14-08-2012, 11:55 AM
Multi - Parameter Monitoring Systems for Coal Mines Based on Wireless Sensor Network Technology
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INTRODUCTION
Now most coal mine safety monitoring systems use cables and fixed sensor networks, but with the mining face moving, monitoring blind spot will appear. Coal mine safety monitoring system based on wireless sensor network can timely and accurately reflect dynamic situation of staff in the underground regions to ground computer system. So that managers can keep the distribution of underground staff and the trajectory of each miner, in order to schedule and manage them reasonably.
Gateway has the advantages of ease to implement, low cost, and a greater diversity in supporting the internetworking on different networks by means of the isolated operation. Carefully exam of the traditional gateway indicates that it suffers from the following two common drawbacks: 1) it is lack of flexibilities in applications. Generally, traditional gateway was designed for specific applications using data communication protocols strongly coupled with the applications. When there is a change of the application field or there is a new node with new function being added to the networks, the gateway must be changed accordingly or be redesigned to adapt to the changes. 2) The access method of the traditional gateway is inconvenient. Firstly, data receiving from a zigbee via the gateway is only in an indirect way, such as querying the daemon application that runs on the gateway. In this case, the service provider needs to design special client software for the remote users. Therefore, when the services change, the client has to be remodeled accordingly. Moreover, if the operating system of the clients is changed, the client software needs to be designed correspondingly. Secondly, it is difficult for the users to access the interested nodes directly via the traditional gateway. They must query the gateway application and filter the interest data indirectly.
LITERATURE SURVEY
Coal mining is the most dangerous occupation in the India, with injury frequency and severity rates several times the average for all industries. Although mine safety improved slightly during the early 1970's, recent trends indicate small decreases in accidents and injuries and, in some cases, increases in accident severity. Experienced miners have lower risks of fatal injuries than inexperienced miners. Workers in small mines are more likely to receive fatal injuries than those in large mines.The thickness of the coal seam mined is not related to the incidence of fatalities. Although conflicting evidence appears in the literature, recent studies find younger miners with much higher disabling injury rates than older miners. Whether a collective bargaining agreement is in effect is unrelated to accident and injury occurrence at a mine site. Studies of the relationships of accident and injuries to the effectiveness of safety training, the number of shifts each day at a mine site, and the time elapsed during a shift until an accident occurs have produced ambiguous results, often as a result of analysis of inadequate data.
Working Principle
The power supply to the micro-controller is given by the voltage regulator 7805. The voltage regulator 7805 converts the 6v AC to 5v DC. The micro-controller is interfaced with zigbee module using RS232 serial communicator. The three sensors sense the information in the coal mine tunnel and send the analog signal to the ADC which then converts to digital signal and transmits to the micro-controller. The ADC is introduced between the micro-controller and the sensors as the micro-controller can intake only the digital signals, hence the ADC helps in converting the analog signals received from the sensors to digital signals which are transmitted to micro-controller.
The zigbee communicates with the other zigbee in the monitoring side and sends the data received from the micro-controller. The data is transmitted in the form of packets. This data is displayed on the monitor for every few seconds. Critical values are set for all these sensors. If any of this critical value is exceeded there will be a buzzer indicating danger so that precautionary measures can be taken.
MICROCONTROLLER
The AT89S52 is a low-power, high-performance CMOS 8-bit microcomputer with 8K bytes of Downloadable Flash programmable and erasable read only memory and 2K bytes of EEPROM. The device is manufactured using Atmel’s high density nonvolatile memory technology and is compatible with the industry standard 80C51 instruction set and pinout. The on-chip Downloadable Flash allows the program memory to be reprogrammed in-system through an SPI serial interface or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Downloadable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications.
The AT89S52 provides the following standard features: 8K bytes of Downloadable Flash, 2K bytes of EEPROM, 256 bytes of RAM, 32 I/O lines, programmable watchdog timer, two Data Pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectablepower saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset.The Downloadable Flash can be changed a single byte at a time and is accessible through the SPI serial interface. Holding RESET active forces the SPI bus into a serial programming interface and allows the program memory to be written to or read from unless Lock Bit 2 has been activated.
Memory
A RAM stands for Random Access Memory, it has basically the same purpose of the RAM in a desktop computer, which is to store some data required during the execution time of different programs. While an EEPROM, also called FLASH memory is a more elaborated ROM (Read Only Memory) which is the memory where the program being executed is stored. Even ifthat's not exactly true, you can compare an EEPROM to the Hard-Disk of a desktop computer from a general point of view. The EEPROM term stands for Electronically Erasable and Programmable Read Only Memory. In microcontrollers, like in any digital system, memory is organized in Registers, Which is the basic unit of construction of a memory. Each register is composed of a number of bits (usually 8) where the data can be stored. In the 8051 family of microcontrollers for example, most registers are 8-bit register, capable of storing values ranging from 0 to 255. In order to use bigger values, various register can be used simultaneously. Figure 5.4 shows a typical 8-bit registers, where the notation D0 to D7 stands for the 8 DATA bits of the register.
UART (Universal Asynchronous Receiver and Transmitter)
One of the microcontroller features making it so powerful is an integrated UART, better known as a serial port. It is a full-duplex port, thus being able to transmit and receive data simultaneously and at different baud rates. Without it, serial data send and receive would be an enormously complicated part of the program in which the pin state is constantly changed and checked at regular intervals. When using UART, all the programmer has to do is to simply select serial port mode and baud rate. When it's done, serial data transmit is nothing but writing to the SBUF register, while data receive represents reading the same register. The microcontroller takes care of not making any error during data transmission.
ANALOG TO DIGITAL CONVERTER
General Description
The ADC0808, ADC0809 data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a 256R voltage divider with analog switch tree and a succes-sive approximation register. The 8-channel multiplexer can directly access any of 8-single-ended analog signals.The device eliminates the need for external zero and full-scale adjustments. Easy interfacing to microprocessors is provided by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE® outputs. The design of the ADC0808, ADC0809 has been optimized by incorporating the most desirable aspects of several A/D conversion techniques. The ADC0808, ADC0809 offers high speed, high accuracy, minimal temperature dependence, excellent long-term accuracy and repeatability, and consumes minimal power. These features make this device ideally suited to applications from process and machine control to consumer and automotive applications.
CONVERTER CHARACTERISTICS
The Converter
The heart of this single chip data acquisition system is its 8-bit analog-to-digital converter. The converter is designed togive fast, accurate, and repeatable conversions over a widerange of temperatures. The converter is partitioned into 3 major sections: the 256R ladder network, the successive approximation register, and the comparator. The converter'sdigital outputs are positive true.The 256R ladder network approach (Figure 1) was chosenover the conventional R/2R ladder because of its inherentmonotonicity, which guarantees no missing digital codes.Monotonicity is particularly important in closed loop feedbackcontrol systems. A non-monotonic relationship can cause oscillations that will be catastrophic for the system. Additionally,the 256R network does not cause load variations on the reference voltage.The bottom resistor and the top resistor of the ladder networkin Figure 1 are not the same value as the remainder of thenetwork. The difference in these resistors causes the outputcharacteristic to be symmetrical with the zero and full-scalepoints of the transfer curve. The first output transition occurswhen the analog signal has reached +½ LSB and succeedingoutput transitions occur every 1 LSB later up to full-scale.