This paper describes the cryogenic control system and associated instrumentation of the test facility for 3 pre-series units of the LHC Cryogenic Distribution Line. For each unit, the process automation is based on a Programmable Logic Con-troller implementing more than 30 closed control loops and handling alarms, in-terlocks and overall process management. More than 160 sensors and actuators are distributed over 150 m on a Profibus DP/PA network. Parameterization, cali-bration and diagnosis are remotely available through the bus. Considering the diversity, amount and geographical distribution of the instru-mentation involved, this is a representative approach to the cryogenic control system for CERN's next accelerator

Bager, T

Balle, C

Bertrand, G

Casas-Cubillos, J

Gomes, P

Parente, C

Riddone, G

Suraci, A

CERN Document Server

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHEuropean Laboratory for Particle PhysicsINSTRUMENTATION, FIELD NETWORK AND PROCESS AUTOMATIONFOR  THE LHC CRYOGENIC LINE TESTST. Bager, Ch. Balle, G. Bertrand*, J. Casas-Cubillos, P. Gomes, Cl. Parente, G. Riddone, A. SuraciThis paper describes the cryogenic control system and associated instrumentation of the test facility for 3pre-series units of the LHC Cryogenic Distribution Line. For each unit, the process automation is basedon a Programmable Logic Con-troller implementing more than 30 closed control loops and handlingalarms, in-terlocks and overall process management. More than 160 sensors and actuators are distributedover 150 m on a Profibus DP/PA network. Parameterization, cali-bration and diagnosis are remotelyavailable through the bus.Considering the diversity, amount and geographical distribution of the instru-mentation involved, this isa representative approach to the cryogenic control system for CERN's next accelerator.LHC Division* SGTE Travaux Electriques, Technoparc Gessien, rue Gustav Eiffel, 01630 Saint-Genis-Pouilly, FrancePresented at the Eighteenth International Cryogenic Engineering Conference (ICEC 18)21-25 February 2000, Bombay Mumbai, IndiaGeneva, Large Hadron Collider ProjectAdministrative SecretariatLHC DivisionCERNCH - 1211 Geneva 23SwitzerlandLHC Project Report 395Abstract26 July 20001Instrumentation, Field Network and Process Automation for the LHC Cryogenic Line TestsTroels Bager, Christophe Balle, Guy Bertrand*, Juan Casas, Paulo Gomes, Claudia P rente,Germana Riddone, Antonio SuraciLHC Division, CERN, 1211 Geneva 23, Switzerland* SGTE Travaux Electriques, Technoparc Gessien, rue Gustav Eiffel, 01630 Saint-Genis-Pouilly, FranceThis paper describes the cryogenic control system and associated instrumentationof the test facility for 3 pre-series units of the LHC Cryogenic Distribution Line.For each unit, the process automation is based on a Programmable Logic Con-troller implementing more than 30 closed control loops and handling alarms, i-terlocks and overall process management. More than 160 sensors and actuatorsare distributed over 150 m on a Profibus DP/PA network. Parameterization, cali-bration and diagnosis are remotely available through the bus.Considering the diversity, amount and geographical distribution of the instru-mentation involved, this is a representative approach to the cryogenic controlsystem for CERN’s next accelerator.1 INTRODUCTIONThe Large Hadron Collider (LHC), currently under construction at CERN [1], will make use of 1700main superconducting magnets distributed along a 27 km circular tunnel and operating in superfluid he-lium below 2 K. A Cryogenic Distribution Line (QRL) [2], mounted in parallel to the magnets, will feedthem through jumper connections every 107 m. Several thousand sensors and actuators will be mountedeither on the magnets or on the QRL, scattered along the LHC circumference.Therefore, it is important to investigate process automation based on instrumentation distributedover industrial field networks. This will simplify considerably the cabling, configuration and mainte-nance, compared to typical point to point connections between process controllers and field devices.Three pre-series Test Cells of the QRL, delivered by different suppliers, will be tested during 2000to validate their thermal and mechanical design. For each Test Cell there are more than 160 sensors andactuators, distributed over 150 m on a Profibus DP/PA network. A Programmable Logic Controller (PLC)implements 34 Closed Control Loops (CCL) and handles alarms, interlocks and the process phase se-quencing. All instrumentation is accessed either through Profibus remote I/O cards or directly on ProfibusDP or PA; parameterization, calibration and diagnosis are remotely available, through the bus.2 CRYOGENIC LINE TEST FACILITYEach QRL Test Cell [3] (~110 m length) comprises an LHC standard cryogenic distribution cell (PipeModule) and one Service Module at each end (SI and SA). The Service Modules include the valves andjumper connections to feed later on the magnets cooling loops.For each Test Cell, an additional set of four End Boxes is used to supply (TS) and to return (TR)cryogens to the main cooling circuits and to simulate the interfaces to the magnets (TI and TA). Theyhouse the four phase separators and control valves necessary for the Test Cell operation. In order to dis-criminate the heat load of the QRL Test Cell from that of the auxiliary End Boxes, the later are evaluatedin a dedicated test set-up where a Link Module replaces the Test Cell.The cryogen used to cool the Test Cell is helium, saturated at 4.2 K and gaseous at 80 K. A 10 m3dewar fills a phase separator in the Supply Cryostat with liquid helium, to be distributed to the threeTest Cells. For pre-cooling the Test Cells, circulated helium gas will be cooled by liquid nitrogen, fed bya 50 m3 Tank.23 PROCESS CONTROLThe cryogenic process of each Test Cell is controlled by a PLC (Siemens® PU413-2DP) running 34CCL with a sampling time of 2.5 s, which is well adapted to the plant characteristics. The process man-agement includes several phases such as cool down, nominal operation, warm-up and thermal cycling.Software interlocks, on the liquid helium level of the End Boxes’ phase separators, close the associ-ated filling valves to prevent overflow and stop the liquid heaters when the level is too low. All otherelectrical heaters are software-interlocked to associated thermometers, inhibiting them at too high tem-perature; moreover, for high-power heaters (>1 kW) additional hardware interlocks on the actual tem-perature of the heating element operate independ ntly of the PLC working status.Alarms are provided to notify the operator when the liquid level or the gas pressure in the phaseseparators are too high. The test set-up can be fully automatically operated without human intervention24 h per day. Upon an alarm occurrence the operator is warned, either by e-mail or cellular phone.An Engineering Work Station (EWS) is used for PLC programming and configuration, parameter-ization and maintenance of intelligent devices. The cryogenic operation and the data storage are per-formed by an Operator Work Station (OWS), running PCVue32™ (Arc Informatique®) as SupervisoryApplication Control and Data Acquisition and directly accessing the PLC data base of process vari bles.4 PROFIBUS NETWORKProfibus is a Master-Slave serial data communication system, networking decentralized digital controllersand field devices. Masters are active stations, like the PLC or the EWS, that manage the data communi-cation on the bus; they can take control of the bus, via token exchange, and send messages without exter-nal request. Slaves are peripheral devices such as remote I/O, valve positioners and measurement trans-mitters, that communicate under request. The Profibus network comprises DP and PA segments.4.1 Profibus DPProfibus DP, based on EN 50170 standard, is specifically dedicated to fast data exchange between auto-mation systems and distributed peripherals. The communication medium can either be a twisted-pairshielded copper cable or an optical fiber; via the copper cable, the transmission conforms to the EIARS485 standard, in a linear network topology. The cable length per bus segment ranges from 100 m ( t12 Mbit/s) up to 1200 m (93.75 kbit/s); the maximum number of stations per segment is 32. Using RS485repeaters, the bus length can be extended by a factor of 10 and the number of stations increased to 127.The DP network of each Test Cell (Figure 1) consists in a 150 m long segment, that operates at1.5 Mbit/s and comprises 23 nodes, including EWS, PLC, DP/PA Link, 15 remote I/O stations (ET200M)and 5 Mass Flow Meters (MFM).Figure 1  Field network4.2 Profibus PAProfibus PA is based on EN 50170, like Profibus DP, and uses a transmission technology according to theIEC 61158-2 standard, in a linear and tree network topology. It provides data communication, at31.25 kbit/s, and power supply through the same twisted-pair shielded copper cable. The maximum cablelength, including star branches, is 560 m; each branch is limited to 30 m or 120 m, according to the num-ber of branches. The maximum number of stations in a PA network is 32.3The DP/PA Coupler (Siemens®) provides galvanic isolation and transmission technology conversionbetween both type of segments; communication speed on the DP side is 45.45 kbit/s. The current avail-able to feed the stations is limited to 400 mA. The DP/PA Link (Siemens®) allows to distribute higherpower consumption over up to 5 Couplers, yet on the same PA network. The number of stations is stilllimited to 32, but communication speed on the DP segment is no more limited to 45.45 kbit/s.The PA network of each Test Cell consists in two linear segments, with 11 and 12 stations and alength of 50 and 150 m respectively; it includes 20 intelligent valve positioners and 3 pressure transmit-ters, consuming 12 and 10 mA respectively. The positioners incorporate a current consumption limitter(16 mA) to avoid blocking the bus in case of failure. A single DP/PA Link and two Couplers are used.5 INSTRUMENTATIONThe 121 sensors per Test Cell comprise 99 thermometers, 7 level-, 5 flow- and 10 pressure- transmitters.The actuators consist of 28 valves and 20 heaters, corresponding to 47 kW of controlled electrical power;among these actuators, 34 are PID-controlled whereas the others are on/off devices.Fifteen remote I/O stations (Siemens® ET200M,Figure 2) are used for reading most of the input sig-nals (115 analog and 58 digital) and for controllingheaters and non-intelligent valves (3 analog and 29digital outputs); this represents 88 % of the totalchannel count (236). Each I/O station communicateswith the PLC via Profibus DP.At the extremities of the Test Cell (Figure3),two racks house the PLC, the signal conditioners forthe End Boxes’ thermometry and level measurement,and the associated I/O stations. Next to each of them, a relay cabinet controls the powering of the heaters.Temperatures are measured with three types of sensors: Platinum, Carbon (AllenBradley®) and Cr-noxTM (LakeShore®) that cover respectively the 30...300 K, 1.6…100 K and 1.6...300 K ranges. Platinumsensors are read directly by ET200M using an R-4-wire configuration, without any intermediate signalconditioning. CernoxTM and Carbon sensors are read by CERN-developed linear multi-range signal condi-tioners [4], whose 4-20 mA outputs are sent to ET200M. As all these sensors are non-linear, the resis-tance is converted into temperature (Kelvin scale) by a linear interpolation routine running on the PLC.Liquid helium levels in the phase separators are measured with superconducting wire gauges(Twickenham Scientific Instruments®); to minimize the dissipated heat, the sensor excitation is pulsed.Their 4-20 mA current-loop outputs are read by ET200M. Liquid nitrogen levels in the Tank and in theSubcooler are measured with differential pressure transmitters (Endress+Hauser®), communicatingthrough Profibus PA.Intelligent Mass-Flow Meters (MFM) (Brooks®) communicate directly on Profibus DP. The pressureon the nitrogen Tank is read by a Profibus PA transmitter (Endress+Hauser®); pressure transmitters (Dan-foss®) on all the phase separators and on some pipes have 4-20 mA outputs to ET200M.Figure 3  Layout of a QRL Test Cell, showing End Boxes, relay cabinets and instrumentation racksThe pneumatic valves (Kämmer®) with intelligent positioners (Siemens® SIPART PS2) communicatethrough Profibus PA. In case of loss of communication or power, the positioner drives the actuator to itsfail-safe position. Furthermore, the compressed air circuit between each positioner and the re pectiveFigure 2  Conditioners and ET200M I/O4actuator can be cut by an electromagnetic-valve; this action is simultaneous for all pneumatic valves andis driven either by a manual switch or by an ET200M digital output. Three classical analog control valvesare driven with 4-20 mA (from ET200M) and have digital end-switches; five on/off valves are driven by0/24 V digital outputs (also from ET200M).Electrical heaters are powered through 220 V AC solid state relays, with average power regulated bypulse-width modulation technique; the relays are driven by ET200M digital outputs.6 END BOX TEST FACILITYA preliminary test on each of the three sets of EndBoxes is being carried out (Figure 4). Due to the lim-ited spatial extension, the DP segment is reduced to afew tens of meters, permitting operation at 12 Mbit/s.More than 40% of the full Test Cell instruments areused, including 85% of the heaters and 30% of thevalves and thermometers.During this test, the final version of both signalacquisition racks is commissioned, allowing to checkthe Profibus network, assess and adjust sensors’ accu-racy and tune PIDs and phase sequence.7 CONCLUSIONThe process automation and field network, with distributed I/O and smart instrumentation, has been suc-cessfully implemented and commissioned for the QRL End Box test. Its extension for the full QRLTest Cell is in progress.As for another Profibus network formerly implemented at CERN [5], the commissioning of the re-mote I/O and intelligent valve positioners was straightforward. However, despite being on the market foralready one year, certain DP intelligent devices still show some problems. Occasionally, power interrup-tion leads to permanent device malfunction, with communication loss or bus jamming, possibly due togalvanic isolation issues. This can be circumvented by using their 4-20 mA output. Moreover, the func-tionality is not yet as advertised by the manufacturer: a missing function was fixed on the configurationfile but not on the device firmware. Bad electrical contacts on internal connectors have been solved by thereplacement of connector type. Interaction with the manufacturer is going on to solve these troubles.The utilization of a Profibus DP trace monitor software, running on the EWS, has been helpful tovisualize the availability of devices and the data exchange between partners in the network. Process D-vice Manager (Siemens® PDM) has been used for configuration and parameterization of the PA devices.Its current version is limited to 16 nodes and only runs on a EWS c nected to the DP bus and to thePLC. A new release with unrestricted number of devices and access not limited to Profibus will soon beused.Connection to PLC through the Local Area Network and the interoperation of the PLCs of differentTest Cells are under consideration.REFERENCES1. The LHC Study Group, The Large Hadron Collider Conceptual Design, CERN/AC/95-05.2. Erdt, W.K., Riddone, G., Trant, R. The Cryogenic Distribution Line for the LHC: Functional Specification and ConceptualDesign, In: Proc. CEC/ICMC99, Montreal, Canada.3. Livran, J., Mouron, G., Parente, C., Ridonne, G., Rybkowski, D., Veillet, N. A Cryogenic Test Setup for the Qualificationof Pre-series Units for the LHC Cryogenic Distribution Line, paper presented at this co ference.4. Casas, J., Gomes, P., Henrichsen, K.N., Jordung, U., Rodriguez-Ruiz, M.A. Signal Conditioning for CryogenicThermometry in the LHC, In: Proc. CEC/ICMC99, Montreal, Canada.5. Casas, J., Gomes, P., Jordung, U., Metral, L., Serio, L., Suraci A. Process Automation of a 600 A HTS Current LeadCryogenic Test Facility Using a Field Network with Smart Instrumentation, In: Proc. ICALEPCS99, Trieste, Italy.Figure 4  End Boxes and Link Module

Instrumentation, Field Network And Process Automation for the LHC Cryogenic Line Tests

Instrumentation, Field Network And Process Automation for the LHC Cryogenic Line Tests

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