AU697530B2

AU697530B2 - Distance measuring device

Info

Publication number: AU697530B2
Application number: AU24843/95A
Authority: AU
Inventors: Ronald John Wyber
Original assignee: PACIFIC RIM SYSTEMS Pty Ltd
Current assignee: PACIFIC RIM SYSTEMS Pty Ltd
Priority date: 1995-02-24
Filing date: 1995-07-05
Publication date: 1998-10-08
Anticipated expiration: 2015-07-05
Also published as: AU2484395A

Description

I -I r a I i UIIUI 1 P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 **ee °o S

ORIGINAL

0" COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "DISTANCE MEASURING DEVICE" The following statement is a full description of this invention, :l including the best method of performing it known to the Applicant:- 2 This invention relates to the determination of the distance to a remote target by acoustic techniques of the kind formerly called sound navigation ranging, but now usually referred to as by the contraction sonar.

Conventional sonar devices function by emitting a high frequency or ultra-sonic sound pulse towards a distant target, detecting the echo or reflected pulse from the target, measuring the time interval between the emission of the pulse and its return from the target, and calculating the distance of the target from the device, having regard to the known velocity of sound in the medium between the device and the target.

0 Sonar was proposed initially for the detection and location of underwater targets, and has been developed to a very sophisticated level in respect of that usage. The present invention proposes to use4 0, 0e analogous devices in air.

15 The present invention arose in response to a need to measure the depths of boreholes such, as those typically used for the emplacement of explosives in mining and quarrying operations. Hitherto such measurements have been determined by plumbing the hole using a 0:weighted tape or the like. This has been -a time consuming and laborious operation, and the present invention was developed to alleviate those deficiencies in the prior art.

In experiments leading to the present invention it was found that conventional sonar equipment was unsuitable for application to the depth measurement of boreholes. Attempts to use conventional equipment at the mouth of a borehole in attempts to detect an echo from the bottom of the borehole were unsuccessful because of multiple iI s

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f 11 0* 0 *o 0 0000 0 00 0 On 0 3 echoes and reverberations from the walls of the borehole, which masked the echo from the bottom and made accurate and repeatable measurements impossible.

According to the invention, the outgoing acoustic pulse is carefully shaped and its frequency selected to avoid such reverberation and, for preference, the returned signal is heavily filtered to largely remove the acoustic effects of machinery routinely operating on mine sites.

The invention consists in measuring apparatus for determining the distance to a remote target of the kind comprising an emitter transducer for emitting a sound pulse, a detector transducer for receiving a reflected pulse from a target surface, and electronic means comprising timer means to measure the time interval between the time of emission and the time of detection, and calculator means to calculate the distance to the target having regard to the time interval and the velocity of sound 15 in the intervening medium, characterised in that the frequency of the emitted sound pulse is no more than 500 cycles per second.

In preferred embodiments the equipment is further characterised in that the emitted pulse has a maximum duration of two cycles of substantially full amplitude.

In preferred embodiments the equipment is a self-contained, battery powered unit and said electronic means further comprise means to display and preferably store the distance of the target. For preference the electronic means also include a thermometer providing an electrical signal proportional to the ambient medium temperature, and the calculator means take into account the variation of the speed of sound in the medium with variation of the temperature.

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4 By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the accompanying drawings.

Figure 1 is a block diagram of a measuring apparatus according to the invention.

Figure 2 is an illustration of the wave form of the pulse emitted by the apparatus of figure 1.

The illustrated apparatus is suitable for determining the length of a borehole. It comprises a small carry box 3 containing the electronic means and a separate transceiver unit 4 comprising an emitter transducer and a detector transducer. The box 3 is preferably furnished with shoulder straps to facilitate it being carried from place to place.

The transceiver unit 4 is adapted to be positioned at or within the mouth of a borehole and to transmit a sound pulse into the borehole and receive reflected sound therefrom. For preference several transceiver units 4 may be provided. Each will function interchangeably with the electronic means within the box 3. Each such unit comprises a loudspeaker 5 and a microphone 6, suitably mounted and shrouded in either an aluminium or PVC housing for protection. The smaller units may have a 10 cm diameter speaker, which is suitable for boreholes of up to say 30 cm diameter. A larger transceiver unit may have a 15 cm speaker and although larger and heavier is able to successfully measure boreholes up to 40 cm in diameter with depths to 80 metres.

The transceiver unit 4 may be mounted onto a telescopic pole, for example a 1.2/2.4 metre telescopic aluminiumn pole, via about 0.5 metres

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of flexible conduit. This enables it to be positioned at the mouth of a borehole, even though the hole in question may not be easily closely approached by the operator. The unit 4 is connected to the electronic means within the box 3 by an appropriate, extensible, multi-core cable 7 extending through the pole to the box, for example a 1.5 metre curly cord terminating in one half of a conventional 8 pin circular connector.

The electronic means comprise a microprocessor 8, in this instance that microprocessor is an 8 bit CMOS micro-controller with an internal Analogue to Digital Converter (A/D CONV), an internal erasable programmable memory (EPROM) with a storage capacity of at least 8 Kilobytes for storing the software, and peripherals connected to the IN/OUT terminals of the microprocessor.

4 11% e..e Those peripherals include a key pad 9 that is permanently accessible or is accessible when a lid of the box 3 has been opened or removed, a display unit, for example a liquid crystal display (LCD) and a power controller 11.

measurement may be initiated by an operator pressing a button .V ~of the key pad 5 to instruct the microprocessor to proceed. At the same 0 time the operator may input a code to identify the borehole and a temperature value, being an estimate of the air temperature within the borehole. The depth of the borehole is then displayed along with the identifying code, within about 2 seconds on the display screen The electronic means are powered by a battery 12 housed within the electronics enclosure box 3. It may be a 12 volt 1.3AH sealed Lead Acid battery. This provides enough capacity for a normal days operation with some to spare. The power supply for the microprocessor 8 and its 6 internal logic is provided by a power control 11 which regulates the 1 2v battery supply to 5 volts. A power logic circuit is preferably provided to shut the power supply down after approximately 30 seconds of inactivity to preserve battery energy. A simple battery charger circuit 13 is incorporated to allow the battery to be charged in situ from a conventional AC general purpose power outlet. Alternatively an external charger 14 may be used, being an 1 8v DC power pack, connected via a front panel connector. The battery 12 is preferably of the sealed leadacid type to make re-charging easy and to avoid the inconvenient memory effects associated with NiCad batteries.

The electronic means generate the output pulse waveform and receive and process the returned acoustic signal under the control of the microprocessor 8.

7 The pulse is stored as a linear array of, say, 90 samples within the EPROM memory and is read out under control of the microcontroller when the "Measure" button is pressed. This stream of 8 bit digital samples is fed to an external 8 bit Digital to Analogue converter chip 15 at a rate of, say, 10,000 samples per second. The resulting analogue waveform is applied to the speaker 5 via a power amplifier 16 fed from the raw 12v battery power supply.

The returned acoustic signal from the microphone 6 is amplified and filtered with an active 4 pole filter 17 centred on 380 Hz. This signal is then applied to the Digital to Analogue converter within the microcontroller 8 which samples the waveform at, say, 2304 samples per second. Say 1024 samples are taken, which corresponds to a maximum borehole depth of approximately 80 metres.

411 7 The sampled waveform is then cross-correlated with the outgoing waveform re-sampled from 10,000 to 2304 samples per second. The resulting corrollelogram represents a filtered version of the returned signal in the time domain which is then analysed to find the peak value.

The corresponding sample number is then used to compute the total time taken for the pulse to travel down the hole and back up again.

This time interval is then used to compute the depth of the hole. The speed of sound used to compute the distance is corrected for the effects of temperature using the temperature set in by the operator.

"Ou"AUVA16 1 0 *0 *a e o a* eo a The display 10 may be a 24 character by 2 line Liquid Crystal Display (LCD) which is controlled directly from the Micro-controller I/O lines. I/O lines are also used to access a storage memory 18, which may be a 32 kilobyte Non Volatile Random Access Memory (RAM) chip.

This RAM chip 18 has an internal Lithium battery to preserve stored 15 data under all circumstances including low 12v battery voltage and absence of the battery 12. The storage time is approximately ten years after the chip is first powered up.

The pulse length is largely determined by the minimum hole depth 44*0 to be measured. In air at 20 0 C, sound travels 1 metre in approximately 20 2.9 ms, therefore, for a 5 metre hole, the interval between pulse out and pulse in is 29 ms. The preferred pulse length, as shown in figure 2, is 9 ms.

The frequency of' the pulse is a compromise between high attenuation and the need for large speakers at the low end and by the effects of reverberation at the high end. The effective range is 10 Hz to 500 Hz. The frequency used is 380 Hz. As may be seen from figure 2 pulse shape has a full amplitude over about 1.5 cycles only.

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:g The signal to noise ratio of the returned pulse depends on: i Power of the transmitted pulse ii Attenuation of the pulse on the round trip iii Attenuation on reflection from the bottom of the hole iv Coupling losses on entry and exit of the pulse to/from the transceiver unit v Prevailing noise level in the hole.

For this exemplary embodiment, the power into the speaker is 4 Watts rms and the impedance of the speaker is 8 Ohms. This gives adequate S/N ratio with the range of transceiver units for depths up to metres in a typical mining acoustic noise environment.

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Claims

1. Measuring apparatus for determining the distance to a remote target of the kind comprising an emitter transducer for emitting a sound pulse, a detector transducer for receiving a reflected pulse from a target surface, and electronic means comprising timer means to measure the time interval between the time of emission and the time of detection, and calculator means to calculate the distance to the target having regard to the time interval and the velocity of sound in the intervening medium, characterised in that the frequency of the emitted sound pulse is no more than 500 cycles per second.

2. Measuring apparatus according to claim 1 further characterised in that the emitted pulse has a maximum duration of two cycles of substantially full amplitude.

3. Measuring apparatus according to claim 1 or claim 2 15 wherein said electronic means further comprise means to display the distance of the target.

4. Measuring apparatus according to any one of the preceding claims wherein said electronic means further comprise means to store the distance of the target.

5. Measuring apparatus according to any one of the preceding claims wherein the electronic means also include a thermometer providing an electrical signal proportional to the ambient medium temperature, and the calculator means take into account the variation of the speed of sound iii the medium with variation of the temperature. Ij 4 i I ii i i i i\ i 1 a I 1 i; I I-

6. Measuring apparatus according to any one of the preceding claims wherein the emitter transducer and the detector transducer form a separate transceiver unit connected to the electronic reans.

7. Measuring apparatus according to claim 6 comprising at least one further separate transceiver unit, each further unit comprising an emitter transducer and a detector transducer and each unit adapted to function interchangeably with the electronic means.

8. Measuring apparatus according to any one of the preceding claims wherein the electronic means comprise a microprocessor having a micro-controller with an internal Analogue to Digital Converter, an gb- °internal erasable programmable memory, and peripherals.

9. Measuring apparatus according to claim 8 wherein the peripherals include a key pad that is permanently accessible or is readily accessible, and a power controller.

10. Measuring apparatus according to any one of the preceding ~claims wherein the apparatus is a self-contained, battery powered unit.

11. Measuring apparatus substantially as hereinbefore described with reference to the accompanying drawings. Applicant PACIFIC RIM SYSTEMS PTY. LTD. Date 03 July 1995 Attorney ROBERT G. SHELSTON F.I.P.A.A. of CARTER SMITH BEADLE I r- 1 ABSTRACT Measuring apparatus for determining the depth of a borehole comprises an emitter transducer 5 able to be positioned at the mouth of the "rehole for directing a sound pulse down the borehole, a detector tnwcducer 6 adjacent the emitter transducer for receiving an echo from the bottom of the borehole and electronic means 3 comprising timer me af to measure the time interval between the time of emission and the time oT detection and calculator means to calculate the depth of the borehole having regdAd to the time interval and the velocity of sound in air at the temperature pertaining in the borehole, characterised in that the frequency of the emitted sound pulse is no more than 500 cycles per second. Figure 1 .444~ oB 4 4*4 044 I 4.44 4 4 *44 IT f