Process Identification through Test on Cryogenic System

UNICOS (UNified Industrial Control System) is the CERN object-based control standard for the cryogenics of the LHC and its experiments. It includes a variety of embedded functions, dedicated to the specific cryogenic processes. To enlarge the capabilities of the standard it is proposed to integrate the parametrical identification step in the control system of large scale cryogenic plants. Different methods of parametrical identification have been tested and the results were combined to obtain a better model. The main objective of the work is to find a compromise between an easy-to-use solution and a good level of process identification model. The study focuses on identification protocol for large delayed system, the measurement consistency and correlation between different inputs and outputs. Furthermore the paper describes in details, the results and the tests carried out on parametrical identification investigations with large scale systems

Advanced Control Facility for the CERN-UNICOS Framework

CERN, during last decade, has extensively applied the CERN/UNICOS framework to large scale cryoplant control system. An increase of interested to advanced control techniques and innovative simulation environment applied to cryogenic processes has also occur. Since new control algorithm development into UNICOS framework requires significant time, a control testing platform which can be externally connected can improve and simplify the procedure of testing advanced controllers implementation. In this context, the present paper describes the development of a control testing tool at CERN, which allows rapid control strategies implementation through the Matlab/Simulink® environment, coupled with the large scale cryogenics UNICOS control system or with the CERN PROCOS simulation environment. The time delays which are inherently introduced by network links and communication protocols are analyzed and experimentally identified. Security and reliability issues are also discussed

Multicontroller: an object programming approach to introduce advanced control algorithms for the GCS large scale project

The GCS (Gas Control System) project team at CERN uses a Model Driven Approach with a Framework - UNICOS (UNified Industrial COntrol System) - based on PLC (Programming Language Controller) and SCADA (Supervisory Control And Data Acquisition) technologies. The first' UNICOS versions were able to provide a PID (Proportional Integrative Derivative) controller whereas the Gas Systems required more advanced control strategies. The MultiController is a new UNICOS object which provides the following advanced control algorithms: Smith Predictor, PFC (Predictive Function Control), RST* and GPC (Global Predictive Control). Its design is based on a monolithic entity with a global structure definition which is able to capture the desired set of parameters of any specific control algorithm supported by the object. The SCADA system -- PVSS - supervises the MultiController operation. The PVSS interface provides users with supervision faceplate, in particular it links any MultiController with recipes: the GCS experts are able to capture sets of relevant advanced control algorithm parameters to reuse them later. Starting by exposing the MultiController object design and implementation for a PVSS and Schneider PLC solution, this paper finishes by highlighting the benefits of the MultiController with the GCS applications

Comparison of different cryogenic control strategies via simulation applied to a superconducting magnet test bench at CERN

Industrial process controllers for cryogenic systems used in test facilities for superconducting magnets are typically PIDs, tuned by operational expertise according to users' requirements (covering cryogenic transients and associated thermo-mechanical constraints). In this paper, an alternative fully-automatic solution, equally based on PID controllers, is proposed. Following the comparison of the operational expertise and alternative fully-automatic approaches, a new process control configuration, based on an estimated multiple-input/multiple-output (MIMO) model is proposed. The new MIMO model-based approach fulfils the required operational constraints while improving performance compared to existing solutions. The analysis and design work is carried out using both theoretical and numerical tools and is validated on the case study of the High Field Magnet (HFM) cryogenic test bench running at the SM18 test facility located at CERN. The proposed solution have been validated by simulation using the CERN ECOSIMPRO software tools using the cryogenic library (CRYOLIB [1]) developed at CERN

The Detector Safety System of NA62 Experiment

??? at the CERN SPS. The Detector Safety System (DSS) developed at CERN is responsible for assuring the protection of the experiment’s equipment

LHC-GCS Process Tuning: selection and use of PID and Smith predictor for the regulations of the LHC experiments' gas systems

The LHC experiment’s Gas Control System (LHC GCS) has to provide LHC experiments with homogeneous control systems (supervision and process control layers) for their 23 gas systems. The LHC GCS process control layer is based on Programmable Logic Controllers (PLCs), Field-Buses and on a library, UNICOS (UNified Industrial COntrol System). Its supervision layer is based on a commercial SCADA system and on the JCOP and UNICOS PVSS frameworks. A typical LHC experiment’s gas system is composed of up to ten modules, dedicated to specific functions (e.g. mixing, purification, circulation). Most of modules require control loops for the regulation of pressures, temperatures and flows or ratios of gases. The control loops of the 23 gas systems can be implemented using the same tools, but need specific tuning according to their respective size, volume, pipe lengths and required accuracy. Most of the control loops can be implemented by means a standard PID (Proportional, Integral and Derivative) controller. When this is not appropriate the Smith Predictor can be used as an alternative. This paper will describe the limitations of a standard PID approach as well as the results of the Smith Predictor implementation when a PID controller is insufficient. It will also explain the feasibility, identification, testing and the conclusions of both approaches

Liquid helium level regulation improvement in the LHC electrical distribution feedboxes

An important cryogenic equipment of the Large Hadron Collider (LHC) consists in the electrical distribution feedboxes (DFBs) which are used to power the superconducting magnets of the accelerator. These feedboxes contain the current leads achieving the electrical transition between the copper cables at ambient temperature to the Niobium-Titanium wires at cryogenic temperature, immersed in a liquid helium bath at 4.5 K. This liquid helium bath must be regulated at a defined level to allow the powering of the LHC, and this regulation often caused non-availabilities in the past. This paper presents the development of a new control scheme, coupled to the existing PID level controller, significantly improving this regulation, and rejecting disturbances in a highly efficient manner. First, a dynamic model of the DFBs was developed in the EcosimPro software using the CRYOLIB library to reproduce in simulation the regulation issues. In a second step, the new proposed regulation modes were tested and validated in simulation. Finally, the paper will present the results obtained in 2021 on a real DFBs operation in the LHC, validating the new control approach prior its massive deployment all around the LHC cryogenics

A Simulation Study for the Virtual Commissioning of the CERN Central Helium Liquefier

This paper describes the implication of dynamic simulation in cryogenics processes. The simulation aims to prepare plant commissioning and operation, and to validate the efficiency of the new process control logic. PLC programs have been tested on a process simulator integrating physical models of valves, heat exchangers, turbines, phase separator, and helium data. The model has shown the capacity to reproduce cold-box dynamic behaviour, from 300 K to 4.5 K

A Fuzzy-Oriented Solution for Automatic Distribution of Limited Resources According to Priority Lists

This project provides a solution for problems in which there is a limited cryogen resource that supplies several clients in parallel, which can cause the resource’s depletion. This study emerged from the need to solve a specific problem of the Cryogenics Group of the European Organization for Nuclear Research (CERN). A generic solution is proposed for the application in a larger number of situations. The solution is based on the Fuzzy algorithm model, which bases itself on the human reasoning as a problem-solving technique. The Fuzzy approach is presented as well as the limited resource distribution problem, via a cryogenic simulation tools. The paper describes also the comparison of the fuzzy solutions with a former one that has been previously adopted by CERN’s Cryogenic Group

Assessment of a low-cost angle-meter based on resistance measurements

In this work, an accurate, low-cost electronic angle-meter is designed, manufactured and metrologically characterized. The idea at the basis of the proposed electronic goniometer is to transduce the mechanical rotation into the variation of an electrical quantity, namely a resistance. Then, such a variation can be easily measured through a low-cost multimeter used as an ohmmeter. The metrological characterization of the prototype demonstrated that the proposed system can achieve an uncertainty as low as 1◦ with costs of an order of magnitude lower than devices currently available on the market. In practical applications, this device can be used for the metrological characterization of heading instrumentation thanks to an isolated rotating plate on which several devices can be placed