FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(Section 10 and Rule 13)
1. TITLE OF THE INVENTION:
SYSTEM AND METHOD FOR MEASURING LEVEL OF LIQUID
2. APPLICANT:
(a) Name: Intelux Electronics Pvt. Ltd.
(b) Nationality: Indian
(c) Address: Unit-2, Electronic Co-Op Estate, Pune - Satara Road,
Pune -110009, India
The following specification particularly describes the invention and the manner in which it is to be performed:
FIELD OF INVENTION:
The present invention relates to a system for measuring level of liquid and more particularly, the present invention relates to the system for measuring the level of liquid using capacitive sensors.
BACKGROUND:
Sensors are one of the most important components of electronics industry. Their application ranges from cars, machines, aerospace, medicine, manufacturing and robotics. Selection of a sensor for a particular application depends upon the accuracy required, response time, deployable conditions and the like. For example, telecom towers that are located at various locations need to be powered by continuous power supply. Diesel generators are used as an alternate power backup at each cell tower site to prevent unexpected disruptions. These sites powered by diesel generators, require regular refueling. Fuel level sensors are required to monitor the level of fuel in the generators installed at these sites. Conventional fuel level sensors/systems available in the market are the ones used in automobile process industry. These are float switch type, float level type, capacitive type, magnetic type and ultrasonic type. The problems with these sensors are that the ultrasonic oil sensors do not work for low height oil tanks; float type and magnetic type sensors are not accurate and capacitive sensors are available for big tanks only. Thus, all these sensors have a limitation in providing accurate information of the level of fuel.
Due to the absence of any accurate method to monitor the fuel level, the cellular infrastructure companies are not able to evaluate the backup time since the quantity of available fuel cannot be determined precisely and monitor the fuel consumption in order to understand the performance of various diesel generators. Also, the companies are not able to accurately measure the performance against the load of the equipment in the shelter. These companies are also unable to assess the pilferage of diesel or adulteration during the transportation of diesel to telecom sites or from the generator oil tank and the wastage while filling the diesel in the generators. Moreover, a method to access the data is also not available. Further, the available sensors have a limitation in keeping the data in memory and they transmit only analog information.
In view of the above, there is a strong need to develop a system that addresses the above need and provides accurate level measurement information in real-time.
SUMMARY OF THE INVENTION
The present invention overcomes the aforesaid drawbacks and provides a system and method for measuring the level of liquid in a container.

In an embodiment, a system for measuring the level of liquid is provided. It includes a pair of printed circuit board (PCB) based probes such that the probes are separated by a predefined distance. The probes correspond to the two plates of a capacitor. Further, the system includes a capacitance to digital convertor in communication with the PCB based probes and a processing unit in communication with the capacitance to digital convertor for calculating at least the level of a liquid in a container based upon the capacitances measured across the PCB based probes.
In another embodiment, a method for measuring the level of a liquid in a container is provided. The method comprises measuring the capacitive difference between a pair of printed circuit board (PCB) based probes and converting the capacitive difference to a digital value. Further, the method comprises calculating at least the level of the liquid in the container based upon the digital value that corresponds to capacitive difference across the PCB based probes.
BRIEF DESCRIPTION OF DRAWINGS
The present invention will now be described with reference to accompanying drawings:
Fig 1 illustrates a block diagram of a system 100 for measuring the level of liquid in accordance with an embodiment of the present invention.
Fig 2 illustrates the bock diagram of a processing unit in accordance with an embodiment of the present invention.
Fig 3 is an exemplary demonstration of fuel pilferage in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention.

The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The terms including and/or containing, as used herein, are defined as comprising (i.e., open language). The term coupled/communicates, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
Fig 1 illustrates a block diagram of a system 100 for measuring the level of liquid. The system 100 comprises of a pair of Printed Circuit Board (PCB) based probes 102 with a capacitance to digital convertor 104 and a processing unit 106. The probes 102 are printed on a PCB for measuring the capacitance when it is immersed in a liquid, for example, diesel. The probe is specially designed to measure the level of liquid in a container (also, referred to as tank). The design of the probe depends on the size of the tank/container and the amount of capacitance needed. For example, if the system is employed for fuel measurement in generators at telecom sites, then for the tank of height 200 mm, and required capacitance range 4pF-20pF, the probe length would be around 175 mm and the thickness would be around 1.5 mm. The printed circuit board is a two layer PCB on which one side a pair of probes 108 & 110 are plotted separated by a predefined distance and on the other side, a ground plate is plotted. The ground plate is used to suppress the electrical noises etc. The predefined distance is calculated based on the capacitance needed and the size of the container. In the example relating to generators at telecom sites, the predefined distance between the probes would be in the range of 1-2 mm. The probes 108 & 110 correspond to the two plates of a capacitor and are used to measure the capacitance for a given liquid. The probes are coated with a special material that includes without limitation resins, epoxy and other potting materials, in order to avoid corrosion. The PCB is constructed such that one probe say 108, is permanently placed in the liquid and provides fixed capacitance for the given liquid medium. This acts as a base reference C2. The other probe say probe 110, accounts for changes in the level of liquid and provide CI. The change of capacitance in CI with respect to C2 provides for the difference in the level of the liquid.
The capacitance between the two probes 108 & 110 changes when a dielectric is introduced between them. In the present invention, the liquid acts as a dielectric between the two probes 108 & 110. As the level of liquid increases, the dielectric increases and in turn the capacitance also increases. This value of capacitance is compared with a set of values pre-stored in a memory. The values provide a correlation between original capacitance and the corresponding dielectric value which in turn provides the extent of the depth of the dielectric quantity, namely, the liquid. The capacitance values across the two probes provide the exact change in the level of liquid. It is

important to note that accuracy of up to 1% can be achieved by selecting the dimensions of the capacitance plates based upon the height and distance between the probes. Further, the total capacitance of a given liquid may lay within a range, for example 20pF - 4PF.
The capacitance to digital converter 104 interfaces with the PCB based probes 108 & 110. The capacitance to digital convertor 104 generates and feeds the excitation voltage to the probes 108 & 110 to measure their capacitances at regular intervals. In an exemplary embodiment, capacitance to digital convertor 104 may be AD7746 from Analog devices. The capacitance to digital convertor 104 communicates with the processing unit 106. The convertor 104 may communicate via an in-built or an external interface with the processing unit, including without limitation Inter IC (Integrated Circuit) Communication (I2C) interface or a Universal Serial Bus (USB) interface. The convertor 104 transfers the measured values of capacitances to the processing unit 106 via its interface.
The processing unit 106 converts the received values of the capacitances to the corresponding liquid level in the container. Though the invention can be used to measure the level of liquid without any height limitations, the invention provides better results when used to measure the level of liquid in shallow containers, for example of height up to 12 ft. Detailed description of the processing unit 106 will now be described with reference to Fig 2.
The processing unit 106 includes a real-time clock 202, a memory 204, an interface 206, a controller 208 and a communication interface (CI) 210. Optionally, the processing unit may include a display 212, and a keypad 214. The processing unit 106 receives the capacitance values from the convertor 104 via the interface 202. The interface 202 may be one of without limitation, I2C interface, RS232, RS485 etc. The interface 202 in turn communicates with the controller 208 that converts the capacitance values to liquid level using a look up table provided with the memory 206. The memory 206 may store without limitation fuel filled with date, time and quantity, fuel pilferage with date, time and quantity, fuel filled and fuel pilferage on hourly basis with date, time and fuel quality i.e. if any mixing is done or any change in fuel quality, on the basis of capacitance reference & current capacitance at zero level ratios with date and time quantity. An exemplary computation can be as follows:
On receipt of the values of the capacitances, the difference in the two values is computed. A look-up table with the differences being mapped to PCB level is referred to find the PCB level for the corresponding difference. An exemplary table (Table 1) is as follows:

Pcb level(mm) Capacitance-1(uF) Capacitance-2(uF) Difference


0 0.27200 0.05050 0.00287
10 0.27487 0.05062 0.00663
20 0.28150 0.05062 0.00650
30 0.28800 0.05050 0.00675
40 0.29475 0.05062 0.00712
50 0.30187 0.05075 0.00663
60 0.30850 0.05087 0.00737
70 0.31587 0.05087 0.00750
80 0.32337 0.05100 0.00738
90 0.33075 0.05112 0.00650
100 0.33725 0.05112 0.00637
HO 0.34362 0.05125 0.00613
120 0.34975 0.05137 0.00600
Table 1
Once the PCB level is obtained, the level of liquid can be calculated by translating the PCB level data to the volume of the container. For example, if 1mm corresponds to 1 liter then accordingly the PCB level value is translated to the corresponding number of liters in the container.
Further, the controller 208 stores the capacitance values, the level of liquid calculated and the time stamping in the memory 206. The controller 208 monitors the liquid level increment, decrement and gives the net liquid addition and subtraction against the time. In case the invention is employed for fuel level measurement in generators, the controller 208 may be provided with special functions like diesel generator (DG) rotations per minute (RPM) measurement, DG canopy temperature measurement, tamper proof DG run hours meter and DG health monitoring like HCT, LLOP built in. This feature gives additional advantage to the controller 208 in correlating the liquid level consumption against liquid theft etc.
In an embodiment, the amount of liquid filled can be calculated as follows. The liquid which is already present in the container is considered as the initial level. When the liquid is filled in between, the level can be calculated as the difference between the present level and initial level. This difference provides the quantity of liquid filled at any time. Thus, the time, date and quantity of liquid at that time is monitored to .calculate the exact liquid level at any time.

In an exemplary embodiment, liquid pilferage for example, fuel pilferage can be calculated as follows. Consider, DG works on full load condition when the load capacity is 25KVA and consumes 1 liter of fuel. This result in a 1:1 ratio of fuel consumed: time. If the load decreases, then the ratio will change as DG will consume less fuel, so it can be 0.9:1. This situation indicates under consumption of fuel. However, if the ratio increases, consider 1.5:1, it indicates fuel pilferage as DG cannot consume fuel more than full load condition. In case fuel is filled in between, then the records saved are looked up and the value is calculated accordingly, namely,
Actual Consumption = Fuel consumed before fuel filling + Fuel consumed after fuel filling.
An exemplary demonstration of fuel pilferage is shown in Fig 3. A horizontal line indicates DG is off as indicated by Tl. At normal condition the graph plot between the time on x-axis and fuel consumption in liters on Y-axis should be linear as marked T2. If there is an abrupt change in fuel consumption as marked T3, it indicates either fuel been added or removed from the tank.
Referring back to Fig 2, the controller 208 may display information like liquid level, liquid consumption, etc on the display 212. The display can be for example, 2*16 liquid crystal display (LCD). Further, the controller 208 is interfaced with the communication interface 210 for example, RS485 or RS 232 interface, for transmitting the measured data to a remote location for example, through RS485 modbus protocol. Data can be transmitted over a packed-switched or a circuit-switched network. This enables real-time monitoring of the level of liquid in a container situated at remote locations and does not require continuous manual monitoring of the level of liquid in the tank.
In addition, the invention is provided with an alarm system to alert against extreme conditions like liquid pilferage, liquid below a threshold in a container, etc.
Using the above system, the instant invention provides the accuracy of measurement upto 99.95% against temperature, humidity, density variation and adulteration even in low height liquid tanks even up to the height of 5mm; checks purity of liquid and is tamper proof. Moreover, the instant invention not only measures the level of liquid but also measures the quality and quantity of liquid consumed over the certain time period.

We claim:
1. A system for measuring the level of liquid comprising:
• a pair of printed circuit board (PCB) based probes such that the probes are separated by a predefined distance, wherein the probes correspond to the two plates of a capacitor;
• a capacitance to digital converter in communication with the PCB based probes; and
• a processing unit in communication with the capacitance to digital converter for calculating at least the level of liquid in a container based upon the capacitances measured across the PCB based probes.

2. The system as claimed in claim 1 wherein, the dielectric between the probes depends upon the level of liquid in the container.
3. The system as claimed in claim 1 wherein, the processing unit calculates liquid pilferage.
4. The system as claimed in claim 1 further comprising a communication interface communicating with the processing unit, wherein the interface provides for transmission of at least the data corresponding to the level of liquid.
5. The system as claimed in claim 1 further comprising a memory for recording the data received from the PCB based probes, the capacitance to digital converter and the processing unit.
6. The system as claimed in claim 1 further comprising an alarm for indicating extreme conditions of the level of the liquid.
7. A method for measuring the level of a liquid in a container, the method comprising:

• measuring the capacitive difference between a pair of printed circuit board (PCB) based probes;
• converting the capacitive difference to a digital value; and
• calculating at least the level of the liquid in the container based upon the digital value that corresponds to capacitive difference across the PCB based probes.
8. The method as claimed in claim 7 further comprising calculating liquid pilferage from the
container.

9. The method as claimed in claim 7 further comprising transmitting at least at least the data corresponding to the level of liquid in the container.
10. The method as claimed in claim 7 further comprising providing an alert to indicate an extreme condition of the level of the liquid.