GB2188420A

GB2188420A - Ultrasonic range finding

Info

Publication number: GB2188420A
Application number: GB08607369A
Authority: GB
Inventors: Leslie Melbourne Barrett
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1986-03-25
Filing date: 1986-03-25
Publication date: 1987-09-30
Anticipated expiration: 2006-03-25
Also published as: GB2188420B; GB8607369D0

Abstract

Range measurements are made by transmitting an ultrasonic signal of periodic waveform by means of transmitter (10) towards a target (16), receiving the echo at receiver (14), measuring the phase difference between the transmitted and received signals using a phasemeter (18), adjusting the transmitted signal frequency of a manually adjustable variable frequency oscillator (12) and measuring the resulting phase difference between the transmitted and received signals, and computing from the known transmitted signal frequencies and phase differences, a value for the range of the target (16). In an alternative arrangement, the pair of transmitted signal frequencies used may be such that they render the transmitted and received signals in phase but in such a way that the number of wavelengths spanning the path of travel differ by an integral number, eg 1, of wavelengths. <IMAGE>

Description

SPECIFICATION Ultrasonic range finding This invention relates to ultrasonic range finding.

It is well-known to measure range by measuring the transit time taken for an ultrasound pulse travel to and return from a target. It is also known to employ a phase measuring method, as described in "Ultrasonic Testing of Materials" (J and H Krautkramer), Third Edition, Page 286.

The known phase measuring method involves the use of continuous waves of constant frequency and comparing the phase displacement of the echo with respect to the transmitted signal. This necessarily means that, if the range is greater than one wavelength, the approximate distance must be known and consequently the method does not provide a direct measure of the absolute value of the range.

The object of the present invention is to provide an improved method for ultrasonic range finding.

According to one aspect of the present invention there is provided a method of ultrasonic range finding of a target comprising transmitting a first signal of predetermined frequency towards the target and receiving the resulting echo, transmitting a second signal of a predetermined but different frequency towards the target and receiving the resulting echo, determining the phase relationships between each transmitted signal and its respective echo and deriving from said frequencies and said phase relationships a measure of the range of the target.

According to a second aspect of the present invention there is provided a method of ultrasonic range finding of a target comprising transmitting a signal having a periodic waveform towards the target and receiving the resulting echo, varying the frequency of the transmitted signals to derive, for two different frequencies of the transmitted signal, phase relationships between the transmitted and echo signals which differ by 360" or an integral multiple thereof, and deriving from said frequencies a measure of the range of the target;; The latter aspect of the invention may be implemented for example by initially adjusting the frequency of the transmitted signal until the transmitted and echo signals are phase, recording the frequency fl at which this condition prevails, adjusting the frequency of the transmitted signal to shift the relative phase between the transmitted and echo signals until the two signals are again in phase, recording the new frequency f2 at which the in-phase condition prevails and deriving the range D from the difference between the frequencies f1 and f2 using the relationship D=c/2F where F is the absolute value of the difference between f1 and f2 and c is the velocity of sound in the particular medium-which may be liquid sodium for example where the method is employed for measurements under sodium in liquid metal cooled nuclear reactors.

The invention will now be described by way of example only with reference to the accompanying drawing, the sole Figure of which illustrates diagrammatically apparatus for carrying out the method of the invention.

The apparatus comprises a continuous wave ultrasonic transmitter 10 energised by means of a manually adjustable variable frequency oscillator 12, an ultrasonic receiver 14 for receiving the echo produced as a result of reflection of the transmitted signal from a target 16 and a phase meter 18 for measuring the phase difference between the transmitted signal and the received signal (after the latter has been amplified by amplifier 20). The phase meter 18 may include an indicator 22 for providing the operator with a visual output of the measured phase difference.

Assuming the distance between the transducers 10, 14 and the target is D/2, it will be seen that at frequency fl 6 D=n1 + . 1 (1) 360 where A1 is the corresponding wavelength, 0 is the relative phase between the transmitted and received signals and n is an integer representing the whole number of wavelengths spanning the path extending from the transmitter to the receiver.

If the frequency of the oscillator 12 is now adjusted to a frequency f2 close to f1 then 62 D = nA2 + . A2 (2) 360 solving for n, 1 (O2-161) n= . (3) 360 (A,-A2) and substituting for n in (1) and using the relation c=f c 0 2 D= . (4) f1-f2 360 and hence the range of the target may be readily determined.

In liquid sodium using 5 MHz signals at 250"C, a phase change of 360" is equivalent to a change in target range of 0.25mm. Simple phasemeters are available which are capable of measuring phase differences to a precision of 1/100 of a cycle and hence it will be seen that target ranges can be measured to a high degree of precision.

If desired, the foregoing method may be simplified by using frequencies f1 and f2 which both render the transmitted and received signals in phase but in such a way that the number of wavelenths spanning the path of travel differ, eg by 1. Thus, initially, the frequency of the oscillator 12 is adjusted to a frequency f1 in which the transmitted and received signals are in phase, ie the distance D is spanned by a whole number of wavelengths and D=nA, (5) If the frequency is increased until the two signals are again in phase but so that D is now spanned by n+1 wavelengths then D=(n+1) A2 (6) solving for n, n=A2 (A1-A2) (7) substituting for n in (5) gives D=A1 A2 (A1-A2) (8) ie D=c/(f2-f1) (9) and hence the target range can be determined directly from the frequency difference, assuming the velocity of sound c for the medium is known at the temperature prevailing.

The range calculations may be performed automatically by means of a microprocessor. Thus, as shown in the drawing the analogue output of the phase meter 18 is digitised by means of A to D converter 24 and fed along with the output of the frequency meter 26 to a microprocessor 28 via parallel registers 30. The microprocessor is programmed to perform the calculations and may provide a read-out via a printer and/or'digital display.

Claims

1. A method of ultrasonic range finding of a target comprising transmitting a first signal of predetermined frequency towards the target and receiving the resulting echo, transmitting a second signal of a predetermined but different frequency towards the target and receiving the resulting echo, determining the phase relationships between each transmitted signal and its respective echo and deriving from said frequencies and said phase relationships a measure of the range of the target.

2. A method of ultrasonic range finding of a target comprising transmitting a signal having a periodic waveform towards the target and receiving the resulting echo, varying the frequency of the transmitted signals to derive, for two different frequencies of the transmitted signal, phase relationships between the transmitted and echo signals which differ by 360 or an integral multiple thereof, and deriving from said frequencies a measure of the range of the target.

3. A method as claimed in Claim 2 including initially adjusting the frequency of the transmitted signal until the transmitted and echo signals are in phase, recording the frequency f1 at which this condition prevails, adjusting the frequency of the transmitted signal to shift the relative phase between the transmitted and echo signals until the two signals are again in phase, recording the new frequency f2 at which the in-phase condition prevails and deriving the range D from the difference between the frequencies f1 and f2 using the relationship D=c/2F where F is the absolute value of the difference between f1 and f2 and c is the velocity of sound.

4. A method of ultrasonic range finding substantially as hereinbefore described with reference to the accompanying drawings.