The DCS (Detector Control System) of the ALICE experiment at LHC aims to integrate, configure, and monitor all the participating sub-detectors. The HMPID (High Momentum Particle Identification Detector), based on a Ring Imaging Cherenkov, is one of the ALICE sub-detectors. Its control system (CS) has to ensure the detector configuration, standalone running mode for test and maintenance, and integration in the ALICE DCS. In order to design the HMPID CS, we present in this paper an approach based on the GRAFCET Model. First results from the application of the GRAFCET to the liquid circulation apparatus, an HMPID subsystem, are reported. The impact of the solutions for the HV-LV sub-systems on the CS is also presented

De Cataldo, G

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The Detector Control System for the HMPID in the ALICE Experiment at LHC.De Cataldo, G.for the ALICE collaborationINFN sez. Bari,  Via G. Amendola 173, 70126 Bari, Italygiacinto.decataldo@ba.infn.itAbstractThe DCS (Detector Control System) of the ALICEexperiment at LHC aims to integrate, configure, andmonitor all the participating sub-detectors.The HMPID (High Momentum ParticleIdentification Detector), based on a Ring ImagingCherenkov, is one of the ALICE sub-detectors. Itscontrol system (CS) has to ensure the detectorconfiguration, standalone running mode for test andmaintenance, and integration in the ALICE DCS.In order to design the HMPID CS, we present inthis paper an approach based on the GRAFCET Model.First results from the application of the GRAFCET tothe liquid circulation apparatus, an HMPID sub-system, are reported. The impact of the solutions forthe HV-LV sub-systems on the CS is also presented.I. INTRODUCTIONALICE [1] is one of the four experiments plannedto run at the Large Hadron Collider at CERN. Since itis located in an underground tunnel and it will not beaccessible during the LHC running period, an efficientDCS has to be implemented in order to remotelyconfigure, monitor and maintain the detector.The DCS reacts to events that can take fromfraction of second to some hours to develop therefore itmay also be named Slow Control System.The ALICE DCS architecture [2] is based on threelayers: the process layer, the control layer and thesupervisory layer. In the first one are detectors, sensorsand actuators; in the second are controller devicesreading data from the process layer and sending therecommands. These devices supporting the TCP/IPprotocol are networked and exchange information withthe supervisory layer by means of the OPCserver/client model. In the third layer the supervisorysoftware provides the user panels (MMI, Machine ManInterfaces) where all the relevant information about thestatus of the detector are displayed. CERN has selectedthe PVSS II package as Supervisory Control And DataAcquisition system (SCADA) [3] where the MMI willbe developed. In Fig. 1 is shown a possible DCS architecturewhere the functionality of each device is reported.In order to build a CS, two main phases should beaccomplished: design and implementation.In the design phase a map of the detector sub-systems (i.e. gas, LV, HV etc..), and a list ofrequirements for each of them, as well as for thedetector, have to be provided. These requirementsinclude all the actions to be performed to run properlythe detector.When the list and sub-systems have been definedthen a graphic tool, which assumes the CS as a finitestate machine, can be adopted for its representation,validation and simulation.This approach is very effective especially when acomplex CS, consisting of concurrent hierarchicalprocesses, must be designed. In addition these tools canalso produce an Instruction List (IL) which fits therequirements of the control devices defined during theimplementation phase.Figure 1: Architecture of the ALICE DetectorControl SystemII. THE DCS OF THE HMPIDA. DCS designGenerally for small CS the design phase isperformed simultaneously with the implementation ofthe software in the control devices.The HMPID [4] consists of an array of 7 MWPC’swith a CsI photo-cathode. To run it properly about1500 parameters have to be controlled thus resulting ina quite complex CS.According to the HMPID operational conditions,the following sub-systems and relative lists ofrequirements have been defined: physical parameters(P&T of environment), LV, HV, liquid radiatorcirculation apparatus and gas.In this paper, we intend to verify the benefits ofdesigning the CS of such a detector by means of agraphical tool, in a software-assisted environment, notdepending on the chosen technology.The GRAFCET (GRAphe Fonctionel de CommandeEtape/Transition) model has been selected [5].GRAFCET was introduced in France in 1977. It is agraphical tool developed to design industrial controlsystems assumed as a finite state machine.To explore its capabilities, we applied this modelon the liquid circulator sub-system. The concerned CSincludes only a small number of devices and isdesigned for a particular application, nevertheless itcovers all layers of a complete CS.Since the HV-LV sub-systems are crucial for theDCS structure (for both economic and technicalaspects), before including them in this test, we havestudied the impact on the DCS for a couple of solutionsthat will be presented in section E.B. The Control System for the liquidcirculation systemA prototype of the circulation system was built andequipped with Siemens PLC’s as control devices [6].The IL (control software) was written according to theFunctional Control Block (FCB), a technique foreseenin the Step7 (the Siemens PLC programminglanguage). In this work we have developed, in the freewareenvironment GRAF7-C [5], the CS including itsrepresentation, validation, and simulation as well as thecorresponding IL written in  Step7.In Fig. 2, is reported the schematic diagram of theliquid circulation system. It consists of a main tank, apump, a column and a radiator module. At first thecolumn and then the radiator module are filled throughsome cleaning filters (not shown in the figure) with thepumped liquid. A fixed hydrostatic head (heightdifference between the column overflow and the outletat the top of the radiator) allows the radiator module tobe fed by gravity. Liquid from the radiator outlet fallsunimpeded towards the main tank.Fig. 3 shows the GRAFCET representing the CSfor the liquid circulation system. Each state isnumbered and according to its value, the representingvariable can assume the active or NOT active value.On the right of each state, in the relevant rectangle, arereported the actions performed by the CS.To move from one state to another the booleancondition for the transition must be fulfilled.Figure 2: Schematic of the circulation system in the controlpanel of its simulationA relevant aspect of this model is the possibility todefine a master GRAFCET, that when activated canforce the normal (or slave) GRAFCET to a predefinedstate. As an example, if the system in Fig. 3 is stoppedthen the state 11 becomes active and the normalGRAFCET is forced on the state 2 which becomesactive. Then the STOP variable becomes true.C. CS validation and simulationIn order to validate the CS, a qualitative simulationof the circulation system has been written in the Cprogramming language. It exchanges data with therunning GRAFCET in the GRAF7-C environment. Theleft side of the control panel in Fig. 2 shows the statusof variables in the GRAFCET. At the bottom of thesame panel some failure conditions can be simulated,consequently all the related alarm conditions may beverified by the GRAFCET and flagged on the panel.This procedure has been very effective in order todefine and verify the alarm conditions necessary tosafely operate our circulation system and eventuallyour detector.In addition this simulation has proven to be usefulfor user training and system maintenance.  TheGRAFCET and related simulation are available on theweb site [7].Normal MasterFigure 3: GRAFCET representation of the control system for the liquid radiator circulation system.D. CS implementationAccording to the norm IEC 61131-3 relative to theimplementation of a GRAFCET into a PLC, weproduced the IL written in Step7 from the GRAFCETin Fig. 3.Meanwhile we have also investigated the possibilityto buy some industrial software as CoDESys [8] andAUTOMGEN [9] where the CS design as well as theIL can be done in more reliable and assisted conditions.This CS consists at the end of a graphical userinterface (in the supervisory layer) and an IL running inthe control layer. Since many CPUs are there available,we think that some control software should be locallyrunning in order to bring the detector in a safe statewhen a supervisory system crash might happen. Inother words the control layer should not be solelydevoted to send data from the process layer to thesupervisory one but also able of autonomous decisions.This will simplify the structure and debugging ofsupervisory software when the ALICE DCS will beimplemented.E. Definition of the HV-LV sub-systemsIn order to evaluate impacts and costs of the HV-LV solutions on the HMPID DCS, we divided theHMPID module in 12 elementary segments (Fig. 4).Each one consists of a defined FEE number of channelsfacing 24 anode wires. This geometricalcorrespondence is imposed from the operatingcondition of this detector based on a CsI solid statephoto cathode. Indeed in case of LV or HV failure, thefault segment can be switched OFF, with the propersequence, independently from the others.Assuming this segmentation, in order to design theLV-HV CS we are exploring two possibilities:the first one, shown in fig 5, is based on a CAENHV-LV frame, with OPC server and supportingTCP/IP protocol. It allows its complete remote controland integration in the HMPID DCS;the second one is a custom solution based on highcurrent low cost LV units controlled via auxiliaryelectronics and PLC devices. In this case the HVsystem is still based on the CAEN frame. Fig. 6 showsthe hardware and software diagram for a single LVchannel. In order to switch ON/OFF a channel, tomonitor the absorbed current and detect the faultconditions, this solution requires dedicated controlsoftware running in the PLC’s CPU. In addition thiscustom solution will affect the FEE and readoutelectronics (RO) since some components (voltageregulator, current sensors..) have to be installed in theFEE-RO PC boards.Figure 4: HMPID HV-FEE segmentationAlthough this custom solution seems to be about30% less expensive then the commercial ones,additional manpower to develop the control softwareand auxiliary electronics is necessary. In addition itrequires a non-standard maintenance compared to whatis ensured on long-term operation by companies whichsupply crates with proper connectivity and LV moduleswith complete remote control. Moreover, the customsolution is not based on LV floating units as the CAENones thus resulting in a more difficult matching withthe HMPID ground level. Although we are inclined toadopt the HV-LV power supply system based on theCAEN SY1527 (or 527) frame, we intend anyhow toexplore better both these solutions especially reducingthe HMPID segmentation.F. DiscussionOur opinion on using the GRAFCET model inorder to design a CS is positive. In fact the controloperated in the GRAF7-C environment while thecontrol system is drawn, the representation of the CS asa finite state machine, the validation of the final design,are very helpful tools.From what we have learned on GRAFCET webelieve that this design procedure can be extended (ifadopted), to the custom LV solution as well as to thephysical parameter sub-system which is also based onADC modules of a PLC. In fact according to thepressure and temperature values measured on theHMPID, many related actions will be taken. To handlesuch a complex system, the GRAFCET approach couldfinally becomes mandatory.In addition as reported in [10], we also believe thatthis model will be useful when the HMPID CS will bedesigned. In fact the detector configuration through thesetting of five sub-system, the CS validation andsimulation, and the alarm condition management, mayprofit again of the GRAFCET model. Therefore, atpresent we are encouraged to pursue this approach.Figure 5: DCS representation with HV-LV CAEN basedsolutionFigure 6: controlling scheme of LV channel based oncustom solutionG. ConclusionThe application of the GRAFCET model indesigning a control system seems very effective. Therepresentation, validation, and simulation of the controlsystem for the HMPID liquid circulation apparatus, inthe freeware environment GRAF7-C, have shown thepotentiality of this approach. We intend to explore thepossibility to extend this method to the completeHMPID CS using industrial software environment asCoDeSys or AUTOMGEN. Although more expensivethen a custom solution, we are inclined to adopt theHV-LV CAEN systems based on the frame SY 1527(or 527), since its complete remote control whichallows an easy integration in the DCS.FEES1FEES12FEES6ADC S1 ADC S2ADC S3 ADC S4MCM S7 MCM S9 MCM S12MCM S1 MCM S3 MCM S6HVS1HVS6HVS12DigitalOutputModuleSM421Hardware and software for a single channel controlFromPower SupplyVoltage RegulatorCurrentSensingAnalogInputModuleSM431ToElectronics:GassiplexMEM,TTLand ADCLocal  Software  InteractionLocal  Software  InteractionPLC SiemensOPCServerFaultRem V regulator+5 MIC29301-5BU+2.7 MIC2941ABU-2.7 LM2991TRelayEna/Dis pinHMPIDModuleRadiatorGasGassiplexTTL+MEMADCHVElectronicsphys.par.: P,T.Subs. 2)Subs. 1)Subs. 3)Subs. 5)Subs. 4)HMPID DCS layoutPLC SIEMENSAnalog anddigital I/OAnalog inputDigital OutputSY527Killing sign. for each HV chHS / CAENETTo othersSY527ALICE SubdetectorSCADAsystemA303Ethernet LANTCP/IPOPC/DCOMWinNT+OPC ServerAxxxA549A549A549A549A821Under design3V 5A 8-6ch?AxxxAxxx6V 4A 4 ch6V 4A 4 chWith sensing wireWith sensing wireH. AcknowledgementsI would like to thank Marc Sciamanna (PhD at theFaculté Polytechnique de Mons, Belgique) for hisinvaluable help in introducing the GRAFCET model,A. Franco (INFN sez. Bari, Italy) for the fundamentalcontributions on all the subjects of this work, H.Milcent (IT/CO CERN) for the useful discussions onthe Siemens PLC programming technique.III. REFERENCES[1] ALICE Technical Proposal CERN/LHCC 95-71[2] ALICE 98-23 Int. Note/DAQ/DCS/Trigger[3] http://wwwlhc.cern.ch/Controls/WG/ScadaWG.html[4] HMPID Technical Design Report,CERN/LHCC 98-19 [5] A control system for a prototype of the liquidcirculation system of HMPID (ALICE Experiment); M.Sciamanna, internal status report ALICE DCS group[6] A control system for the ALICE-HMPID liquiddistribution prototype using off the shell components;ALICE INT-99-14[7]http://richpc1.ba.infn.it/reserved/DCS/Grafcet/GRAFCEThome.html[8] http://www.codesys.de/[9] http://www.irai.com/[10] Using a GRAFCET as Conception Tool for acontrol System, About the differences between codingand specification phase; M. Sciamanna, internal statusreport ALICE DCS group.

The detector control system for the HMPID in the ALICE experiment at LHC

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