Level detector for fluent material

• US 5,943,294 A
• Filed: 05/01/1998
• Issued: 08/24/1999
• Est. Priority Date: 04/08/1997
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Milltronics, Ltd. (Titan Pacific Resources Ltd.)
• Inventors: Bleszynski, Stanislaw, Cherek, Bogdan
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US09/070,727
• Time in Patent Office: 480 Days
• Field of Search: 367/908, 367/98, 73/290 V, 340/621
• US Class Current: 367/98
• CPC Class Codes: G01F 23/2965 Measuring attenuation of transmitted waves
• CPC Class Codes: G01F 23/2967 for discrete levels
• CPC Class Codes: G01S 7/521 Constructional features
• CPC Class Codes: G01S 7/526 Receivers
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level

Abstract

A vibrating probe for detecting a threshold level within a vessel of fluent material, particularly a liquid, includes: an ultrasonic acoustic transducer assembly comprising a transducer element having a natural resonant frequency, and loading elements effective to shift that frequency to an effective resonant frequency of the assembly, the assembly being supported within the vessel and including a coupling member to couple the transducer acoustically to liquid reaching the threshold level, a transmitter generating pulses applied to the transducer element for repeatedly exciting the transducer element to cause the transducer assembly to resonate at its effective resonant frequency, a circuit for measuring the effective resonant frequency of the transducer over a ringdown period following cessation of each pulse, and a circuit for comparing the effective resonant frequency measured during the ringdown period following each pulse with a predetermined threshold level. The threshold level is selected so as to distinguish between the effective resonant frequency of the assembly in free air and a lower effective resonant frequency when coupled to fluent material through the coupling member. The damping effect of the fluent material, particularly if a viscous liquid, may accelerate the ringdown to an extent such that vibration is effectively suppressed before the end of the frequency measurement, thus further depressing the apparent measured frequency.

Claims

1. A vibratory probe for detecting a threshold level of fluent material within a vessel, comprising an ultrasonic acoustic transducer assembly having an effective resonant frequency, a structure for supporting the assembly from above within the vessel, the assembly including a depending coupling member disposed to depend into and to couple the transducer acoustically to fluent material at the threshold level, a transmitter for applying repeated pulses to the transducer to cause it to resonate at said effective resonant frequency, a receiver coupled determines whether a ring down characteristics of transducer assembly has been altered beyond a predetermined threshold.

2. A vibratory probe for detecting a threshold level of fluent material, particularly a liquid, within a vessel comprising of an ultrasonic acoustic transducer assembly having a transducer element having a natural resonant frequency, and loading elements effective to shift that frequency to an effective resonant frequency the assembly being supported within the vessel and including a coupling member to couple the transducer acoustically to liquid reaching the threshold level, a transmitter generating pulse applied to the transducer element for repeatedly exciting the transducer element to cause the transducer assembly to resonate at its effective resonant frequency, a circuit for counting the effective resonant frequency of the transducer over a ringdown period after cessation of each pulse, and a circuit for comparing the effective resonant frequency counted during the ringdown period following each pulse with a predetermined frequency.

3. A vibratory probe according to claim 2, wherein the counting circuit is operative only while the amplitude of the ringdown is above a predetermined amplitude, whereby a rapid ringdown below the predetermined amplitude truncates the count.