Design of industrial coal composition analysis system based on S3C44B0X

Gangue is a solid waste discharged during coal mining and coal washing. It is a black-gray rock associated with coal seams during the coal formation process. There are more than 1,500 gangue mountains in the country, with a total volume of more than 3 billion tons, accounting for more than 40% of China's total industrial solid waste emissions. The large-scale stacking of gangue not only occupies land resources, but also causes environmental pollution. Using washed medium coal and gangue to mix and burn to generate electricity is an effective way to solve pollution. In 2009, the comprehensive utilization of gangue exceeded 390 million tons, and the utilization rate reached more than 70%. How to quickly and accurately quantitatively analyze the proportion of coal and gangue in mixed fuel has become a problem that regulatory authorities and enterprises need to solve. To solve the above problems, this paper designs an embedded quantitative analysis system based on the ARM7 chip S3C44BOX, which integrates data acquisition, processing, and display, and can transmit data to a remote PC through the network.

1 System Principle and Overall Design

1.1 System Principle

It is a low-energy gamma ray, and its interaction with matter is mainly the photoelectric effect. Different substances have different mass coefficients for gamma rays due to their different atomic numbers, which means that the absorption coefficient of mixed fuels of coal and gangue prepared in different proportions will change significantly. Therefore, by measuring the radioactivity intensity, the mixing ratio of coal and gangue in the mixed fuel can be analyzed.

Using monoenergetic, narrow beam gamma rays to irradiate the mixed fuel, the following can be obtained by theoretical deduction:

In the formula: αc, αg are the weight percentages of coal and gangue in the mixed fuel respectively; μc, μg, μp are the mass absorption coefficients of coal, gangue and mixed fuel respectively; μm is the mass absorption coefficient to be measured; I0, I are the intensities of the γ-ray before and after passing through the object respectively; V is the net volume of the standard sample box, d is the thickness of the sample in the box, both of which can be regarded as known constants; ρ is the sample density.

Therefore, the weight percentage of coal and gangue can be calculated by only measuring the intensity of gamma rays before and after irradiating the mixed fuel and the mass of the mixed fuel.

1.2 Overall system design

The system mainly includes a γ-ray source, a detector, a data acquisition circuit, a precision electronic balance, an S3C44BOX hardware platform, an LCD display, and a network interface. The hardware block diagram is shown in Figure 1.

The core of the system is the S3C44BOX microprocessor, which is a 16/32 b RISC processor launched by Samsung. It uses a 2.5 VARM7TDMI core, 0.25/μm process COMS standard macro cells and storage compiler. It provides a wealth of built-in components, including 8 KB Cache, internal SRAM, 2-channel URAT with automatic handshake, 4-channel DMA, system manager, RT-C, I/O port, LCD controller, etc., which well meet the system design requirements. S3C44BOX can easily expand a network interface to realize network transmission of data. In addition, S3C44BOX provides more than 70 I/O ports, which greatly facilitates future function expansion.

The signal acquisition circuit collects the energy signal of the gamma ray, and the precision electronic balance synchronously measures the mass signal of the mixed fuel and transmits the data to the processor through the RS 232 serial port. The S3C44BOX processes the collected data to obtain the mixing ratio of coal and gangue, and displays it on the LCD screen. At the same time, the data can be transmitted to a remote PC through the network interface for later analysis.

2 System Function Module Design

2.1 γ-ray intensity detection part

It consists of several parts including a detector, a linear amplifier circuit, a pulse amplitude analysis circuit, etc. The principle block diagram is shown in Figure 2.

The NaI scintillation detector outputs a pulse signal that is proportional to the incident gamma rays. The greater the intensity of the incident gamma rays, the more pulses the detector outputs per unit time.

The linear amplifier circuit amplifies and shapes the pulse output by the detector to meet the requirements of the subsequent signal processing equipment. The LM138 integrated operational amplifier has a bandwidth of 15 MHz and a conversion speed of 50 V/μs. The LM138 first amplifies the γ pulse, then shapes it, and finally outputs it through the buffer amplifier.

The pulse amplitude analysis circuit consists of two discriminators and one anti-coincidence circuit. The two discriminators set the upper and lower thresholds of the counting pulse respectively. The difference between the upper and lower thresholds is the channel width. The anti-coincidence circuit outputs the pulse within the set channel width. See Figure 3.

The upper and lower thresholds of the pulse amplitude analysis circuit select the full-energy peak pulse of the gamma ray and send it to the counter of the microprocessor for counting. The gamma ray intensity can be measured based on the number of pulses falling within this channel width per unit time.

2.2 Quality signal acquisition part

The system uses JA2003 precision electronic balance to measure the mass of mixed fuel. It adopts patented ceramic capacitor weighing technology and integrates a user temperature compensation circuit, which has the advantages of high measurement accuracy. JA2003 has a standard RS 232 interface, which can easily realize communication with S3C44BOX.

When the balance is connected to S3C44BOX, the immediate print symbol "#" can be used to transmit data. The data displayed by the balance will be transmitted to the processor in the form of a string. The data format is as follows:

+/- 1 2 3 4 5 6 ． CO C1 C2 C3 CR LF The first six are digital areas, usually preceded by a sign (+ or -). C0 is a space, C1 is a space when the balance is set to automatic mode, C2 indicates the output unit, if the unit set on the balance is gram, "g" is transmitted, C3 indicates the stability of data transmission, space indicates unstable, "s" indicates stable transmission, CR and LF represent carriage return and line feed respectively.

2.3 Network transmission part

RTL8019AS is an Ethernet controller produced by Realtek in Taiwan. It is suitable for EthernetⅡ, IEEE 802.3, full-duplex, and can simultaneously transmit and receive at a rate of 10 Mb/s. It supports 8b and 16b data buses. RTL8019AS can be divided into local DMA channel and remote DMA channel. Local DMA completes the data exchange between the controller and the network cable. The main processor only needs to operate the remote DMA to send and receive data. The link between RTL8019AS and S3C44BOX is shown in Figure 4.

When the system sends data to the network, the D[0:15] data is sent to the RTL8019AS send buffer through the remote DMA, and then a transmission command is issued. After the RTL8019AS completes the transmission of the previous frame, it completes the transmission of this frame. When receiving data, the D[0:15] data is inverted by 74F163245 and then transmitted to the processor.

At the same time, an 8.4-inch 640×480 TFTLCD screen is expanded as the human-machine interface.

3 Software Design

The system uses μClinux operating system, which is properly tailored and optimized based on standard Linux to form a highly optimized and compact code Linux. Although it is small in size, it still retains most of the advantages of Linux and is very suitable for embedded system applications.

Based on the μClinux kernel, the RS 232 serial port driver, LCD driver and network interface driver were written. The device driver shields the hardware details so that the operating system can read and write it like a normal file.

In order to save data for a long time, the system adds JFFS2 file system when μClinux is compiled. The operating system manages the FLASH space through the J17FS2 file system, which can not only save various parameters set by the system, but also save the collected data in the form of files in FLASH, which will not be lost even if the power is off.

The local software is written in C language under Linux, and is cross-compiled to get a program suitable for running in μClinux. This application uses multi-threaded programming, dividing the system work into γ-ray intensity detection thread, serial communication thread, data processing thread, LCD display thread, and network transmission thread. Each thread is a relatively independent working submodule and can work simultaneously, which is conducive to improving real-time performance.

The gamma-ray intensity detection thread is responsible for collecting pulse signals; the serial communication thread is responsible for collecting the quality signal of the coal and gangue mixed fuel; the data processing thread is responsible for processing the two channels of data collected to obtain the mixing ratio of coal and gangue respectively; the LCD display thread displays the mixing ratio of coal and gangue; the network transmission thread transmits the processed data to the remote PC.

4 Conclusion

The industrial coal composition quantitative analysis system based on S3C44BOX microprocessor has simple circuit design, easy operation, strong reliability and good human-machine interface. It can be equipped in the laboratories of thermal power plants and monitoring departments to conduct rapid quantitative analysis of the composition of mixed fuels.

Since gangue itself contains a certain amount of coal, the distinction between gangue and coal is reduced, resulting in measurement errors. Therefore, how to reasonably select the correction value when measuring the mass absorption coefficient of mixed fuel becomes the key to accurate measurement, which can be determined through a large number of experiments.