Korotaev, Yu V

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THE PC BASED CONTROL AND DATA ACQUISITION SYSTEMOF LEPTAI.KorotaevJoint Institute for Nuclear Research, Dubna, Russian FederationAbstractThe Low Energy Positron Toroidal Accumulator(LEPTA) is expected to provide experiments with anintense flux of positronium. The control and dataacquisition system consists of PCs connected other toeach and with the institute computers via an Ethernetnetwork. They are grouped in accordance with thefunctions of the LEPTA equipment and the beaminstrumentation. Device control and data acquisition areperformed via CAMAC, GPIB and special designedmicrocontroller interfaces.1   INTRODUCTIONThe storage ring LEPTA [1] is composed of a cyclicsystem of solenoids surrounded by common magneticshielding. The vacuum chamber of the ring is locatedinside the solenoids. The positron injector has its ownmagnetic and vacuum system and connects with the ringat the straight section.LEPTA consists of the following general elements:1) a septum solenoid dedicated to injection of the positronbeam and superposition and separation of the beams inthe horizontal plane. In the section inside the solenoid inthe longitudinal field region the following devices areplaced:- two septum coils producing transverse magneticfields and placed symmetrically below and under theequilibrium orbit,- kicker coils for injection and extraction of thecirculating positron beam,- the gun of the electron cooling system;2) two toroidal solenoids bend the beams by an angle of1800 – here the superposition and separation of the beamsoccur in the vertical plane;3) an electron cooling section for the positrons, whichincludes also:- pick-up stations of the diagnostic system,- an RF cavity using for bunching of the positronbeam,- also to investigate the possibility of betatronacceleration of the particles we plan to install a betatronyoke in this section;4) the electron collector, which is placed outside themagnetic shielding near the solenoid    septum;5) the injector of the low energy positrons including thebeam instrumentation system at the entrance of the ring.2  CONTROL SYSTEM CONFIGURATIONThe control system of LEPTA is based to the compatiblewith IBM personal computers. With the development ofthe LEPTA complex the number of PCs will be increased.The choice of operating system is MS Windows 98. Iteasily allows multithread software applications. Also ithas good enough network and access possibilities. Thespeed of the operating system is sufficient too, becauseLEPTA doesn’t require real-time control operations.The main function of the control system is theacquisition and the storage of data from all signals, thecomparison with preventative and alarms levels and thegraphical presentation of general status and the history ofselected signals. The PC provides the warning alerts if asignal value exceeds the alarm level. If nothing is done isswitched OFF automatically. An algorithm of the alarmturn off LEPTA is prepared together with experimentersin details.The control system has two main parts: hardware andsoftware.2.1    HardwareThe LEPTA control system is divided into two levels(Fig.1). The upper level consists of IBM compatible PCs.They communicate with each to other via a local areanetwork. This net uses the Institute Ethernet cablecommunication. The lower level consists of engineering,experimental and test facilities, and also beam diagnosticinstrumentation. At present the total number of signals tobe controlled and monitored is about 200. The lower levelis all the control subsystems with CAMAC hardware andspecial measurement equipment for the I/O dataacquisition and control. CAMAC hardware can beconnected to any computer with 1 MBaud serial links.There will be measurement equipment, which will beconnected to PC’s with GPIB links.There are about twenty signals, which should bemeasured precisely to have stable operation of LEPTA.This is especially true for current values of some magnetelements, for the electron beam energy and for kickerpulse amplitudes. Precision measurement with resolution20 and 24 bits requires about 200 ms or more. Tominimize the duration of measurement processes specialmeasurement cards [2] with on-board microcontrollershave been designed. The AT90S2313 and AT90S4414International Conference on Accelerator and Large Experimental Physics Control Systems648International Conference  Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, Italychips from Atmel provide local control of the AD7714chips from Analog Devices, previous data analysis andcommunication with PCs.To minimize the number of CAMAC crates for themeasurement of several signals, which are under differenthigh voltage potentials nearly identical measurementcards are used. Connection to PCs is performed via ahigh-voltage optical couple.Figure 1: Hardware configuration.2.2    SoftwareSoftware programs are written using C++ Builder. Thecontrol system software architecture is hierarchical withfour functional layers: equipment control, accumulatordevices, service and operator interface (Fig.2). Each ofthe four layers performs specific functions, with well-defined interfaces to the layers immediately above andbelow it. The software interface between layers is realisedthrough procedure calls that may involve communicationover local area networks. Standardised remote procedurecall protocols are used between the software processesthat operate on the different computers of the controlsystem. An object-oriented approach is taken throughoutthe software development.2.2.1    Equipment ControlThere is only one equipment control layer which directlyperforms I/O to external devices and handles signals forevents. All control and data acquisition transactions withLEPTA equipment takes place in this layer or in theequipment itself. The equipment control layer receivesstandardized messages from an accumulator device object(ADO) layer which contains commands and set points forthe equipment or requests for data. The equipment controllayer is responsible for translating a standard datarepresentation in the control system to a suitable formatfor devices and device control modules. It performs thenecessary conversions where analog control is requiredby equipment.  For equipment with a digital interface, thislayer is responsible for presenting data to the equipmentin proper digital form.Figure 2: Software configuration.2.2.2    Accumulator Devices Objects (ADO’s)The ADOs layer comprises a set of ADOs that provide anobject-oriented image of the LEPTA equipment in theapplication environment. This image is independent ofdetails of the equipment control layer or equipment itself.ADOs will be implemented as C++ classes that contain asoftware data structure and the full set of actions ormethods that are needed to control and monitor theLEPTA devices. The application interface to the ADOconsists of standardized I/O operations of get, set and soon. When the ADO layer responds to a request from thecomputer services layer, data is transformed andformatted as necessary. These operations may includesequenced state transitions, conversion to/fromengineering or physics units and filtering of statusinformation for equipment monitoring. The standardinterface to the ADO layer is uniform for all subsystems.ADOs in the control system will be namedcorrespondingly the LEPTA devices or subsystems.2.2.3    ServiceThe functions provided by the Services layer includethose usually provided by any interactive, networkedcomputer system, plus special functions that are neededby control systems. Usual control system functions,which will be provided, include:- communication protocol support,- computer security,- network management tools,1. Engineering facility2. Experiment facility3. Test facility4. Beam diagnosticsLEPTANetworkSerial CAMAC and GPIB linksPCPCOperator interfaceServiceAccumulator DeviceObjects (ADOs)Equipment controlSynchronization649- remote login,- network file systems,- printer support.The communication is based on Windows Socket anduses the TCP/IP protocol.In addition to generic functions and customapplications programs, the following control systemfunctions will be supported at this layer:- data analysis and viewing,- message support,- relational database management,- archiving and restoring of accelerator objects.Data analysis process is performed under clearalgorithms. That will guarantee stable operation ofLEPTA. Analyzed data is viewed as graphical objects,which helps an operator to access the cause of an alarmcase. For instance, if a parameter has a range of normalwork and its value is inside this frame, the color ofgraphical object is green. In case the value is near analarm border the color changes to yellow and if it is outthe normal range – red.Any action of an operator, which can lead thechanging of any parameter, is accompanied by warningmessages.All data is recorded into a temporary buffer, whichcontains the last values of all signals, and into thetemporary data archive, where all values of all parametersare saved for the last half hour. In the case of an alarm, anoperator can recall the data from the temporary dataarchive to the data archive of alarm conditions. It helps toanalyze the history of the alarm appearance to eliminatesuch situations in the future. The structure of archives iscompatible with the structure of commercial relationaldatabases. The mechanism of the data recording isillustrated in Fig.3.Figure 3: Mechanism of data recording.2.2.4     Operator InterfaceThe user interface layer provides the man-machineinterface for the control of LEPTA. It supports aninteractive graphical user interface, as well as passivegraphical and text displays and files for operation andanalysis. This interface contains modern, user-friendlygraphical input and output objects, such as pull-down andpop-up menus, menu bars, buttons, check lists, forms, textand graphical output, etc.At present now the total number of measured andcontrolled signals of LEPTA is about 200. For operationof the implemented and ready to work equipment onlytwo computers are used. Specially designed measurementboards with microcontrollers AT90S2313 andAT90S4414 from Atmel economise the PC's processortime and minimise the total number of CAMAC crates.The writing of software with a C++ Builder allowed acontrol system with a modern man-machine interface.This work is supported by INTAS (Grant #96-0966) andRFBR (Grants #96-02-17211 and #99-02-17716).5    REFERENCES[1] I.Meshkov, et al., "Design and construction ofLEPTA", to be published.[2] Yu.Korotaev, "Measurement board based on themicrocontroller", to be published.Data bufferof last values(RAM)Archive ofnormal data(HDD)Temporarydata bufferduring 30 min(RAM)Archive ofalarm data(HDD)Record every30 minutes Record in thealarm caseData3    CONCLUSIONS4    ACKNOWLEDGEMENTS650

The PC Based Control and Data Acquisition System of LEPTA

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