Self-generating differential pressure measurement for liquid nitrogen and other liquids

• US 6,776,038 B1
• Filed: 04/02/2003
• Issued: 08/17/2004
• Est. Priority Date: 04/16/2002
• Status: Active Grant

• Current Assignee: Pacer Digital Systems Incorporated
• Original Assignee: Pacer Digital Systems Incorporated
• Inventors: Oeff, J. Warren, Horton, Kevin Eldon
• Primary Examiner(s): Williams, Herzon
• Assistant Examiner(s): FRANK, RODNEY T
• Application Number:
  US10/405,864
• Time in Patent Office: 503 Days
• Field of Search: 732/99, 732/90.R, 732/92, 732/95
• US Class Current: 73/299
• CPC Class Codes: G01F 23/14 by measurement of pressure

Abstract

The depth of a cryogenic liquid in a Dewar may be ascertained by inserting a measurement probe into the container. The measurement probe includes a hollow tube having a proximal end and an open distal end, a heater operationally connected within the tube and positioned substantially adjacent the distal end, a pressure sensor operationally connected within the tube and positioned substantially adjacent the proximal end, and a microcontroller in electric communication with the heater and with the pressure sensor. The distal end of the measurement probe is placed against the bottom of the container, liquid from the container enters the tube, and is evaporated by the heater. The gas pressure in the tube between the heater and the pressure sensor is increased, until the gas pressure in the tube is equal to the pressure exerted by the liquid in the Dewar. A quasi-equilibrium condition (dependent upon continued heat supplied from the heater) is achieved between the gas pressure in the tube and the pressure from the liquid in the Dewar. A voltage output signal is generated from the pressure sensor proportional to the gas pressure in the tube and is correlated with a liquid depth value. The liquid depth value is then output.

Claims

1. A system for measuring the depth of a liquid in a container, comprising in combination:

a single walled tube having a proximal opening, a distal opening and a generally cylindrical body extending therebetween defining the border between a tube interior and a tube exterior;

a resistance heater positioned within the tube substantially adjacent the distal end;

a microcontroller in electrical communication with the resistor;

a pressure sensor connected in pneumatic communication with the proximal opening of the tube;

wherein the pressure sensor forms a pneumatic seal with the tube;

wherein the microcontroller is adapted to selectively actuate the resistance heater;

wherein actuation of the resistance heater evaporatively removes liquid from the tube; and

wherein fluidic communication between the tube interior and the tube exterior is restricted to the distal opening.

2. The system of claim 1 wherein the pressure sensor produces a voltage output signal having a signal strength proportional to the pressure experienced by the pressure sensor.

3. The system of claim 2 wherein the pressure sensor further comprises a piezoelectric material.

4. The system of claim 2 wherein the microcontroller is programmed to calculate a liquid depth when supplied with a voltage output signal from the pressure sensor.

5. The system of claim 1 wherein when actuated, the heater supplies a substantially constant heat output.

6. A sensor device, comprising in combination:

a heater;

a sleeve at least partially enclosing the heater;

a microcontroller in electric communication with the heater;

a transducer in electric communication with the microcontroller and positioned in pneumatic communication with the sleeve;

wherein the microcontroller is adapted to receive signals from the transducer;

wherein the microcontroller is adapted to actuate current to flow through the heater;

wherein the sleeve defines an enclosure with a single opening through which fluids may substantially flow; and

wherein the heater is positioned substantially adjacent the single opening.

7. The sensor device of claim 6 wherein the sleeve further comprises an enclosure having a proximal end and a distal end;

wherein the distal end is open to fluidic flow therethrough;

wherein the proximal end further includes the transducer; and

wherein the proximal end is substantially closed to fluidic flow.

8. The sensor device of claim 6 wherein the transducer generates an output voltage signal that varies linearly as a function of pressure applied to the transducer.

9. The sensor device of claim 8 transducer is adapted to communicate the output voltage signal to the microcontroller and wherein the microcontroller is preprogrammed to use the output voltage signal to calculate the depth of a liquid.

10. The sensor device of claims 9 wherein the microprocessor is adapted to receive data regarding the liquid density and wherein the microcontroller is preprogrammed to use the data regarding the liquid density to calculate the depth of a liquid.

11. The sensor device of claim 6 wherein the heater is an electrical resistance heater.

12. A method for measuring the level of liquid in a container, comprising the steps of:

a) inserting measurement probe into the container, the measurement probe further comprising;

a hollow tube having a proximal end and an open distal end;

a heater operationally connected within the tube and positioned substantially adjacent the distal end;

a pressure sensor operationally connected within the tube and positioned substantially adjacent the proximal end; and

a microcontroller in electric communication with the heater and with the pressure sensor;

b) resting the distal end of the measurement probe against the bottom of the container;

c) boiling the liquid in the tube to remove substantially all of the liquid between the heater and the pressure sensor;

d) measuring the gas pressure in the tube; and

e) calculating the depth of liquid in the container.

13. The method of claim 12 wherein the pressure sensor generates an output voltage signal that varies linearly as a function of pressure applied to the pressure sensor.

14. The method of claim 13 wherein step d further comprises measuring the output voltage signal.

15. The method of claim 13 wherein the microcontroller is preprogrammed with a first voltage signal value associated with zero liquid depth and with a second voltage signal value associated with a nonzero liquid depth;

and wherein a step e) further comprises using the first voltage signal value associated with zero liquid depth and the second voltage signal value associated with a nonzero liquid depth to linearly extrapolate a liquid depth output value from the output voltage signal.

16. A method for ascertaining the depth of a cryogenic liquid in a Dewar, comprising the steps of:

a) inserting a measurement probe into the container, the measurement probe further comprising;

a hollow tube having a proximal end and an open distal end;

a heater operationally connected within the tube and positioned substantially adjacent the distal end;

a pressure sensor operationally connected within the tube and positioned substantially adjacent the proximal end; and

a microcontroller in electric communication with the heater and with the pressure sensor;

b) resting the distal end of the measurement probe against the bottom of the container;

c) evaporating a portion of the liquid in the tube between the heater and the pressure sensor;

d) increasing the gas pressure in the tube between the heater and the pressure sensor to increase the pressure on the pressure sensor and urge liquid out of the tube leaving a residual amount of liquid in the tube;

e) achieving a quasi-equilibrium condition between the gas pressure in the tube and the residual amount of liquid in the tube;

f) generating a voltage output signal from the pressure sensor proportional to the gas pressure in the tube;

g) correlating the voltage output signal with a liquid depth value; and

h) outputting the liquid depth value;

wherein liquid enters the tube as it is inserted into the container.

17. The method of claim 16 wherein step g) is a linear extrapolation.

18. The method of claim 16 wherein the step g) is a calculation.