Preface In recent years, with the continuous development of China's economy, the demand for industrial and domestic oil has been increasing, making the work of oil depots increasingly heavy in terms of production and management. With the continuous popularization and development of computer technology, automated quantitative filling systems for truck and rail tank cars have developed rapidly. In addition to completing functions such as quantitative control, program control, interlocking control, and operation monitoring, they have added many automated filling management functions, achieving significant results in safe production, high efficiency and energy saving, reduced environmental pollution, and improved economic benefits. This achieves the use of advanced industrial control technology, network technology, database technology, and other related high-tech technologies to manage and control the operation of oil depots. I: Introduction to the Distributed Quantitative Loading Management System The oil tank filling quantitative loading control system (Figure 1) consists of an industrial control computer, a billing machine, a setpoint controller, and a communication module. The industrial control computer is the host computer, and the setpoint controller is the slave computer. One industrial control computer can manage multiple setpoint controllers. The industrial control computer is connected to a local area network or billing system to achieve data sharing. The industrial control computer allows for system settings, oil dispensing parameter settings, debugging parameter settings, system editing, real-time oil dispensing control, online or offline oil dispensing, and recording of historical data. Simultaneously, the lower-level computer transmits oil dispensing data to the upper-level computer in real time, displays the oil dispensing status on the interface, and provides alarm prompts in case of faults. Historical data can also be queried and reports printed. This distributed quantitative loading control and management system is suitable for the petrochemical industry, enabling comprehensive automation of management across all business processes in oil depots and the chemical industry. It provides automated monitoring of oil depots and their various work processes, assisting oil depot managers in more efficient and accurate business processing. Based on a local area network environment, the system automatically collects dynamic data from various monitoring environments through a unified monitoring interface. Based on this monitoring data, it generates various reports (such as oil dispensing reports, undispensed oil reports, annual, monthly, and daily reports) and detailed tables, facilitating business statistics and queries. Powerful query functions allow for searching ticket numbers, reports, etc., in multiple ways. Furthermore, the system forms a complete business information feedback and supervision control mechanism, providing strong support for scientific operation management and decision-making in oil depot enterprises. The distributed quantitative loading control and management system consists of functional modules such as oil dispensing, monitoring, management, finance, query, reporting, help, and system settings, covering all major aspects of the current oil depot business process. The system uses a user-friendly interface; operators only need basic computer skills and can become proficient after simple training. Figure 1: Oil Tank Quantitative Loading Control System . Features of the Distributed Quantitative Loading System: 1.1 Oil dispensing is measured in kilograms, with weight calibration based on weighing, and actual measurement errors within 0.2%. Temperature sensors at each cargo location are installed at the flow meter inlet; therefore, when switching between different oil tanks, temperature compensation follows the change in oil type, with intelligent temperature detection error ±0.1℃. Integrated IC modules control oil dispensing. 1.2 The entire oil dispensing process uses intelligent fuzzy control, and the electro-hydraulic valve switching control uses a multi-segment control method, automatically adjusting the oil dispensing flow rate without user intervention. The entire oil dispensing process is free of any "water hammer" phenomenon. 1.3 Real-time static electricity and oil spill detection ensure oil dispensing safety. 1.4 Static electricity, oil spill, pump, valve, and temperature status are displayed on-site, providing a clear and concise overview of the operating status. 1.5 Each storage location is independent, so shutdown, switching, or malfunction will not affect other storage locations or the operation of the entire system. 1.6 Power outages or operational interruptions are recorded in the database. 1.7 Operators are managed with assigned access rights, ensuring clear responsibilities. 1.8 Various data reports are provided for convenient accounting and management. 1.9 System functional modules can be modified or added according to user requirements. 2. Composition of the Distributed Quantitative Loading System: 2.1 Upper-Level Management System Software 2.1.1 Upper Computer: During the oil dispensing process, the upper computer receives real-time oil dispensing data from the setpoint controller, such as actual weight, actual volume, oil temperature, etc., and displays this real-time information on the display interface. When an alarm occurs, the operator can take measures such as pausing or canceling the oil dispensing. The upper computer communicates with the lower computer via a communication module. It not only archives the data transmitted from the lower computer in a database but also queries and authorizes invoices transmitted from the lower computer, ensuring smooth production. It is the central system of the entire system, capable of real-time monitoring and management of all aspects of the system and automatically generating various oil production reports, such as daily, monthly, and annual reports. 2.1.2 Invoicing Machine: The invoicing machine shares data with the upper computer, verifying the document number before each oil dispensing. Before dispensing, the upper computer sends the set parameters, such as the oil location number, oil type, quantity value, and unit of measurement, to the lower computer. 2.1.3 Communication between the Host Computer and the Invoicing System The host computer and the invoicing system communicate via a high-speed LAN switch, ensuring fast data transmission speed and high security and reliability. 2.1.4 Host Computer Software The host computer development software uses Borland Delphi 7, and the database uses Microsoft SQL Server to implement information storage, retrieval, etc. Since its inception, Borland Delphi has been one of the most important application development systems under the Windows environment, capable of developing a wide variety of applications, from low-level software to upper-level user-facing software. The host computer is divided into three levels: operator, administrator, and super administrator. Different accounts log in to the system and enjoy different operating permissions. The operator has the lowest permissions, able to access menus such as oil spreading, editing, statistical queries, and parameter settings; the administrator can access the above menus and system settings; the super administrator has the highest permissions, able to perform all operations in the main menu and manage other operators. Operators can change their own passwords, but only the super administrator can set permissions, i.e., assign new usernames and passwords to other users. Depending on the situation at the oil dispensing site, oil dispensing methods can be divided into stand-alone oil dispensing and networked oil dispensing: In networked oil dispensing, the host computer and the invoicing system share data; in stand-alone oil dispensing, the system is disconnected from the invoicing system. Control methods can be divided into host control and setpoint controller control: Host control refers to the host computer controlling the setpoint controller to perform the oil dispensing operation; the setpoint controller directly controls the oil dispensing when the network is disconnected, in which case the slave computer saves important data during oil dispensing, and immediately transmits the oil dispensing information to the host computer once the network is reconnected. In most cases, host control is used. Before the host computer starts oil dispensing, system settings need to be performed, including: setting the total number of storage locations and the status of each location; parameter settings, including the specific oil storage location number, oil type, density, etc., and these set values ​​are sent to the slave computer. Based on the site conditions, an oil depot dispensing system display interface was designed in the host computer. It includes displays for individual storage locations and tables showing the overall dispensing status, including the oil type, fixed quantity, fixed unit, actual weight, actual volume, density, temperature, and online/offline dispensing status for each location. After dispensing is completed, important data such as the operator at the time, dispensing location number, oil type, purchasing unit, and document number are saved in the database as a long-term backup and for future retrieval. There are four query methods: by time, by oil type, by document number, and by customer. Query results can be printed out in report form. The host computer directly exchanges data with the setpoint controller. It not only archives the data from the slave computer in a database but also queries and authorizes invoices from the slave computer, ensuring smooth production. As the central system, it can monitor and manage all aspects of the system in real time, ensuring functions such as printing delivery receipts, printing reports of undelivered oil, monitoring oil delivery status, querying material discharge records, querying customer records, setting and modifying parameters, modifying oil product and price parameters, displaying loading arm position status, and monitoring operating status. It can also automatically generate various oil production reports, such as daily, monthly, and annual reports. 3. Slave Computer System Design and Selection of the Setpoint Controller: The setpoint controller is a computer instrument that uses a 78E58 advanced single-chip microcomputer as the CPU for quantitative control. During the design and selection process, the setpoint controller must meet the requirements of high reliability, powerful functions, stable performance, strong applicability, and convenient maintenance and operation. When used in conjunction with solenoid valves or electro-hydraulic valves, it achieves automatic quantitative filling. It can measure flow rate by mass or volume, and parameters can be easily entered via the keyboard, displaying instantaneous and cumulative values. The setpoint controller is equipped with a temperature sensor interface, electrostatic connection interface, spill prevention interface, and communication interfaces (RS232, RS485) to network with a higher-level management system for automatic control and quantitative filling. Direct 220V AC mains input makes the DH6409V setpoint controller very easy to install. Since the loading site is an explosion-proof environment, all electrical equipment and instruments installed on-site must be explosion-proof, and the setpoint controller should be an explosion-proof instrument. To save investment and facilitate installation, a dual-channel explosion-proof setpoint controller is selected, allowing one controller to control the quantitative filling operation of two metering pipelines. The setpoint controller (see Figure 2) is used in conjunction with high-precision flow meters, thermometers, explosion-proof electro-hydraulic valves, and other instruments to provide temperature compensation for the flow rate of the measured fluid. It performs program control, quantitative control, overflow prevention interlocking, and grounding interlocking control throughout the loading process. The setpoint controller has an explosion-proof rating of dIIBT6 in petrochemical design. Installed on-site, it is controlled and monitored by operators. Signals are transmitted to the control room via RS-232 to RS-422/485 communication interfaces for display, tabulation, and printing, achieving decentralized control and centralized management in the petrochemical industry. 3.1 The setpoint controller can perform the following functions [1] (see Table 1): 3.1.1 Flow coefficient setting: Different flow coefficients can be set using different pulse output flow meters to facilitate unit conversion. The coefficient setting range is 0.0001～9999. 3.1.2 Quantitative setting: The loading quantity can be preset. When the cumulative flow reaches this value, the instrument sends a control signal to close the valve, achieving the purpose of quantitative control. 3.1.3 Temperature compensation: The flow rate can be converted into the standard volumetric flow rate at 20℃ in real time according to the medium temperature. 3.1.4 Anti-overflow interlock: When the loading liquid level exceeds the limit, the liquid level switch installed on the upper part of the loading arm will activate, and the instrument will send a signal to control the loading to stop and issue an alarm signal to prevent liquid overflow. 3.1.5 Grounding Interlock: During loading (tanker truck) operations, the tanker truck must be properly grounded to prevent excessive static electricity. When the quantitative controller detects a grounding resistance greater than 1000 ohms, it will immediately signal to stop loading, close the valves, and issue an alarm. 3.1.6 Communication: Communication interface is RS-232 to RS-422/485; baud rate is 1200, 2400, 4800, 9600; maximum distance: 1.2km. Table 1: Function Table of the Setpoint Controller. 3.2 Main Technical Specifications of the Lower-Level Controller: 3.2.1 Power Supply: AC220V±10%, 50Hz±2%. 3.2.2 Input Signals: a. Flow Rate: 0～3KHz voltage square wave or current pulse, contact signal. b. Temperature: Pt100 resistance temperature detector (RTD) c. Valve feedback: Passive contact d. Level switch: Passive contact 3.2.3. Output signal: 3 channels of 220VAC/5A switch signal 3.2.4. Communication: RS232, 485, 4-20mA current signal 3.2.5. Static grounding: Used in conjunction with a static clamp to form a static interlock 3.2.6. Data protection: The controller automatically protects data from loss when power is lost. 3.2.7 Temperature Compensation Range: Within -20℃ to +120℃, when forming a system with a primary meter (instrument accuracy 0.2-0.5 class), the metering accuracy is adjustable to <0.3%. 3.2.8 Accuracy: a. Flow cumulative error: ±(0.1FS%+1 digit) b. Temperature display error: ±1℃ 3.2.9 Settable Values: a. Quantitative setting range: 1～99999 b. Density setting range: 0.0001～2.0000 c. Coefficient setting range: 0.0001～9999. 3.2.10 Operating Mode: Continuous operation 3.2.11 Operating Conditions: a. Ambient temperature: -10℃～+55℃ b. Relative humidity: Not greater than 85% c. Explosion degree of flammable gas or flammable liquid vapor in the environment: Class II B, natural temperature T6 level. 4. Design and Selection of Power Control Cabinet The power control cabinet is the high-voltage component of the entire system, and its role is crucial. Besides providing power to the setpoint controller, it also contains control circuits for electro-hydraulic valves and pump drive circuits. It is the control center of the actuators, primarily responsible for power switching, signal indication, and pump and valve actuation. Its characteristics are as follows: 4.1 Contains the power switch for the entire system's setpoint controller. 4.2 Contains the drive circuits for the entire system's electro-hydraulic valves. 4.3 Contains the pump drive circuits for the entire system. 4.4 Contains the pump start indicator for the entire system. 4.5 Contains various power indicators. 4.7 Contains a power filtering system. The external dimensions of the power control cabinet are 800×600×1600mm (length×width×height), including power switch, signal indicator, DC power supply, relay, and wiring terminals. 5. Working principle and design selection of explosion-proof electro-hydraulic valve [2] The FBDF series CNC electro-hydraulic valve is composed of one normally open solenoid valve, one normally closed solenoid valve, and two 3/8” small ball valves (needle valves) (as shown in Figure 3). The normally open solenoid valve is installed on the upstream pipeline of the controlled circuit, and the normally closed solenoid valve is installed on the downstream pipeline of the controlled circuit. During the pipeline transportation of the medium, when it is necessary to open the valve, the computer sends a valve opening signal, the normally open solenoid valve is energized (closed), and the normally closed solenoid valve is energized (opened). At this time, the chamber channel from the upstream to the main valve diaphragm is blocked, and the channel from the main valve diaphragm to the downstream is opened. At this time, the pressure at the bottom of the diaphragm is higher than the pressure at the top, and the medium in the chamber of the main valve diaphragm is discharged to the downstream pipeline through the normally closed solenoid valve channel, and the main valve is opened. When the valve needs to be closed, the computer sends a valve closing signal, causing the normally open solenoid valve to open and the normally closed solenoid valve to close. At this time, the passage from the upstream to the chamber on the main valve diaphragm is opened, while the passage from the main valve diaphragm chamber to the downstream is closed. The high-pressure medium from upstream enters the chamber on the main valve diaphragm through the normally open solenoid valve. At this point, the pressure on the upper and lower parts of the diaphragm is equal, and the main valve closes under the action of the spring force. During the opening and closing of the main valve, the normally open solenoid valve is energized (closed), and the normally closed solenoid valve is de-energized (closed). At this time, both the upstream and downstream passages are in a closed state, and the medium pressure is concentrated in the chamber on the main valve diaphragm, causing the main valve to be locked in a fixed open position due to the hydraulic differential, thus maintaining a constant flow rate at the main valve outlet. When the upstream flow rate changes, the computer sends a signal to the corresponding solenoid valve based on the feedback signal from the flow meter, allowing it to automatically readjust to the preset flow rate value. The FBDF series CNC electro-hydraulic valve has two small ball valves (needle valves) in the controlled circuit as response valves of the main valve. One ball valve in the upstream controlled circuit is a shut-off regulating valve, and the other in the downstream controlled circuit is an open regulating valve. The opening and closing of the main valve can be finely adjusted by changing the opening degree of the two small ball valves (needle valves) according to the viscosity of the medium and the actual pipeline pressure. The closing degree of the small ball valves (needle valves) does not exceed 4/5 of the full scale. The FBDF series CNC electro-hydraulic valve also has a small ball valve in the downstream control circuit as a manual control valve. When there is a power failure or the solenoid valve is not working, this valve can be manually operated to open or close the main valve; it can also be used to detect whether the valve core diaphragm is damaged. Figure 3 shows the control principle diagram of the electro-hydraulic valve. 6. Design and selection of flow meters & filters (see Table 2) Table 2: Main component materials and nominal pressure accuracy class 0.5, 0.2 (generally -10℃～+60℃) Operating medium temperature: LC-A, LC-E: (-20℃～+100℃) LC-Q: (-20℃～+60℃) LC-A and LC-E can reach 200℃ with the addition of a high-temperature heat sink under high-temperature adjustment. Remote display on-site explosion-proof rating: ExiaⅡCT5,dⅡBT4 7 Design and selection of electrostatic oil overflow protector 7.1 Principle: The SLA-S electrostatic oil overflow protector uses an electrostatic grounding clamp to detect the electrostatic grounding connection. When the electrostatic grounding is not connected or the grounding is poor, oil cannot be dispensed; a probe monitors the safe liquid level. When the liquid being filled touches the probe, the oil overflow protector emits an audible and visual alarm, and simultaneously outputs a corresponding signal to the loading control system, automatically cutting off the control valve and delivery pump, thus making the filling process safer. Suitable for distributed loading control systems. 7.2 Technical parameters: Explosion-proof rating: ExdⅡBT4 Signal output: Switch quantity or level quantity Working power supply: DC12V or AC220V Working current: 15mA Ambient temperature: -30℃～+60℃ Figure 4: Installation diagram of electrostatic oil overflow protector 8. Design and selection of communication module Isolation RS-232 to RS-422/485 converter with a transmission rate of up to 115.2KBPS 3000VDC isolation protection network connection distance up to 4000 feet with automatic data flow control, RS-485 using RS-232 software RS-232 interface connector: hole type DB-9 Power consumption: 1.2W Operating temperature: -10℃ to 70℃ Power requirements: +10 to +30V Power and data flow indicator for fault diagnosis Figure 5: Communication diagram of loading system 9. Hardware configuration list of quantitative control system (see Table 3) 10 Power control cabinet External dimensions: 150×500×700mm including power switch, signal indicator, DC power supply, relay, terminal block References: [1] Lu Demin, Zhang Zhenji, Huang Buyu. Petrochemical Automation Control Design Manual. [M]. Chemical Industry Press. 2002, pp. 1074-1076.