GB2153998A

GB2153998A - Apparatus for measuring distance ultrasonically

Info

Publication number: GB2153998A
Application number: GB08501252A
Authority: GB
Inventors: John Alexis Mardas
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-01-20
Filing date: 1985-01-18
Publication date: 1985-08-29
Also published as: HK74189A; GB8501252D0; GB2153998B; GB8401617D0

Abstract

The apparatus comprises: a transmitter US1 for transmitting an ultrasonic signal to an object whose distance from the apparatus is to be measured; a receiver US2 for receiving a reflected signal from the object; a control unit including timing means adapted to measure time lapsed between transmission of the ultrasonic signal and reception of the reflected signal, and calculating means to calculate the distance between the apparatus and the object using a value for the speed of the transmitted and reflected signals in air; variable voltage generating means whose voltage controls the timing means and is dependent on ambient temperature whereby variations in said speed are compensated; and indicating means LCD to indicate a value of said distance. The control unit may be programmed by switches SW2-7 to multiply a current distance value with stored perpendicular distance values to calculate areas and volumes. The apparatus is particularly suitable for determining the dimensions of a room. <IMAGE>

Description

SPECIFICATION Apparatus for measuring distance This invention relates to an apparatus for measuring distance, for example for ascertaining the dimensions of a room.

In accordance with one aspect of the present invention, there is provided an apparatus for measuring distance, the apparatus comprising: a transmitter for transmitting a signal to an object whose distance from the apparatus is to be measured; a receiver for receiving a reflected signal from the object; a control unit which emits a first signal to the transmitter for transmission to the object and which receives a second signal from the receiver, the control unit including timing means adapted to measure time lapsed between emission of the first signal and reception of the second signal, and calculating means to calculate the distance between the apparatus and the object using a value for said lapsed time and a value for the speed of the transmitted and reflected signals in air;; a variable voltage generating means whose voltage controls the timing means and is dependent on ambient temperature whereby variations in said speed are compensated; and an indicating means to indicate a value of said distance.

The apparatus may further comprise a further variable voltage generating means, whose voltage controls the timing means and is dependent on ambient altitude and humidity, whereby variations in said speed due to altitude and humidity are compensated.

The calculating means may be capable of calculating, from first and second values for said distance, an average value to be indicated by the indicating means.

Alternatively, the indicating means may be capable of indicating successive values for said distance.

In accordance with another aspect of the present invention, there is provided an apparatus for measuring distance, the apparatus comprising: a transmitter for transmitting a signal to an object whose distance from the apparatus is to be measured; a receiver for receiving a reflected signal from the object; a control unit which emits a first signal to the transmitter for transmission to the object and which receives a second signal from the receiver, the control unit including timing means adapted to measure the time lapsed between emission of the first signal and reception of the second signal and calculating means to calculate the distance between the apparatus and the object using a value for said lapsed time and a value for the speed of the transmitted and reflected signals in air; and an indicating means to indicate a value of said distance, wherein the calculating means is capable of calculating, from values of two mutually perpendicular distances calculated in succession, a desired area, and, from values of three mutually perpendicular distances calculated in succession, a desired volume.

Preferably the control unit comprises a microcontroller driven by a crystal controlled oscillator.

The indicating means is conveniently an LCD display, but it may be any other display, for example a display with provision for a verbal indication to be made via a speech synthesiser.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a circuit diagram of an apparatus in accordance with an embodiment of the present invention; and Fig. 2 is a block diagram of another embodiment of the present invention.

Referring to Fig. 1 the first embodiment comprises a microcontroller IC1, for example such as is manufactured by Motorola, driven by a crystal XT1 controlled oscillator or a ceramic resonator. A second, temperature controlled, oscillator IC2 drives the internal timer of the microcontroller.

The apparatus has as its power source a battery capable of supplying 6V, for example four 1.5V alkaline (AA) pen-cells.

The frequency of a temperature controlled oscillator IC2 tracks the variations in sound velocity due to changes in ambient temperature. Compensation for the change in sound velocity with ambient temperature is achieved by varying the oscillator frequency by applying a variable voltage to the oscillator IC2. It will be appreciated that, with the use of similar circuits, speed variations due to changes in altitude and/or humidity could also be compensated.

A transistor T7 functions as a temperature sensing probe and generates a variable voltage in accordance with ambient temperature, automatically recalibrating the apparatus according to air temperature variations. A multiturn potentiometer RV1 is used for fine calibration of the oscillator.

To make a measurement, a clear, flat target area which will permit the device to receive a clear echo is selected. A switch SW enables either switch SW1 or switch SW2 to be ON.

The rear of a unit housing the apparatus is placed against one end of the dimension to be taken and the appropriate switch depressed according to the desired operational mode (described in more detail hereinafter).

For long range measurements the surface from which the echo signal is being reflected should be firm and not made from an absorbent material such as soft fabric or carpet.

These surfaces have a tendency to absorb sound and give little or no echo, reducing the range of the apparatus according to the degree of absorption. Most surfaces will reflect the ultra-sonic signal, but the range of the apparatus will be dependent on the degree of signal absorption.

By making contact on switch SW1 or SW2, the microcontroller ICI starts a counter and generates a 40 kHz signal on pin 9. This is stepped-up by a transformer TR 1 which is connected on output pin 9 of the microcontroller IC1, and whose output drives the ultrasonic transmitter US1. A reflected signal from a target is received by an ultra-sonic receiver US2 and is current amplified by an FET T1 1 and a transistor T1 2 connected as an emitter follower. The amplitude of the reflected signal decreases with the distance travelled, and an electronic attenuator IC5 is incorporated to compensate for this effect, a linear-decreasing ramp from an operational amplifier IC6 being applied to the control input of the attenuator IC5.The height and slope of the ramp are adjusted by potentiometers RV2 and RV3 respectively. The ramp is reset at the leading edge of every 40 kHz burst which may occur at any period of between 2 to 5 pulses a second, dependent on distance from the target area.

The output of attenuator IC5 is connected to a voltage amplifier and filter IC6b, a detector circuit, and a comparator IC6c. The amplifier compensated signal is then voltage amplified and filtered by the dual op-amp circuit IC6b and is envelope detected by the detector circuit which drives the voltage comparator op-amp IC6c. The output of the comparator interrupts the microcontroller IC1.

On occurrence of an interrupt, the microcontroller reads the value of the counter and executes the necessary computations to convert this data to a distance. This information is presented in a multiplexed form on a 6 digit 7-segment LED display 100 for a period of approximately 1 50 milliseconds and then a new cycle is recommenced. The display 100 may be provided with an anti-glare filter.

With switch SW1 ON a repetitive linear measurement occurs. The microcontroller IC1 takes two measurements at a time and then computes and displays an average figure. Alternatively, with switch SW1 continually depressed, the display can be continually updated.

If no signal is echoed back and received for a period of approximately 250 milliseconds following a transmission burst, the processor generates an error signal, indicated by LED1, that the measurement being sought is beyond the range of the apparatus.

With switch SW2 ON, a single-shot measurement is employed. The microcontroller takes two measurements and displays an average figure. In the single-shot mode, the measurement is displayed for as long as SW2 is depressed and for a further period of 7 seconds following the release of SW2 during which time the information is stored in a memory for the purpose of further computations. If, within the period that the measurement is being displayed, SW2 is depressed for a second time, the new information is processed with the information already available in the memory for the purpose of computing an effective area. The result is displayed for as long as SW2 is depressed, and for a further period of 7 seconds following the release of SW2, and the information is stored in the memory for the purpose of final computations.A further depression of SW2 within the display period causes the microcontroller IC1 to take a final set of measurements for the computation and display of an effective volume. The volume information will be displayed for as long as SW2 is depressed and a further 7 seconds thereafter. A further depression of SW2 within the display period commences a new cycle starting with a linear measurement. If at any time within the 7 second delay period, a cancellation of the operation is required, depression of switch SW1 cancels the time constant by discharging capacitor C2 via diode D5 into IC3d.

The microcontroller is also capable, in addition to multiplying values of distances, of adding or subtracting such values.

A voltage doubler T9-T1 0 steps up the voltage of 6V supplied from the battery in order to supply the receiver and transmitter parts of the circuit with the required higher voltage of 9V. A voltage regulator 78L05 regulates the stepped-up voltage 9V down to 5V to drive the electronic attenuator IC5 and oscillator IC2 and for use as a voltage reference for the generation of the linear decreasing ramp from IC6.

The 6-digit LED display allows the display of up to 999999 cubic feet (or a suitable metric value) in the volume measurement mode. On linear distance measurements, the display operates as follows: the least significant digit displays quarters of an inch; the next 2 digits to the left separated by a decimal point display inches; and the following digits separated by a second decimal point display feet.

On area measurement the least significant digit displays 1 Oths of a square foot; and the following digits separated by a decimal point display square feet. No second decimal point appears in this mode.

On volume measurements, numbers on the display represent cubic feet and no decimal point is displayed.

It will be appreciated that appropriate adaption could be made for metric values to be displayed.

To obtain an accurate measurement, account must be taken of the physical length of the enclosure containing the electronic boards between the rear external surface of the enclosing box and the target. Therefore, a minor adjustment in the software may be required if cabinets of different dimensions are used allowing the microprocessor to add the physical length of the box to the computed distance and display the sum of both, which represents the distance from the point of measurement.

The maximum distance which can be measured with free-standing ultra-sonic transducers is greater than 33 feet for an echo from a proper target. The transducers may be placed in remote locations to obtain measurements of awkward distances. However, with the addition of simple, narrow-angle acoustic horns, which may be part of the unit or external add-on devices, the maximum distance which may be measured will be in the order of 100 feet. The unit may be manufactured of plastic.

If the microcontroller is a (68705) EPROM, of the type used on prototype evaluation boards, the current consumption of the apparatus is approximately 200mA. With a mass programmable version of the microcontroller, for example 6805P2, the current consumption is approximately 1 60my. A further economy on current consumption may be achieved with the use of a smaller LED display. The four 1 .5V AA alkaline cells have a typical capacity of two Ampere hours.

The apparatus is capable of a resolution of about i 1 /4 inch and an accuracy of about + 0.15% (between 0" and 40"C).

The apparatus may include a further comparator, for presetting a distance to be measured, there being provision for indicating when such distance has been attained.

For the purpose of recording information relating to the measured distances, a dual track micro cassette or other recorder could be connected to the apparatus for the purpose of recording verbal memoranda and/or displayed digital information.

Further information from the apparatus could also be transmitted in serial form over a pair of wires or through any other transmitting media for the purpose of remote monitoring, for example of continuously changing levels of silos or tanks; and a print out mechanism could be connected to the apparatus.

Referring to Fig. 2, the second embodiment comprises a microcontroller IC1, for example such as is manufactured by Texas Instruments, incorporating a crystal controlled oscillator and an Uncommitted Logic Array (ULA) or fully customised integrated circuit such as is manufactured by Ferranti Electronics Ltd., containing electronic circuits for the purpose of signal processing, display and voltage regulation.

The apparatus has as its power source a battery capable of supplying 9V, for example a PP3 layer battery.

Compensation for the change in sound velocity with ambient temperature is achieved by the use of circuits in the ULA. It will be appreciated that, with the use of appropriate sensors, speed variations due to changes in altitude and/or humidity could also be compensated.

A temperature sensing probe generates an input to the ULA which, in turn, presents the information to the microcontroller. A potentimeter RV1 is used for fine calibration of the instrument.

To make a measurement, a clear flat target area, which will permit the device to receive a clear echo, is selected. A switch SW1 switches the instrument on. The rear of a unit housing the apparatus is placed against one end of the dimension to be taken and switch SW2 is depressed.

For optimum range, the surface from which the echo signal is being reflected should be flat, solid and not made from an acoustically absorbent material.

By making contact on switch SW2 the microcontroller 1C1 generates a burst of 40KHz signal or a signal at another appropriate frequency. This is stepped up by a transformer TR 1 which is driven by a transistor Q1 and whose output drives an ultrasonic transmitter US1. A reflected signal from a target is received by an ultrasonic receiver US2 and is input directly to the ULA, IC2.

The amplitude of the reflected signal decreases with the distance travelled, and an electronic attenuator is incorporated in the ULA to compensate for this effect, a decreasing ramp being applied to the control input of the attenuator. The ramp is initiated at the start of every ultrasonic burst which may occur at a frequency of between 1 and 3 bursts per second depending on distance from the target.

The attenuated signal undergoes amplification and other signal processing prior to interfacing with the microcontroller, which executes the necessary computations to convert this data to a distance. This information is presented on a 6 digit 7 segment LCD display.

With switch SW2 depressed, a repetitive linear measurement occurs. If no echo signal is detected for a period of approximately 200 milliseconds following a transmission burst, the processor generates an error signal which is indicated by the display indicating that the measurement being sought is beyond the capability of the apparatus.

When switch SW2 is released, the current measurement is completed if in progress, and the last measurement is frozen on the display.

If switch SW3 is depressed an addition is performed and if switch SW4 is depressed a subtraction is performed.

If switch SW5 is depressed a multiplication is performed for the purposes of computing areas and volumes.

The ULA incorporates a voltage regulator circuit which drops the battery voltage by means of a transistor Q2. This circuit also detects low battery votlage and causes a low battery indicator to be illuminated on the display when the voltage drops below approximately 7 volts.

The LCD disPlay incorporates 6 digits and a number of annunciators. Switch SW6 selects imperial or metric units. In imperial mode distance is displayed in feet and inches, areas are displayed in ft2 and volumes are displayed in ft3.

In metric mode, distances are displayed in metres and centimetres, areas are displayed in m2 and volumes are displayed in m3.

Switch SW7 selects forward or reverse display. In forward mode the display is normal.

In reverse mode the display is reversed for the purpose of reading values from the opposite viewing direction for as long as switch SW2 is depressed.

In all modes the units are indicated by appropriate annunciators.

To obtain an accurate measurement, account must be taken of the physical length of the enclosure containing the circuit board. To allow for different sizes of enclosure, a minor adjustment in software is required.

The maximum distance which can be measured with free-standing ultra-sonic transducers is greater than 50 feet for an echo from a proper target. The transducers may be placed in remote locations to obtain measurements of awkward distances.

However, with the addition of simple, narrowangle acoustic horns, which may be part of the unit or external add-on devicesa, the maximum distance which may be measured will be in the order of 100 feet. The unit may be manufactured of plastic.

If the microcontroller is of the type used on prototype evaluation boards, the current consumption of the apparatus is approximately 200mA. With a mass programmable version of the microcontroller, the current consumption will be considerably less. An alkaline PP3 battery has a typical capacity of 0.5 Ampere hours.

The apparatus has a resolution of 2 inch and an accuracy of + 0.15% (between 0 C and 40"C).

For the purpose of recording information relating to the measured distances a dual track micro cassette or other recorder could be connected to the apparatus for the purpose of recording verbal memoranda and/or display of digital information.

Claims

1. An apparatus for measuring distance, the apparatus comprising: a transmitter for transmitting a signal to an object whose distance from the apparatus is to be measured; a receiver for receiving a reflected signal from the object; a control unit which emits a first signal to the transmitter for transmission to the object and which receives a second signal from the receiver, the control unit including timing means adapted to measure time lapsed between emission of the first signal and reception of the second signal, and calculating means to calculate the distance between the apparatus and the object using a value for said lapsed time and a value for the speed of the transmitted and reflected signals in air; a variable voltage generating means whose voltage controls the timing means and is dependent on ambient temperature whereby variations in said speed are compensated; and an indicating means to indicate a value of said distance.

2. Apparatus according to claim 1, which comprises a further variable voltage generating means, whose voltage controls the timing means and is dependent on ambient altitude and humidity, whereby variations in said speed due to altitude and humidity are compensated.

3. Apparatus according to claim 1 or 2, wherein the calculating means is capable of calculating, from first and second values for said distance, an average value to be indicated by the indicating means.

4. Apparatus according to claim 1 or 2, wherein the indicating means is capable of indicating successive values for said distance.

5. An apparatus for measuring distance, the apparatus comprising: a transmitter for transmitting a signal to an object whose distance from the apparatus is to be measured; a receiver for receiving a reflected signal from the object; a control unit which emits a first signal to the transmitter for transmission to the object and which receives a second signal from the receiver, the control unit including timing means adapted to measure the time lapsed between emission of the first signal and reception of the second signal, and calculating means to calculate the distance between the apparatus and the object using a value for said lapsed time and a value for the speed of the transmitted and reflected signals in air; and an indicating means to indicate a value of said distance, wherein the calculating means is capable of calculating, from values of two mutually perpendicular distances calculated in succession, a desired area, and, from values of three mutually perpendicular distances calculated in succession, a desired volume.

6. Apparatus according to any preceding claim, wherein the control unit comprises a microcontroller driven by a crystal controlled oscillator.

7. Apparatus for measuring distance, substantially as herein described with reference to Fig. 1 of the accompanying drawings.

8. Apparatus for measuring distance, substantially as herein described with reference to Fig. 2 of the accompanying drawings.