GB2060899A - Continuous measurement of changes in the distance between measuring points - Google Patents

Abstract

A flexible line 7 extends from the housing 1 of a position sensor arranged at one measuring point and is connected by loop 8 to the other measuring point. The line 7 is wound on a drum 6 which, through gearwheels 9, 14, 18, drives a potentiometer 20 against the load of a clock-spring 13. A voltage determined by potentiometer 20 is converted into a frequency modulated signal which is transmitted to a remote station, e.g. to monitor rock deformations in coal mining. <IMAGE>

Description

SPECIFICATION Continuous measurement of changes in the distance between measuring points This invention relates to a method for the continuous measurement of changes in the distance between measuring points, in particular for determining the effects of mine working in coal mining. The invention also relates to a position sensor for carrying out the method.

The distances between measuring points are measured for the most varied reasons, particularly in coal mining. Thus for example deformations or deformation rates of the rock can be determined with respect to time components by monitoring the distances between such measuring points. Similar path measurements are for example desirable in order to monitor any change in the position of the conveying device in dipping faces and galleries. In this case, such measurements are generally made using tape measures or foot rules.

In order to make such measurements, the measuring points have to be sought underground, and this generally requires the use of at least two people. As the measurements have to be repeated at intervals of a few days, such checks naturally lead to high personnel costs. In particular, if such measurements are to be used in order to investigate the deformation behaviour of the rock, the measurements have to be made at short intervals as otherwise the cross-sectional losses which occur in the underground working can only be later made good by high labour, material, and machine expenditure.

In order in particular to save personnel costs it has therefore been attempted to continuously monitor changes in length between two measuring points with the aid of recorders. The recorders are installed between the measuring points, and continuously record the path position change. By this means, the measurement cost is indeed reduced; however, for the purpose of reading and evaluating the measured values it is still necessary for the individual measuring points to be continually inspected and checked by personnel.

The present invention is therefore concerned, in particular, with monitoring the effects of mine working, in particular rock deformation, by the continuous measurement and evaluation of changes in the position of measuring points. In addition, a position sensor is to be provided which can be connected to the audio frequency transmission systems available underground, and which can treat distance changes of various orders of magnitude.

The invention provides a method in which the straight-line or approximately straight-line deformation paths are converted mechanically into a circular path, the angular variations arising thereby are used in order to influence an applied voltage, transformed into electrical measured values, and then converted into frequency modulated measurement signals.

Such a method makes it possible to convert changes in the distance between measuring points into signals which with the aid of the audio frequency transmission systems already present underground can be fed to an evaluation station positioned above ground, where they can be continuously and centrally indicated and evaluated. Inspection of the individual measuring points therefore becomes uncessary, or becomes limited to cases in which because of abnormalities an expert opinion by an operator becomes absolutely necessary. By this means it is possible to obtain early recognition of rock deformation, conveyor position changes, creeping rock faces, and other such incidents, and to reduce them or completely to halt them by immediate corrective measures.

For carrying out the method, the invention provides a position sensor, which is disposed between the measuring points and senses the occurring measurement changes, wherein 5 pre-stressed rotary drive with a cable line is provided, on a common shaft of which there is disposed a gear wheel which engages with a further gear wheel driving a precision potentiometer connected to an electrical circuit which is supplied by way of remote supply devices and into which a precision voltage/ frequency converter is connected.

With the aid of such a position sensor the changes in the distance between measuring points are converted in a simple manner into measuring signals, so that such a measured value transmitter can be connected to the audio frequency transmission systems used in coal mining, and is also suitable for almost all distance changes to be measured. The measured path is transmitted by means of the prestressed rotary drive to the precision poten tiometer, where it is converted into an electrical signal and then transmitted over the normal audio frequency transmission system. By choosing various carrier wave frequencies a large number of position sensors can be connected to the above-ground evaluation station by means of one and the same line.The demoduiated measuring signal can be made visible above ground in measuring instruments such as recorders and indicators, and can be recorded or fed directly to computers and evaluated. For the measurement itself or for the recording of the measured values, it is not necessary for a position sensor of this type to be examined by operators.

It is particularly advantageous for the indi viduai parts of the position sensor to be fitted into an explosion-proof housing in such a manner that not only is accurate sensing and transmission of the measured value assured, but at the same time paths of from a few centimetres to several metres can be continuously and accurately monitored by replacing individual parts. Mechanical parts such as cable drums and individual gear wheels can be easily interchanged, so that by choosing the drum diameter or the step-up or stepdown ratio and by choosing the potentiometer, the device can be set for the expected distance changes and paths.Thus, the use of a rotary potentiometer capable of up to 10 revolutions gives a substantially greater operating range than the operating range given by the normal known rotary potentiometers having an operating range of O to 340 . Replaceability of the individual parts can be ensured if they are individually fixed by means of a connection plate.

An oscillator and an integrated circuit may be associated with the precision voltage/frequency converter in order to increase measuring accuracy, and matching difficulties are balanced by means of transistors.

After the fitting and adjusting of the position sensor, no inspection or maintenance is necessary afterwards, so that a large number of measuring points can be monitored and evaluated by means of data processing systems without any continuous use of personnel.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a position sensor; Figure 2 is a circuit diagram of the position sensor; and Figure 3 is a block diagram showing the connection between the position sensor and an audio frequency transmission system.

Fig. 1 shows a section through the housing 1 of a position sensor which is of explosionproof construction to satisfy underground requirements. The individual parts are disposed on a connection plate 4 in the interior, i.e. on an inner wall 2 of the housing 1.

The sensor includes a rotary drive 5 comprising a drum 6 located on a shaft 10. A cable line 7 wound on the drum 6 extends through an eyelet 11 in the housing and is to be connected to a measuring point by means of a connection loop 8. The rotary drive 5 is connected to a clock spring 1 3 by way of mutually engaging gear wheels 9, 14. The clock spring 13, which is located together with the gear wheel 14 on a shaft 12, can be pre-stressed to keep the line 7 taut by means of a square shaft 1 5 and a tensioning device 1 6 to the necessary extent as dictated by the expected movements of the measuring point to be monitored relative to the fixed housing, which serves as the second measuring point.

The drum 6 and the gear wheels of the position sensor are so disposed that they can be easily replaced when the lid of the housing is removed. By this means it is possible to adapt the position sensor to the expected conditions without it being necessary to provide or mount a new sensor.

A gear wheel 1 8 which is located on the shaft 1 9 of a precision rotary potentiometer 20, is engaged with the gear wheel 9. When the amount of cable line wound on the drum 6 changes as a result of a change in the distance between the housing 1 and the measuring point to which the loop 8 is connected, the potentiometer shaft 1 9 is turned through an angle proportional to the change in distance. The potentiometer 20 is connected to an electrical part 22 which is screwed on to the mechanical part of the position sensor and which emits a signal representing the angular position of the potentiometer shaft.

The electrical part is shown in greater detail in Fig. 2 with the aid of a circuit diagram, wherein the electrical circuit is indicated overall by 23. The necessary electrical supply for operating the measuring device is talten from the normal remote supply devices, as shown in the blocle diagram of Fig. 3. The frequency modulated signals return by the same path, by which they are transmitted from the position sensor 35, through an audio frequency transmitter 36 and a remote decoupling device 37, to a frequency/voltage converter 38 connected directly to a recorder 39. The necessary electrical cable (not shown) emends through the wall of the housing 1 of the position sensor.

The direct current signal of 1 to 3 V produced by the precision potentiometer 20 is fed to the input of the precision voltage/frequency converter 24. This unit comprises an oscillator having a frequency of between 500 and 1 ,000 Hz. The frequencies are converted to the frequency range 5 to 4 5 Hz by way of an integrated circuit 26, and are available at the output of the electrical circuit or switching circuit 26. This frequency range is suitable for processing in all normal underground transmission systems. Any possible matching difficulties are corrected by means of the transistors 28, 29, which switch on the one hand from zero potential against the positive supply voltage and on the other hand from the positive supply voltage against zero potential. The necessary intrinsically safe supply voltage of + 10 V to + 1 5 V for supplying the electronic system is stabilised inside the device to +8 V with the aid of an IC component 30, so that switching is independent of external voltage fluctuations.

Claims (11)

1. A method of continuously monitoring changes in the distance between two measuring points, comprising providing a mechanical connection between the measuring points, mechanically converting variation of the length of the mechanical connection into angular variation on a circular path, producing a voltage dependent on the angular variation, and converting the voltage into a frequency modulated measurement signal.

2. A position sensor for continuously monitoring changes in the distance between two measuring points, comprising a rotary member which is to be mounted at a first measuring point, a flexible line wound on the rotary member and intended to extend to a second measuring point, pre-stressing means for acting on the rotary member in order to keep the line taut, a potentiometer connected to the rotary member by a mechanical transmission, and a voltage/frequency converter connected to the potentiometer.

3. A position sensor as claimed in claim 2, in which the rotary member has a shaft carrying a gear wheel which engages with a further gear wheel driving the potentiometer.

4. A position sensor as claimed in claim 2 or 3, having an explosion-proof housing from which the flexible line and an electrical cable extend.

5. A position sensor as claimed in any of claims 2 to 4, in which the pre-stressing means comprises a clock spring acting on a shaft connected to the rotary member by a geared transmission.

6. A position sensor as claimed in claim 5, in which the rotary member, the gear wheels, and the clock spring are associated with a connection plate which is releasably fixed to an inner wall of the position sensor.

7. A position sensor as claimed in claim 6, in which the potentiometer is releasably fixed to the connection plate.

8. A position sensor as claimed in any of claims 2 to 7, in which an integrated frequency-conversion circuit is connected to the output of the voltage/frequency converter.

9. A position sensor as claimed in claim 8, in which transistors are connected between the integrated circuit and a signal output of the position sensor.

1 0. A method of continuously monitoring changes in the distance between two measuring points, substantially as described with reference to the accompanying drawings.

11. A position sensor substantially as described with reference to, and as shown in, Figs. 1 and 2 of the accompanying drawings.