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New technologies for obtaining and transmitting aerology information

S. Shkundin
Moscow State Mining University

L. Utyakov
Oceanology institute, Russian Academy of Sciences

V. Zaidenwaurg
Ministry of fuel and Energy industry

ABSTRACT: A telemetry system with distributed sensors, measuring moving gas media is described. The use of inductive input and output from the communications line, which consists of single-strand shielded cable, and the self-contained measurement modules with inductive coupling, increases the operating reliability of the system and results in intrinsically save nongalvanic connections, applicable in the dangerous atmosphere. New means for airgas flow measurements and new means for this measurement information transmitting are described. The technology elaborated for measurements of airgas flow rate and velocity is brand new and implemented, for example, in the acoustics anemometers and spirometers. The sensor of the anemometer looks like cylinder channel with free cross section. Ceramics rings mounted inside the cylinder are radiators and receivers of acoustics vibrations. The sensor has unsurpassed characteristics: sensitivity, inertialesness, dynamic range. The new anemometers are already in usage at several coal mines of Russia for episodically manual ventilation control and now is being adjusted for monitoring systems.


1 INTRODUCTION

Accumulated experience of the monitoring systems operation indicates that the most frequent cause of failure is breakdown of cable insulation at the sensor switching locations. Reliability was increased by inductive feed of data to the communications line and use of self-contained measurement modules with inductive coupling. The inductive method made it possible to use as the communication line a shielded coaxial cable with high operating reliability and throughput capacity. The self-contained modules with inductive coupling made it possible to mount the sets of measuring sensors at any desired locations on the communication line, without splicing the cable, and made possible remote control of their operation. The self-contained measurement module is a functionally improved device that converts sensor readings into a serial binary code and allows two-directional communication with the data collection center.

2 BASICS OF THE SYSTEM

The anemometry information (like any other) is transmitted through electrical coaxial cables nets, based on nongalvanic connections. The net includes Master block, the electronic part of which installed into the slot of PC and several slave blocks, interacting with autonomous sources of information (sensors, for example) through the serial channel. The signals are transmitted through one-wire cargo cable-rope with cargo carrying uninsulated steel covering for about 300 meters length. The maximum number of slaves is determined by the ratio of information power of slaves and the net channel capacity. The connection of the sensor's wires to the cable-rope is made with the help of special embracing element, without any galvanic connection. Such construction of the net makes it very reliable in underground application, sparking proof and able to be increased.



Figure 1. A simplified diagram of the data net.


One of the most important tasks in developing of the underground mines monitoring systems is to increase the safety and reliability of the communication lines.

The measurement circuits of the sensors are connected by a channel switch to an analog-digital converter. From the converter, the serial code is fed to a modulator, where the two binary levels are represented by two carrier frequencies from an auxiliary oscillator. The signal is amplified and fed to the inductive coupler, which feeds the information to the communication line and receives commands. The command signals are fed to the duty amplifier, then to the band filters and the decoder. The system include a power supply for all modules. The operation of the module is controlled by a timing and program unit, which include a quartz timer and frequency divider that emits timing and command pulses. The module is powered by a battery. The duty amplifier, decoder, and timer are constantly on. The other circuits, operating in the pulsed mode, are powered by the voltage converter.

The standard Token Bus protocol is being used in the net ARCNET (ANSI 878.1) with the transmitting velocity up to 312.5 /sec. On the physical level DIPULSE coding with passive pause is used. Figure 2 illustrates the time diagram, the frequency DIPULSE impulse is twice higher comparative to the velocity of the information transmitting.

Fig 2. Time diagram for binary data 1-1-0.

Each connection of the net is the standard inductive coupling (IC) with shorting strap, connected with appropriate electronics slave module by the coaxial cable. Measured attenuation of the signal in (IC) does not exceed 40 dB.

Each electronic unit is constructed on the basis of the controller-cheap ARCNET (Standard Microsystems Corporation COM20020 (http://www.smsc.com/), which maintains all low level functions of a web: a bidirectional data exchange with determination of the mistakes, reconfiguration and diagnostics of the web.

The Microcontroller AT89252 program (http://www.atmel.com/) ensures data exchange with an independent device by means of the series channel RS-232c with the rate 19.2 Kbit/s and administers buffer memory, where it accumulates instrument data and decoding of the parcels accepted from the master'. The microcontroller also excites a repeated exchange with master in the case of accidental errors in the web.

The input and output amplifiers are forming a powerful output signal (up to 12 W in impulse) and amplification (up to 80 dB) of the received impulses, accordingly.

Overall dimensions of the electronic unit slave: 50 ? 120 ? 25 mm. Average consumption in a receive mode 0.25 W, and in a transmission mode- 3 W.

The unit master electronic circuit is easier, as far as the COM20020 is controlled by PC with the help of internal ISA bus, and for data buffering the resources of the computer are used.

The software of a web on the PC represents the driver under WINDOWS, organizing as many separate bidirectional channels as needed for the present number of clusters and implementing completely transparent information exchange with devices. This driver can serve for construction of a specialized envelope with the purpose of processing and submission of the received data.

The electronics and battery unit is contained in a sturdy cylindrical stainless steel housing and is attached to its end cap. On the exterior of the cap are the measurement sensors, and sealed connectors if remote sensors are used. The housing has two cable clamps, including the inductive coupler, to attach the module to the cable. The inductive coupler consists of a toroidal transformer with a gapped ferrite core, through which the cable passes; the EMFs induced in the outer braiding and in the central strand differ in magnitude..

The possibility of real-time processing of the incoming information by a surface-based computer allows an adaptive measurement regime to be used by altering the module interrogation frequency as the processes that are being studied change. Self-contained operation is also possible, in which each module makes measurements and send information at specified time intervals determined by the timer.

The experimental studies showed that it was possible to operate at frequencies of up to 1 MHz. In addition, some groups of sensors can operate at different frequencies. Thus the system can serve dozens of measuring modules, controlling high-frequency processes.

The system has high noise immunity. With a potential of 10 V applied to the inductive coupler, the useful signal level at the output of the receiver was 10-12 mV. The signal-to-noise ratio was about 20 dB. The possibility of rapid installation and removal of modules at any points along the line considerably simplified both experimentation and the servicing of the system.

4 NEW ANEMOMETRY SENSORS

The careful analysis of publications and preliminary laboratory estimation have showed that on the one hand acoustical methods in flow measurements have not realized their potential possibilities, and on the other hand non of the existing acoustics means of measurement of the flow allows to create anemometer, which should be able:

- to measure speeds of flow in the range of (0.05 ... 30) m/s;

- not to add aerodynamics resistance in the controlled flow,

- not to disturb aerodynamics curve;

- to measure average flow speed in the cross section;

- to have stabile characteristics, allowing to decrease error.

The suggested measurement method satisfies all mentioned here demands. The method of measurement based on airacoustic interaction involves vibrations excitation in the cylindrical wave guide-air duct, their reception at some distance

from the excitation point and a comparative analysis of radiated and received vibrations as a result of which an informative signal (e.g., vibration phase difference) is singled out, which serves as a flow rate measure. It differs from others known in that waves are being radiated and received by excitement of the air conduit elements, acoustically isolated from each other. This method gives accuracy and provides exception of air conduit effect on the aerodynamics field of air-gas flow.

The description of wave propagation process in the tubes without flow was suggested by E.Scuchic. From this description we made the conclusion which waves could spread in the round channel of the given diameter. The spread rate of wave fronts of these vibrations is equal to one of sound velocity in open space with the same medium. In the air-gas channel the sound speed in the direction of the wave guide axe is expressed: For better correspondence with real physical phenomenon in the mathematics model it is necessary to take into consideration the error, coursed by the acoustical waves reflection from the open ends of the anemometer.

The means of the correction determination, corresponding to the reflected waves field with the help of normal modes reflection coefficient calculation is offered. The means named is based on the sewing together method.

The analytic dependencies of the velocities upon the dimensions, channel walls material and air-gas medium characteristics have been got using G. Gohnson's and K. Ogimoto's work.

The apparatus includes a primary measuring transducer and an electronic block. The principle of transducer operation is based again on the dependence of the velocity of the acoustic vibrations arriving to the receiver upon the air-gas velocity. The apparatus measures the momentary value of the velocity and records the data in its memory, process and integrates it during a fixed period of time; i.e. inhale and exhale, etc. The result is the determination of the air-gas mixture volume passed through the measuring conduit. The comparison of the phases of the radiated and the received vibrations provides the momentary rate of flow. The main feature of the above method is the immediate introduction of vibration into the medium being measured without reflecting/refracting surfaces and sound conductors.

In conclusion, the following merits could be noticed.

The above process of measuring does not disturb of inhibit the regime of the flow being measured.

No moving elements and rolling parts.

Low air-dynamic resistance of the sensitive element, relative to the total length and cross section of the passage.

Wide dynamic range, up 200.

The possibility of measuring low rates of flow (up to 200 ml/s).

Minimal inertia (less than 2 ? 10 -3 s).

5 CONCLUSION

The new technology for obtaining of the flowmetry information getting and transition has been developed. The method of measurement differs from others known in that the process of radiating of vibrations into the gas flow traveling through the air duct and the manner in which they are received. It does not destroy the aerodynamic structure of the flow, does not add any aerodynamic resistance, is practically inertialess, reacts to the average velocity in the cross-section. The method of information transition allows to avoid all difficulties coursed with connections in the dangerous circuits.

REFERENCES

Belogrudov G.S., Utyakov L.L., Shekhvatov B.V. et al. USSR Patent 843261: An inductive coupler for contactless transmission of signals. B.I., No. 24, 47, 1986.

Puchkov L.A. Shkundin S.Z, oth: The method of measurement of air-gas flow velocity . Author's certificate 16822590, 1991.

Scuchic E. Basic acoustics. Moscow 1976, vol.2, pages 112-116.

Gohnoson E. & Ogimoto K. Sound radiation from a finite length unfledged circular duct with uniform axial flow. Acoustic Society of America papers. 68, 1980.

Shkundin S,Z , Kremleva O.A, Rumiantceva V.A

Theory of acoustic Anemometry. Academy of mining science publishing house, Moscow, 2001.

 
 
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