Apparatus for the determination of the fill state of material in a container

• US 6,249,244 B1
• Filed: 10/26/1999
• Issued: 06/19/2001
• Est. Priority Date: 07/29/1999
• Status: Expired due to Term

• Current Assignee: Endress+Hauser GmbH+Co (ENDRESS)
• Original Assignee: Endress+Hauser GmbH+Co (ENDRESS)
• Inventors: Heidecke, Frank
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US09/427,338
• Time in Patent Office: 602 Days
• Field of Search: 342/123, 342/124, 367/908, 732/90.V, 732/90.R
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level

Abstract

This invention relates to an apparatus for the determination of the fill state of solid or liquid material in a container with a signal-generating/transmitting unit, a receiving unit, a time-delay circuit which transforms the high-frequency signals into low-frequency signals, and an evaluating unit. The invention includes a time-delay circuit having a first circuit element with a time constant r₁ driven by input pulses in synchronization with the transmission repetition frequency (f₁) and which generates a non-linear output signal, a second circuit element with a time constant (T₂) greater than time constant (T₁) driven by input pulses with a frequency (f₂) which is less than the transmission repetition frequency (f₁) and which generates a non-linear output signal, and a third circuit element which detects in each period of the transmission repetition frequency (f₁) an intersection of the output signal of the first circuit element and the output signal of the second circuit element and supplies an output signal to an evaluation unit to determine the fill state of the material in the container.

Claims

1. An apparatus for the determination of the fill state of material in a container comprising:

a signal generating/transmitting unit which generates high-frequency signals with a predetermined transmission repetition frequency (f₁) and transmits them in the direction of a surface of the material so that the high-frequency signals are reflected at the surface of the material, a receiving unit which receives reflected signals, a time-delay circuit which transforms the high-frequency signals into low-frequency signals, the time-delay circuit including a first circuit element having a first time constant (T₁) driven by input pulses synchronized with the transmission repetition frequency (f₁) and which generates a non-linear output signal, a second circuit element having a second time constant (T₂) greater than the first time constant (T₁) driven by pulses with a frequency (f₂) which is less than the transmission repetition frequency (f₁) and which generates a non-linear output signal, and a third circuit element which detects in each period of the transmission repetition frequency (f₁) an intersection of the output signal of the first circuit element and the output signal of the second circuit element and generates an output signal, and an evaluating unit which determines the fill state of the material in the container from the output signal of the third circuit element.

2. The apparatus according to claim 1, further including a fourth circuit element to insure that the input pulses to the first circuit element and the second circuit element have the same voltage level and the same ramp behavior.

3. The apparatus according to claim 1 wherein the first circuit element and the second circuit element are RC circuits having time constants T₁=R₁C₁ and T₂=R₂C₂.

4. The apparatus according to claim 3 wherein the time constants T₁=R₁ C₁, T₂=R₂C₂ of the first circuit element and the second circuit element are chosen so that the quotient of the time constant (T₂) and the time constant (T₁) correspond to a predetermined time delay factor.

5. The apparatus according to claim 3, further including a circuit component connected to the second circuit element to reduce the discharging time of the second circuit element.

6. The apparatus according to claim 1 wherein the third circuit element is a comparator.

7. The apparatus according to claim 6, further including a logical gate array having a first input signal with the frequency (f₂) and a second input signal which is the output signal of the third circuit element.

8. The apparatus according to claim 6 wherein the evaluation unit uses sampling points in the output signal of the third circuit element which lie in the linear range of the comparator.

9. The apparatus according to claim 1, further including a control circuit for controlling a sampling frequency of the low-frequency signals which is outside of a non-linear range of the third circuit element.

10. The apparatus according to claim 1, further including a first control circuit for holding he time constant (T₂) of the second circuit element to a constant value.

11. The apparatus according to claim 1, further including a second control circuit for holding a time extension factor (Δ

t) to a constant value.

12. The apparatus according to claim 1 wherein the transmission repetition frequency (f₁) is a variable quantity.

13. The apparatus according to claim 12 wherein the transmission repetition frequency (f₁) is a function of a distance from the antenna to the surface of the material.