CLIAMS:We Claim:
1. A pressure sensor comprising:
an operative flexible top surface (15) that exhibits property of deformation when pressure is exerted on it;
a first layer of electrolyte solution (20) in contact with said operative flexible top surface (15) and a second layer of electrolyte solution (30) in contact with a bottom base plate, wherein said first layer and second layer of electrolyte solution comprises ions and molecules;
a semi permeable membrane (25) sandwiched between, said first layer of electrolyte solution (20) and said second layer of electrolyte solution (30), said semi permeable membrane (25) permits passage of at least one of said ions or said molecules between said first layer of electrolyte solution (20) and said second layer of electrolyte solution (30); and
two electrodes (35a) and (35b) in contact with said first layer of electrolyte solution (20), said two electrodes connected to a voltage source (40) and a current source (45) for indicating conductivity of said first layer of electrolyte solution (20).
2. The pressure sensor as claimed in claim 1, wherein said first layer of electrolyte solution (20) and said second layer of electrolyte solution (30) are of varying molar concentrations.
3. The pressure sensor as claimed in claim 1, wherein said conductivity of said first layer of electrolyte solution (20) is measured in the form of current value indicated by said current measuring device (45).
4. The pressure sensor as claimed in claim 1, wherein current indicated by said current measuring device (45) is proportional to a pressure value applied on said flexible top surface (15).
5. An electronic controller for indicating pressure, said electronic controller adapted to:
receive a current value from a current measuring device (45); and
retrieve a pressure value that correspond to said current value from a map.
6. The electronic controller as claimed in claim 5, wherein said map is calibrated and stored in memory of said electronic controller. ,TagSPECI:Field of the invention
[0001] This invention relates to a pressure sensor for measuring pressure.
Background of the invention
[0002] There are large numbers of applications where pressure value between two contacting surfaces is required to be detected. Industrial applications, medical applications, research applications are some of the areas where measuring the pressure value is important. Maintaining an optimal pressure value for a particular application is critical. In order to maintain the optimal pressure, the current pressure should be measured so that a pressure controlling device can be used for adjusting the pressure so that the optimal pressure value for that particular application may be maintained. A pressure sensor is used for measuring such pressure. The pressure sensor should be such that it can measure the pressure values over various ranges based on the application.
[0003] A Japanese patent application JP-2006223501 discloses an osmotic pressure sensor for measuring osmotic pressure in a blood sample. Two electrodes are made to contact a human body liquid e.g. blood sample. The electrodes perform electric conduction from which osmotic pressure is estimated, when alternating current (AC) voltage is applied between electrodes. The sensor measures osmotic pressure by suction using capillary phenomena.
Brief description of the accompanying drawings
[0004] Figure 1 illustrates a pressure sensor, in accordance with an embodiment of the present disclosure.
Detailed description
[0005] Figure 1 illustrates a pressure sensor, in accordance with an embodiment of the present disclosure.
[0006] The pressure sensor comprises an operative flexible top surface 15 that exhibits property of deformation when pressure is exerted on it, a first layer of electrolyte solution 20 in contact with the operative flexible top surface 15 and a second layer of electrolyte solution 30 in contact with a bottom base plate 50, a semi permeable membrane 25 sandwiched between, the first layer and the second layer of electrolyte solution, the semi permeable membrane 25 permits passage of at least one of ions or molecules between the first and second layer of electrolyte solution. The pressure sensor also comprises two electrodes 35a and 35b in contact with the first layer of electrolyte solution 20 and connected to a voltage source 40 and a current source 45. The two electrodes 35a and 35b are used for measuring conductivity of the first layer of electrolyte solution 20. The pressure sensor further comprises a current measuring device 45 connected in series with the voltage source 40 for indicating the conductivity of the first layer of electrolyte solution 20.
[0007] The pressure sensor comprises a flexible top surface 15. The flexible top surface 15 may be made up of an epoxy based material or vulcanized rubber material so that it undergoes deformation when pressure is applied on its surface. The flexible top surface 15 in the pressure sensor is arranged such that it is pressed against the first layer of electrolyte solution 20 when it undergoes deformation when the pressure is applied on its surface.
[0008] The electrolyte solution comprises salts mixed in an aqueous media. Examples of the salts include, but are not limited to, sodium chloride, potassium chloride, calcium chloride and magnesium chloride. These salts ionize when mixed in aqueous media. The aqueous media may include, but is not limited to, gelatin, aqueous based paste, cellulose based paste. The electrolyte solution is arranged in the form of layers. In order to arrange the electrolyte solution in the form of layers, the electrolyte solution may be drawn in the form of strips and layered. The first layer of electrolyte solution 20 is in contact with the flexible top surface 15 and the second layer of electrolyte solution 30 is in contact with a bottom base plate.
[0009] The first layer and the second layer of electrolyte solution are of varying molar concentrations for permitting flow of ions or the aqueous medium between the layers of electrolyte solution through the semi permeable membrane 25.
[00010] A semi permeable membrane 25 is sandwiched between the first layer and the second layer of electrolyte solution. The semi permeable membrane 25 may be either a cellulose based membrane or a polymer based membrane. Perforations in the semi permeable membrane 25 allows either the molecules of the aqueous media to pass through it or may allow ions of the salts to pass through it.
[00011] Two electrodes 35a and 35b are in contact with the first layer of electrolyte solution 20. Any material capable of conducting can be used as electrodes. Examples of the materials used as electrodes include, but are not limited to, gold, silver, graphite and copper. One electrode is connected to positive terminal of the voltage source 40 and another electrode is connected to the negative terminal of the voltage source 40 through the current measuring device 45. The voltage source 40 is a battery. The current measuring device 45 is usually an ammeter that is connected to the voltage source 40 such that they are in series with each other.
[00012] The electrode that is connected to the positive terminal of the voltage source 40 is positively charged and the electrode that is connected to the negative terminal of the voltage source 40 is negatively charged. As a result, there is flow of electrons from the negatively charged electrode towards the positively charged electrode through the electrolyte solution. Such flow of electrons through the electrolyte solution constitutes flow of current and is referred to as the conductivity of the electrolyte solution. The conductivity of the electrolyte solution depends on the quantity of aqueous medium present in the electrolyte solution. When large quantity of aqueous medium is present, the conductivity of the electrolyte solution decreases because the aqueous medium offers resistance for the movement of electrons in the electrolyte solution. If the quantity of aqueous medium in the electrolyte solution decreases then the conductivity of the electrolyte solution increases since the resistance for the flow of electrons decreases as the aqueous medium quantity is decreased. The conductivity of the electrolyte solution is indicated by the current measuring device 45.
[00013] When no pressure is applied on the flexible top surface 15 and a constant voltage source 40 is supplied, there still exists some flow of electrons from the negatively charged electrode to the positively charged electrode through the first layer of the electrolyte solution. This flow of electrons when no pressure is applied on the flexible top surface 15 constitutes a current. Such current flowing through the first layer of electrolyte solution 20 is referred to as reference current.
[00014] The working of the pressure sensor is as explained in this paragraph. When pressure is applied on the flexible top surface 15, it undergoes deformation. This causes the flexible top surface 15 to press against the first layer of electrolyte solution 20 with a particular pressure. When pressure is applied on the first layer of electrolyte solution 20, molecules of aqueous medium present in the first layer of electrolyte solution 20 forces its movement towards the second layer of electrolyte solution 30 through the semi-permeable membrane. The molecules moving towards the second layer of electrolyte solution 30 depends on the pressure aplied on the first layer of electrolyte solution 20.
[00015] Such movement of the aqueous medium from the first layer of electrolyte solution 20 towards the second layer of electrolyte solution 30 causes increase in conductivity of the first layer of electrolyte solution 20. Such increase in conductivity is indicated by the increase in the flow of current with respect to the reference current.
[00016] A working example of the pressure sensor is described in the following paragraphs for the purpose of understanding the disclosure.
[00017] One working example is the use of the pressure sensor in a common rail for measuring rail pressure.
[00018] The pressure sensor is placed in the common rail such that the fuel is in contact with the flexible top surface 15. This arrangement causes the pressure of the fuel to be applied on the flexible top surface 15. When the pressure is applied, the flexible top surface 15 presses against the first layer of electrolyte solution 20. This causes the molecules of the aqueous medium from the first layer of electrolyte solution 20 to move towards the second layer of electrolyte solution 30 through the semi permeable membrane 25. Such movement of the molecules through the semi permeable membrane 25 causes increase in conductivity of the first layer of electrolyte solution 20 since resistance for the movement of the electrons are reduced since the quantity of aqueous medium in the first layer of electrolyte solution 20 is reduced.
[00019] For illustration purpose, it is considered that the current flowing through the first layer of electrolyte solution 20 when no pressure is applied on the flexible top surface 15 is 5mA which is also referred to as reference current. When the fuel in the rail exerts pressure on the flexible top surface 15, the current flowing through the first layer of electrolyte solution 20 becomes higher with respect to the reference current. Let such increase in current be 5.5mA. This current is indicated by the current measuring device 45.
[00020] The current measuring device 45 is also connected to an electronic controller that reads the increased current value. The electronic controller retrieves a pressure value that corresponds to 5.5mA from a map that is stored in the memory of the electronic controller. Let us consider that for a current of 5.5mA the pressure value retrieved from the map is 1100 bar. Hence, it can be inferred that the pressure of the fuel present in the common rail is 1100 bar.
[00021] In yet another example, let us consider if the current measured is 6mA. Then the pressure value corresponding to 6mA is retrieved from the map. Let the pressure value corresponding to 6mA be 1200 bar. Hence, it can be inferred that the rail pressure is 1200 bar. It should be noted that the current and pressure values are exemplary values for the purpose of clear understanding and these are not the actual values.
[00022] Similarly by mapping the current value to the pressure values, the pressure sensor can sense the pressure in various other fields. Such mapping of the current value to the pressure values are pre calibrated based on the application.
[00023] Some of the other applications where pressure value is determined using the pressure sensor presented in this disclosure include tire pressure sensing, sensing pressure of fluid in a tank and an airflow sensor.
[00024] An electronic controller for indicating pressure applied on a pressure sensor is adapted to receive a current value from a current measuring device 45. The current value defines the degree of conductivity of the electrolyte solution. Upon receiving the current value, the electronic controller retrieves a pressure value that correspond to the current value that was received from a map. Such a map is stored in the memory of the electronic controller.
[00025] The map is pre-calibrated based on the application where the pressure sensor is placed. The map includes a plurality of current values associated with corresponding pressure values. The range of values of the current and associated pressure values vary with respect to the application.
[00026] It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to the material of the semi permeable membrane, electrolyte solution, type of voltage source, type of current measuring device, are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.