Adjustable ultrasonic level measurement device

• US 4,221,004 A
• Filed: 08/03/1978
• Issued: 09/02/1980
• Est. Priority Date: 08/03/1978
• Status: Expired due to Term

• Current Assignee: Robertshaw Controls Company (Schneider Electric SE)
• Original Assignee: Robertshaw Controls Company (Schneider Electric SE)
• Inventors: Combs, Charles M., Goodwin, Perry H. Jr.
• Primary Examiner(s): Farley, Richard A.
• Application Number:
  US05/930,667
• Time in Patent Office: 761 Days
• Field of Search: 340/1 L, 73/290 V, 367/95, 367/97, 367/112, 367/114, 367/900, 367/908
• US Class Current: 367/114
• CPC Class Codes: G01F 23/2962 Measuring transit time of reflected waves
• CPC Class Codes: G01S 15/18 wherein range gates are used
• CPC Class Codes: Y10S 367/90 Sonar time varied gain control systems
• CPC Class Codes: Y10S 367/902 Speed of sound compensation
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level

Abstract

An ulrasonic liquid level measurement device is used to measure the depth of a flowing liquid in a channel using an ultrasonic transducer that is positioned out of contact with the liquid and above and directed toward the channel. An ultrasonic burst is directed toward the channel and the reflected echo from the surface of the liquid is returned and sensed by the transducer. The transit time of ultrasonic transmission and echo return is indicative of the liquid level. An adjustable discriminator is provided to specify a maximum liquid level in the channel and a minimum liquid level, which, typically is the floor of the channel. The maximum and minimum levels are adjustable to accomodate variable channel configurations and transducer mounting arrangements. Automatic adjustment is provided to compensate for different cable lengths which may be used to connect the ultrasonic transducer to the transducer driver and receiving section. Temperature compensation is provided to compensate for changes in ultrasonic transmission propogation through ambient air with temperature, and time variable gain amplification is provided to compensate for geometric spreading of reflected ultrasonic energy echo pulses and for air path absorption.

Claims

1. An ultrasonic level flow detector for measuring the depth of a fluid flowing in a channel comprising:

ultrasonic transducer means mounted above said channel for transmitting ultrasonic signals toward said channel and for receiving reflected ultrasonic signals therefrom;

receiving means for detecting ultrasonic signals received by said ultrasonic transducer means;

echo signal registration means coupled to said receiver for registering the occurence of an echo signal;

indicator means connected to said echo signal registration means for expressing the occurrence of said echo signal as an indication of fluid flow level;

adjustable discriminator means connected to said echo signal registration means to provide a maximum level signal at a minimum signal transit and reflection time and a minimum level signal at a maximum signal transit and reflection time, and to gate said echo signal registration means to receive an echo signal only during the interval therebetween; and

time dependent non-linear gain amplification means interposed between said echo signal registration means and said indicator means for non-linearily increasing amplication of said echo signal as an increasing function of elapsed time between occurrence of said maximum level signal and said echo signal.

2. An ultrasonic level flow detector according to claim 1 further characterized in that said adjustable discriminator means includes selector means for manually and adjustably controlling the generation of said maximum level signal.

3. An ultrasonic level flow detector according to claim 1 further characterized in that said adjustable discriminator means includes selector means for manually and adjustably controlling the generation of said minimum level signal.

4. An ultrasonic level flow detector according to claim 1 further comprising counting means connected to said echo signal registration means to count minimum level signals, a reset lead connected to said receiver for resetting said counter each time an echo signal is received by said receiver, and lost echo indicating means connected to said counting means for signifying the absence of receipt of an echo signal by said receiver upon reaching a predetermined count of minimum level signals.

5. An ultrasonic level flow detector according to claim 1 wherein said receiver further includes a frequency band pass filter to limit said echo signals to ultrasonic signals within a prescribed frequency range.

6. An ultrasonic level flow detector according to claim 1 further comprising means for manually adjusting the duration and amplitude of said ultrasonic signals transmitted toward said channel.

7. An ultrasonic level flow detector for measuring the depth of a flowing fluid in a channel comprising:

ultrasonic transducer means mounted above said channel for transmitting ultrasonic signals toward said channel and for receiving reflected ultrasonic signals therefrom;

receiving means for detecting ultrasonic signals received by said ultrasonic transducer means;

echo signal registration means coupled to said receiver for registering the occurrence of an echo signal;

indicator means connected to said echo signal registration means for expressing the occurrence of said echo signal as an indication of fluid flow level;

adjustable discriminator means connected to said echo signal registration means to provide a maximum level signal at a minimum signal transit and reflection time and a minimum level signal at a maximum signal transit and reflection time, and to gate said echo registration means to receive an echo signal only during the interval therebetween; and

a programmable read only memory interposed between said echo signal registration means and said indicator means for increasing amplification of said echo signal as a function of the time of occurrence thereof within the time interval between said minimum and maximum signal transit and reflection times.

8. An ultrasonic level flow detector according to claim 7 wherein said receiver comprises an adjustable threshold level discriminator for establishing a minimum amplitude for echo signals for registration in said echo signal registration means.

9. An ultrasonic level flow detector according to claim 7 further characterized in that said echo signal registration means includes a memory latch for retaining the most recently registered echo signal as an input to said indicator means until updated by a subsequently registered echo signal.

10. An ultrasonic level flow detector according to claim 7 further comprising temperature monitoring means for monitoring the ambient temperature above said flowing fluid and coupled to said adjustable discriminator means for automatically varying said minimum and maximum transit reflection times to vary the occurrence of said maximum and minimum level signals with ambient temperature.

11. An ultrasonic level flow detector for measuring the depth of a flowing fluid in a channel comprising;

ultrasonic transducer means mounted above said channel for transmitting ultrasonic signals toward said channel and for receiving reflected ultrasonic signals therefrom;

receiving means for detecting ultrasonic signals received by said ultrasonic transducer means;

echo signal registration means coupled to said receiver for registering the occurrence of an echo signal;

indicator means connected to said echo signal registration means for expressing the occurrence of said echo signal as an indication of fluid flow level;

adjustable discriminator means connected to said echo signal registration means to provide a maximum level signal at a minimum signal transit and reflection time and a minimum level signal at a maximum signal transit and reflection time, and to gate said echo signal registration means to receive an echo signal only during the interval therebetween; and

resonance matching means for varying the frequency of ultrasonic signals transmitted toward said channel to match the resonant frequency of said ultrasonic transducer means.

12. An ultrasonic level flow detector according to claim 11 further comprising manual adjusting means for said resonance matching means.

13. An ultrasonic level flow detector for measuring the depth of a flowing fluid in a channel comprising

ultrasonic transducer means mounted above said channel for transmitting ultrasonic signals toward said channel and for receiving reflected ultrasonic signals therefrom;

receiving means for detecting ultrasonic signals received by said ultrasonic transducer means;

echo signal registration means coupled to said receiver for registering the occurrence of an echo signal;

indicator means connected to said echo signal registration means for expressing the occurrence of said echo signal as an indication of fluid flow level; and

an ultrasonic driver,

a connecting cable joining said transducer to said receiver and to said ultrasonic driver, and

cable impedence compensation means interposed between said cable and said receiver and said ultrasonic driver to automatically stabilize the strength of ultrasonic signals transmitted and echo signals received irrespective of connecting cable length.

14. An ultrasonic liquid level measurement device for detecting ultrasonic echoes reflected through air from a liquid interface therewith from liquid residing within a solid floored confinement comprising:

an ultrasonic transducer for transmitting ultrasonic signals toward the floor of said confinement;

a receiver responsive to reflected ultrasonic signals to produce an electrical echo signal;

oscillator means connected to said receiver and to said transducer for generating electrical timing signals during a measurement interval;

adjustable discriminator means connected to said oscillator means to count timing signals to generate a maximum liquid level signal and a minimum liquid level signal corresponding respectively to manually adjustable minimum and maximum ultrasonic signal transmission and reflection times and including a manual coarse adjustment to designate counting totals of said timing signals at which said maximum and minimum level signals are generated and a manual fine adjustment to alter the frequency at which said timing signals are generated;

echo signal registration means connected to said discriminator means and to said oscillator means for counting timing signals during the interval between said maximum level signal and said echo signal, and for registering the timing signal count accumulated therebetween as a portion of the interval between said maximum and minimum ultrasonic signal transmission and reflection times; and

indicator means connected to said echo signal registration means to transform said timing signal count accumulated in said echo signal registration means to a perceptable indication of liquid level.

15. An ultrasonic liquid level measurement device according to claim 14 further comprising an alarm system operatively responsive to the accumulated count in said echo signal registration means to generate alarm indications whenever said accumulated count falls beyond acceptable upper and lower limits.

16. An ultrasonic liquid level measurement device according to claim 14 further characterized in that said adjustable discriminator means includes manually operable test controls for suppressing the registration of said echo signals in said echo signal registration means and for selectively registering said maximum level signal and said minimum level signal in said echo signal registration means in place of said echo signal.

17. An ultrasonic liquid level measurement device for detecting ultrasonic echoes reflected through air from a liquid interface therewith from liquid residing within a solid floored confinement comprising:

an ultrasonic transducer for transmitting ultrasonic signals toward the floor of said confinement;

a receiver responsive to reflected ultrasonic signals to produce an electrical echo signal;

oscillator means connected to said receiver and to said transducer for generating electrical timing signals during a measurement interval;

adjustable discriminator means connected to said oscillator means to count timing signals to generate a maximum liquid level signal and a minimum liquid level signal corresponding respectively to manually adjustable minimum and maximum ultrasonic signal transmission and reflection times;

echo signal registration means connected to said discriminator means and to said oscillator means for counting timing signals during the interval between said maximum level signal and said echo signal, and for registering the timing signal count accumulated therebetween as a portion of the interval between said maximum and minimum ultrasonic signal transmission and reflection times;

indicator means connected to said echo signal registration means to transform said timing signal count accumulated in said echo signal registration means to a perceptable indication of liquid level;

electrical cable means coupling said ultrasonic transducer to said oscillator means, and

compensation means interposed between said ultrasonic transducer and said oscillator to automatically stabilize attenuation of electrical signal propogation through said electrical cable means.

18. An ultrasonic level flow detector for measuring the depth of a flowing fluid in a channel comprising:

ultrasonic transducer means mounted above said channel for transmitting ultrasonic signals toward said channel and for receiving reflected ultrasonic therefrom;

receiving means for detecting ultrasonic signals received by said ultrasonic transducer means;

a delay circuit connected to said receiving means and to said ultrasonic transducer means for establishing a minimum delay between the transmission of successive ones of said ultrasonic signals toward said channel;

echo signal registration means coupled to said receiver for registering the occurrence of an echo signal;

indicator means connected to said echo signal registration means for expressing the occurrence of said echo signal as an indication of fluid flow level; and

adjustable discriminator means connected to said echo signal registration means to provide a maximum level signal at a minimum signal transit and reflection time and a minimum level signal at a maximum signal transit and reflection time, and to gate said echo signal registration means to receive an echo signal only during the interval therebetween.