The European Organization for Nuclear Research (CERN), the world’s largest particle physics laboratory, was founded in 1954, and it straddles the border between France and Switzerland near Geneva. It was one of Europe's first joint ventures and now has 22 member nations, which include Austria, Belgium, Bulgaria, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Spain, Sweden, Switzerland and United Kingdom, as well as numerous associate members and observer-status nations.
CERN is home to various experiments, facilities and accelerators, the most notable being the Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator, which first became operational in 2008. The LHC is a 27-km pipe ring containing superconducting magnets and a number of accelerating structures (Figure 1). Inside the accelerator, particle beams travel around the ring in opposite directions via ultrahigh vacuum tubes at speeds close to that of light itself before they collide.
The beams are guided by the electromagnets, built from electric-cable coils operating in a superconducting state. To conduct electricity without resistance, the accelerator is connected to a liquid-helium distribution system, which chills the magnets to ‑271.3 °C, a temperature that is colder than outer space.
A machine that large with that many condition variables requires a unique monitoring system to ensure all devices are working properly. In 2007, before the LHC came on-line, individuals from CERN’s engineering department, along with input from the radioprotection group of CERN’s health, safety and environment (HSE) department, began discussing the need for condition monitoring in the tunnel, and the result is as grand as the LHC itself. Meet TIM, the train inspection monorail. TIM is a mechatronic system designed to provide unmanned actions in the LHC tunnel when there is no active beam (Figure 2). The first TIM was installed in 2014 and has since performed a number of inspections of critical sectors of the LHC. Two TIM units are in operation in the LHC.
TIM performs several surveillance operations, such as visual inspection, measurement of oxygen, temperature and radiation level. With TIM, the operation downtime for workers performing these surveys in the LHC tunnel is reduced, meaning reduction in personnel exposure to hazards, such as radiation dose and oxygen deficiency.
The TIM control system consists of a fail-safe onboard PLC controller and I/O modules, an onboard industrial PC (IPC) and a graphical user interface for operating from the surface. The PLC system is the main controller of TIM’s operation.
Processing all of the information from the sensors and controlling the actuators, the PLC is in charge of performing customizable autonomous measurements. Along with a set of different sensors, the PLC is also responsible for the safety aspects, such as obstacle detection, in order to avoid damages to both TIM and the LHC machine.
The onboard data-saving is performed in the IPC, which features a data storage and acquisition system.
The fail-safe PLCs of the train are Siemens S7-300, which is the standard series for all of the section projects. The IPC is Siemens, as well, which guarantees the needed robustness for the operation environment. TIM’s HMI is developed in LabView and has a modular design, which minimizes the time of maintenance and addition of new features.
TIM is equipped with multiple environment sensing devices such as oxygen sensor, temperature sensor and radiation probe. These sensors are integrated directly in the PLC system, which shares the data with the IPC. Regarding visual sensing, TIM features pan-tilt-zoom (PTZ) cameras, high-definition (HD) cameras and a thermal camera, which are directly connected to the network and accessible from IPC and human-machine interface. The specific components were chosen because of their appropriateness to the application.
Some of the sensors, such as the radiation probe, the oxygen sensor and the thermal camera, are calibrated once per year or every two years. Others, such as the PTZ and HD cameras, do not need calibration. The temperature sensor is simply replaced if it fails. Every few months, during technical stops of the LHC, a series of maintenance procedures are performed on the TIM train, including calibration of sensors, if necessary.
TIM communicates with the surface via universal mobile telecommunications service (UMTS) 4G, which is present in all of the 27 km of LHC tunnel. The sensing data is sent to a central database and published in an internal website, where it can be easily compared and analyzed.
TIM’s HMI has a very user-friendly design and has no need for expert operators. It provides feedback from all of the sensors and allows the operators to customize the measurement surveys according to their needs. Visual inspections are done with the HMI, as well (Figure 3). TIM’s motion system is a dc motor and a motor drive, which is connected to and controlled by the PLC.
Due to the 27 km of LHC tunnel, two TIM units are installed and operating in different sectors for covering the complete ring. More units are intended to be installed in the near future, in order to minimize the time for inspecting the LHC.
In the time of operation, TIM has saved a considerable amount of personnel time in exposure to hazards.