectly with change in the level of the liquid. The change in the properties of these electrical or electronic elements is utilized to determine the level of the liquid. For instance, in capacitive type level sensors, (he capacitance of a capacitor depends on the amount of dielectric present. Any change in the level of the liquid that acts as a dielectric, causes a change in the capacitance, which can be measured to indicate the change in the level of the liquid. The use of capacitive elements is problematic as they are prone to corrosion and weathering, being in direct contact with the liquid. huTthermore, some liquid level sensors also utilize electromagnetic effect of current to detect the level of liquid. However, these sensors are susceptible to external electromagnetic fields.
Many conventional systems employed for measuring the level of liquid, for example, the systems using lloat switches typically provide indication regarding only two levels of the liquid. When the level of the liquid is above a marked level, the system indicates it as HIGH or ON.

When the level of the liquid reaches below the marked level, the system indicates it as l-OW or Ol'F, rhe system does not provide any indication for an intermediate level. Usually, ii is desirable to have a system that can indicate an intermediate level, such that the quantity of ihc liquid can be estimated.
Hence, there is a need for a system which provides real time information about the Icvci of the liquid present in the container. Even more, the system should be simple, robust, durable and free from vt'car and tear.
SUMMARY
The subject matter described herein is directed to a system for determining the level of a liquid stored in a container. According to an embodiment of the present subject matter, the system includes a sensing unit and a control unit. The sensing unit generates signals indicative of the level of the liquid whereas control unit determines the level of the liquid based on the signals. The control unit and sensing unit are electrically coupled. The system also includes an output means that receives signals from control unit and indicates the level of liquid.
The sensing unit includes a heating element and a thermally sensitive element. The heating clement on being heated up to a predetermined level dissipates heat that in turn is sensed by the thermally sensitive element. The rate of heat dissipated by the heating clement depends upon the portion of the heating element immersed in the liquid. Thus, this rate of heal dissipation signifies the level of the liquid.
The subject maUer described herein is further directed to a method for determining the level of a liquid stored in a container. According to an embodiment of the present subject matter, the method is initialed with the steps of determining the initial temperature of the sensing unit, ■fhc initial temperature is indicative of the temperature of the surroundings of the sensing unit. The method further involves heating the heating clement for a specified interval of lime. Upon being heated, the healing element dissipates heat. The thermally sensitive unit senses the heal dissipated by the heating element at a plurality of instances to determine the rate of dissipation of heat. The thermally sensitive unit sends signals corresponding to the rate of dissipation to the control unit. The control unit determines the level of the liquid by processing and interpreting the signal send by the thermally sensitive unit against pre-detcrmined signal values stored in a

memory component of the control unit at the specified initial temperature. The liquid level is then indicated using an output means.
fhe system provides a durable liquid level sensing device for detecting level of liquids in a container. Even more the system is robust and does not have any moving parts. The system advantageously provides reading of an intermediate level of the liquid, fhe sensor provides a real time indication of the liquid level.
These and other features, aspects, and advantages of the present subject matter wilt become better understood with reference to the following description and appended claims. This .summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identity key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
BRIEF DESCRIPTION OF DRAWINGS
The above and other features, aspects, and advantages of the subject matter will become bcuer understood with regard to the following description, appended claims, and accompanying drawings. In the figures, the lelt-mosl digit(s) of a reference number identifies the [Igure in which the reference number first appears. The use of the same reference number in different figures indicates similar or identical items.
Fig. la illustrates an exemplarj' system for detecting the level of a liquid in a container.
Fig. lb illustrates a block diagram of the system of Fig. la for detecting the level of a liquid in a container.
Fig. 2a illustrates an exemplary embodiment of a probe of the system of Fig. la.
Fig. 2b illustrates an exemplary embodiment of a Up of the probe illustrated in Fig. 2a that is immersed in the liquid.
Fig. 3 illustrates an exemplary circuit diagram showing various components ol' the system of F"ig. la.

Fig, 4 illustrates an exemplary method for detecting the level of liquid in a container.
Fig. 5 illustrates an exemplary graphical representation illustrating initial temperature values corresponding to operating circuit signals.
Fij;. 6 illustrates an exemplary graphical representation showing liquid level corresponding to operating circuit signals at a predetermined initial temperature.
DETAILKD OESCRIVTION
"["he subject mailer described herein is directed to a system for detcnnining the level ot" liquids .stored in a container. The system includes a probe placed in the container. The probe includes a sensing unit provided at its tip, which is immersed partially or completely in the liquid. The sensing unit includes a heating element and a thermally sensitive clement. The heating element is heated and hence temperature of the thermally sensitive element being in thermal contact with the heating element increases. The thermally sensitive element shows a variation in its electrical properties in proportion to the temperature change. The thcnnally sensitive element provides signals corresponding to change in its electrical property to a control unit. Ihc control unit has an operating circuit and a central processing unit (CPU), The operating circuit is used to delect the magnitude of change in the electrical property and to generate equivalent electrical signals corresponding to the change in the electrical property, I'he electrical signals are processed and interpreted in a central processing unit (CPU),
The signals are first recorded keeping the supply to the heating element OVV. The signals thus recorded are processed and interpreted against pre-determined values stored in a memory ol the CPU. "fhese signals correspond to initial temperature corresponding to temperature of the surrounding in which the sensing unit is placed. Subsequently, the heating clement is provided with power for a predetermined interval of time, 'fhis increases the temperature of the Iieating element. The increase in temperature depends on the initial temperature as well as on the portion of the heating clement immersed in the liquid. The thermally sensitive element senses the temperature of the heating element at a plurality of instances over the period of heating and sends conesponding signals to an operating circuit The operating circuits converts the signal into equivalent electrical signals which are read by the CPU. The CPU processes and interprcis the

signals against prc-detcrmined values of signals corresponding to liquid level at a certain initial Icmperalurc stored in a memory component of the CPU.
The control unit is thus configured to indicate the level of the liquid in accordance with the signals it receives from the heat sensitive element. The system also includes an ovitput means for indicating the level of the liquid with one or more of audio and visual signals.
In one embodiment, the method and system is implemented in a cooling system to indicate the level of coolant available therein. In another embodiment, the method and system is implemented in an engine for determining the level of engine oil in the crankcase. In a preferred embodiment, the method and system is implemented in the lubrication system of a vehicle, such as a two-wheeler or a four-wheeler, for determining the level ol' lubrication oil in the crankcase of the vehicle.
The method and system described herein gives indication of the level of the liquid stored in a container and changes to the level of the liquid is reported to the control unit, and the control unit processes the signals in accordance with the change. The disclosed system is robust and durable, as it does not have any moving or rotating parts. The system incorporates the sensing unit positioned in the probe. The probe, having a tubular structure is specifically beneficial in cases where level of liquid stored in concealed or inaccessible containers has to be detected.
Fig. la illustrates an exemplary system 100 for delecting the level of a liquid 102 in an open or sealed container 104. Liquid 102 can be any liquid like engine oil, gearbox oil. or an\ other lubricating oil or any chemical. The examples of the container 104 include any open or sealed container or storage tank or transportation container like crankcase of an engine, gearbox, and others. The system 100 includes a probe 106 having a tip 108 which is immersed partially or completely in the liquid 102 present in the container 104. In one implementation probe 11)6 is attached to the container 104 while in another implementation, the probe 106 is detachable and is a portable means.
The system includes a sensing unit 110, a control unit 112 and an output means 114 as the major components. The sensing unit 110 is provided at the tip 108 of the probe 106 and is used 10 sense the variation in the level of the liquid 102 in the container 104. The sensing unit

110 is electrically coupled to the control unit 112. The control unit 112 determines the level of the liquid based on the signals it receives from the sensing unit 110. The output means 114 indicates the level of the liquid 102 determined by the control unit 112.
Fig. lb illustrates a block diagram of the system 100. The sensing unit 110 comprises a heating element 116 and a thermally sensitive element 118. The heating element 116 is provided wivh power tor a predetermmed interval of time in order to heal the heating clemcnl 116. Upon heating, the temperature of heating element 116 increases depending on the heat dissipation from the heating clemcnl 116. The heat dissipation from the healing element 116 in turn depends, amongst other factors, on the portion of heating element 116 immersed in the liquid 102. 'fhe thcnnatly sensitive clement 118. being thermally coupled to the healing element 116. shows a varialioii in electrical properties in proportion to the temperature of the heating element 116, In one example, thermally sensitive element 118 is a thermistor that shows a variation in electrical resistance with change in temperature. This change in resistance of the heat sensitive element 118 i.s due to the temperature of the heating element 116. Hence, the temperature of the healing clement 116 causes a proportional change in the electrical property of the thermally sensitive element 118. which is in turn indicative of level of the liquid 102,
The control unit 112 is electrically coupled to the sensing unit 110. The control unit 112 includes an operating circuit 120 and a central processing unit (CPU) 122.The operating circuit 120 receives signals from the thermally sensitive element 118. These signals are indicative of the temperature of the heating element 116 and correspond to the change in the properties of the thermally sensitive element 118. The operating circuit 120 produces electrical signals corresponding to the change in the properties of the thermally sensitive clement IIS. The electrical signals produced by the operating circuit 120 arc analyzed and interpreted by the CI'U 122. The CPU 122 compares and interprets the signals produced by the operating circuit 120 against predetermined signal values stored in a memory 126. The CPU 122 present in the control unit 112 sends signals to the output means 114 which produces audio or visual output indicating the level of the liquid 102. The CPU 122 includes one or more of a microprocessor 124 and a memory 126. Power is supplied to sensing unit 110, control unit 112 and output means 114 by a power source 128.

Fig. 2a illustrates an exemplary embodiment of the probe 106 that is placed in the container 104 (not shown in t-ig. 2a) containing the liquid 102. 'I'he probe 106 includes a connector 200, a shield 202, and the tip 108. The tip 108 houses the sensing unit 110. 'fhc lip 108 is immersed partially or completely in the liquid 102. The connector 200 electrically connects the sensing unit 110 to the control unit 112. Additionally, connector 200 is used to supply power lo the probe 108. The shield 202 is utilized in protecting interna! components of the sensing clement 110. In one implementation, the control unit 112 is an integral part of the probe 106. In an alternative implementation the control unit 112 is an external unit depending upon the need and space constraint.
Fij". 2b illustrates an exemplary embodiment of the tip 108 of the probe 106. Ihe tip 108 incorporates the heating element 116 adhered to the heal sensitive element 118. The length ol'the heating element 116 can be varied in different implementations. The length ol' the healing element 116 depends upon the variation in the level of the liquid that may occur in the container 104. Further, the tip 108 includes a printed wiring board 204 for facilitating connections of the electric components on the probe 106. In one implementation, the heating element 116 and the heat sensitive element 118 are fixed together by way of a heat conductive adhesive 206 such as Silicone adhesivcs.
Fig. 3 illustrates an exemplary circuit diagram 300 showing various componenis of the system 100 and their interaction in the detection of the level of the liquid 102. In one implementation, the heat sensitive element 118 is a thermistor 304, and heating clement 116 is a resistor 306. The thermistor 304 may be a positive coefficient thermistor or a negative coeflicicni thermistor.
In one preferred embodiment, the operating circuit 120 present in the control unit 112 is a Whcatsione bridge 302. The thermistor 304 forms one arm of the Wheatstone bridge 302. 'fhc thermistor 304 gets heated by the resistor 306 and due to the resulting temperature rise shows variations in resistance, which imbalances the Wheatstone bridge 302. This variation in the resistance of the thermistor 304 is in accordance with the temperature of the resistor 306, This imbalance in the Wheatstone bridge 302 creates a ditYerential voltage signal across the Wheatstone bridge 302. This differential voltage signal is send to the CPU 122 .

The CPU 122 may ha\e multiple ports, for example, in one implementation; the CPU 122 includes six ports namely PI. P2, P3. P4. P5, and P6. The CPU 122 controls the switching oi' transistor Tl and transistor '\'2 through P6, The resistances R5, R6 and R7 are employed in order lo moderate the current supplied and the circuit 300 is so implemented such that when transistor Tl is conducting transistor T2 is also conducting. The power is supplied to the rcsi.sior 306 from the power source 128 when transistor T2 is conducting. "Fhc port P6 deicrmincs the amount of power to be supplied to the resistor 306.
The CPU 122 receives the differential voltage signals through ports PI and 1*2 and calculates a differential voltage value. The CPU 122 captures the differential voltage signals at a plurality of instances and determines the variation in differential voltage over a predetermined interval of time. The CPU 122 includes predetermined values of variation in dilTercntial voUages corresponding to different levels of liquid 102 immersing the resistor 306 in the container 104. stored in the memory 126. The CPU 122 implements level detection logic to compare ihe variation in differential voltage value with the predetermined differential voltage values stored in the memory 126 in the microprocessor 124. When both the values match, the corresponding level of liquid 102 is indicated as the present level of liquid 102.
In one implementation, the memory 126 may include a database such as a relational database and the CPU 122 may be a personal computer, a laptop, and so on.
'I he CPU 122 further connected to output means 114 such as a digital display, alarm etc. In one implementation. CPU 122 is connected to an audio alarm and a visual alarm via its ports i'3 and P4, respectively, which together form an output means 114 for indicating the level oi the Uc|uid 102. In one implementation, the output means 114 indicates the level of liquid 102 by \va\ of one or more of a visual or audio signal or a combination of both.
Fig. 4 illustrates an exemplary method 400 for determining level of a liquid such as liquid 102 in a container, for instance container 104, in accordance with an embodiment of the subject matter, by means of a flow chart. In a preferred embodiment, method 400 is implemented in the aforementioned system 100.

The method 4O0 is initiated at step 402, wherein the probe 116. having a thermally sensitive clement 118 is placed in the container 104 having the liquid 102. Ibe thermally sensitive clement 116 senses the initial temperature and sends corresponding signals to the operating circuit 120. The operating circuit 120 converts the signal received from thermally sensitive element 116 into electrical signals. The electrical signals produced by operating circuit 120 are read by the CPU 122. I'he electrical signals ate processes and interpreted by the CVU 122. In one implementation, a plurality of signal of the operating circuit 120, over a predctincd interval of time is read by the CPU 122. The plurality of signal recorded is processed in the CPU 122. The processing involves calculating average, weighted mean, moving average etc. in one preferred embodiment, an average of the plurality of signals is calculated. The processed signals arc indicalive of initial temperature corresponding to initial condition. The signals processed by CPU 122 are then analyzed against a pre-delermined signal corresponding to a signal produced b\ the operating circuit 12(1 when probe 106 is in air.
At step 404 of the method 400, it is determined whether the probe 106 is in air or immersed in ihc liquid 102, If the probe 106 is in air, it signifies that the level of the liquid 102 is abnormally low than a predefined threshold level. Consequently, at step 416. an indication is send through the output means 114. In one preferred embodiment output means 114 is an alarm vvhich produces an audio or visual signal indicating the level of the liquid 102 to be below sale level. However, if the probe 106 is not in air it is determined that the probe tip 108 is immersed partially or eomplelely in the liquid 102 and thereupon the level of immersion is determined.
Ihc method 400 progresses to step 406 when it is established, at step 404, that ihc probe 106 is not in air and the probe 106 is partially or completely immersed in the liquid 102. Ai step 406, the pluTalily of electrical signal recorded at the step 402 is evaluated to determine the initial temperature. In one preferred implementation, the signal recorded corresponds to the temperature of the liquid 102. The signal is processed in the CPU 122 and compared against pre-dclined signal values corresponding to initial temperature stored in the memory 126 of the C'PU 122. 'f his comparison is further elaborated in Fig 5. Thus, the initial temperature is determined.
At step 408, power is supplied to the heating element 116 for a pre-delermined interval of time. The heating element 116 gets heated up and the temperature of the heating clement

increases. The temperature increase depends upon the initial temperature and the portion ol' the heating clemcnl 116 immersed in the liquid 102. This increase in the temperature is sensed by the thermally sensitive element 118 present at the proximity of the heating clement 116, This results in change in electrical resistance of the thermally sensitive elemenl US.
The thermally sensitive elemenl 118, being a part of the operating circuit 120 which in one implementation is a Wheatstone bridge 302, creates an imbalance in the Whcalstonc bridge 302. The operating circuit 120 produces electrical signals corresponding to the imbalance created. At step 410, the electrical signal is read at a plurality of instances. In one preferred implementation, the imbalance is recorded as a differential voltage across the Wheatstone bridge 302. A plurality of signal produced by the operating circuit 120 is recorded over a predcllned interval of time is read by the CPU 122,
Ai step 412, the signal provided to the CPU 122 is processed. The processed signals are interpreted against known values of liquid level at a certain initial temperature, which is determined at the step 406. Interpretation of signals takes place in the microprocessor 124 present in the CPU 122 against pre-deiermined values stored in the memory 126 of the CPU. This inlerpretation is further discussed in detail in Fig 6. Thus, liquid level is determined.
At step 414. the liquid level determined at step 412, is compared in the microprocessor 124 with a safe working level of the liquid 102 in the container 104. The value of safe working level is a prc-determined threshold level stored in the memory 126 of the CPU 122. If the level is not safe, a signal is send to the output means 114. The output means 114 which in one preferred implementation is an alarm generates an audio or visual signal indicating the unsafe working lc\el of liquid 102 in the container 104.
At step 418 if the level of liquid 102 in the container 104 is safe, the level is indicated as safe level by the output means 114.
Ihc order in which method 400 is described is not intended to be construed as a limitation, and the steps described can be combined in other ways obvious to a person skilled in the art. Additionally, individual blocks may be added or deleted from the method without departing from the spirit and scope of the subject matter described.

Fig. 5 illustrates an exemplary graphical representation 500 showing initial temperature dX various values of ekctrical signal produced by the operating circuit. 120. In one prefciTed embodiment, the electrical signals produced by the operating circuit 120 is a differential voltage produced across the Wheatstone bridge 302. The graph 500 (i.e.. Equation Curve I.l) depicts the variation in differential voltage (Vi) at diflerent initial temperatures. The graph 500 shows a constant increase in differential voltage (Vi) with an increase in initial temperature (fi). Different values of differential voltage (Vi) are determined at different initial temperature (Ti) and stored in a database in the memory 126 of the CPU 122. The values are determined based on the following formula;
■fi- f(Vi)
where.
f is a function of Vi.
The signals produced by the operating circuit 120 in step 402 of method 400 are processed compared with the predetermined values stored in the memory 126 at step 406 of method 400. The predetermined stored value that matches with a current signal value provides value of the initial temperature.
Fig. 6 illustrates an exemplary graphical representation 600 showing levels oi'lhc liquid 102 in the container 104 at various electrical signal values produced by the operating circuit 120 al the step 410 of method 400. In one preferred embodiment, the signal produced b> the operating circuit 120 is differential voltages (Vt) produced across the Wheatstone bridge 302. Graphs arc drawn between the differential voltage (Vt) across the Wheatstone bridge 302 and level of the liquid 102 al the different initial temperatures ('fi). The graph clearly shows levels of liquid for various differential voltages (Vt) based on formula:
Liquid Level ' f(Vl) for fi
where.
It is initial temperature; and

("is a function of Vt.
Curves 602. 604, 606 are drawn at initial temperature 20 degree Celsius. AO degree Celsius and 90 degree Celsius respectively A direshold limit (LTH) and a minimum limit (l.MIN) show an alarming low level of the liquid 102.
rhc signals produced by the operating circuit 120 in step 410 ol" method 40(1 are processed compared with the predetermined liquid level values stored in the memory 126 at corresponding initial temperature TJ at step 412 of method 400. The predetermined stored value that matches with the signal value provides the liquid level.
Ilius, the aforementioned method 400 and system 100 may be adapted to various applications such as. for example, the method 400 and the system 100 may be employed in a vehicle, such as a two-wheeler, for determining the level of lubrication oil in the crankcasc. In such an implementation, the probe 106, being compact in size, may be altached to the crankcasc of the vehicle. I'urlher, no substantial change in existing design of the vehicle is required. In one implementation the electronic control unit (ECU), preexisting in the vehicle for conlroiling ignition and other associated function may be adapted to receive and process signals from the operating circuit 120 for indicating the level of lubrication oil in the crankcasc. The method 400 and the system 100 indicate, lo a user, the level of lubrication oil at every instance during operation of the vehicle. The previously described versions of the subject matter and equivalent thereof have many advantages, including those which are described above.
Although the subject mailer has been described in considerable detail with reference to ccriain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.

We claim:
1. A system (100) for sensing the level of a liquid (102) in a container (104), said system
(100) comprising:
a sensing unit (110) immersed in said liquid (102);
a control unit (112) electrically coupled to said sensing unit (HO) for interpreting a plurality of signals produced by said sensing element (110), said signals being indicative of the level of said liquid (102); and
an output means (114) for indicating the level of said liquid (102); characierized in that.
said sensing unit (110) comprising:
a heating element (116) receiving power supply for heating said heating clement (116), wherein said heating is controlled by said control unit (112): and
a thermally sensitive element (118) thermally coupled to said healing element (116);
wherein said heating element (116), upon being heated, increases the temperature of the thermally sensitive element (118) and wherein said thermally sensitive clement (118) provides said plurality of signals to said control unit (112).
2. The system (100) as claimed in claim 1, wherein said control unit (112) comprises:
an operating circuit (120); and
a central processing unit (CPU) (122).
3. The system (100) as claimed in claim 2, wherein said operating circuit (120) is a
Wheatstone bridge (302).
4. The system (100) as claimed in claim 1, wherein said output means (114) comprises one
or more of visual or audio signals.
5. fhc system (100) as claimed in claim I, wherein said heating element (116) is a resistor
(306) with a predetermined resistance value.
6. [he system (100) as claimed in claim I, wherein said thermally sensitive clement (118) is
a thermistor (304).
7. A vehicle comprising:

a lubrication system, wherein said lubrication system comprises said 5>'stcm (100) as claimed in claim 1. for indicating level of lubrication oil. S. An engine comprising:
a erankcase. wherein said crankcasc comprises said system (100) as claimed in claim 1, for indicating level of engine oil.
9. A method (400) for sensing the level of a liquid (102) in a container (104). the method
(400) comprising the steps of:
determining the initial temperature of a heating element (U6);
heating said heating element (116) immersed in said liquid (102) for a predetermined time interval:
determining the temperature of said heating element (116) by sensing the temperature of a thermally sensitive element (118), wherein said thcvmally sensitive clement (118) is ihermally coupled to said heating element (116):
detcnnining the level of said liquid (102) corresponding to said initial temperature and said temperature of said heating element (116) by a control unit (112): and
indicating the level of said liquid (102).
10. The method (400) as claimed in claim 9, wherein determining said initial temperature
comprises interpreting signals produced by an operating circuit (120) again.st pre-
deiermined values of signal corresponding to said initial temperature.
11, The method (400) as claimed in claim 9, wherein said heating comprises switching ON and OI~i-' a power supply (128) through one or more transistors for a predetermined interval of time.
12, The method (400) as claimed in claim 9, wherein said sensing comprises determining the variation in magnitude of electrical property of said thermally sensitive element (118) with temperature.
n.ihc method (400) as claimed in claim 12, wherein said electrical propert)' of .said
Ihermally sensitive element (118) is electrical resistance. 14. The method (400) as claimed in claim 9, wherein determining the level of said liquid
(102) comprises:
determining an electrical signal equivalent to change in an electrical property of
said ihermally sensitive element (118) by an operating circuit (120): and

interpreting said electrical signal against pre-determined values of said electrical signal corresponding to the level of said liquid (102) at said initial temperature stored in a CPU {122). 15. The method (400) as claimed in claim 9, wherein indicating the level of said liquid (102) includes providing an audio or visual output through an output mean (114).