Method of testing the integrity of an ultrasonic system for sensing liquid-fluid interfaces

• US 4,299,114 A
• Filed: 06/10/1980
• Issued: 11/10/1981
• Est. Priority Date: 06/10/1980
• Status: Expired due to Term

• Current Assignee: Kay-Ray/Sensall Incorporated
• Original Assignee: Envirotech Corporation (Baker Hughes Company)
• Inventors: Adams, George L., Silvermetz, David
• Primary Examiner(s): YASICH, DANIEL
• Application Number:
  US06/158,109
• Time in Patent Office: 518 Days
• Field of Search: 73/1 H, 73/1 DV, 73/290 V
• US Class Current: 73/1.83
• CPC Class Codes: G01F 23/2961 for discrete levels G01F23/2962 - G01F23/2968 take precedence
• CPC Class Codes: G01F 25/20 of apparatus for measuring liquid level
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level

Abstract

An ultrasonic system for sensing a liquid-fluid interface comprises a support structure (10) to which a transmitting crystal (21) and a receiving crystal (22) are bonded in such a way that the crystals (21 and 22) are positioned opposite each other across a gap (30). Each of the crystals (21 and 22) has a relatively high resonant frequency and a relatively low resonant frequency. An amplifier means (40) and a bandpass filter means (50) are connected to the crystals (21 and 22) to form a feedback loop. In normal operation, the transmitting crystal (21) is excited to resonate at its high resonant frequency in order to cause transmission of an ultrasonic signal across the gap (30) without causing appreciable ultrasonic transmission through the support structure (10) to the receiving crystal (22). When it is desired to test the system for integrity in the absence of liquid in the gap (30), the transmitting crystal (21) is excited to resonate at its low resonant frequency and the passband of the bandpass filter means (50) is shifted to enable low frequency oscillations to occur in the feedback loop due to ultrasonic transmission (i.e., cross-talk) through the support structure (10) between the crystals (21 and 22).

Claims

1. A method for testing the integrity of an ultrasonic system for sensing a liquid-fluid interface in a container, said system comprising:

(a) first and second crystals, each of said crystals having a relatively high resonant frequency and a relatively low resonant frequency;

(b) a support structure with first and second end arms connected by a cross member, said first crystal being bonded to said first end arm and said second crystal being bonded to said second end arm, said first and second crystals being positioned opposite each other across a gap between said first and second end arms in said container;

(c) means for selectively enabling said first crystal to resonate either at its relatively high resonant frequency or at its relatively low resonant frequency, said relatively high resonant frequency being sufficiently high to cause an ultrasonic signal to be transmitted into said gap without causing appreciable ultrasonic transmission through said cross portion of said support structure, said relatively low resonant frequency being sufficiently low to cause transmission of a detectable ultrasonic signal through said cross member; and

(d) means for detecting resonance induced in said second crystal due to resonance of said first crystal at either its relatively high resonance frequency or its relatively low resonance frequency;

said testing method comprising the steps of causing said first crystal to resonate at its relatively low resonant frequency irrespective of whether the liquid-fluid interface lies within said gap in order to cause ultrasonic transmission through said cross member, and detecting resonance in said second crystal at said relatively low resonant frequency, thereby indicating that the ultrasonic system is operational.

2. The method of claim 1 wherein said step of detecting resonance in said second crystal involves causing a feedback loop that includes said first and second crystals to oscillate, and detecting said oscillation in said feedback loop at said relatively low resonant frequency.

3. The method of claim 2 wherein said step of detecting resonance in said second crystal further involves shifting a passband of a bandpass filter in said feedback loop in order to enable said feedback loop to oscillate at said relatively low resonant frequency.

4. The method of claim 3 wherein said step of causing said first crystal to resonate at its relatively low resonant frequency involves causing said first crystal to resonate in a lateral mode generally transverse to a direct path from said first crystal to said second crystal across said gap.

5. An ultrasonic system for sensing a liquid-fluid interface in a container, said system comprising:

(a) first and second crystals, each of said crystals having a relatively high resonant freqency and a relatively low resonant frequency;

(b) a support structure to which said first and second crystals are bonded, said support structure being configured so that said first and second crystals are positioned opposite each other across a gap in said container;

(c) amplifier means and bandpass filter means connected to said first and second crystals so as to form a feedback loop;

(d) means for exciting said first crystal to resonate selectively at said high and low resonant frequencies, said high frequency being sufficiently high to cause an ultrasonic signal to be transmitted across said gap without causing appreciable ultrasonic transmission through said support structure to said second crystal when said liquid-fluid interface lies within said gap, said low frequency being sufficiently low to cause appreciable ultrasonic transmission to said second crystal through said support structure;

(e) switching means for causing said first crystal to resonate at said high frequency and for establishing an operating passband for said bandpass filter means to enable high-frequency oscillations to occur in said feedback loop when said liquid-fluid interface lies within said gap, and means coacting with said switching means for causing said first crystal to resonate at said low frequency and for establishing a testing passband for said bandpass filter means to enable low-frequency oscillations to occur in said feedback loop when said liquid-fluid interface does not lie within said gap, thereby indicating that the integrity of the ultrasonic system is operational.

6. The system of claim 5 wherein said support structure is of generally C-shaped configuration with first and second end arms connected by a cross portion, said first crystal being bonded to said first end arm and said second crystal being bonded to said second end arm, said gap lying between said first and second end arms.

7. The system of claim 6 further comprising detector means for sensing oscillations in said feedback loop.

8. The system of claim 7 further comprising means responsive to said detector means for actuating a servomechanism when oscillations are maintained in said feedback loop due to resonance of said first crystal at said high resonant frequency.

9. The system of claim 8 further comprising integrity test indicative means responsive to said detector means when oscillations are maintained in said feedback loop due to resonance of said first crystal at said low resonant frequency.

10. The system of claim 8 further comprising means for automatically causing periodic oscillations of a selected time duration in said feedback loop at said low frequency.