Gas explosion is the main accident in China’s coal industrial at present. Most of coal companies have installed supervising system to ensure safety in production. However, due to the constraint of present supervising system, the safety supervising department can not master gas distribution in time, the manager and main leaders in charge of safety cannot receive gas alarm information at once.
What the safety supervising system focuses on? The answer is whether the gas concentration, from hundreds to tens of hundreds miles deep ground, is too high, whether there are incipient faults causing fire or self-ignition. It is a puzzle to let the supervising center or managers of upper level to master such conditions. The transmission is among the most important keys. The data from gas concentration sensors are transmitted up to ground, then to the supervising center where the data are analyzed; at last conclusions are sent back down to the well. In such conditions, a short data transmission radius, even one meter shorter, may cause uncovered disaster. For coal fields distribute in wild with long distance between each other, the communication from field to company remains as problems. There are no telephone lines in many fields, no more than optical fiber. What’s the solution?
II. Advantages of GPRS solution
Coal well gas wireless SMS alarm system, employing advanced communication network and information technology, integrates with supervising and control system. Such system samples data real-time, 24 hours and full-spatial, then sends data by SMS to managers at different levels who in charge of safety. With the help of this system, all workers and managers can take part in the system avoiding accidents. The wireless SMS alarm system realized functions of sampling different supervising systems through standard data gateway and supervising data remote wireless transmit based on TCP/IP protocol through GPRS or CDMA networks. At the same time, alarms are sent to related persons’ cell phones.
For signal can not reach deep down the well, optical fiber cables are adopted to connect sensors deep down in wells and surface using digital signals in stead of analog signals to enhance signal precise. When gas concentration, wind velocity exceed the threshold values, or, the load of main fan varies at large amplitude, GPRS data module sends the information at surface to supervising center and persons in charge of safety through SMS at the same. In such conditions, managers and related leaders can master the gas volumes and give commands to coordinate the productions in time.
The GPRS wireless transmit network offers low cost, quickly using and high efficiency data transmit platform for companies who has no wire transmission lines, especially for coal companies spanned large areas.
III. Solution Introduction
1. Coal mine data sampling spot: Well data are sent to the information acquisition equipment through RS232/RS485/TTL firstly, and then, by employing the WIXUM GPRS transparent wireless data transmission terminal, sent to the information center through the dedicate GPRS network of China mobile. This network has no constrain to the location, time, number of the information acquisition point and satisfies the requirements of mountain, county and cross areas.
2. Center station: The proxy servers are connected to the Internet through ADSL, LAN with a fixed IP. When the GPRS data transmit terminal is powered on, it will access to the proxy server according to the preconfigured IP address and set up TCP/IP connection to the supervising center. The host computer in supervising center maintains a list of IP and ID number. When the supervising center requests data from a certain terminal, it will find the terminal according to the IP and ID and send orders to the terminal. This terminal response to the order and, through GPRS, sends data to the endpoint of proxy server where the data are forwarded to the host computer. Till this step, an ask-answer communication flow is finished. The system can satisfy the increases of information acquirement points without expand.
Coal mine information acquirement and transmit system employs WIXUM GPRS DTU. The system, based on China Mobile’s GPRS network, supplies RS232, RS485, TTL connectors and realized wireless connection through GPRS service. The system supports applications of various industries such as credit card real-time authorization, remote control and maintenance of POS, remote service station switch-in, etc. In the coal mine information acquirement and transmit solution, WIXUM GPRS DTU is connected to the data equipment both outlay and embedded.
1. Support three frequencies of GSM/GPRS at 900／1800／1900MHz respectively.
2. Connectors : RS232、RS485、TTL
3. Practical transmit speed at 40Kbps and theoretical speed up to 171Kbps
4. Support operating systems such as Windows95/98/2000/XP and Linux.
5. Support operating systems such as Windows95/98/2000/XP and Linux.
6. Automatic dial-in connection: WIXUMEP-DTU is configured as power-on dial-in connection, and support command connection or remote wakeup connection at the user side as well.
7. Short message backup data channel: Short message backup data channel is activated when the GPRS network is not accessible.
8. Remote maintenance by short message;
9. Real-time supervising the network connection, automatic redial when connection breakdown
10. Supplying master and slave IP, dynamic domain analyzing
11. Heartbeat interval is configurable.
12. Data frame length is configurable.
13. Support VPN security.
14. Easily installation and robust when using.
1. The system has functions including supervising environment parameters such as gas, wind velocity, suction pressure, co, feeding power and wind gate as well as coal bin coal height, water bin water height. Motor parameters including voltage, current, power and safety of mechanistic equipments are also supervised.
2. Adapting larger screen to display more process flow simulation graph, supervising curves, tables and words, ① system generation and operation； ② test points generation and operation； ③ process flow simulation graph display； ④ test points data table display； ⑤ down and up well various of analog parameters’ real-time display in tables, bar charts and varying curves ； ⑥ value and time display of switching variables of down and up well main equipments ； ⑦ Real-time and accumulated product display of crude coal yield ； ⑧ various types of audible alarms in addition to tabled display ； ⑨ clock and date display； ⑩ tracing display of related equipments and software operating instructions .
3. Tabled display functions. Simulation chart and related content includes address, name, unit, alarm threshold, power shut threshold, supervising variables, maxim value, minimum value, power shut command, feeding state, overrun alarm, wrong power shut logic alarm, sensor failure, lock and unlock, etc. Switching variables include address, name, on/off time, state, running time, on/off counters, sensor state and lock/unlock, etc. Accumulated variables include address, name, unit and accumulated value.
4. Real time processing, saving and alarming of various types of information. When sensor data overrun the threshold, acousto-optic alarm will be triggered. At the same time, corresponding item on the supervising host computer changes background color and shines to present the user which equipment alarms and where it was installed.
This system requires extreme safety and stability. Safety means to protect the system from intended or natural destroy and network safety includes communication channel encryption, signal source encryption, login protection, access protection, connect-in protection and firewalls, etc. Stability means the system can run all 7×24 hours without break even though there are faults of either hardware or software.
Data center can connect to mobile GPRS networks via VPN on Internet. The VPN style need not lease private channel and use the present VPN equipment with virtual dial function software installed in terminals, which reduced the cost. Through VPN, the customers need to be authorized by Radius server before connected to the application server and data are encrypted all through the transmission process. Such a process ensures high security, velocity and QoS. On the other hand, data center can adapt APN alternatively and lease private cable to connect to GGSN equipments of Chin Mobile. Such a style is of high security and stable but also high cost. If the system requires high security, a hybrid solution that adds VPN on the basis of APN can enhance the security performance.
1. VPN virtual network: A VPN server is adopted within the industrial’s LAN, and customer VPN sub virtual dial software is installed at terminal. With VPN safety technology, customers are isolated from the Internet by VPN. Data are encrypted all the transmission process and protected from illegal invasion.
2. As SIM card are unique ID, customers are authorized to join the VPN to avoid illegal invasion. By using the China Mobile’s APN and binding SIM cards to it, only the authorized customers with the SIM cards can access the VPN. Other common GPRS terminal on cell phones can not access the APN.
3. For special customers, specific user ID and password are assigned to their mobile terminals. Other customers without such ID and passwords can not log in the system, which enhanced the security.
4. Data encryption: Data are protected by encryption via VPN throughout the transmission procedure.
5. Network connect-in authenticating mechanism: using firewall software with net authentication and security functions to protect system.
The wired style, leasing static IP, is of high cost about 800~1500￥ per month. On contrary, GPRS style has two counting methods. One is by flow, 0.03￥ per k Bytes. The other is charging per month, 20￥ with 1024 k Bytes. This style can satisfy the requirements of coal mine supervising data transmission, and the cost is predicted to decrease in the future. The low communication cost will benefit the manufacturing department. In addition, because the terminals are mobile, the equipments can be easily moved to other new mines when the supervising centers or spots need to move. This feature of GPRS satisfies the coal mine supervising and protects the users’ original investments.