TDR fluid level sensor
A system and method for accurately measuring fluid level in a vessel is provided. Generally, the system contains an elongated portion being a coaxial tube having a hollow center, an arm being coaxial in shape, and a sensor containing a transmitter capable of creating and transmitting an excitation electromagnetic pulse for traversing the elongated portion and the arm, and a receiver for receiving reflected pulses, wherein a proximate end of the elongated portion joins a distal end of the arm in a manner to create a waveguide for an electromagnetic pulse provided by the sensor.
1. A system for accurately measuring fluid level in a vessel, comprising:
an elongated portion being a coaxial tube having a hollow center and a first conductive outer shell;
a shaped coaxial arm comprising a second conductive outer shell; and
a sensor comprising a transmitter capable of creating and transmitting an excitation electromagnetic pulse for traversing the elongated portion and the arm, and a receiver for receiving a reflected pulse,
wherein a proximate end of the elongated portion physically joins a distal end of the arm in a manner to create a continuous waveguide comprising the arm and the elongated portion for an electromagnetic pulse provided by the sensor, the sensor further comprises power supply circuitry, digital logic, and analog circuitry,
wherein the digital logic further comprises a processor, wherein the processor further comprises:
logic configured to initiate the transmitter for sending the excitation electromagnetic pulse,
logic configured to synchronize the receiver to the transmit pulse, and
logic configured to determine temperature of the fluid by measuring actual dielectric constant of the fluid and comparing the measured actual dielectric constant of the fluid to a list of fluids having known dielectric constant values.
2. The system of claim 1 , wherein the first conductive outer shell and the second conductive outer shell are made of a material having a known impedance.
3. The system of claim 2 , wherein the arm is filled with a dielectric having a known impedance.
4. The system of claim 3 , wherein impedance of the dielectric is similar to an impedance of air or an impedance of the fluid being measured.
5. The system of claim 1 , wherein electrical components included within the power supply circuitry are designed to prevent high energy signals from propagating to the fluid being measured by the system.
6. The system of claim 1 , wherein the analog circuitry further comprises the transmitter and the receiver.
7. The system of claim 1 , wherein initiating of the transmitter for sending the excitation electromagnetic pulse is performed by a clock signal from the processor, wherein the same clock signal is sent to the receiver.
8. The system of claim 1 , wherein the processor further comprises logic configured to determine level of the fluid via use of time of flight of the excitation electromagnetic pulse to the end of the elongated portion.
9. The system of claim 1 , wherein the processor further comprises:
logic configured to determine a current level of fluid; and
logic configured to track current fluid level by maintaining the current fluid level within a scan window, wherein the scan window comprises a sampled portion of the reflected pulse corresponding to a segment of the elongated portion, and timing of the scan window is adjusted to keep the current level of the fluid within the scan window.
10. The system of claim 1 , further comprising a low pass filter and associated logic for varying amplitude of the excitation electromagnetic pulse to compensate for variation of signal due to diode variation.
11. The system of claim 1 , wherein the system further comprises a connector for connecting the system to circuitry of an aircraft.
12. The system of claim 1 , wherein the elongated portion, arm, and sensor comprise components that reduce radiation susceptibility or transmission.
13. A system for accurately measuring fluid level in a vessel, comprising:
an elongated portion being a coaxial tube having a hollow center and a first conductive outer shell;
a fixed shaped coaxial arm comprising a second conductive outer shell; and
a sensor comprising a transmitter capable of creating and transmitting an excitation electromagnetic pulse for traversing the elongated portion and the arm, and a receiver for receiving a reflected pulse,
wherein a proximate end of the elongated portion physically joins a distal end of the arm in a manner to create a continuous waveguide comprising the arm and the elongated portion for an electromagnetic pulse provided by the sensor, and
wherein the arm is in the shape of an S.
14. The system of claim 13 , wherein the first conductive outer shell and the second conductive outer shell are made of a material having a known impedance.
15. The system of claim 14 , wherein the arm is filled with a dielectric having a known impedance.
16. The system of claim 15 , wherein impedance of the dielectric is similar to an impedance of air or an impedance of the fluid being measured.
17. The system of claim 13 , wherein the sensor further comprises power supply circuitry, digital logic, and analog circuitry.
18. The system of claim 17 , wherein electrical components included within the power supply circuitry are designed to prevent high energy signals from propagating to the fluid being measured by the system.
19. The system of claim 17 , wherein the analog circuitry further comprises the transmitter and the receiver.
20. The system of claim 17 , wherein the digital logic further comprises a processor, wherein the processor further comprises:
logic configured to initiate the transmitter for sending the excitation electromagnetic pulse; and
logic configured to synchronize the receiver to the transmit pulse.
21. The system of claim 20 , wherein initiating of the transmitter for sending the excitation electromagnetic pulse is performed by a clock signal from the processor, wherein the same clock signal is sent to the receiver.
22. The system of claim 20 , further comprising a thermistor for determining temperature of the fluid, wherein the processor is capable of determining the dielectric constant of the fluid and correlating the dielectric constant to temperature of the fluid.
23. The system of claim 20 , wherein the processor further comprises logic configured to determine level of the fluid via use of time of flight of the excitation electromagnetic pulse to the end of the elongated portion.
24. The system of claim 20 , wherein the processor is capable of determining dielectric constant of the fluid, where temperature of the fluid is known, the processor further comprising:
logic configured to measure perceived length of the elongated portion immersed in the fluid; and
logic configured to calculate the dielectric constant of the fluid from a ratio of the perceived length and a real length of the elongated portion having the fluid therein.
25. The system of claim 20 , wherein the processor further comprises:
logic configured to determine a current level of fluid; and
logic configured to track current fluid level by maintaining the current fluid level within a scan window,
wherein the scan window comprises a sampled portion of the reflected pulse corresponding to a segment of the elongated portion, and timing of the scan window is adjusted to keep the current level of the fluid within the scan window.
26. The system of claim 13 , further comprising a low pass filter and associated logic for varying amplitude of the excitation electromagnetic pulse to compensate for variation of signal due to diode variation.
27. The system of claim 13 , wherein the system further comprises a connector for connecting the system to circuitry of an aircraft.
28. The system of claim 13 , wherein the elongated portion, arm, and sensor comprise components that reduce radiation susceptibility or transmission.