Acoustic range-finding system

• US 5,267,219 A
• Filed: 07/17/1992
• Issued: 11/30/1993
• Est. Priority Date: 07/17/1992
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Milltronics, Ltd. (Titan Pacific Resources Ltd.)
• Inventors: Woodward, Steven J.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US07/914,532
• Time in Patent Office: 501 Days
• Field of Search: 367/903, 367/3, 367/99, 367/135, 381/55
• US Class Current: 367/99
• CPC Class Codes: G01S 15/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurement G01S15/32
• CPC Class Codes: G01S 7/526 Receivers
• CPC Class Codes: Y10S 367/903 Transmit-receive circuitry

Abstract

In an acoustic pulse-echo ranging system, a high impedance piezoelectric transducer element is connected via a transformer to a transmitter, and also directly to a high impedance input of a receiver through a network, in parallel with the transducer element which includes a limiting resistor having a value which is low compared with the impedance of the transducer and a pair of oppositely connected diodes connected across the receiver input, the diodes being in series with the resistor and conducting to complete a damping circuit for large amplitude signals during transmission, and to limit the amplitude of signals applied to the receiver. When the signals are not of sufficient amplitude to cause the diodes to conduct, the damping circuit is normally rendered ineffective, but a further circuit is provided in parallel with the diodes to selectively switch into the network a further smaller resistance which acts both to form an attenuator at the receiver input in conjunction with the damping resistor, and to restore the damping effect. By this means, the dynamic range required by the receiver is much reduced, and effective damping can be applied selectively during reception to reduce the effect of ringing at short ranges. A tuned circuit formed with the transducer by the transformer through which the transmitter drives the transducer is tuned by means of an air gap in the transformer core, which may be adjustable.

Claims

1. An acoustic pulse-echo ranging system comprising a transducer containing a high impedance piezoelectric transducer element, a transmitter for driving the transducer element, a receiver having an input for receiving signals from the transducer element, and a transceiver interface for placing said transmitter and said receiver continuously in connection with the transducer element, wherein the transceiver interface comprises a resistive network establishing a direct resistive connection between the transducer element and the receiver, the network further including an electronically controlled switching element for switching the network between two states, namely a first state in which the transducer element is coupled to the receiver through a first resistive element whose resistance is low compared with the impedance both of the receiver and the transducer such that the network neither substantially damps the transducer element nor attenuates the input to the receiver, and a second state in which the network substantially damps the transducer element and attenuates the input to the receiver by establishing, through a second resistive element, and additional resistive path directly in parallel with the transducer element and having a resistance which is low compared with the impedance of both the transducer and the receiver, and wherein the system includes a controller for controlling the switching element to select the state of the network according to the expected characteristics of an echo to be received by the receiver.

2. The system of claim 1, wherein the second resistive element is of substantially lower value than the first resistive element.

3. The system of claim 2, wherein oppositely polarized diodes are connected in parallel with the second resistive element and the switching element, and the transducer drives the transducer element at a level such that the diodes conduct alternately during operation of the transmitter to place the first resistive element in parallel with the transducer.

4. The system of claim 1, wherein the switching element is a switching transistor.

5. The system of claim 3, wherein the transducer, the transmitter, the receiver and the transceiver interface are located within a common housing.

6. The system of claim 1, wherein the transmitter is connected to the transducer through a transformer having a variable air gap.