Fluid measurement interface systems and methods

A fluid measurement system includes a signal processor and a processing system. The signal processor is configured and adapted to produce a serial word that is indicative of a fluid characteristic that is configured to be communicated externally of the signal processor. The processing system is operatively connected to the signal processor to read the serial word and decode the serial word. A method for transmitting a fluid characteristic between a sensor system and a processing system includes producing a serial word that is indicative of a fluid characteristic value with a signal processor. The method includes transmitting the serial word externally of the signal processor. The method includes reading and decoding the serial word with a processing system to determine the fluid characteristic value.

BACKGROUND

The present disclosure relates to remote fluid sensors, and more particularly to interfaces between remote fluid sensors, such as a fuel dielectric sensor within an integrated density compensation system, and a processing system, such as a fluid characterization system.

2. Description of Related Art

Aircraft use a variety of sensing devices for measuring the height of fuel in tanks and fluid characteristics of the fuel such as density, temperature and fuel dielectric. A processing system receives the fluid characteristic data and fluid level data. This fluid characteristic data is then used to compensate the fluid level measurements to determine the fuel mass. Aviation fuel level sensors use a capacitive sensing device that produces a signal representative of the fuel level as a result of the dielectric value of the fuel immersing the sensor. Because the density and/or dielectric value of fuel can vary with temperature, fuel type, and other parameters, fuel density and dielectric value are also measured utilizing separate density and dielectric detectors.

These characterization value measurements are then used to compensate the measurements of fuel level made by the fuel dielectric level sensors which are located at various points in the fuel tanks. Therefore, a pair of detectors is typically used to provide the characterization of fuel in a tank, one measuring fuel density and the other measuring fuel dielectric value. Power and signal cables typically connect each detector to a central processing system, e.g. an avionics computer, where the fuel mass is calculated by applying the density and dielectric values to the inputs from the various fuel level detectors. The signal cables connecting each dielectric and density detector are typically shielded to reduce electromagnetic interference that could otherwise degrade the signals. An aircraft typically has a fuel tank in each wing, and one or more fuel tanks located in the fuselage. For redundancy, each fuel tank may have multiple pairs of fuel dielectric and density detectors. Accordingly, numerous cables are routed through fuel tanks to provide accurate fuel level measurements in the various fuel tanks on an aircraft, thereby contributing to the weight of the aircraft. Moreover, these cables contribute to the cost of an aircraft during construction, and also during maintenance when cables may require removal and replacement. Power and signal cables typically connect each sensing device to the processing system, where the fuel mass is calculated by applying the density and dielectric values to the inputs from the various fuel level sensors.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved interfaces between the processing system and various sensing devices. The present disclosure provides a solution for this need.

SUMMARY

A fluid measurement system includes a signal processor and a processing system. The signal processor is configured and adapted to produce a serial word that is indicative of a fluid characteristic that is configured to be communicated externally of the signal processor. The processing system is operatively connected to the signal processor to read the serial word and decode the serial word.

In accordance with some embodiments, the serial word is representative of at least one of a density or a capacitance of a fluid. The serial word can include a plurality of bits. Each bit can be a 1 MHz bit cluster. Each 1 MHz bit cluster can include a plurality of 1 MHz pulses, e.g. ranging from 4-8 pulses. The plurality of bits can include a start bit, a plurality of data bits, and a parity bit.

The system can include a power interface between the signal processor and the processing system. The processing system can include an intrinsically safe power source and a current limiter. The current limiter can be between the intrinsically safe power source and the power interface. The processing system can include a velocity of sound signal conditioner to read and decode the serial word. The system can include a two-conductor wire pair between the signal processor and the velocity of sound signal conditioner.

In accordance with another aspect, a method for transmitting a fluid characteristic between a sensor system and a processing system includes producing a serial word that is indicative of a fluid characteristic value with a signal processor. The method includes transmitting the serial word externally of the signal processor. The method includes reading and decoding the serial word with a processing system to determine the fluid characteristic value.

In accordance with some embodiments, producing the serial word includes generating a plurality of bits with the signal processor. The plurality of bits can include a start bit, a plurality of data bits, and a parity bit. Each bit can be a 1 MHz bit cluster, and/or each bit cluster can include a plurality of 1 MHz pulses, e.g. ranging from 4-8 pulses. The method can include limiting current to 50 mA or less with a current limiter between an intrinsically safe power source and a power interface. The reading and decoding of the serial word can be done by a velocity of sound signal conditioner of the processing system. The method can include disabling a velocity of sound transmit function of the velocity of sound signal conditioner. Transmitting the serial word externally can include wirelessly transmitting the serial word from the signal processor to the processing system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a fluid measurement system having a sensor system and a processing system constructed in accordance with the disclosure is shown inFIG. 4and is designated generally by reference character100. Other embodiments of fluid measurement systems and for transmitting data between a sensor system and a processing system in accordance with the disclosure, or aspects thereof, are provided inFIGS. 1A-3 and 5-6, as will be described. The systems and methods described herein can be used in aviation fuel sensor systems to incorporate integrated densitometer and dielectric measurement systems with an existing fuel measurement processor having a velocity of sound processor to determine the fuel mass with increased accuracy and minimal hardware modifications. This permits easier install, reduced cost and minimal downtime.

FIG. 1Ais a perspective view illustrating a portion of the fuel storage tanks onboard an aircraft. Shown inFIG. 1Ais aircraft10, fuselage12, wings14, engines18, wing fuel tank20, center fuel tank22, avionics computer28, and integrated densitometer-compensators30. Aircraft10is an example of an aircraft in which integrated densitometer-compensators30may be employed for fuel density and dielectric value measurement. In the embodiment illustrated inFIGS. 1A-3, aircraft10has fuselage12, two wings14, and four engines18. Fuselage12encloses the payload area of aircraft10, typically consisting of passengers and/or cargo. Avionics computer28is a component in the overall instrumentation and control system of aircraft10. For sake of simplicity in illustration, only one avionics computer28is depicted and interconnecting wires, cables, instrumentation systems, and the like, are not shown. As used in this disclosure, avionics computer28can also be called a remote computing device. Moreover, for simplicity in illustration, the various fuel level sensors that are located in wing fuel tanks20and center fuel tank22are not shown. Operating personnel, instrumentation, and control systems are also contained within fuselage12. Those who are skilled in the art of aircraft instrumentation are familiar with the various avionics systems that may be located onboard aircraft10. Wings14provide aerodynamic lift for airplane10, while also holding engines18. Engines18consume fuel to create thrust for airplane10. Wing fuel tanks20and center fuel tank22hold fuel, which is consumed by engines18.

Wing fuel tank20and center fuel tank22are exemplary of a plurality of fuel tanks that may be located in aircraft10. Those who are skilled in the art of aircraft construction are familiar with the locations of various fuel tanks that may be located therein. For simplicity in illustration, one integrated densitometer-compensator30is shown in left wing fuel tank20and one integrated densitometer-compensator30is shown in center fuel tank22. In a typical embodiment, each wing fuel tank20can have one or more integrated densitometer-compensators30. Additionally, aircraft10can contain one or more center fuel tanks22, with each center fuel tank22having an integrated densitometer-compensator30.

Prior to flying, various fuel tanks within aircraft10may be filled with fuel which is to be consumed by engines18during flight. Prior to and during flight, crew members and/or systems aboard aircraft10can obtain knowledge of the inventory of fuel that exists in each of the various fuel tanks to calculate the mass and mass distribution of fuel stored throughout aircraft10. Obtaining an accurate knowledge of the mass and mass distribution of fuel within aircraft10helps crew members determine take-off and landing parameters, calculate flying range, and adjust trim and balance, for example. In some embodiments, aircraft10may be refueled during flight. The fuel density and dielectric value can change with flight conditions and/or with each refueling. Crew members and/or systems aboard aircraft10may obtain knowledge of the inventory of fuel in each of the various fuel tanks during the refueling operation and after the completion of the refueling operation. Accordingly, systems aboard aircraft10require in-tank sensing of fuel density and dielectric value to perform the proper fuel mass calculations from the various fuel tank level sensors (not shown).

FIG. 1Bis a perspective view of integrated densitometer-compensator30shown inFIG. 1A. Shown inFIG. 1Bare integrated densitometer-compensator30, chassis34, vent ports35, and interface cable36. Most components of integrated densitometer-compensator30are located within chassis34, and will be described inFIGS. 2 and 3. Fuel density measurement, dielectric value measurement, and signal processing takes place onboard integrated densitometer-compensator30, requiring only one external power connection and one communication link to avionics computer28. Accordingly, interface cable36carries power from avionics computer28to integrated densitometer-compensator30, as well as a signal representing the fuel density and dielectric value from integrated densitometer-compensator30to avionics computer28. The power and signal carried by interface cable36will be described in greater detail inFIG. 3.

With continued reference toFIG. 1B, chassis34is a box-like structure that encloses the other primary components of integrated densitometer-compensator30. Several embodiments are available for the design of chassis34, including a solid structure, a cage-like structure, or a mesh-like structure. If a solid structure is used, vent ports35can be included on chassis34to allow for air to escape when chassis34is covered by fuel. Vent ports35can also be used to allow for circulation of fuel through chassis34, so that the density and dielectric value of the fuel being measured by integrated densitometer-compensator30is representative of the surrounding fuel.

In an embodiment, chassis34is an electrically conductive enclosure, thereby shielding the interior components of integrated densitometer-compensator30against electromagnetic interference (EMI). Non-limiting examples of the materials from which chassis34can be constructed include steel, aluminum, aluminum alloys, brass, and other metals. In an alternative embodiment, chassis34can be constructed of a material that does not provide EMI shielding to interior components. For example, in these alternative embodiments, chassis34can be constructed of plastic, fiberglass, or a composite material. In this alternative embodiment, it may be necessary to provide EMI shielding around internal components of integrated densitometer-compensator30. In other embodiments, EMI shielding may not be necessary on integrated densitometer-compensator30.

FIG. 2is a block diagram of the integrated densitometer-compensator interface configuration. Shown inFIG. 2are avionics computer28, integrated densitometer-compensator30, compensator32, densitometer40, signal processor42, and interface cable36. As described inFIG. 1A, avionics computer28is a component in the overall instrumentation and control system of aircraft10, and can also be described as a remote computing device. Compensator32produces a signal that is representative of the dielectric value of fuel immersing integrated densitometer-compensator30. In some embodiments, compensator32can be described as an AC plate compensator because compensator32senses the dielectric value of fuel by applying an AC electrical measuring signal to the electrical capacitive plates within compensator32, thereby detecting the electrical capacitive value of compensator32. The principle of operation of compensator32is based on the measured electrical capacitive value changing in response to the change in the electrical dielectric value of the fuel.

Densitometer40provides a signal that represents the density of the fuel being measured by integrated densitometer-compensator30, thereby providing density compensation to provide an accurate indication of the mass of fuel being measured in wing fuel tanks20and center fuel tank22. As used in this disclosure, the terms “density” and “mass density” are equivalent. Compensating for the density and dielectric value of the fuel is beneficial in providing an accurate indication of the mass of the fuel. Because aircraft10can operate over a wide range of temperatures, the mass density of the fuel can vary, thereby requiring density compensation. The electrical dielectric value of fuel can also vary with fuel temperature, fuel density, and fuel formulation, thereby making it beneficial to provide fuel dielectric value compensation. In some embodiments, densitometer40can be described as a densitometer spool because densitometer40senses the density of the fuel by using a vibrating spool. The principle of operation of densitometer40is based on using a vibrating mechanical spool that is immersed in the fuel. Densitometer40includes an oscillator that that drives the mechanical spool at a mechanical resonant frequency. As the density of the fuel surrounding the mechanical spool of densitometer40varies, the mechanical spool's resonant frequency varies, and densitometer40produces an electrical signal that is representative of the fuel density.

In the embodiment illustrated inFIGS. 1A-3, avionics computer28is connected to integrated densitometer-compensator30by interface cable36, with interface cable36providing power to integrated densitometer-compensator30and also transmitting data between avionics computer28and integrated densitometer-compensator30. Signal processor42receives the electrical capacitance signal that is produced by compensator32and the fuel density signal that is produced by densitometer40. Signal processor42produces a digital signal representative of the density and the dielectric value of fuel being measured by integrated densitometer-compensator30. The digital signal is transmitted to avionics computer28by interface cable36. In some embodiments, interface cable36can transmit digital signals in both directions between avionics computer28and integrated densitometer-compensator30.

In the embodiment illustrated inFIGS. 1A-3, interface cable36transmits power to integrated densitometer-compensator30. In some embodiments, interface cable36transmits electrical power to integrated densitometer-compensator30. In other embodiments, interface cable36transmits optical power to integrated densitometer-compensator30. In some embodiments, the transmission of power by interface cable36to integrated densitometer-compensator30is continuous or substantially continuous during operation of integrated densitometer-compensator30. In other embodiments, the transmission of power by interface cable36to integrated densitometer-compensator30is intermittent during operation of integrated densitometer-compensator30. In yet other embodiments, the transmission of power by interface cable36to integrated densitometer-compensator30may occur when integrated densitometer-compensator30is not providing data to avionics computer28. For example, in some embodiments, integrated densitometer-compensator30can include an internal electrical energy storage system that is charged when integrated densitometer-compensator30is not transmitting data to avionics computer28. Interface cable36and the power supply for integrated densitometer-compensator30will be discussed in greater detail inFIG. 3.

The integrated densitometer-compensator interface configuration shown inFIG. 2is representative of the connection of integrated densitometer-compensator30on aircraft10. As noted inFIG. 1A, wing fuel tanks20and center fuel tank22can each include one or more integrated densitometer-compensators30. In some embodiments, all integrated densitometer-compensators30on aircraft10can be connected to a single avionics computer28. In other embodiments, aircraft10can contain multiple avionics computers28. In these other embodiments, the connection of integrated densitometer-compensators30to avionics computers28can be versatile, with the interface cable36of a particular integrated densitometer-compensator30being switchable between avionics computers28. In other embodiments, integrated densitometer-compensators30can be daisy-chained together, with interface cable36from one integrated densitometer-compensator30being connected to another integrated densitometer-compensator30, thereby allowing avionics computer28to communicate with and provide power to more than one integrated densitometer-compensator30. In yet other embodiments, integrated densitometer-compensators30can be daisy-chained together with other sensors.

As described in more detail below related to the embodiment of system100, integrated densitometer-compensator30produces a serial word that represents the density and dielectric value of fuel being measured by integrated densitometer-compensator30. Accordingly, each individual integrated densitometer-compensator30can include a unique address, allowing for two or more integrated densitometer-compensators30to be daisy-chained together along a single interface cable36. In other embodiments, integrated densitometer-compensator30can wirelessly transmit the serial word (including a unique address) to a wireless receiving device (not shown), which is connected to avionics computer28. As used in this disclosure, “serial word” is used to describe a digital serial data stream being transmitted by integrated densitometer-compensator30, with this data stream including digital representations of the density and dielectric value of fuel being measured by integrated densitometer-compensator30. Under some operating conditions, integrated densitometer-compensator30can transmit a serial word that represents only the density or the dielectric value of the fuel. Under other operating conditions, integrated densitometer-compensator30can transmit a serial word that provides data other than the density or the dielectric value of the fuel. The “serial word” may also include a device address, checksum bits, and any other data, and it may be of any word size.

FIG. 3is a block diagram of integrated densitometer-compensator30ofFIG. 2. Shown inFIG. 3are integrated densitometer-compensator30, compensator32, chassis34, interface cable36, compensator signal conditioner38, densitometer40, signal processor42, densitometer signal conditioner44, microprocessor46, power supply48, and serial driver50. Signal processor42includes compensator signal conditioner38, densitometer signal conditioner44, microprocessor46, power supply48, and serial driver50. It is contemplated that microprocessor46can include two discrete microprocessors, each corresponding to a respective one of densitometer signal conditioner44and compensator signal conditioner38. Compensator32has an electrical capacitance value that varies with the dielectric value of fuel. Compensator signal conditioner38supplies an electrical signal to compensator32to measure the electrical capacitance value of compensator32. In the embodiment illustrated inFIGS. 1A-3, compensator signal conditioner38produces an AC signal that has a frequency ranging from 6 KHz-18 KHZ, and amplitude ranging from 5-10 V p-p. In some embodiments the AC signal produced by compensator signal conditioner38can be lower in frequency than 6 KHz or higher in frequency than 18 KHz. In other embodiments the AC signal produced by compensator signal conditioner38can be lower in amplitude than 5 V p-p or higher in amplitude than 10 V p-p. In yet other embodiments compensator signal conditioner38can produce a non-AC signal that detects the electrical capacitance value of compensator32.

Densitometer40is a vibrating mechanical spool that has a resonant frequency that varies with the density of the fuel being measured by integrated densitometer-compensator30. Densitometer signal conditioner44includes an oscillator that drives densitometer40and a resonance detector circuit that maintains the resonant frequency of densitometer40. As the density of the fuel surrounding densitometer40varies, the resonant frequency of densitometer40varies, and densitometer signal conditioner44adjusts the loop gain to maintain a resonant frequency while also producing a signal output that is representative of the fuel density. In the embodiment illustrated inFIGS. 1A-3, densitometer signal conditioner44can support self-resonance within the frequency range from 10-20 KHZ in densitometer40. In some embodiments the frequency can be lower in frequency than 10 KHz or higher in frequency than 20 KHz. The performance and frequency response of densitometer40is highly dependent on the mechanical and physical properties of the particular densitometer40that is used in a particular embodiment. Because densitometer40includes a mechanically vibrating spool, normal variations that can occur in manufacturing processes can result in each particular embodiment of densitometer40having a frequency response function that is unique. Accordingly, densitometer40can include a resistor network (not shown) that is established during the manufacturing process of densitometer40that identifies the polynomial coefficients of the frequency response curve of densitometer40to densitometer signal conditioner44. In the embodiment illustrated inFIGS. 1A-3, integrated densitometer-compensator30includes microprocessor46for digital signal processing. Accordingly, densitometer signal conditioner44can be programmed can be programmed with firmware values that provide a digital representation of the polynomial coefficients of the frequency response curve of densitometer40. In the embodiment illustrated inFIGS. 1A-3, firmware values programmed into densitometer signal conditioner44provide the polynomial coefficients needed to represent the frequency response curve of densitometer40, and a resistor network is not used.

Microprocessor46provides the signal processing for integrated densitometer-compensator30. In the embodiment illustrated inFIGS. 1A-3, microprocessor46performs both analog and digital signal processing. Microprocessor46includes an analog-to-digital converter (ADC) that produces a digital representation of the electrical capacitance value produced by compensator signal conditioner38. Microprocessor46also includes an analog-to-digital converter (ADC) that produces a digital representation of the fuel density value produced by densitometer signal conditioner44. As described earlier, microprocessor46can also include firmware that is programmed with a digital representation of the polynomial coefficients of the frequency response curve of densitometer40, for integrated densitometer-compensator30to provide an accurate representation of the density and dielectric value of fuel being measured. Microprocessor46can also include firmware and volatile and/or non-volatile memory for storing software, program instructions, compensation values, and other data that can be used by integrated densitometer-compensator30. In some embodiments, microprocessor46can include a circuit board containing several electrical components including a commercially-available digital microprocessor, analog-to-digital converters (ADCs), firmware chips, volatile, and/or nonvolatile memory chips. In other embodiments, microprocessor46can include one or more application-specific integrated circuits (ASICs) without deviating from the scope of the present disclosure. Microprocessor46may also be abbreviated as μprocessor46. All circuits that perform the signal processing for integrated densitometer-compensator30are within the scope of the present disclosure.

Power supply48provides electrical power to compensator signal conditioner38, densitometer signal conditioner44, microprocessor46, and serial driver50. In the embodiment illustrated inFIGS. 1A-3, power supply48receives power from avionics computer28via interface cable36. In one embodiment, power supply48can receive electrical power from avionics computer28, with interface cable36including a two-conductor wire pair. In this embodiment, power supply48conditions the received electrical power for distribution to the components within integrated densitometer-compensator30that require electrical power. The electrical power received from avionics computer28can be a direct current, an alternating current, or a hybrid waveform that conveys electrical power. The electrical power received from avionics computer28can be continuous or intermittent. Power supply48can also include an electrical energy storage device (not illustrated) that provides power to integrated densitometer-compensator30during periods when power is not being received from avionics computer28. The electrical storage device can include, for example, a rechargeable electrochemical battery or an electrical capacitor.

In another embodiment, power supply48can receive optical power from avionics computer28, with interface cable36including an optical fiber that transmits light. In this embodiment, power supply48can include an optical receptor cell (not illustrated) that converts optical power into electricity. The optical receptor cell can include one or more photovoltaic cells, or other devices, that convert optical power into electrical power. The optical power received from avionics computer28can be continuous or intermittent. Power supply48can also include an electrical energy storage (not illustrated) device that provides power to integrated densitometer-compensator30during periods when power is not being received from avionics computer28. The electrical storage device can include, for example, a rechargeable electrochemical battery or an electrical capacitor.

In yet another embodiment, power supply48can include a long-life electrical storage device (not illustrated) that is charged at or after the time it is installed in integrated densitometer-compensator30, and which powers integrated densitometer-compensator30for a span of time. A non-limiting example of a long-life electrical storage device is a lithium battery.

Serial driver receives50receives the digital representation of the fuel density and dielectric value that is measured by integrated densitometer-compensator30and transmits a serial data word to avionics computer28through interface cable36. In one embodiment, serial driver50produces an electrical transmission of a serial data word with interface cable36including a two-conductor wire pair. The serial data word can also include an identifier for the particular integrated densitometer-compensator30producing the communication, thereby allowing for multiple integrated densitometer-compensators30to communicate with avionics computer28via interface cable36. A single two-conductor wire pair can be used for transmitting electrical power from avionics computer28to integrated densitometer-compensator30, and for transmitting the serial data word from integrated densitometer-compensator30to avionics computer28. In one embodiment, the electrical serial data word transmission can occur simultaneously with the electrical power transmission by modulating the electrical power transmission. Non-limiting examples of electrical power modulation that can be used include frequency shift keying (FSK), amplitude shift keying (ASK), and phase shift keying (PSK). In another embodiment, the serial word transmission can occur periodically, with a timing protocol being used that allows alternating transmission of data and electrical power over interface cable36. In yet another embodiment, a two-conductor wire pair can be used for transmitting electrical power from avionics computer28to integrated densitometer-compensator30, and a different two-conductor wire pair can be used for transmitting the serial data word from integrated densitometer-compensator30to avionics computer28. In the embodiment illustrated inFIGS. 1A-3, electrical shielding is not required on interface cable36because the signal processing occurs within integrated densitometer-compensator30, and neither the power supply nor the serial word requires transmission within a shielded cable.

In another embodiment, serial driver50produces an optical transmission of a serial data word with interface cable36including an optical fiber. The serial data word can also include an identification code for the particular integrated densitometer-compensator30producing the communication, thereby allowing for multiple integrated densitometer-compensators30to communicate with avionics computer28via interface cable36. In this embodiment, two or more integrated densitometer-compensators30can be daisy-chained together via interface cable36.

In yet another embodiment, a single optical fiber can be used for transmitting optical power from avionics computer28to integrated densitometer-compensator30, and for also transmitting the serial data word from integrated densitometer-compensator30to avionics computer28. In one embodiment, the optical serial data word transmission can occur simultaneously with the optical power transmission by modulating the optical power transmission. Non-limiting examples of optical power modulation that can be used include frequency shift keying (FSK), amplitude shift keying (ASK), and phase shift keying (PSK). In another embodiment, a separate optical wavelength can be used for transmitting optical power and data over the same optical fiber. In yet another embodiment, the serial word transmission can occur periodically, with a timing protocol being used that allows alternating transmission of data and optical power over interface cable36. In yet another embodiment, an optical fiber can be used for transmitting optical power from avionics computer28to integrated densitometer-compensator30, and a different optical fiber can be used for transmitting the serial data word from integrated densitometer-compensator30to avionics computer28.

Although an advantage of the present disclosure is to reduce the number of conductors on interface cable36, thereby reducing the weight and cost associated with those conductors, benefit is still achieved in using two optical fibers because of the generally light weight and low cost of optical fibers as compared to using multiple shielded electrical cables.

In yet another embodiment, interface cable36can include both an optical fiber and a two-wire electrical pair. In this other embodiment, the optical fiber can be used for transmitting either optical power or the serial word, and the two-wire electrical pair can be used for transmitting the other.

The several embodiments described above refer to the electrical conductors within interface cable36as two-wire pairs. It should be appreciated that cables having more than two wires can perform the same function as described above, and are therefore within the scope of the present disclosure. For example, two two-wire pairs could be replaced with a four-wire cable, with equivalent results. Two two-wire pairs could also be replaced with a three-wire cable, in which one conductor is common to the other two, thereby achieving substantially similar results. In an alternative embodiment, a single wire electrical conductor could be used, with the fuel tank structure providing the electrical return path. Although this may not be a preferred embodiment in aviation systems, a single-wire conductor could be used with other applications of integrated densitometer-compensator30.

In yet another embodiment, integrated densitometer-compensator30can be used without interface cable36. In this embodiment, serial driver50can transmit the serial data word wirelessly utilizing any of a number of wireless signal transmissions including, without limitation, radio frequency, acoustical, and optical. In this embodiment, integrated densitometer-compensator30can be powered by an internal energy storage device and/or by a power supply that receives power wirelessly.

Integrated densitometer-compensator30was described in this disclosure using the example of wing fuel tanks20and center fuel tanks22being located with avionics computer28onboard aircraft10, with this exemplary configuration not being limiting. For example, integrated densitometer-compensator30can be deployed anywhere it is desired to measure the density and dielectric value of a fluid, whether onboard an aircraft, other vehicle, or in a non-vehicle setting such as in an industrial setting. Moreover, the deployment of integrated densitometer-compensator30is not limited to closed tanks, but application can also be found within pipes and channels, and on open containers such as sumps and pits. Finally, any computing device can replace avionics computer28, regardless of the type of computing device or the proximity between it and integrated densitometer-compensator30. Integrated densitometer-compensator30can measure density with more accuracy than traditional inferential systems, e.g. integrated densitometer-compensator30can be a 1% of full mass improvement over traditional systems.

Another embodiment of a fluid measurement system100is shown inFIG. 4. System100includes a sensor system102, which is substantially the same as integrated densitometer-compensator30and its various embodiments, described above. System100includes a processing system104, which is resident in avionics computer28and its embodiments, described above. Processing system104can include many elements similar to those of avionics computer28and also includes a current limiter116, which is described in more detail below. Elements of integrated densitometer30and avionics computer28can readily be incorporated into system100illustrated inFIGS. 4-6, and system100can readily be incorporated into aircraft10in a similar manner to that described above relative to integrated densitometer30and avionics computer28.

As shown inFIG. 4, fluid measurement system100includes a power interface112between signal processor42and the processing system104. Processing system104includes an intrinsically safe (IS) power source114and a current limiter116. IS power source114is a +5V power rail and current limiter116operates at 25 mA and 50 μJ under normal operating conditions, at 50 mA and 200 μJ under fault and/or tank shorted conditions, and/or 125 mA and 200 μJ under lightning conditions. Current limiter116is positioned between IS power source114and power interface112. Processing system includes an Input/Output (I/O) connector pin to connect with the power and ground conductors of interface112. Processing system104includes a velocity of sound signal conditioner118to read and decode the serial word. System100includes data interface120, e.g. a two-conductor wire pair120, between signal processor42and the velocity of sound signal conditioner118. Power interface112and data interface120are harnessed together as a single cable, e.g. similar to that of interface cable36and/or the other various embodiments thereof described above.

With reference now toFIGS. 4-5, sensor system102includes a signal processor42, like signal processor42ofFIGS. 1A-3, described above. Sensor system102produces a serial word that represents the density and dielectric value of fuel being measured by sensor system102via the AC compensator32and the spool densitometer40. Signal processor42includes compensator a signal conditioner38, a densitometer signal conditioner44, a microprocessor46, a power supply48, and serial driver50. In conjunction with densitometer signal conditioner44, microprocessor46configured and adapted to produce a serial word106athat is indicative of a density and, in conjunction with compensator a signal conditioner38is configured and adapted to produce a serial word106bthat is indicative of a capacitance of the fluid. Together, serial word106aindicative of density and serial word106bindicative of capacitance make up a pair. Each pair of words106a/106bis separated by approximately 600 microseconds, in some embodiments. Each word in a given pair, in some embodiments, is separated by 100 microseconds. For example, the second word, e.g.106b, in the pair is separated from the first word, e.g.106aby approximately 100 microseconds. Each serial word106a/106bincludes a plurality of bits108. Each bit108is a 1 MHz bit108cluster108ahaving four 1 MHz pulses110a-110d. While shown as having four pulses, those skilled in the art will readily appreciate that each bit cluster can include a plurality of 1 MHz pulses. For example, four to eight pulses. The plurality of bits108include a start bit108a, a plurality of data bits108b-o, and a parity bit108p. Processing system104is operatively connected to signal processor42to read the serial words106a/106band decode the serial words106a/106b. Processing system104can include software that replaces the inferred density value traditionally provided by a velocity of sound signal conditioner118with a density measurement from densitometer40.

Accordingly, each individual sensor system102, e.g. each integrated densitometer-compensator, can include a unique address, allowing for two or more integrated densitometer-compensators102to be daisy-chained together along a single data interface120, as described above. In other embodiments, integrated densitometer-compensator102can wirelessly transmit the serial words106a/106b(including a unique address) to a wireless receiving device (not shown), which is connected to processing system104. As used in this disclosure, “serial word” is used to describe a digital serial data stream being transmitted by integrated densitometer-compensator102, with this data stream including digital representations of the density and dielectric value of fuel being measured by integrated densitometer-compensator102. Under some operating conditions, integrated densitometer-compensator102can transmit a serial word that represents only the density or the dielectric value of the fuel. Under other operating conditions, integrated densitometer-compensator102can transmit a serial word that provides data other than the density or the dielectric value of the fuel. The “serial word” may also include a device address, checksum bits, and any other data, and it may be of any word size.

As shown inFIG. 6, a method200for transmitting a fluid characteristic between a sensor system, e.g. sensor system102, and a processing system, e.g. processing system104, includes producing a serial word that is indicative of a fluid characteristic value with a signal processor, e.g. signal processor42, as indicated schematically by box202. Before producing the serial word, a first signal can be generated with a first device, e.g. compensator a signal conditioner38, that is indicative of the dielectric value of the fluid (as measured by compensator32) and a second signal with a second device, e.g. densitometer signal conditioner44, that is indicative of the density of the fluid (as measured with densitometer40). The signal processor then produces a digital signal in the form of a serial word that is indicative of the dielectric value and the density of the fluid, based on the first signal and the second signal. The method includes disabling a velocity of sound (VOS) transmit function of the VOS signal conditioner, e.g. VOS signal conditioner118, as indicated schematically by box203, in order to eliminate signal bus contention on the drive (e.g. data interface120) an allow for improved communication between the VOS signal conditioner and the signal processor. No transmission from the VOS signal conditioner to the signal processor would be required in conjunction with the sensor system. The receiving function of the VOS is still enabled in order to receive and read the serial word, described in more detail below. Producing the serial word includes generating a plurality of bits with the signal processor, as indicated schematically by box204. Each bit is a 1 MHz bit cluster, e.g. bit cluster108a-108p. Each bit cluster includes a plurality of 1 MHz pulses, e.g. four pulses110a-110d. The plurality of bits include a start bit, e.g. start bit108a, a plurality of data bits, e.g. data bits108a-108o, and a parity bit, e.g. parity bit108p.

Once generated, the method200includes transmitting the serial word externally of the signal processor, as indicated schematically by box206. The method includes reading and decoding the serial word with the velocity of sound signal conditioner of the processing system, as indicated schematically by box208. Method200includes determining a fuel characteristic, e.g. the density, capacitance, and, ultimately, the fuel mass, as indicated schematically by box210. The method200includes limiting current to 50 mA or less and 200 μJ with a current limiter, e.g. current limiter116, as indicated schematically by box201. The method can also include limiting energy storage components in the sensor system to 4 μF based on 5 V potential. Method200can also include updating the software of the processing system such that the fuel mass calculation replaces the inferred density value traditionally provided by a velocity of sound signal conditioner with the density measurement from a densitometer, e.g. densitometer40.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments of the present invention. A system for determining the dielectric value and a density of a fluid according to an exemplary embodiment of this disclosure, among other possible things, includes a first device configured to produce a first signal that is indicative of the dielectric value of the fluid; a second device configured to produce a second signal that is indicative of the density of the fluid; and a signal processor in operable communication with both the first device and the second device, the signal processor configured to calculate a digital signal that is indicative of the dielectric value and the density of the fluid that can be communicated externally of the signal processor.

A further embodiment of the foregoing system, wherein the first device is comprised of a compensator configured to produce an electrical capacitance signal that is indicative of the dielectric value of the fluid and a compensator signal conditioner electrically connected to the compensator, configured to produce an electrical signal that is indicative of the electrical capacitance signal; the second device is comprised of a densitometer spool configured to produce a mechanical response that is indicative of the density of the fluid and a densitometer signal conditioner electromagnetically connected to the densitometer spool, configured to produce an electrical signal that is indicative of the mechanical response; and the signal processor is comprised of a microprocessor configured to store a plurality of correction factors representing the mechanical response and calculate the digital signal that is representative of the dielectric value and the density of the fluid, and a serial driver configured to produce a serial word that is representative of the digital signal and modulate a carrier signal wherein the modulated carrier signal is representative of the serial word.

A further embodiment of the foregoing system, further comprising a power supply, the power supply configured to provide electrical power to the compensator signal conditioner, the densitometer signal conditioner, the microprocessor, and the serial driver.

A further embodiment of the foregoing system, further comprising an energy storage device, wherein the energy storage device is configured to store electrical energy.

A further embodiment of the foregoing system, further comprising a data interface, the data interface configured to transmit the serial word.

A further embodiment of the foregoing system, wherein the power supply is configured to: receive electrical input power via the power interface; convert the electrical input power into electrical power; and provide the electrical power to the compensator signal conditioner, the densitometer signal conditioner, the microprocessor, and the serial driver.

A further embodiment of the foregoing system, wherein the power supply is configured to: receive optical input power via the power interface; convert the optical input power into electrical power; and provide the electrical power to the compensator signal conditioner, the densitometer signal conditioner, the microprocessor, and the serial driver.

A further embodiment of the foregoing system, wherein the data interface is comprised of a two-wire electrical pair; the serial driver is configured to transmit the serial word over the two-wire electrical pair; and the power supply is configured to receive electrical input power over the two-wire electrical pair.

A further embodiment of the foregoing system, wherein the serial driver is configured to transmit the serial word wirelessly.

A further embodiment of the foregoing system, wherein the data interface is comprised of an optical fiber; the serial driver is configured to transmit the serial word over the optical fiber;

and the power supply is configured to receive optical input power over the optical fiber.

A further embodiment of the foregoing system, wherein the serial driver is configured to transmit the serial word utilizing digital encoding selected from the group consisting of: frequency shift keying, amplitude shift keying, phase shift keying.

A further embodiment of the foregoing system, wherein the serial driver is configured to transmit the serial word utilizing a first wavelength of light; and the power supply is configured to receive optical input power utilizing a second wavelength of light.

A further embodiment of the foregoing system, wherein the serial driver has an identification code, and the serial word further comprises the identification code.

A system for measuring a dielectric value and a density of a fluid in a tank, the system comprising: a remote computing device; a first device configured to produce a first signal that is indicative of the dielectric value of the fluid; a second device configured to produce a second signal that is indicative of the density of the fluid; and a signal processor electrically connected to both the first device and the second device, the signal processor configured to produce a first electrical signal that is representative of the first signal, produce a second electrical signal that is representative of the second signal, calculate a digital signal that is representative of the dielectric value and the density of the fluid, produce a serial word that is indicative of the digital signal, and modulate a carrier signal, wherein the modulating is representative of the serial word; a power supply configured to receive power input from the remote computing device; and an data interface configured to: transmit the serial word to the remote computing device and transmit input power from the remote computing device to the power supply.

A further embodiment of the foregoing system, wherein the interface further comprises a two-wire pair; and the power supply is configured to receive electrical power input from the remote computing device via the two-wire pair; and the signal processor is configured to transmit the serial word to the remote computing device via the two-wire pair.

A further embodiment of the foregoing system, wherein the interface cable further comprises an optical fiber; and the power supply is configured to receive optical power input from the remote computing device via the optical fiber; and the signal processor is configured to transmit the serial word to the remote computing device via the optical fiber.

A further embodiment of the foregoing system, wherein the signal processor is configured to transmit the serial word utilizing digital encoding selected from the group consisting of: frequency shift keying, amplitude shift keying, phase shift keying.

A further embodiment of the foregoing system, wherein the signal processor is configured to transmit the serial word utilizing a first wavelength of light; and the power supply is configured to receive optical input power utilizing a second wavelength of light.

A method for determining a dielectric value and a density of a fluid within a tank comprising the steps of: producing, via a first device disposed at the tank, a first signal indicating the dielectric value of the fluid; producing, via a second device disposed at the tank, a second signal indicating the density of the fluid; calculating, in a signal processor disposed at the tank, a digital signal that is indicative of the dielectric value and the density of the fluid, based on the first signal and the second sign; and transmitting the digital signal externally of the signal processor.

A further embodiment of the foregoing method, further comprising producing, by the signal processor, a serial word that is representative of the digital signal; modulating, by the signal processor, a carrier signal, wherein the modulated carrier signal is representative of the serial word; and transmitting, by an interface cable, the modulated carrier signal.

A fluid measurement system, among other possible things, includes a signal processor and a processing system. The signal processor is configured and adapted to produce a serial word that is indicative of a fluid characteristic that is configured to be communicated externally of the signal processor. The processing system is operatively connected to the signal processor to read the serial word and decode the serial word.

A further embodiment of the foregoing system, wherein the serial word is representative of at least one of a density or a capacitance of a fluid.

A further embodiment of the foregoing system, wherein the serial word includes a plurality of bits. Each bit can be a 1 MHz bit cluster.

A further embodiment of the foregoing system, wherein the plurality of bits includes a start bit, a plurality of data bits, and a parity bit.

A further embodiment of the foregoing system, wherein each 1 MHz bit cluster includes a plurality of 1 MHz pulses.

A further embodiment of the foregoing system, wherein the system includes a power interface between the signal processor and the processing system.

A further embodiment of the foregoing system, wherein the processing system includes an intrinsically safe power source and a current limiter.

A further embodiment of the foregoing system, wherein the current limiter is between the intrinsically safe power source and the power interface.

A further embodiment of the foregoing system, wherein the processing system includes a velocity of sound signal conditioner to read and decode the serial word.

A further embodiment of the foregoing system, wherein the system includes a two-conductor wire pair between the signal processor and the velocity of sound signal conditioner.

A method for transmitting a fluid characteristic between a sensor system and a processing system includes producing a serial word that is indicative of a fluid characteristic value with a signal processor. The method includes transmitting the serial word externally of the signal processor. The method includes reading and decoding the serial word with a processing system to determine the fluid characteristic value.

A further embodiment of the foregoing method, wherein producing the serial word includes generating a plurality of bits with the signal processor.

A further embodiment of the foregoing method, wherein the plurality of bits include a start bit, a plurality of data bits, and a parity bit. Each bit can be a 1 MHz bit cluster, and/or each bit cluster can include a plurality of 1 MHz pulses.

A further embodiment of the foregoing method, wherein the method includes limiting current to 50 mA or less with a current limiter between an intrinsically safe power source and a power interface.

A further embodiment of the foregoing method, wherein the reading and decoding of the serial word is done by a velocity of sound signal conditioner of the processing system.

A further embodiment of the foregoing method, wherein the method includes disabling a velocity of sound transmit function of the velocity of sound signal conditioner.

A further embodiment of the foregoing method, wherein transmitting the serial word includes wirelessly transmitting the serial word from the signal processor to the processing system.

The methods and systems of the present disclosure, as described above and shown in the drawings provide for a sensor system and processing system with superior properties including easier install, reduced cost and minimal downtime. While the apparatus and methods of the subject disclosure have been shown and described with reference to certain embodiments, those skilled in the art will readily appreciate that change and/or modifications may be made thereto without departing from the scope of the subject disclosure.