Electro-optic sensor for levelmeter providing output signal with frequency modulated by surface level

• US 6,581,461 B1
• Filed: 05/25/2000
• Issued: 06/24/2003
• Est. Priority Date: 05/25/2000
• Status: Expired due to Fees

• Current Assignee: Trinity Industries Incorporated
• Original Assignee: TRN Business Trust
• Inventors: Díaz, Herman
• Primary Examiner(s): Larkin, Daniel S.
• Assistant Examiner(s): JACKSON, ANDRE K
• Application Number:
  US09/578,938
• Time in Patent Office: 1,125 Days
• Field of Search: 732/90.R, 733/04, 250/577
• US Class Current: 340/619
• CPC Class Codes: G01F 23/2928 using light reflected on the material surface

Abstract

An opto-electric levelmeter having a sensor that provides an output signal whose frequency represents the surface level of liquid in a container. The sensor'"'"'s circuitry includes an oscillation circuit that uses “optical feedback” to modulate the sensor output signal. The signal is delivered to a monitor that provides an output signal for the user. The monitor also permits adjustment for both high and low levels of a particular container. The monitor sends electrical energy to the sensor, and receives the sensor output signal on the same electrical link.

Claims

1. An opto-electric levelmeter for measuring the level of liquid in a container, comprising:

a sensor having at least a light emitting diode and a phototransistor, said sensor operable to provide a sensor output signal whose frequency is related to the distance of the sensor from the surface of the liquid;

a monitor that receives the sensor output signal and that has at least linearizing circuitry for linearizing the sensor output signal, level detection circuitry for converting the output signal to a signal representing the level of liquid in the container, and adjustment circuitry for adjusting the level detection circuitry.

2. The levelmeter of claim 1, wherein the monitor delivers electrical energy to the sensor via an electrical link.

3. The levelmeter of claim 2, wherein the monitor receives the sensor output signal on the same electrical link that is used to deliver electrical energy to the sensor.

4. The levelmeter of claim 1, wherein the sensor has a light emitting diode for emitting light to the surface of the liquid and an optical transistor for detecting light reflected from the surface.

5. The levelmeter of claim 4, wherein the sensor further has an oscillation circuit for providing the sensor output signal, the oscillation circuit having a feedback loop that includes the optical link between the photodiode and the optical transistor.

6. The levelmeter of claim 1, wherein the linearization circuit represents an inverse transfer function.

7. The levelmeter of claim 1, wherein the adjustment circuitry comprises at least one potentiometer.

8. The levelmeter of claim 1, wherein the adjustment circuitry permits adjustment of both a low level and a high level of the level detection circuitry.

9. The levelmeter of claim 1, wherein the monitor further has impedance conversion circuitry for converting the sensor output signal from a sinusoidal signal to a square wave signal.

10. An opto-electric sensor that provides an output signal representing the level of liquid in a container, comprising:

a light emitting diode that emits light toward the surface of the liquid;

an optical transistor that detects light reflected from the surface of the liquid, thereby providing an optical link between the light emitting diode and the optical transistor;

an oscillation circuit formed in part by the optical link between the light emitting diode and the optical transistor, wherein the oscillation circuit generates a sensor output signal whose frequency is representative of the level of liquid in the container; and

a electrical port for delivering the sensor output signal to a remote monitor.

11. The sensor of claim 10, wherein the oscillation circuit has an operational amplifier and wherein the optical link is in a feedback loop of the operational amplifier.

12. The sensor of claim 10, wherein the sensor receives electrical energy from a remote source via an electrical link.

13. The sensor of claim 10, wherein the sensor output signal is transmitted from the sensor by the same electrical port that delivers electrical energy.

14. The sensor of claim 10, further comprising a current transmitter for converting the sensor output signal to a signal in which the liquid level is represented by current information.

15. A method of sensing the level of liquid in a container, comprising the steps of:

installing a sensor internal to the container;

using the sensor to emit light to the surface of the liquid, to detect light reflected from the surface, and to generate a sensor output signal whose frequency represents the level of liquid in the container;

transmitting the sensor output signal to a remote monitor;

linearizing the sensor output signal; and

converting the sensor output signal to a monitor output signal representing the level of liquid in the tank, such that the liquid level may be communicated to a user.

16. The method of claim 15, further comprising the step of calibrating the sensor by placing, under the sensor, a surface whose reflective characteristics are the same as a known level of the liquid.

17. The method of claim 15, wherein the sensor output signal is a frequency modulated signal, whose frequency represents the level of liquid.

18. The method of claim 15, further comprising the step of delivering electrical energy to the sensor and wherein the transmitting step is accomplished using the same electrical link as the delivering step.

19. A method of sensing the level of liquid in a container, comprising the steps of:

installing a sensor internal to the container;

calibrating the sensor by placing, under the sensor, a surface whose reflective characteristics are the same as a known level of the liquid;

using the sensor to emit light to the surface of the liquid, to detect light reflected from the surface, and to generate a sensor output signal whose frequency represents the level of liquid in the container;

transmitting the sensor output signal to a remote monitor; and

using the monitor to convert the sensor output signal to a monitor output signal representing the level of liquid in the tank, such that the liquid level may be communicated to a user.

20. The method of claim 19, further comprising the steps of displaying the liquid level in the form of an optical display, detecting the optical display, delivering a calibration signal representing the optical display to the monitor, and using the calibration signal to automatically adjust the monitor.