CERN is now setting up String 2, a full-size prototype of a regular cell of the LHC arc. It is composed of two quadrupole, six dipole magnets, and a separate cryogenic distribution line (QRL) for the supply and recovery of the cryogen. An electrical feed box (DFB), with up to 38 High Temperature Superconducting (HTS) leads, powers the magnets. About 700 sensors and actuators are distributed along four Profibus DP and two Profibus PA field buses. The process automation is handled by two controllers, running 126 Closed Control Loops (CCL). This paper describes the cryogenic control system, associated instrumentation, and their commissioning

Bager, T

Balle, C

Blanco-Viñuela, E

Casas-Cubillos, J

Gomes, P

Pelletier, S

Serio, L

Suraci, A

Vauthier, N

arXiv

CERN is now setting up String 2, a full-size prototype of a regular cell of the LHC arc. It is composed of two quadrupole, six dipole magnets, and a separate cryogenic distribution line (QRL) for the supply and recovery of the cryogen. An electrical feed box (DFB), with up to 38 High Temperature Superconducting (HTS) leads, powers the magnets. About 700 sensors and actuators are distributed along four Profibus DP and two Profibus PA field buses. The process automation is handled by two controllers, running 126 Closed Control Loops (CCL). This paper describes the cryogenic control system, associated instrumentation, and their commissioning.CERN is now setting up String 2, a full-size prototype of a regular cell of the LHC arc. It is composed of two quadrupole, six dipole magnets, and a separate cryogenic distribution line (QRL) for the supply and recovery of the cryogen. An electrical feed box (DFB), with up to 38 High Temperature Superconducting (HTS) leads, powers the magnets. About 700 sensors and actuators are distributed along four Profibus DP and two Profibus PA field buses. The process automation is handled by two controllers, running 126 Closed Control Loops (CCL). This paper describes the cryogenic control system, associated instrumentation, and their commissioning

Bager, T.

Balle, C.

Blanco, E.

Casas, J.

Gomes, P.

Serio, L.

Suraci, A.

Vauthier, N.

Pelletier, S.

CERN Document Server

TUAP065INSTRUMENTATION, FIELD NETWORK AND PROCESS AUTOMATIONFOR THE CRYOGENIC SYSTEM OF THE LHC TEST STRINGT. Bager, Ch. Balle, E. Blanco, J. Casas, P. Gomes, L. Serio, A. Suraci, N. Vauthier,LHC Division, CERN 1211 Geneva 23, SwitzerlandS. Pelletier, Soteb National Elektro, 60 rue Clement Ader, 01630 St Genis-Pouilly, FranceAbstractCERN is now setting up String 2 [1], a full-size proto-type of a regular cell of the LHC arc. It is composed oftwo quadrupole, six dipole magnets, and a separatecryogenic distribution line (QRL) for the supply andrecovery of the cryogen. An electrical feed box (DFB),with up to 38 High Temperature Superconducting (HTS)leads, powers the magnets.About 700 sensors and actuators are distributed alongfour Profibus DP and two Profibus PA field buses. Theprocess automation is handled by two controllers, running126 Closed Control Loops (CCL).This paper describes the cryogenic control system,associated instrumentation, and their commissioning.1 LAYOUTString 2 consists of two consecutive LHC half-cells,comprising: two quadrupoles, six 15 m dipoles, theirmultipole correctors, and the QRL. The chain of magnetsis terminated, on the upstream end, by the DFB and, onthe downstream end, by the Magnet Return-Box (MRB).The QRL is terminated by its feed and return boxes(QLISF and QLISR).The DFB houses 3 pairs of 13 kA and 16 pairs of600 A current leads, to feed 11 electrical circuits. TheMRB contains the short circuits and the connection to theQRL, simulating the jumper of the following cell. A6 kW/4.5 K refrigerator supplies and recovers thecryogen. Fifteen power converters supply the magnets’electrical circuits.String 2 has a length of about 120m and follows thetunnel curvature of the LHC machine (Figure 1). Most ofits elements are heavily instrumented for the experimentalprogram. String 2 is being assembled in two phases.Phase 1 started to be commissioned in April 2001; itcomprises all elements except the three dipoles of thesecond half-cell, which will be added in early 2002.Figure 1: overview of String 22 PROCESS CONTROL2.1 StructureThe String 2 cryogenic process [2] is handled by twoindustrial Programmable Logic Controllers (PLC), fromSiemens (CPU-S7-414-3DP). One of them is dedicated tothe magnets and QRL cryogenics (PLC1), whereas theother controls the DFB cryogenics (PLC2).The refrigerator and its coupling to String 2 arecontrolled by an ABB based system, not reported here.An Engineering WorkStation (EWS) can be remotelyconnected to the PLCs, through Profibus DP or Ethernet.It is used to program the PLCs and to directly accessintelligent devices, for configuration, parameterizationand monitoring.The cryogenic operation and data storage areperformed on an Operating WorkStation (OWS), linkedto the PLCs through Ethernet. It runs the SupervisoryControl And Data Acquisition (SCADA), which is basedon PcVue32 and was developed by BARC, India, and bythe CERN/LHC/IAS group.Transients on some process variables are recorded bya fast VME + LabView data acquisition system,developed by INCAA, Netherlands, and by IAS group.2.2 Main ProgramEvery 100 ms, the main program of each PLC checksif any of the following routines is scheduled for execution(Table 1): CCL, input acquisition, phase sequencer,interlocks, alarms and communication. The time-stampassociated to every call is available to the OWS.Table 1: instrumentation and routine count per PLCPLC1 PLC2 totalprocess inputs 326 290 616process outputs 39 42 81total I/O 365 332 697CCLs 32+7x2=46 4+38x2=80 126alarms always valid 16 5 21alarms for specific phases 25 5 30interlocks 27 6+38x2=82 1092.3 Inputs, Outputs and CCLsEvery one of the 81 process outputs (actuators) ishandled by a CCL routine, which implements a PIDalgorithm. Half of the actuators have a double PID,whereby one out of two process inputs can be selected onthe OWS. This leads to 126 PIDs.The process input to a PID can be filtered (first-orderlow-pass) or substituted by a constant value. Twosetpoints, and their respective offsets, are selectable foreach PID; an instantaneous modification of the setpointvalue can be limited in slope.A PID can be in one of the following modes, by orderof increasing priority: automatic, forced by process,manual or interlocked. The PID output is respectively:calculated, forced by the process conditions, set by theoperator, or driven into a safe position.CCLs are scheduled for execution with a rate (up to1Hz) fixed according to the process characteristics. Someheaters have their average power regulated by a Pulse-Width Modulation technique (PWM). Their CCLs arecalculated every 10 s and their digital output updatedevery 100 ms, leading to a 1% resolution.The about 500 inputs not used in CCLs are read by theacquisition routines and made available in the OWS, formonitoring and diagnostics.2.4 Process PhasesA process phase sequencer tests the start/stopconditions for every operational phase, such as cool-down, normal operation, magnet powering, quenchrecovery and warm-up. Associated to each phase,automatic actions are programmed for each actuator:choose each of two PIDs, choose each of two setpoints,regulate or force to close or to open, with or withoutramp. These automatic actions can be overridden bymanual or interlocked modes.2.5 InterlocksAbout 30 general interlock conditions are available, inorder to force actuators into a safe position, like:   close valves when liquid level or pressure are high;   power-off level indicators if  no liquid is present;   stop heaters if a risk of thermal runaway exists.Moreover, 80 interlocks protect the HTS current leadsagainst excessive cooling: each valve controlling thecooling of the current leads is interlocked with twotemperatures at the warm end of the lead.The interlock thresholds are editable on the OWS andthe associated process values and status bit are displayed.This status bit is also visible on each actuator’s PIDfaceplate. Interlocks override automatic and manualactions and they cannot be disabled.For high-power heaters (>1 kW), local hardwareinterlocks are activated by the actual temperature of eachheating element, independently from the PLC.2.6 AlarmsAbout 20 alarm conditions are always tested, while 30others are valid only in specific phases of the process. Asfor the interlocks, the threshold for each alarm conditionis editable on the OWS and the process value and statusbit are displayed. Two enable bits are available for alarmactivation and for outgoing signal generation.If any of the enabled alarms lasts more than 1 minutewithout being acknowledged, or if the communicationwith a PLC is idle for more than 5 minutes, the OWSautomatically warns the operator. A message with thetype of alarm is sent through email or cellular phone.Additionally, when any of the enabled alarms lastsmore than 1 minute, or if either PLCs stops, a globalhardwired signal is sent to the CERN Technical ControlRoom (TCR). The responsible person will then be calledafter a given time. This global signal can also beenabled/disabled/forced by software and hardware.2.7 CommunicationSpecific routines exchange information between bothPLCs and receive data from other systems, such as therefrigerator and the magnet power converter.On the other hand, critical signals are hardwired:   status of refrigerator, vacuum and quench detection;   interlocks to refrigerator and power converters;   alarm to the TCR.3 FIELDBUS NETWORKSInstrumentation is spread along the string over 120 m.Most of the process inputs and outputs are accessed bythe PLCs through various fieldbus segments (Figure 2).Figure 2: Layout and fieldbus networksIntelligent devices are directly connected toProfibus PA, operating at 31.25 kbit/s. Conventionaldevices are connected to analog or digital modules onremote I/O stations (ET200M® from Siemens), whichcommunicate on Profibus DP, running at 1.5 Mbit/s.3.1 Network PLC1To cover the instrumentation distributed along themagnets and the QRL, three DP and two PA segmentshave been used.The sensors that will be used in the LHC machine aredistributed over two DP segments, each of them 150 mlong. If one of these is down, the sensors on the other willstill be enough to run the machine. Each segmentcomprises 4 remote I/O stations, housed in crates undereach dipole, as for the LHC machine.The third DP segment, extending for about 250 m,gathers instrumentation specific to the experimentalprogram of String 2. Sixteen I/O stations are accommo-dated in ten racks behind the QRL, whereas 8 other aredirectly hooked on the QRL. Also on this DP segment arethe two PA segments; they include 7 intelligent valvesand 3 pressure sensors, installed at one end of the QRL,and 2 valves at the other end. The PLC and some I/Ostations are installed in two racks.3.2 Network PLC2Most of the DFB instrumentation is grouped on asingle and short DP segment: 8 I/O stations and a PAsegment that handles one intelligent valve positioner.The 38 valves, on the cooling inlets of the currentleads, are driven by local PLC output modules. All theI/O stations and the PLC are installed in two racks. Thisconfiguration is representative of the LHC machine,where the PLC and I/O stations of the DFB will beclustered in radiation protected areas.4 INSTRUMENTATION4.1 TemperatureMore than 400 resistive temperature sensors, of threetypes, are used in String 2 (Table 2). As all of them arenon-linear, the measured resistance is converted intotemperature by an interpolation table. Each Cernox™ andCarbon have a specific table, whereas all Platinum havethe same one.Table 2: temperature sensorsType Quantity range coveredPlatinum 295 300 K …  30 KCernox™ 115 300 K … 1.6 KCarbon 22 100 K … 1.6 KIn general, Platinum thermometers are directly read byanalog input modules as a four-wire resistor, without anyintermediate signal conditioning.Most of the Cernox™ and Carbon thermometers areread through linear multi-range signal conditioners(STMS), which produce 4-20 mA magnitude and two bitsindicating the range. Logarithmic signal conditioners(LOG) are used for sampling rates faster than a fewseconds and have a single 4-20 mA output. Both STMSand LOG are in-house developments [3].In the current leads, galvanic isolation up to 5 kV isprovided by:   IPAC® conditioners for 190 Platinum thermometers   STMS conditioners and fuses for 6 Cernox™.4.2 PressureOn pipes and vessels, absolute pressures up to100 mbar or to 25 bar are measured by warm transducers,with integrated electronics; three of them operate onProfibus PA whereas 16 other have 4-20mA outputs. Thecold mass pressures are measured by 11 passive low-voltage sensors, immersed in liquid helium; their signalconditioners have 4-20mA outputs.4.3 Liquid LevelThe eight liquid helium levels inside the vessels and inthe superfluid heat exchanger are measured withsuperconducting-wire gauges (Twickenham ScientificInstruments). To minimize self-heating, the sensors areread in 3s pulsed-mode. The output is 4-20 mA.4.4 FlowTwo mass-flow controllers, ten mass-flow meters andtwo cryogenic Coriolis mass flow-meters are used tocontrol flow rates and to assess thermal performances.They are read via 4-20 mA current-loops.4.5 HeatersElectrical heaters are used to warm-up cold gaseoushelium leaving String 2, and to evaporate liquid helium inphase separators and in the magnet cold masses.Twenty-one low-power heaters are driven by levelmodulated DC voltage. Five higher power heaters, up to64 kW, are supplied through 220 VAC solid state relays,via the PWM technique. Most of these are in series withprogrammable relays (Sineax), activated according to thetemperature of the respective heating element.4.6 ValvesTen pneumatic valves with intelligent positioners(Sipart® PS2, from Siemens) are spread on the twoProfibus PA segments. Thirty-four classical analog valvesare driven with 4-20 mA. Five on/off valves are driven by0-24 V digital outputs.5 COMMISSIONINGStarting in April 2001, most of the instrumentationand control was checked while the last components werebeing assembled.Every instrument had its signal chain verified from themachine to the PLC and to the SCADA. This includedcabling, signal processing, coherence between PLC andSCADA databases, and synoptic view. Phases, interlocksand alarms were tested by changing thresholds, while theactuators were inhibited.Before the final closure of the vacuum vessel, severalproblems were identified. They were repaired wheneverthe instrument or cables were still accessible. The originof these issues has been traced to:   sensor name and serial number mismatch;   installation procedure not followed;   broken wires, sensors failure.All instruments required for the cooling loops wereavailable when cool-down from 300 K to 4.5 K started,on August 7. The process was gradually set into auto-matic mode, and the machine could be left unattended.Apart from the unavoidable time spent for trouble-shooting the components and instrumentation notoperating as expected, the overall cool-down from 300 Kto 1.9 K took just over 2 weeks, as expected. Once atnominal temperature (1.9 K), the dipole and quadrupolecircuits were powered to nominal current (11 850 A).Only then, the control loops were fine-tuned, and cold-mass thermometers and pressure sensors were verified forhigh accuracy.During cool-down, the analysis of temperature pro-files showed additional inversions and identificationerrors, mainly on the current leads thermometers.6 CONCLUSIONThe installation and commissioning of String 2 cryo-genic instrumentation and control was very educative, inview of the methods to be implemented for LHC. Thestructure of software and hardware documentation wasenhanced. Software routines were improved. In the future,sensors installation procedures must be carefully respect-ed, in terms of materials, positioning, and follow-updocumentation. In this way, precious time can be saved.We wish to express our acknowledgement to theoperators team, who gave us valuable help during thecommissioning of instruments and programs.REFERENCES[1] F. Bordry et al., “The LHC Test String 2: Design Study”, LHCProject Report, March 1998.[2] L. Serio, “The Process of the Cryogenic System for String 2:Functional Analysis”, LHC-XMS-ES-0004, LHC EngeneeringSpecification, Feb 2001.[3] J. Casas et al., “Signal Conditioning for Cryogenic Thermometryin the LHC”, CEC/IMC99, Montreal, Canada, July 1999.

Instrumentation, Field Network and Process Automation for the Cryogenic System of the LHC Test String

Instrumentation, Field Network and Process Automation for the Cryogenic System of the LHC Test String

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