Arrangement for measuring the level of contents in a container

• US 6,539,794 B1
• Filed: 09/02/1999
• Issued: 04/01/2003
• Est. Priority Date: 02/18/1994
• Status: Expired due to Term

• Current Assignee: Johanngeorg Otto, Wolfgang Lubcke
• Original Assignee: Johanngeorg Otto, Wolfgang Lubcke
• Inventors: Lubcke, Wolfgang, Otto, Johanngeorg
• Primary Examiner(s): Larkin, Daniel S.
• Assistant Examiner(s): FRANK, RODNEY T
• Application Number:
  US09/388,673
• Time in Patent Office: 1,307 Days
• Field of Search: 732/90.V, 73/1.H, 340/621, 367/908
• US Class Current: 73/290.00V
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01F 23/296 Acoustic waves
• CPC Class Codes: G01F 23/2962 Measuring transit time of reflected waves
• CPC Class Codes: G01F 25/24 Testing proper functioning of electronic circuits
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level

Abstract

A continuous measurement of the level of contents in a container is effected by a level measuring device functioning in accordance with the transit time principle by means of waves transmitted from a position located above the highest possible contents level onto the surface of the material in the container. A measuring circuit determines the contents level from the transit time of the useful echo reflected from the material surface. In addition, one or more limit sensors are located at the container, each of which furnishes a signal indicating whether the contents level is above or below a level to be monitored by the limit sensor and which is situated between the minimum and maximum contents levels of the container. The measuring circuit receives the output signals of all limit sensors and uses these output signals to check and eventually to correct the contents level measured value determined by the level measuring device. In particular, the measuring result furnished by the level measuring device can be compared with an exact contents level value every time the contents level reaches the level monitored by a limit sensor whereby the level indication of the limit sensor changes its status. In certain cases, a single limit sensor is sufficient for this purpose, which monitors a contents level which is regularly exceeded or undershot in the normal use of the container.

Claims

1. A two-wire measuring apparatus for measuring the level of the material in a container, the material in the container defining a surface, the apparatus comprising:

a level sensor mounted at the highest possible level to the container;

an electromagnetic wave antenna extending from said level sensor into the container;

a measuring circuit connected to said level sensor; and

a two-wire process control loop connected to said measuring circuit,

wherein

said process control loop supplies a current signal which is variable between 4-20 ma,

said level sensor generating electromagnetic waves to be transmitted through said electromagnetic wave antenna to the surface of the material in the container and for receiving from the surface, electromagnetic waves reflected from the surface through said electromagnetic wave antenna, and

said measuring circuit analyzing said reflected electromagnetic waves, forming thereby an echo function from the output signal of said level sensor representing the echo amplitudes as a function of distance over the whole measuring range, compares a portion of the echo function to a stored empty echo function to determine a measured value of the contents level, and, when triggered, compares the measured value of the contents level to a predefined level and conveys the result to said two-wire process control loop.

2. The two-wire measuring apparatus as defined in claim 1, further comprising:

a first limit sensor mounted to the container and connected to said measuring circuit to indicate whether the material level in the container is above or below a first predefined level monitored by said first limit sensor.

3. The two-wire measuring apparatus as defined in claim 2, further comprising:

a second limit sensor mounted to the container and connected to said measuring circuit for monitoring a second predefined level, said first and second predefined levels being within a measuring range of the two-wire measuring apparatus, said first limit sensor supplying a first output signal to said measuring circuit indicating whether the material level in said container is above or below said first predefined level, and said second limit sensor supplying a second output signal to said measuring circuit indicating whether the material level in said container is above or below said second predefined level, wherein at least one of said first and second output signals is used to determine an error in the material level measurement carried out by the two-wire measuring apparatus.

4. The two-wire measuring apparatus as defined in claim 1, further comprising:

a power supply connected to said two-wire process control loop for providing the sole source of power for said level sensor and said measuring circuit.

5. The two-wire measuring apparatus as defined in claim 1, wherein said measuring circuit includes a microprocessor operable for determining the echo function.

6. The two-wire measuring apparatus as defined in claim 1, wherein the electromagnetic waves are short pulses.

7. The two-wire measuring apparatus as defined in claim 1, wherein the electromagnetic waves are continuous waves.

8. The two-wire measuring apparatus as defined in claim 1, wherein the echo function represents the amplitudes of the electromagnetic waves received by said level sensor as a function of distance over an entire measuring angle for the level of the material in said container.

9. The two-wire measuring apparatus as defined in claim 1, wherein said measuring circuit determines a corresponding empty echo function representing amplitudes of electromagnetic waves received by said level sensor as a function of distance when said container contains approximately none of the material, comparing the echo function with the corresponding empty echo function to identify a portion of the echo function that is representative of the electromagnetic waves reflected by the surface.

10. The two-wire measuring apparatus as defined in claim 9, wherein the empty echo function is a limit curve.

11. The two-wire measuring apparatus as defined in claim 9, wherein said measuring circuit determines a limit curve by adding a constant to the empty echo function, and evaluates only peaks of the echo function that are located above the limit curve.

12. The two-wire measuring apparatus as defined in claim 9, wherein the empty echo function is actualized by replacing a portion of the empty echo function associated with distances above the level of the material in said container with a portion of the echo function associated with the distance above the level of the material in said container.

13. A two-wire measuring apparatus for measuring the level of the material in a container, the material in the container defining a surface, the apparatus comprising:

a two-wire process control loop;

a level sensor mounted at the highest possible level to the container;

an electromagnetic wave antenna extending from said level sensor into the container;

a measuring circuit connected to said level sensor;

a two-wire process control loop connected to said measuring circuit;

a first limit sensor mounted to the container and connected to said measuring circuit to indicate whether the material level in the container is above or below a first predefined level monitored by said first limit sensor; and

a second limit sensor mounted to the container and connected to said measuring circuit for monitoring a second predefined level, said first and second predefined levels being within a measuring range of the two-wire measuring apparatus, said first limit sensor applying a first output signal to said measuring circuit indicating whether the material level in said container is above or below said first predefined level, and said second limit sensor supplying a second output signal to said measuring circuit indicating whether the material level in said container is above or below said second predefined level, wherein

at least of said first and second output signals is used to determine an error in the material level measurement carried out by the two-wire measuring apparatus,

said process control loop supplies a current signal which is variable between 4-20 ma,

said level sensor generating said electromagnetic waves to be transmitted through said electromagnetic wave antenna to the surface of the material in the container and for receiving from the surface, electromagnetic waves reflected from the surface through said electromagnetic wave antenna,

said measuring circuit analyzing said reflected electromagnetic waves, forming thereby an echo function from which the distance from the surface of the material in the container to said level sensor is determined and conveyed by said two-wire process control group, and

when said first limit sensor indicates that the material level is above said first predefined level and said second limit sensor indicates that the material level is below said second predefined level, said measuring circuit compares a portion of a current echo function representing the amplitudes of the electromagnetic waves reflected from the surface as a function of the region between said first predefined level and said second predefined level with a stored empty echo function to determine a useful electromagnetic wave reflected from the surface of the material in said container and to determine a measured value of the material level from the transit time of the useful electromagnetic wave.

14. The two-wire measuring apparatus as defined in claim 13, wherein, when the output signal of one of said first and second limit sensors changes status, said measuring circuit performs a level comparison, comprising the one of said first and second predefined levels with the measured value of the material level determined at the same time by said measuring circuit from the transit time of the useful electromagnetic wave to determine an error of the material level measurement carried out by the two-wire measuring apparatus.

15. The two-wire measuring apparatus as defined in claim 14, wherein each time the error determined in the level comparison exceeds a give error limit said measuring circuit actualizes the stored empty echo function from the starting point of the stored empty echo function to an intermediate point of the stored empty echo function corresponding to the one of said first and second predefined levels monitored by the one of said first and second limit sensors whose output signal changed status.

16. The two-wire measuring apparatus as defined in claim 14, wherein, when the output signal of one of said first and second limit sensors changes its status, said measuring circuit actualizes the stored empty echo function from the starting point of the stored empty echo function to an intermediate point of the stored empty echo function corresponding to the one of said first and second predefined levels monitored by the one of said first and second limit sensors whose output signal changed status.

17. A two-wire measuring apparatus for measuring the level of the material in a container, the material in the container defining a surface, the apparatus comprising:

a level sensor mounted at the highest possible level to the container;

an electromagnetic wave antenna extending from said level sensor into the container;

a measuring circuit connected to said level sensor; and

a two-wire process control loop connected to said measuring circuit,

wherein

said process control loop supplies a current signal which is variable between 4-20 ma,

said level sensor generating electromagnetic waves to be transmitted through said electromagnetic wave antenna to the surface of the material in the container and for receiving from the surface, electromagnetic waves reflected from the surface through said electromagnetic wave antenna, and

said measuring circuit analyzing said reflected electromagnetic waves, forming thereby an echo function from which the distance from the surface of the material in the container to said level sensor is determined and conveyed by said two-wire process control loop, said measuring circuit evaluating only a portion of the echo function corresponding to distances between two predetermined levels of said container.