Development of intelligent automatic water intake system for open-pit mine

In order to solve the problem that the automation level of water intake system in open-pit mine is relatively low and the phenomenon of fault shutdown occurs from time to time, this paper innovatively develops an intelligent automatic water intake system based on LabVIEW suitable for open-pit mine. On the basis of extensive investigation of field conditions and in-depth analysis of domestic and foreign open-pit mine water intake system, the overall design scheme of this system was put forward. The selection of electric gate valve, ball valve, various sensors and Siemens 1200 series PLC was completed. The system software which integrates system initialization subroutine, pump rotation start-stop subroutine, sensor polling subroutine, fault protection and alarm subroutine was compiled. The monitoring software of Upper machine was developed based on LabVIEW software platform. The field debugging and operation results show that the system realizes the real-time monitoring of the operation state of the water intake unit, the on-demand start and stop and the intelligent rotation control of the water pump, which greatly reduces the labor intensity of the workers, prolongs the service life of the equipment, greatly improves the intelligent operation and maintenance level of pumping units of open-pit mine, and lays a solid foundation for green mining.


Introduction
The developed countries with abundant mineral resources abroad have studied the coal mine water intake system for many years earlier than China, and have realized the intelligent control and energy saving control of the coal mine water intake system.In particular, Canada, Russia, Finland and other developed countries with a large number of advanced technologies have fully realized the automatic and accurate control of the water intake system [1].
Under the background of the current ''double carbon'' target goal, coal, as the most important basic energy and energy security ballast stone in China, must also take the road of ''intelligent, green and low carbon'' mining and utilization [2][3][4].With the rapid development of large-scale and intelligent mining technology of coal resources, the automatic water intake system plays an important role in the production, dust reduction and greening of open-pit mines.At present, the automation level of water intake system in most open-pit mines in China is relatively low, and the water intake operation must

General system design
According to the analysis of the actual situation of the open-pit mine, on the basis of introducing the principle of series submersible pump water intake, the overall design scheme of the system is elaborated in detail, including the system topology structure and system function design [6][7].

Water intake principle of series submersible pump
In order to solve the problem that the large drop of water level in four seasons affects the normal water intake, this system adopts the positive pressure water intake mode of centrifugal pump with equal flow submersible pump in series at the end of suction pipe [8].The working principle of the pump unit is as follows: start the submersible pump first, open the electric ball valve of the exhaust pipeline at the same time, inject water and exhaust from the submersible pump to the centrifugal pump, close the electric ball valve after the positive pressure value of the exhaust pipeline is stable, and then start the centrifugal pump.When the water pressure of the outlet pipeline meets the requirements, open the electric gate valve for water intake operation.The structure of pump unit and pipeline is shown in Figure 1 [9].

System topology structure
The system sets up Upper Machine in the ground monitoring center and Lower Machine in the field water intake pump room.The programmable controller (PLC) is the core control unit of Lower Machine.It collects and monitors various working conditions such as water level, outlet pipeline pressure, pipeline flow, motor voltage and current through various sensors.PLC comprehensively analyzes and processes the parameters of each working condition, and outputs the results of logical operation to the actuator according to the program written in advance.The actuator controls the start and stop of the pump and the valve switch to realize the automatic and intelligent start and stop of the pump and achieve the purpose of unattended operation.At the same time, PLC transmits data to the touch screen on the field control cabinet and Upper Machine in the ground monitoring center through RS485 and the Ethernet interface respectively.Upper Machine dynamically displays the running state and operating parameters of the pump unit, the working state of the system and the fault alarm information in real time by means of graphics, data and text, so as to realize the unmanned intelligent operation of the water intake system in open-pit mine [10][11].
The topology of intelligent water intake monitoring system in open-pit mine is shown in Figure 2, which mainly includes three parts: (1) Upper Machine: Upper Machine is composed of industrial computer, operating system software and configuration software.The analysis, judgment and processing of the state parameters of the water intake system collected by Lower Machine are realized.After the communication between Upper Machine and Lower Machine is established, the parameters can be set remotely and the pump startstop and valve switch can be controlled.
(2) Lower Machine: Lower Machine is composed of control cabinet, actuator and sensor.The control cabinet is composed of touch screen, PLC, isolation safety barrier, relay, switching power supply and terminal unit.The actuator is composed of soft starter and frequency converter.Sensor includes liquid level sensor, pressure sensor and flow sensor.
(3) The controlled equipment: The controlled equipment mainly includes centrifugal pump and submersible pump supporting motor, electric ball valve and electric gate valve.PLC controls the controlled equipment to take water through the actuator.

System function design
According to the actual needs of the site, the system has the following functions: (1) Data acquisition and real-time monitoring.The data of water level, pipeline pressure, pipeline flow, motor bearing temperature, motor working voltage and working current are collected and displayed in real time.
(2) Multiple control modes.There are five control modes: remote manual, remote semi-automatic, field manual, field semi-automatic and automatic.(a) Remote manual mode: remote control of a single device through Upper machine.(b) Remote semi-automatic mode: the system is started and stopped by one key through Upper machine.(c) Field manual mode: manual operation of the on-site button to control the equipment separately.(d) Field semi-automatic mode: manual operation of the console button to achieve one-click start and stop of the system.(e) Automatic mode: The system automatically detects the parameters of each working condition, controls the intelligent rotation and start-stop of the pump, and reasonably dispatches the pump operation.
(3) Intelligent rotation and switching of pumps.When performing the water intake task, the system automatically selects the pump with relatively few start-up times and cumulative running time according to the principle of uniform wear of the equipment.
(4) Fault protection.It includes abnormal pressure protection of exhaust pipeline, abnormal flow protection of outlet pipeline, over temperature protection of motor and PLC fault protection.
(5) Abnormal alarm.When the system detects that a device fails or a parameter exceeds the preset threshold, the on-site touch screen and the monitoring interface of Upper Machine in the ground monitoring center will send out corresponding alarm signals and display the operation status of the relevant water intake equipment.
(6) User management.The system sets multi-level operation passwords with different permissions for operators in different positions.
(7) Information storage and information query.The working condition parameter information and equipment status information in the water pump room can be recorded in real time to the historical database for the staff to query in the future [12].

System hardware design
The hardware structure of the system is shown in Figure 3, which mainly includes PLC control cabinet, Upper Machine, sensitive elements, actuator, centrifugal pump, submersible pump, electric ball valve and electric gate valve.In this system, the core processor selects Siemens S7-1200 series PLC, which is the key to the whole control system.Its digital input signal includes system one key start and stop, running mode selection and control mode selection; the digital output signal includes indicating lights (operation, reset, power failure, fault and alarm indicating lights ) and alarm bells ; the signals of state of electric gate valve, state of electric ball valve, exhaust pipeline pressure and so on are transmitted to CPU module through RS485 bus interface.The CPU module analyzes and processes the collected signals, outputs the results of logical operation to the actuator according to the corresponding process flow, and drives the corresponding actuator (the frequency converter and the soft starter) to control the pumps and valves, so as to complete the water intake operation.In addition, the field touch screen realizes local communication with the CPU module through RS485, and the CPU module realizes remote communication with Upper Machine in the ground monitoring center through Ethernet interface.

PLC selection
The system uses S7-1200 small PLC produced by Siemens to complete data acquisition and processing.The controller can meet the needs of small and medium-sized automation systems, and has the advantages of rich instructions, high reliability, compact design, easy expansion, and low cost.There are many types of S7-1200 PLC host models.CPU 1214C DC/DC/ DC module is selected in this system.

Sensor selection
As the ''eye'' of the whole system, the quality of the sensor directly determines the accuracy of the system data acquisition, and indirectly affects the logical judgment of PLC.According to the principle of sensor selection, the sensor is selected and designed.The selection results are shown in Table 1.All sensors are connected to PLC by RS485 communication.

Valve selection
In order to achieve the goal of ' fully automatic unattended ', the system selects electric gate valve and electric ball valve to replace the existing mechanical gate valve and ball valve.The specific selection is as follows: (1) Electric gate valve: The electric gate valve model used in this system is Z941H, which has two modes of manual control and automatic control.
(2) Electric ball valve: Electric ball valve is used to exhaust the centrifugal pump.The electric ball valve model specification used in this system is ZDRO, which can not only perform exhaust operation through buttons in the field manual control mode, but also automatically exhaust in the automatic control mode.

System software design
Combined with the overall design of the system, on the basis of completing the hardware design of the intelligent automatic water intake system, the software of the system was designed.It mainly includes the software design of Upper Machine and the software design of Lower Machine.The monitoring software of Upper Machine has the functions of system management, monitoring screen, parameter setting, data management, historical report and query statistics.The software of Lower Machine mainly includes system initialization subroutine, module anomaly detection subroutine, input signal processing subroutine, control mode selection subroutine, pump intelligent rotation subroutine, fault protection subroutine, fault alarm subroutine, human-computer interaction interface (HMI) display subroutine and communication data refresh subroutine.The two together construct the software system of intelligent automatic water intake in open-pit mine [13].

The software design of Upper Machine
The monitoring screen of Upper Machine was designed based on LabVIEW software.The software uses graphical editing language and has many drivers.It is suitable for a variety of communication interfaces and can simulate the actual operating conditions of field devices.It has the advantages of intuitive screen and convenient operation [14].The software of Upper Machine can display the water level, exhaust pipeline pressure, outlet pipeline pressure and so on in real time through graphics and text.At the same time, the equipment fault alarm can be recorded to achieve real-time monitoring and recording.The functions of the software of Upper Machine mainly include: system management, realtime monitoring, parameter setting, data management, historical reports and query statistics.The specific introduction is as follows: (1) System management: used to process user-related information, including user login rights management, historical curve query rights management, remote control rights management and login history information management functions.
(2) Real-time monitoring: for real-time display of main parameter information, including: water level, pipeline flow, exhaust pipeline pressure and so on.
(3) Parameter setting: including the setting of communication parameters and alarm parameters.
(4) Data management: including database data storage and data processing.
(5) Historical reports: including daily, monthly, annual report automatic generation and other functions, convenient for technical personnel to consult.
(6) Query statistics: including user login history query, pump start and stop query and equipment failure query.

The software design of Lower Machine
This system uses STEP 7 V15 Basic as the software development platform of Lower Machine.The software provides users with a clear and intuitive interface and a task-oriented intelligent editor.It has the advantages of powerful function, convenient programming and flexibility.
Using the function module programming method, each module completes a specific task.The modules can not only be nested with each other, but also can be structured by calling each other, which is conducive to the modification and debugging of the program.The software of Lower Machine is mainly composed of the main program and each function subroutine.The main program completes the water intake and monitoring tasks by calling each function subroutine.According to the functional requirements of the system, the PLC main program flow is shown in Figure 4, including system initialization subroutine, module anomaly detection subroutine, input signal processing subroutine and so on.

System debugging and field application
The experimental platform was built in the laboratory, and the whole system has been debugged for many times, including the accuracy test of the sensitive elements and the function test of the system.Taking the data measured by the field industrial instrument as the real value, it is compared with the data collected and saved by the system many times and the maximum reference error is calculated.The calculation results show that the measurement accuracy of the system for pressure, flow and liquid level can reach 1.0, which meets the system design requirements.The Upper Machine debugging interface of the system in the field manual control mode is shown in Figure 5, which can display the system information and pump operation parameters in real time, including communication status, control mode, working unit, pump group start and stop status and so on.At the same time, the blue rectangular block under the interface expands and contracts with the change of water level, which can visually display the water level.The five control modes of the system can operate reliably and switch smoothly.The communication between Lower Machine and Upper Machine is real-time and reliable, and the data transmission error rate is less than 1×10 -6 , which meets the system design index.The realtime data display of the touch screen and Upper Machine in the ground monitoring center is consistent, which can realize fault protection and abnormal alarm, and achieve the expected goal.
At present, the system has been put into operation in Hequ Open-pit Coal Mine, and everything is running normally.The field operation results show that the parameters of each working condition and the operation information of the water intake equipment can be transmitted to Lower Machine in time and displayed on the touch screen.The system can operate reliably and switch freely in multiple control modes.The Ethernet interface can complete data transmission safely and reliably.The software of Upper Machine can display the operating parameters and the operation status of the field equipment in real time, remotely control the field water intake equipment, and query the user login, equipment failure and historical alarm information by relying on historical reports and query statistics.

Conclusions
In view of the low level of automation water intake system in most open-pit mines in China, an intelligent automatic water intake system suitable for open-pit mines was developed.
(1) To solve the problem that the water level drop in four seasons affects the normal water intake, the positive pressure water intake mode that the centrifugal pump in series with equal flow submersible pump at the end of the suction pipe was designed.The software and hardware of the system was developed.The system functions of data acquisition and real-time monitoring, intelligent rotation and switching of water pump, combination of multiple control modes, fault protection and abnormal alarm was realized.The intelligent level and reliability of water intake system were improved.
(2) The laboratory test and field operation results show that the system realizes the ' unattended ' operation of the functions of real-time monitoring of the operation status of the water intake unit, ondemand start and stop of the pump and intelligent rotation control.Compared with the previous system that mainly relies on manual water intake operation, this system is more stable, safe and reliable, which greatly reduces the labor intensity of workers, improves personal safety, prolongs the service life of equipment, and greatly improves the intelligent operation and maintenance level of open-pit mine water intake system.
(3) The improvement direction of the system: (a) The system is equipped with a single weak current control system.When the water intake unit fails to obtain the fault information of these hardware devices due to overload, overcurrent, or abnormal conditions of frequency converters and soft starters, the reliability of the water intake system is reduced.Therefore, the integration of on-site water intake electronic control system is the development direction and potential of the future system.(b) This system can apply PHM (Prognostics and Health Management) technology to the fault analysis of centrifugal pumps in subsequent research.Through in-depth analysis and mining of centrifugal pump operation data, the life prediction of centrifugal pumps and the prediction and judgment of some key faults can be realized.

Figure 1 .
Figure 1.Pump unit and pipeline structure diagram.