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

Claim 3

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.

Claim 4

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.

Claim 5

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.

Claim 6

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.

Claim 7

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.

Claim 8

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.

Claim 9

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

Claim 10

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.

Claim 11

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.

Claim 12

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.