ES2338512B2 - MULTIPULSE SYSTEM FOR DISTANCE MEASUREMENT AND CABLE LENGTH. - Google Patents

Abstract

Multi-pulse distance measurement system and cable length

The system proposed in the present invention will be based on multiple repetition of a pulsed signal that allows measure distances and cable lengths without contact with them, with millimeters precision, with ranges that go from decimeters to several kilometers depending on the times used in the repetition of the pulses.

At both ends of the distance to be measured is find an electronics responsible for repeating and forwarding back the pulse to the other end. This electronics is based on a monostable precision that every time you receive a pulse generates a new pulse with a preset delay allowing the computation of The length to measure.

Description

Multi-pulse distance measurement system and cable length

Technical sector

Electronic instrumentation, devices electronic measurement of physical parameters, sensors and electronic transducers

Introduction

At present the measurement of distances without contacts is basically made by measuring the time of flight, the time it takes for a wave to travel between the extremes of the distance to measure. The flight time is proportional to the distance to be measured, so that d = t x v, where d is the distance a measure, t the time taken by the wave to reach from one end to another of the distance to be measured and v the propagation speed of the wave between the ends to be measured.

Depending on the type of wave, the devices can be qualified in: sonar ultrasounds, which They use sound waves, lasers, which use light and devices radio frequency, when an electromagnetic wave is used.

On the other hand they are classified according to the distance to be measured, the necessary precision, depending on the measurement in indoor or outdoor and the allowed cost is used one or the other technology.

For measuring distances less than 10 meters with millimeters to centimeters accuracy and low cost Ultrasound or sonar is the most used technology.

When submillimeter accuracies are required and distances from millimeters to tens of meters the laser usually Be the technology used. The cost depends a lot on the range and the desired accuracy When the laser beam sweeps, it stops detect distances from one point to different points in the environment, the device is called "range finder". This device is widely used by robots or autonomous navigation vehicles for Detect possible obstacles along the way. Given the complexity range finders technique cost is usually high.

For measurements from tens of meters to several kilometers and usually with low precision devices Radio frequency are those used, called RADAR in the Most cases

The distance measurement is closely related to location systems, since measuring two or more distances where there is a common point it is possible to detect the position or location of that common point.

The main methods for systems Location are:

one.

TOA (Time of Arrival) or Arrival Time, based on send a pulse from the point to be located and see how long it takes in getting the answer from 2 or more repeater stations, by triangulation position is calculated with low accuracy (tens of meters). The mobile phone network uses this system to location.

2.

TDOA (Time Difference on Arrival) or Difference of arrival times, is based on sending a signal from the mobile and see the time difference with which it reaches different stations base.

3.

AOA (Angle of Arrival) or Angle of Arrival. Is based in detecting the angle of arrival at the common point from several base stations, triangulation detects the position.

Four.

RSSI Received Signal Strength Indicator or Power of the received signal, this system is based on that to the captured signal by an RF receiver decreases with the square of the distance between sender and receiver, this method is not accurate because changes atmospheric can also attenuate the radio frequency signal in addition to the bounces that the signal has between transmission and reception they can attenuate or amplify the received signal depending on the direct and reflected signal may or may not be in phase.

There are also techniques based on combination of 2 or more of the methods described above.

Both the TOA and TDOA flight time It is behind the location system.

Whenever you talk about outdoor location the GPS Global Positioning System, system TDOA based where the base stations are satellites artificial geostationary developed by the government of United States, the Russian alternative is called GLONASS and the European GALILEO. GPS systems have had great acceptance in the market in recent years so its price has fallen considerably when working with various accuracies meters, finding GPS in the market at relatively low prices low.

The system proposed in the present invention will be based on multiple repetition of a pulsed signal that allows measure distances and cable lengths with millimeters accuracy with ranges ranging from decimeters to several kilometers depending on the times used in the repetition of the pulses, (see figures 2 and 3). It can also be used for mobile position determination (robots or similar), radiated signals, cable measurements.

Specifically for the calculation of distance or Cable length can be used any means of transmission provided that a pulse can be repeated between the ends to be measured and be sent simultaneously both ways.

State of the art

Various developments are known for the Measurement of distances by repeating pulses.

Document US4269506 discloses an apparatus for measure the influence of physical parameters on the length of a road. The GB591041 patent shows a radio method and system RF pulse emission navigation.

At the same time, the developments described in GB593151 and GB539952 describe a measurement system of radio time intervals and a method of measuring distance between two points in space through reflection of waves, respectively, based on the determination of flight time. In the system proposed here does not measure the flight time, by On the contrary, it is based on generating and measuring a frequency through the Endless repetition of an electric pulse that is sent between ends of the distance or length of the cable to be measured.

Among the systems disclosed for the measurement of distances you can also highlight a method and device to measure precisely the length using the reflectometry technique of time domain (EP0336025), in which a signal generator delivers a pulse on an electromagnetic transmission line at along which moves a target adapted to produce a partial reflection of the signal at the position along the line in which it is located. A flip-flop device detects the signal reflected, which together with processing means provides a measure precise of the length of the transmission line between its end Input and white.

This device that works with a single pulse, measuring the flight time on a cable or transmission line, You need to measure times in the PS range. But nevertheless, our system works with a pulse that repeats indefinitely between the ends of the distance or cable to be measured generating frequencies mainly between 1 and 1000 KHz depending on the range to be measured and the time taken in the repetition of the pulses. These frequencies correspond to periods between 1 and 1000 microseconds, times several orders of magnitude greater than that the device proposed in patent EP0336025 needs. He measuring immensely longer times greatly simplifies the design of the circuit for which components are required in this case common electronic devices, thus reducing the cost considerably Of the device.

On the other hand, there is a description included in document CN1598616 also published as
WO2005031258, close to the state of the art, and which is based on the determination of the period of the oscillation, at the same time the following pulse is emitted after the reception of the reflected pulse.

In addition, in our case, a development is provided based on frequency, being the emission of electronic pulses and continuous, while in the system described in CN1598616 the pulses are optical for which the use of mirrors is required for the repetition of the pulses.

On the other hand, the range of patent measures CN1598616 is 150 m and with resolution 15 mm both prefixed by the used electronics In our case, range and resolution are adjustable by repeater delay.

Additionally, electronics for Pulse repetition described herein is based on the use of monostable while in document CN1598616 requires an MC10131, a dual master-slave type D flip-flop

Finally, and as a summary, the main difference between our invention and the aforementioned, is that Our device plays with user adjustable delay for the repetition of the pulses. By this adjustment of the delays set the working frequency range and resolution as far.

Description of the invention

The proposed system is based on repetition continued from an electrical pulse that propagates through the distance to be measured in both directions (figure 1). At both ends of the distance to be measured is an electronics in charge of Repeat and forward the pulse back to the other end. Bliss electronics is based on a monostable precision that every time a pulse is received generates a new pulse with a delay preset (T_ {R} in Figure 1). Assume a zero distance to measure, the two extremes are superimposed, the time taken by The pulse to perform a cycle or period will be:

T = 2T_ {R}

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Since at both ends the same delay T_ {R} is introduced. If the two ends are separated a distance d the time taken by the pulse to perform a cycle will be:

T = 2T_ {R} + 2T_ {V} = 2 (T_ {R} + TV})

Where T_ {V} is the flight time or time used by the pulse-wave to travel from one end to another of the distance to be measured, from Terminal 1 to Terminal 2 one way and back see figure 1. Since the propagation speed is constant we will have to:

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where d is the distance to be measured and v The speed of propagation. Since the pulse is repeated indefinitely at both ends, such repetition generates a frequency f that can be expressed as the inverse of period T previously defined so you have that:

one

The appropriate selection of the repetition or delay time, identical at both ends, allows to set the maximum and minimum frequency for a given range of distances to be measured. On the other hand the resolution and precision of the measurement is directly related to the variation of the frequency versus the variation of the distance, mathematically \ Deltaf / \ Deltad. This relationship varies significantly with the delay time T_ {R} chosen. In figure 2 it is observed how both f and Δf decrease sharply and non-linearly with the increase of the distance to be measured, (note that the axis "y" in figure 2 is logarithmic). The most appropriate delay time T_ {R} will depend on the range of distances to be measured as well as the resolution and accuracy required in the measure of "d". In Figure 2 it can be seen that the resolution and accuracy increase when reducing the delay time T_R, but said reduction has the disadvantage of considerably increasing the frequencies to be measured which depending on the range can complicate the electronics.

The following table shows the variations of the measured frequency f for different times of TR delay, f0 is the frequency detected for distance 0, f1Km is the frequency detected for d = 1 Km, Δf0 is the variation of the frequency detected between 0 and 1 meter of distance to measure d., and finally Δf1Km is frequency variation per meter between 1000 and 1001 meters away d.

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Description of the figures

Figure 1: A block structure is shown of the device where the two terminals are appreciated: Terminal 1 and Terminal 2 representing the extremes of the distance to be measured or the ends of the cable whose length you want to measure, in this figure also appear the times used by the signal or pulse in your Endless repetition between terminals. These times are two: T_ {V} or flight time, time taken by the pulse to travel from to each other terminal and T_ {R} time taken by the pulse to be repeated in each terminal.

Figure 2: Graph showing how the frequency generated depending on the distance to be measured and the time T_ {R} used to repeat the pulse at each end or terminal

Figure 3: Graph showing the decreases in the frequency generated by increments in 1 meter of the distance to to size. These frequency decreases are directly related to the resolution of the measure as major changes in the frequency to be measured per meter of increase in distance, it implies greater capacity to solve in the resolution of the distance to measure. As in Figure 2, the decrements are shown in the frequency for different repetition times T_ {R}.

Embodiments of the invention

An example for the measurement of cable lengths that can be implemented through a microcontroller with an external clock running at 20 MHz. The main tasks of the microcontroller are:

one

Generate the first pulse that is sent from the Terminal 1 to Terminal 2.

2

Detect the frequency f generated using a counter of internal pulses of the microcontroller.

3

Convert the frequency f measured into distance d by equation 1.

In addition to the microcontroller mentioned, it you need to incorporate a monostable in each terminal to repeat the pulses and a radio frequency transmitter and receiver pair, or transceiver available in the market through manufacturers such as Easy radio, Rfsolutions, Radiometrix, Aurel or others.

When the system is used for measuring cable length, the pulses are sent directly through the cable whose length you want to measure not being used in this case radio frequency equipment. For the measurement of cable length, make a simple calibration consisting of measuring the speed of transmission of the pulse through the cable, v in the last of the previous equations. Just look at the frequency generated for a cable whose length is known and find v according to the aforementioned equation.

Depending on the range of distances or length of cables to be measured and according to the precision and resolution required in the measurement, the repetition time TR is adjusted, in this way to increase the accuracy and resolution has to decrease TR at the same time that the frequency variation must also be taken into account in the range of measurements.

In this way for distances of tens of meters (range of 10 to 100 m) a TR = 1 µS is recommended for that an accuracy of ± 1 mm is obtained. For larger ranges by example between 500 m and 1 KM a TR = 10 µS is recommended for that an accuracy of ± 10 cm is obtained.

To avoid interference between the two paths covered by the pulse, from terminal 1 to 2 and from terminal 2 to 1, two different radio carrier frequencies are chosen frequency. However, since this is an example to measure cable lengths are not necessary radio modules, being in this case a simple system calibration is necessary to detect the speed of propagation of the wave in the cable.

In this way a reliable system is achieved, Precise and economical for the measurement of cable length.

If you want to measure distances simply Radio modules should be added.

Claims (1)

1. Procedure for measuring distances and cable lengths characterized by:

TO)

Continuously circulate a single pulse of electro-magnetic, optical, ultrasonic or similar, that allows to be transmitted between the ends of the cable or distance to measure.

B)

Repeat with a controlled and form delay Continuous pulse to generate, in most cases, a frequency in the kilohertz range, measurable in any of the cable ends or distance to be measured.

C)

Control of the time it takes to repeat the pulse at each end to set the range of frequencies generated and the resolution most appropriate to each situation. The relationship between the generated frequency f , the delay time arbitrarily set by the user at each end T R, the distance to be measured d and the propagation speed of the wave ν, is described by the following equation:

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D)

Nonlinear variation of the frequency generated with the distance to be measured according to the following equation.

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