WO1990008966A1

WO1990008966A1 - Ultrasonic distance measuring

Info

Publication number: WO1990008966A1
Application number: PCT/AU1990/000036
Authority: WO
Inventors: Gordon Edward Beazley; Colin Trevor Promasky; Leslie G. Richards; Robert Sidney Stirling
Original assignee: Hawk Measurement Systems Pty. Limited
Priority date: 1989-02-02
Filing date: 1990-02-02
Publication date: 1990-08-09
Also published as: IL93268A

Abstract

An ultra-sonic pulse-echo distance measuring apparatus including a transducer and an associated pulse generator to provide an ultra-sonic signal and a receiver to receive echoes of the signal produced by the transducer, the receiver having means whereby groups of echoes received from an individual signal from the transducer are incorporated into a table and from the table the shortest path echo, which is analogous to the distance to be measured can be obtained and the distance reading achieved; the apparatus can have means whereby the table can be continually updated to include changes in environmental variables which changes are incorporated into a dynamic character set which is stored in a nonvolatile memory. The transmitted pulse shape and frequency can be varied to compensate for low signal/noise ratios or if echo is embedded in the signal resulting from the transmitter being pulsed and subsequent ringing.

Description

ULTRASCNIC DI ST/&NCE N€ASURING

This invention relates to ultra-sonic pulse measuring apparatus and a method of operation of such apparatus.

The general principal of ultra-sonic pulse-echo distance measuring is known. For example sonar measures distances underwater by the transmission of a pulse of sound and measuring the time taken for the sound to be reflected from a target .

Theoretically this is very simple but practically, of course, one has to be sure that the signal identified as the reflected signal is in fact the first reflection from the article and there can be great complexities in ascertaining that the correct signal is being measured.

When such arrangements are used in enclosed spaces, such as in bins or silos which, for convenience will be referred to herein as bins, to measure the height of the contents this problem is exacerbated as the signal not only bounces off the required surface, the surface of the material in the bin, but also bounces off the sides of the bin and there can also be multiple reflections.

Also, because the surface of the material in the bin is usually somewhat broken it can be that the strongest reflected signals are not those from the surface but are rather some of the signals from the bin itself .

It is thus necessary to provide means whereby the correct signal is identified so that an accurate measurement of distance can be acheived.

When providing an ultra-sonic signal for such purposes it is necessary to ensure that the signal is transmitted into the area with maximum eff iciency, to give a powerful signal so that all significant echoes can be readily easily detected and measured .

The invention in its broadest sense provides an ultra-sonic pulse-echo distance measuring apparatus including a transducer and an associated pulse generator to provide an ultra-sonic signal and receiver to receive echoes of the signal produced by the transducer, the receiver having means whereby groups of echoes received from an individual signal from the transducer are incorporated into a table and from this table the shortest path echo, which is analogous to the distance to be measured, can be obtained and a distance reading achieved.

In order that the invention may be more readily understood we shall describe particular aspects of the invention being in an unltra-sonic pulse-echo distance measuring apparatus, means for improving the accuracy, repeatability, and reliability of the in applications where the shortest path echo as measured by the receiver is smaller than following multi path echos and embodying electronic circuitry and firmware which provides a table of parameters which describes the relationship between each of the related group of echoes under varying environmental conditions, reflecting surface conditions and d i s tance .

The apparatus comprises an electronics assembly and a transducer. The transducer is installed suitably so that it is in line with the Direction of movement of the material surface being monitored. The electronics assembly, which can include a pulse generator to actuate the transducer to provide pulses or pulse trains, a receiver which can detect the echoes or echo qroups and means, which can comprise firrrware and micro-processor control which can manipulate the echoes to form a dynamic table for use in comparison , and an output means which may be alphanumer i cal is installed at a convenient location. The transducer assembly by connection of a suitable length of specified electric cable.

This table of parameters is established and adjusted as time goes on and conditions changed. Statistical analysis is performed by the mi cor pr oc essor firrrware to yield data which characterizes the group of echoes and therefore enables the shotest path echo to be chosen from the group of echoes under subsequent operating conditions.

In another aspect of the invention, we provide a method of improving reliabi lity of ultra- sonic pulse-echo distance measuring apparatus by deriving characteristics of the transmission path through analysis of echo signals under varying environmental conditions.

From the results obtained, under controlled conditions, we produce a table of parameters which is then stored so that it is accessable for later measurements. This table is then accessed and used to derive the expected response to subsequent transmitted pulses automaticall and continuously.

As further measurements are obtained, a history of pertinent response characteristics is developed on the basis of changes in the environment. As the history is being developed a time- series analysis of response characteristics is performed. The result of this analysis becomes part of the succeeding analysis and so on unti l account has been taken of all relevant conditions.

The resulting dynamic parameter set is preferably stored in non-volatile memory so as to avoid loss of history in the event of power failure and, when completed, is available for comparison purposes to give a measurement on pulses being transmi t ted.

In a second aspect of the invention, we provide means for detection the echo in transmit/receive ultra- sonic pulse-echo apparatus where the reflection surface is at such a small distance from the transmit receiver that the echo signal is embedded in the signal which occurs as a result of the transducer being pulsed and its subsequent ringing.

The concept embodies electronic circuitry and microprocessor firmvare which allows control of the carrier frequency and receiver characteristics. Such also includes measurements of ringing signal characteristics and determination of the transducer undertones and overtones and the corresponding transducer and receiver filter responses.

Where it is determined that the reflection surface is at a dis tance within the "deadband", the transducer and receiver are operated at a suitable undertone or overtone frequency. The preferred frequency is determined from analysis of transducer and receiver response over a range of frequencies. At such preferred frequency the echo is passed by the filter whilst the ringing signal is substantially attenuated. ^"*"

A further aspect as part of the invention is the quick and reliable detection of the echo in ultra-sonic pulse-echo distance measuring apparatus in environments where echo is embedded is noise and echo magnitude to noise ratio is close to 0 dB. The circuitry and firrrware enables control of transmitted pulse shape carrier frequency and the frequency response of the receiver.

Such an arrangement enables measurement of relative noise signal pararmeters.

When the signal to noise ration is low, such condition is detected and the relevant parameters describing the noise are derived. Transmitted pulse shape and carrier frequency are then varied and the receiver characteristics are varied in harmony .

This yields corresponding variations in the echo shape whilst noise charac eristics remain relatively constant.

We also provide an isolated switching module which comprises a hybrid circuit block performing the function of an almost perfect solid state switch for routing ultra-sonic transducer signals, the switch having benefits far exceeding that of convent ional mechanical relays.

This module has the capacity of faithfully switching transmitted bursts of energy having very high voltage and current transients as well as swttchinq minute received signals with negligable contribution to noise.

The electronics assembly can be mated with any one of a number of different types of transducers (where types are class if ied by operating frequency, transmitted power and sensit ivity) and the electronics assembly is made to detect which type of transducer it is mated with and to automatically adjust its operating parameters to suit.

We prefer to provide an alphanumeric readout which can display messages in a number of different languages. By this means users can select from a list, the language of their choice for display of inf ormation.

Whi lst we have described herin certain aspects of the invention it is to be understood that these could be varied within the general disclosure without depart ing from the spirit and scope of the invent ion.

Claims

The Claims defining the invention are as follows:

1. An ultra-sonic pulse-echo distance measuring apparatus including a transducer and an associated pulse generator to provide an ultra-sonic signal and receiver to receive echoes of the signal produced by the transducer, the receiver having means whereby groups of echoes received from an individual signal from the transducer are incorporated into a table and from this table the shortest path echo, which is analogous to the distance to be measured, can be obtained and a distance reading achi eved .

2. An apparatus as claimed in claim 1 wherein further groups of echoes are added to the table on the transmission of pulses under varying environmental cond it ions .

3. An apparatus as claimed in claim 2 wherein a time-series analysis of the groups of echoes permits updating of the table to include any env ir ormen ta 1 variables.

A. An apparatus as claimed in any preceding claim wherein the dynamic character set comprising the table is stored in non-volatile memory.

5. An apparatus as claimed in any preceding claim wherein when the shortest path echo is embedded in the original pulse or its subsequent ringing, the transducer and receiver are operated at an undertone or overtone frequency .

6. An apparatus as claimed in claim 5 wherein the apparatus comprises a filter circuit which attenuates the original pulse and ringing therefrom.

7. An apparatus as claimed in claim 4 wherein, when the shortest path echo is embedded in noise, the parameters describing the noise are derived and the transmitted pulse shape and frequency are varied to provide an echo which can be separated from the noise and the receiver characteristics ae altered to accord with the characteristics of the altered transmitted pulses.

8. An apparatus as claimed in any preceding claim wherein the pulse generator which actuates the transducer can detect the operating cha rac ter is i tcs of the transducer and can provide a pulse to sat is f actora 1 ly drive the t ransducer .

9. An apparatus as claimed in any preceding claim wherein the receiver can operate to derive echo groups from different transducers which can sat is f actora 11 y be added to or compared with the table.

10. An apparatus as claimed in any preceding claim wherein the apparatus can provide an output in any required f orm.

11. An apparatus as claimed in claim 10 wherein the output is alpha numeric and wherein words can be displayed in different languages.

12. An apparatus as claimed in any preceding claim wherein the transducer is located in a volume to be measured and the pulse generator and the receiver are located externally thereof .