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A fluid measuring device for use in a fluid storage tank, comprising a logic operation unit, a capacitive sensor, and a capacitance sensing circuit; wherein the capacitance sensing circuit is driven by the constant current input to perform the detection of the capacitance value of the capacitive sen

A fluid measuring device for use in a fluid storage tank, comprising a logic operation unit, a capacitive sensor, and a capacitance sensing circuit; wherein the capacitance sensing circuit is driven by the constant current input to perform the detection of the capacitance value of the capacitive sensor, then perform the conversion from the capacitance value into the signal on the physical characteristics of the fluid body by the logic operation unit. The signal on the physical characteristics can include any of the concentration, density, and surface level of the fluid body. Furthermore, the capacitive sensor can further comprise a reference capacitor and a detection capacitor for detecting the fluid, the latter capacitance is obtained from a differential circuit of the capacitance sensing circuit.

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What is claimed is: 1. A fluid measuring device, comprising: a logic operation unit with a switching signal output port for outputting a control signal; a capacitive sensor for generating a corresponding electrical signal in response to at least one physical property of a body of fluid; and a capac

What is claimed is: 1. A fluid measuring device, comprising: a logic operation unit with a switching signal output port for outputting a control signal; a capacitive sensor for generating a corresponding electrical signal in response to at least one physical property of a body of fluid; and a capacitance sensing circuit, comprising: a constant current source including a constant current source output electrical contact for outputting an electrical signal of the constant current source; a switch including a control terminal, a signal input port, and a signal output port; a voltage comparator including a high potential input port, a low potential input port, and signal output port, wherein the potential of the low potential input port is a reference voltage; and a time calculator for accumulating the time of the signal output from the voltage comparator, comprising: an electrical contact forming an electrical connection with the signal output port of the voltage comparator; another electrical contact forming another electrical connection with the switching signal output port of the logic operation unit; and a further electrical contact for outputting the accumulated time to the logic operation unit in the form of an electrical signal; wherein the constant current source is electrically connected to the signal input port of the switch, the capacitive sensor, and the high potential input port of the voltage comparator respectively through the constant current source output electrical contact; and the other terminals of the switch and the capacitive sensor are connected to ground, resulting in the electrical connection of the switch and the capacitive sensor in parallel. 2. The fluid measuring device as claimed in claim 1, wherein: in an initial state, the switching signal output port of the logic operation unit outputs a logic high signal to turn on the signal input port and signal output port of the switch, thereby discharging the capacitive sensor; after a first stage in time, the switching signal output port of the logic operation unit outputs a signal to turn off the signal input port and signal output port of the switch, at the same time the switching signal output port of the logic operation unit outputs another signal to clear the accumulated time record in the time calculator to restart the time accumulation, enabling under the constant current source of the capacitance sensing circuit continuously to input the signal the capacitive sensor will be constantly charged and rise the voltage of the first electrical contact to approach the reference voltage of the voltage comparator; after a second stage in time, the voltage across the capacitive sensor exceeds the reference voltage and raises the output voltage of the signal output port of the voltage comparator from negative potential to positive potential then sent to the time calculator, enabling the time calculator to stop accumulating the time and hence obtain the time difference between the time at first stage and second stage; and at the same time when the time calculator stops the time accumulation, the time difference electrical signal is sent to the logic operation unit as the corresponding physical information derived from the time difference. 3. The fluid measuring device as claimed in claim 2, wherein: the logic operation unit further comprises performing a back stage algorithm on the capacitance of the capacitive sensor in order to obtain the at least one physical property of the body of fluid; and the at least one physical property is selected from one of the concentration, density, and surface level of the body of fluid. 4. The fluid measuring device as claimed in claim 1, wherein the capacitance sensing circuit and the logic operation unit can be integrated in the form of either an electrical circuit or an integrated circuit (IC). 5. The fluid measuring device as claimed in claim 1, wherein the switch is selected from one of a MOS switch or transistor switch. 6. The fluid measuring device as claimed in claim 1, wherein the capacitive sensor is disposed within a fluid fuel tank of a fuel cell system, where the fluid fuel tank contains the fluid fuel and the capacitive sensor is used to detect the at least one physical property of the fluid fuel to generate the corresponding electrical signal. 7. The fluid measuring device as claimed in claim 6, wherein: in an initial state, the switching signal output port of the logic operation unit outputs a logic high signal to turn on the signal input port and signal output port of the switch, thereby discharging the capacitive sensor; after a first stage in time, the switching signal output port of the logic operation unit outputs a signal to turn off the signal input port and signal output port of the switch, at the same time the switching signal output port of the logic operation unit outputs another signal to clear the accumulated time record in the time calculator to restart the time accumulation, enabling under the constant current source of the capacitance sensing circuit continuously to input the signal the capacitive sensor will be constantly charged and rise the voltage of the first electrical contact to approach the reference voltage of the voltage comparator; after a second stage in time, the voltage across the capacitive sensor exceeds the reference voltage, enabling the signal output port of the voltage comparator to output a voltage signal to the time calculator and hence the time calculator stops accumulating the time to obtain the time difference between the time at first stage and second stage; and at the same time when the time calculator stops the time accumulation, the time difference electrical signal is sent to the logic operation unit as the corresponding physical information derived from the time difference. 8. The fluid measuring device as claimed in claim 7, wherein: the logic operation unit further comprises performing a back stage algorithm on the capacitance of the capacitive sensor to obtain the at least one physical property of the body of fluid; and the at least one physical property is selected from one of the concentration, density, and surface level of the body of fluid. 9. The fluid measuring device as claimed in claim 1, wherein: the logic operation unit converts the electrical signal from the capacitor into the surface level information of the fluid fuel; and the surface level information of the fluid fuel can be further output as image data to be displayed on a display device. 10. The fluid measuring device as claimed in claim 9, wherein: the display device is a computer system, and the logic operation unit is electrically connected to a signal I/O port of the computer system; and the surface level information of the fluid fuel is sent to the computer system to be displayed as image or text format on the display device in order to allow a user to monitor the remaining fluid fuel level of the fuel cell system. 11. A fluid measuring device, comprising: a logic operation unit with a first switching signal output port and a second switching signal output port for outputting a respective control signal; a capacitive sensor consisting of a first capacitor and second capacitor, where the capacitors respectively respond to the surrounding materials and result in the corresponding capacitive characteristics; and a capacitance sensing circuit, comprising: a first constant current source including a first constant current source output electrical contact for outputting an electrical signal of the constant current source; a second constant current source including a second constant current source output electrical contact for outputting an electrical signal of the constant current source; a first switch including a control terminal, a signal input port and a signal output port; a second switch including a control terminal, a signal input port and a signal output port; a voltage differential amplifier including a high potential input port, a low potential input port, and a signal output port; and a time calculator for accumulating the time of the signal output from the voltage differential amplifier, comprising: a first electrical contact forming the electrical connection with the signal output port of the voltage differential amplifier; a second electrical contact and a third electrical contact forming the respective electrical connection with the first switching signal output port and second switching signal output port of the logic operation unit; and a fourth electrical contact outputting the accumulated time to the logic operation unit in the form of electrical signal; wherein the first constant current source through the first constant current source output electrical contact, and the second constant current source through the second constant current source output electrical contact are electrically connected to the signal input port of the first switch, the signal input port of the second switch, the first capacitive sensor, the second capacitive sensor, the low potential input port of the voltage differential amplifier, and the high potential input port of the voltage differential amplifier, respectively; and wherein the other terminals of the switches and the capacitive sensors are connected to ground, resulting in the electrical connection of the first switch and the first capacitive sensor in parallel, and the electrical connection of the second switch and the second capacitive sensor in parallel. 12. The fluid measuring device as claimed in claim 11, wherein the first capacitive sensor and the second capacitive sensor have a specific size ratio providing a specific capacitance ratio. 13. The fluid measuring device as claimed in claim 12, wherein the amount of the current from the first constant current source and the second constant current source is set based on the specific capacitance ratio. 14. The fluid measuring device as claimed in claim 11, wherein: in a initial state, each of the switching signal output ports of the logic operation unit outputs a logic high signal to turn on the signal input port and signal output port of each switch, thereby discharging the capacitive sensor; and after a first stage in time, each of the switching signal output port of the logic operation unit outputs a signal to turn off the signal input port and signal output port of each switch, at the same time the switching signal output port of the logic operation unit outputs another signal to clear the accumulated time record in the time calculator to restart the time accumulation. 15. The fluid measuring device as claimed in claim 11, wherein: the capacitance sensing circuit is in the first stage in time, the switching signal output port of the logic operation unit outputs a signal to turn off the signal input port and signal output port of the first switch, as well as the signal input port and signal output port of the second switch; the logic operation unit clears the accumulated time record in the time calculator to restart the time accumulation, enabling the first capacitor and the second capacitor will be continuously charged and rise the voltage on the second electrical contact and the voltage on the third electrical contact; after the second stage in time, the voltage on the second electrical contact and the voltage on the third electrical contact reaches saturation and results in the constant voltage difference between the second electrical contact and the third electrical contact, thereby the logic operation unit stops accumulating the time to obtain the time difference between the time at first stage and second stage; and at the time when the logic operation unit stops accumulating the time, the logic operation unit calculates the capacitance of the second capacitor according to the time difference and the capacitance of the first capacitor. 16. The fluid measuring device as claimed in claim 11, wherein: the logic operation unit further comprises performing a back stage algorithm on the capacitance of the second capacitor of the capacitive sensor to obtain at least one physical property of a body of fluid; and the at least one physical property is selected from one of the concentration, density, and surface level of the body of fluid. 17. The fluid measuring device as claimed in claim 11, wherein the capacitance sensing circuit and the logic operation unit can be integrated in the form of either an electrical circuit or an integrated circuit (IC). 18. The fluid measuring device as claimed in claim 11, wherein: the voltage comparator is a voltage differential amplifier, and further comprises a first comparator, a second comparator, a first resistor, a second resistor, a third resistor, a fourth resistor, and a fifth resistor; the second electrical contact is electrically connected to the high potential port of the first comparator, the third electrical contact is electrically connected to the high potential port of the second comparator, the signal output port of the first comparator is electrically connected to the second electrical contact; the low potential port of the first comparator, the first resistor, and the low potential port of the second comparator are electrically connected in series; and one terminal of the second resistor is connected to ground and another terminal is electrically connected to the low potential port of the second comparator, one terminal of the third resistor is electrically connected to the low potential port of the second comparator and another terminal is electrically connected to the signal output port of the second comparator, one terminal of the fourth resistor is electrically connected to the signal output port of the second comparator and another terminal is electrically connected to the grounded low potential port of the first comparator, one terminal of the fifth resistor is electrically connected to the low potential port of the first comparator and another terminal is electrically connected to the signal output port of the first comparator. 19. The fluid measuring device as claimed in claim 11, wherein the voltage comparator is used to amplify the difference between the voltage on the second electrical contact and the voltage on the third electrical contact. 20. The fluid measuring device as claimed in claim 11, wherein the capacitance sensing circuit and the logic operation unit can be integrated in the form of either an electrical circuit or an integrated circuit (IC). 21. The fluid measuring device as claimed in claim 11, wherein: the first capacitor corresponds to an accommodation space, and the accommodation space is a locally enclosed space in a fluid fuel tank and does not store any fluid fuel; the second capacitor corresponds to the fluid fuel storage space in the fluid fuel tank; and the capacitance value from the first capacitor is a reference capacitance in the absence of fluid, and the second capacitor can use the measured capacitance from the first capacitor by proportion and set the resulting value as the initial capacitance in the absence of fluid. 22. The fluid measuring device as claimed in claim 11, wherein the logic operation unit converts the electrical signals from the capacitors into the surface level information of stored fluid fuel, and the surface level information of the stored fluid fuel can be further output as image data to be displayed on a display device. 23. The fluid measuring device as claimed in claim 22, wherein: the display device is a computer system, and the logic operation unit is electrically connected to a signal I/O port of the computer system; and the surface level information of the fluid fuel is sent to the computer system to be displayed as image or text format on the display device, in order to allow a user to monitor the remaining fluid fuel level of the fuel cell system.