Abstract: This paper describes the procedures and key points of the supervision work during the construction of the AFC system of Nanjing Metro Line 1, as well as the achievements made through quality control. Keywords: AFC system; supervision; quality control; metro construction 1 Introduction to the AFC system project of Nanjing Metro Line 1 The AFC system of 16 stations, Zhujiang Road control center and Xiaoxing training base of Nanjing Metro Line 1 was jointly designed, produced, supplied, installed and debugged by Thales of France and Nanjing Panda Electronics Co., Ltd., and provided with project management, testing, training, commissioning and maintenance services. The AFC system consists of a central computer, coding system, key management system, station server, station ticketing workstation and AFC terminal equipment (automatic ticket vending machine, automatic ticket checking machine, semi-automatic ticket vending machine, portable ticket checking machine), ticket card, operation auxiliary equipment, training equipment and software system (Figure 1). 2 Quality control process of AFC system 2.1 Drawing review stage (1) The AFC equipment, ticket booth location and the layout of equipment in the ticket booth (room) must meet the requirements of metro operation and facilitate passengers to buy tickets and enter and exit the station. The layout of the Nanjing Metro AFC system in the station is generally reasonable and the design is humane. However, there have been cases where passengers have difficulty purchasing tickets and the operation staff have difficulty working properly due to design interface problems. These problems should be discovered as early as possible during the drawing review stage and changed in time. (2) During the drawing review stage, the supervisor should carefully review the relative positions of the automatic ticket gate and the billboards, directional signs, automatic ticket gate and the blind path and railings. For equipment with positional conflicts, the overall design unit should instruct the relevant departments to complete the corresponding design changes in time. 2.2 AFC equipment entry acceptance stage (1) The uninterruptible power supply (UPS), station server, central server, etc., should be accepted in accordance with the contract. Due to the rapid development of the computer industry and the rapid product updates, corresponding measures should be taken when drafting the contract. The contract document for the AFC system of Nanjing Metro Line 1 clearly stipulates: "Due to the rapid updates of computer equipment, the seller shall determine the selection criteria based on the buyer's needs and quote prices according to the equipment selection and configuration at the time of bidding; when the equipment is delivered, the buyer has the right to require the contractor to provide computer equipment according to the mainstream models and configurations of the same grade at the time of delivery, without considering any additional costs." In order to ensure the normal operation of the metro, the AFC system supervisors should understand the current status of computer hardware. During the construction process, Nanjing Metro changed the type of some computer equipment and the computer memory capacity. (2) During the factory acceptance process of AFC terminal equipment, the testing of the basic functions of the equipment should be strengthened. For AFC terminal equipment, the electromagnetic radiation protection, high voltage resistance, and the recognition performance of coin receivers and banknote receivers should be tested during the factory acceptance process, because it is difficult to conduct similar tests after the equipment is moved to the site. (3) The internal component layout and integrated wiring of the equipment should be reasonable. The maintenance keyboard and passenger display of the automatic ticket gate should be located at one end of the machine to facilitate the normal work of maintenance personnel; the integrated wiring method should not hinder the daily work of staff to replace ticket boxes, cash boxes, etc.; in addition, unreasonable wiring methods are prone to damage to cables. (4) If there are surface burrs inside the equipment, the contractor must be required to rectify them thoroughly during the factory acceptance. Although these problems do not affect the normal performance and appearance quality of the equipment, they will bring great difficulties to the normal operation of maintenance personnel and customer service personnel. After the automatic ticket vending machine and automatic ticket gate are officially put into operation, customer service personnel often need to replace the ticket boxes and cash boxes inside the equipment. If there are many burrs inside the equipment, it is very easy to cause injury to the staff. During the commissioning stage of the Nanjing Metro AFC system, the supervisor, owner, and technical personnel of the construction unit were all scratched. Although the manufacturer rectified the burr problem inside the equipment on site, the rectification effect was not ideal due to the limitations of the site conditions. 2.3 AFC system equipment installation stage (1) Strengthen the on-site supervision of key processes and key parts such as measurement and layout, wire trough pre-embedding, and waterproofing. During the measurement and layout process, it is essential to strengthen the inspection work and confirm the construction measurement and layout results in accordance with the requirements of the drawings and construction specifications. The connection between the two cable trays and the junction between the cable tray and the junction box are all places where water seepage is likely to occur. Therefore, before laying the cable trays, it is necessary to test whether the waterproofing measures of the construction unit meet the design requirements. Only after proving that the waterproofing measures can meet the relevant requirements can the cable tray laying work begin. (2) Strengthen the inspection of the internal cable markings of the equipment, especially the cables added due to engineering changes. The Nanjing Metro AFC system supervisor strictly inspected the markings of the power and signal lines in accordance with the requirements of the specifications and construction documents during the on-site testing of the automatic ticket gate, automatic ticket vending machine, and power distribution cabinet. (3) The height of the junction box outlet of the on-site automatic ticket vending machine and automatic ticket gate must be higher than the design decoration ground elevation. Only in this way can the overall waterproof performance of the AFC system be guaranteed. Although the junctions between the automatic ticket vending machine, the automatic ticket checking machine and the ground are waterproofed, water can still enter the cable tray of the AFC system through the reserved junction box of the automatic ticket vending machine and the automatic ticket checking machine, which will affect the performance of the entire AFC system. (4) During the on-site construction, the relative positions of the installed AFC terminal equipment with the blind path, advertising box, directional sign, railing, etc. should be checked in a timely manner. If any problems are found, they should be reported in a timely manner and the relevant responsible units should be instructed to complete the rectification in a timely manner. (5) The power distribution box (AP) used by the AFC system should be functionally tested in a timely manner. If the AP box cannot meet the normal working requirements of the AFC, it should be replaced in a timely manner. Two problems have occurred in the use of AP boxes in the Nanjing Metro AFC system: ① The AP box does not have an automatic switching function. When one of the power supplies in the station fails, the AFC system cannot work normally; ② The power supply provided to the AP box of the AFC system is only one incoming line. The AFC system belongs to the first-level load and should be powered by two power supplies, one main and one backup, with end switching. 2.4 AFC system debugging stage (1) Debugging of single equipment. During the testing of a single device, if three or more consecutive failures or two identical failures occur on the same device, the device will be considered unqualified. In this case, the contractor must replace or repair the device free of charge. The focus of the basic function test is the stability of the coin receiver, banknote receiver, and single-journey ticket (TOKEN) issuing device of the automatic ticket vending machine, and the working condition of the fan door of the automatic ticket gate under different environments. The human-machine interface display of automatic ticket vending machines (Figure 2), automatic ticket gates, and semi-automatic ticket vending machines should conform to human-centered design. Although the Nanjing Metro AFC system still has some deficiencies in human-centered design, the overall effect is good. The human-machine interface of the currently operating automatic ticket gates and semi-automatic ticket vending machines can be improved in two aspects: ① Change the display content of the human-machine interface when the semi-automatic ticket vending machine enters the pause service mode. When the semi-automatic ticket vending machine enters the pause service mode due to equipment failure or human factors, the information provided by the passenger display (PID) of the semi-automatic ticket vending machine should be "Ticket booth closed". Since there are usually more than one semi-automatic ticket vending machine in each ticket booth, the ticket booth may still be in service when one of the semi-automatic ticket vending machines is out of service. ② Change the content of the human-machine interface of the automatic ticket gate in service. Currently, the content displayed on the human-machine interface of the automatic ticket gate in service is "Please touch the ticket", but in fact the real ticket card detector is located at "Please swipe card" (Figure 3). In actual operation, passengers often swipe their cards on the PID. (2) Testing of the station subsystem. It mainly includes monitoring test and command test. The monitoring test mainly checks whether the station computer can monitor the station AFC equipment in real time. The focus of the test is whether the station computer can monitor the corresponding degraded operation mode status of the equipment when the on-site AFC terminal equipment is running in degraded mode. The command test mainly checks whether the on-site equipment has made corresponding changes by sending commands or group commands to the AFC equipment one by one through the station computer. The focus of the test is whether the station computer can issue degraded operation instructions to the corresponding equipment when the AFC system is running in degraded mode. (3) System integration test. All AFC equipment and systems on Line 1 will be tested, including: load testing using simulated transaction data; and testing under fault conditions. (4) 72-hour continuous test. All equipment that has passed the subsystem test will be connected for uninterrupted joint functional testing. During the 72-hour test, the AFC system should demonstrate that its integrity, operability, stability, and performance meet the design requirements under actual operating conditions. During the 72-hour continuous test, all contracted equipment, materials, and systems will operate continuously without faults according to the actual operating mode. If a fault occurs, causing the test to be interrupted, the contractor must troubleshoot the fault and restart the test within the time frame specified in the contract. After the test, the mean time between failures (MTBF), equipment MTBF, availability, and other performance indicators of each system will be preliminarily evaluated based on the test data. If the safety and availability indicators do not meet the contract requirements during the 72-hour test, the test will be considered a failure. 3. Conclusion With the concerted efforts of the supervision personnel, the construction quality of the Nanjing Metro AFC system project was effectively controlled. Hardware and software problems that arose during construction were rectified in a timely manner. The project was completed on schedule and passed the final acceptance inspection by the owner, quality inspection station, and supervision unit in one go, creating conditions for the smooth opening of the Nanjing Metro.