Ultrasonic sensor

• US 4,785,664 A
• Filed: 04/28/1986
• Issued: 11/22/1988
• Est. Priority Date: 04/28/1986
• Status: Expired due to Fees

• Current Assignee: Kay-Ray/Sensall Incorporated
• Original Assignee: Kay Jay, LLC
• Inventors: Reebs, Stephen R.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Worth, W. Morris
• Application Number:
  US06/856,812
• Time in Patent Office: 939 Days
• Field of Search: 73/290 R, 73/290 V, 340/621, 367/901, 367/908, 367/127, 367/124, 367/115, 367/114, 367/99
• US Class Current: 73/290.00V
• CPC Class Codes: G01F 23/2962 Measuring transit time of reflected waves
• CPC Class Codes: G01S 7/527 Extracting wanted echo signals Doppler systems G01S15/50
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level

Abstract

An improved ultrasonic system for detecting the level of a material that has a surface, for example a liquid level inside of a tank, which improves the ability to detect levels particularly when the tank is nearly full. A transmitted ultrasonic signal from a transducer is reflected against the material in the tank, and when received back at the transducer, an output pulse is provided from the transducer. The distance or level is determined by determining the time between the transmission and the reflected signal. A comparator compares the signal from the transducer with a reference and provides an output when a pulse of greater magnitude than the reference is received. In order to avoid problems of high output signals caused by vibration of the transducer after a control signal is removed until the transducer reaches rest (called "ring down" time), the reference signal is adjusted on a time basis so that it initially will be above the expected level of any unwanted "ring down" signal, but it will recognize a valid reflected signal when the tank level is close to full because the reflected signal also will have a high magnitude, and the reference signal will decrease with time to a desired level where lower magnitude reflected signals associated with lower tank levels will be properly identified.

Claims

1. An improved ultrasonic system for detecting a level of a material in a container having a local speed of sound therein by converting time of ultrasonic transmission into an indication of distance and for providing a level signal to a readout means, including means for measuring the time from transmission of a transmitted ultrasonic signal from ultrasonic transmission means toward the material to receipt of a return signal by second means the measured time representing the level of the material relative to the ultrasonic transmission means according to the local speed of sound, which transmitted signal ceases after a time of transmission, further including means for comparing the magnitude of all received signals to the magnitude of a reference signal wherein the second means detects only the return signal which has a greater magnitude than the reference signal, and including means for adjusting the reference signal to decreasing magnitudes on a time basis after ceasing transmission of a transmitted ultrasonic signal to substantially eliminate detection by the comparing means of signals caused by transducer ring down, and means for converting time measured by the means for measuring time to the level signal supplied to the readout means.

2. An improved ultrasonic system for determining a distance to an ultrasonic reflecting surface comprising:

ultrasonic transducer means for transmitting ultrasonic signals and controlled to cease transmission of signals after a selected time period but which transducer means continues to vibrate, ring down, and send ultrasonic signals having a decreasing magnitude after the transducer means has been controlled to cease transmission, and including means for receiving ultrasonic signals, the time interval between the transmission of the transmitted ultrasonic signals and the receipt of a respective reflected return signal representing the distance from the transducer means to the ultrasonic reflecting surface;

reference means coupled to the transducer means for generating a reference signal;

means coupled to the transducer means for comparing the received signals to the reference signal, and providing a comparator output when a received signal is greater than the reference signal;

means for controlling the reference signal at a level that is substantially representative of the magnitude of signals which emanate from the transducer means after the transducer means has been controlled to cease transmission, such that signals due to ring down are substantially eliminated as a source of comparator outputs but reflected return signals provide comparator outputs even before ring down ceases; and

means for measuring the time between the transmission of a transmitted signal and a corresponding comparator output and for providing an indication of the distance from the transducer means to the reflecting surface.

3. An improved ultrasonic system according to claim 2 further comprising controller means coupled to the transducer means for controlling at least one time period for the transmitted ultrasonic signals.

4. An ultrasonic distance measuring system for detecting distance from a transducer to an ultrasonic wave reflecting surface by measuring the time between commencement of transmitting an ultrasonic signal in response to a control signal and the time of receipt of a reflected return signal received by the system, which return signal has a magnitude, the measured time being representative of the distance to the surface, wherein the transducer continues to vibrate and cause reducing magnitude ultrasonic signals for a time after the control signal has ceased, comprising:

means for comparing the return signal to a reference signal and for providing a comparator output

means for providing the reference signal at a controlled magnitude which is greater than the magnitude of the signals from the transducer sensed when the control signal commences transmitting said ultrasonic signal, and which reduces the reference signal as a function of time after the control signal has ceased, to maintain the reference signal magnitude above but substantially corresponding to the reducing magnitude ultrasonic signals caused by the vibration of the transducer after the control signal has ceased; and

means for measuring the time between the commencement of transmission of the ultrasonic signal and the corresponding comparator output and for providing an indication of distance from the transducer to the ultrasonic reflecting surface as a function of such time.

5. The ultrasonic distance measuring system of claim 4 wherein said means for providing the reference signal at a controlled magnitude comprises a capacitor which is charged when the ultrasonic signal is being transmitted by the transducer in response to the control signal, and which capacitor is discharged at a controlled rate subsequent to the time that the control signal ceases.

6. A method of measuring the level of a material in a space comprising:

transmitting an ultrasonic signal toward the material level, the ultrasonic signal having a selected controlled duration and the transmitting ceasing after a preselected period of time, the ultrasonic transducer having the characteristic of continuing to vibrate to form a continued ultrasonic signal of decreasing magnitude for a period of time after such transmitting ceases;

providing a transducer output signals from the transducer as a function of signals received thereby subsequent to transmission including ultrasonic signals reflected from the material in the space;

comparing the transducer output signals with respect to a reference signal to determine when an output signal is greater in magnitude than the magnitude of the reference signal and then providing a comparator output;

maintaining the reference signal at a sufficient magnitude which is greater in magnitude than the transmitted signal during transmission of the ultrasonic signal;

thereafter reducing the magnitude of the reference signal to a level as a function of time, so that the reference signal maintains a magntiude higher than the continued ultrasonic transducer output signal magnitude caused by vibration of the transducer after transmission has ceased as the continued ultrasonic signal decreases in magnitude; and

measuring the time from initiation of a transmitted signal to receipt of a comparator output representing receipt of a corresponding reflected signal and determining the level of material from such time.