Appolonio, M

Galimberti, A

Presacco, R

CERN Document Server

A CONTROL AND DATA ACQUISITION SYSTEM BASED ON THE PXIBUS FOR THE NEW PHOTON BEAM POSITION MONITOR PROTOTYPEA. Galimberti , M. Appolonio, Sincrotrone Trieste, Trieste, Italy1R. Presacco, Politecnico di Milano, Milano, Italy                                                1 galimberti@elettra.trieste.itAbstractUsually, in large experimental physics facilities, systemsbased on the VME bus, are widely used both for the lowerlevel of the control system and for data acquisition. It iscommon to use this environment also for thoseapplications that do not really need its features. The PXIbus is an industrial extension of the well-known PCI busused in the desktop computer industry. It may represent aless expensive alternative platform for controlling acomplex experimental set-up increasing also the systemperformances. The development of a new generation ofdiagnostic detectors at Elettra allows investigating thisopportunity. The design of its control and data acquisitionsystem is based on the PXI bus and it is fully described inthe paper. The benefits and the inconveniences of thisplatform are then discussed. Besides real-timeapplications, based on a commercial DSP board, are alsodiscussed with their integration in the PXI system.1 INTRODUCTIONAn UHV test chamber with a detector prototype tocharacterise is an ideal environment for testing theportability and the performances of new industrial standardproducts in the experimental physics world. The aim is tohave a compact and rugged system not very expensive butwith also real time capability. So, we have built up acomplete data acquisition and control system based on thePXI bus from National Instruments. The system providesboth low priority tasks as the chamber controls and highperformance deterministic data acquisition capability.A project for the development of a novel photon beamposition monitor (PBPM) for the high brilliance beamlineof ELETTRA has been used for testing this system [1]. Itis very common to have limited experiments or particularmeasures or tests set-up, which need such a kind ofsystems.2 THE SYSTEM SPECIFICATIONSThe new PBPM is based on a system of blades thatintercepts the photons and, instead of measuring thephotoemitted currents, collects the photoemitted electronsand performs an energy characterisation. After which acalculation of beam position is done [2]. This novelapproach to the PBPM requires a more complexmechanical layout and more sophisticated electronics. Inorder to collect and analyse the photoemitted electrons, wehave adopted a technique commonly used for high-resolution electron spectroscopy. An electrostatic energyselector has been chosen as this has the advantage ofbeing more reproducible and faster to vary than a magnetictype. We have designed a custom Electron EnergyAnalyser (EEA) composed by an input lens set-up and ahemispherical dispersing element. The system may bedivided into two parts: an UHV chamber with its controlsand the detector with its settings and data acquisition. Infig. 1 is depicted the detector layout.Figure 1: The New PBPM prototype layout.A three-axis manipulator has to be controlled with greataccuracy according with the output of three high precisionoptical encoders. A link with the Ethernet network has tobe assured for acquiring, from the mains control systems,the machine status and the beamline parameterscontinuously. Besides, the vacuum and the thermalconditions are to be monitored. All these tasks have notstrict timing constraints. On the other hand, the detectorcontrols are more critical. First, a high voltage powersupply system, which configures this electrostatic device,has to be continuously checked and remotely controlled.Then a multiple mode data acquisition system has to beprovided. Two different ways of data acquisition areneeded: counting mode and current mode. Each mode has adedicated electronics: the former detects the fast pulse traincoming out from the analyser and counts them. The latterintegrates, with a configurable constant time, the signal.Subsequently, in both cases, the data is processed in orderto find the vertical beam centre.3 THE HARDWARE & SOFTWAREPLATFORM3.1 Host Computer and Operating SystemWe take into account several considerations for the choiceof the HW platform. In particular, we need a flexible andscalable solution within a rugged industrial packagesuitable for the hard environment of a synchrotronInternational Conference on Accelerator and Large Experimental Physics Control Systems418International Conference  Accel rator and L rge Experim ntal Physics Control Systems, 1999, Trieste, Italyradiation facility. The functionality of the system mightvary over the time and more devices might be addedwhenever. Besides, compatibility with the more commonsoftware environments is mandatory. Moreover, anaffordable price has to combine with the highperformances requested for some data acquisition paths.So, a PC-based technology solution has been chosen.Because the PCI bus does not satisfy our requirements, weadopt an extension of the industrial CompactPCI bus: thePXI bus from National Instruments. As operative system,we have chosen Windows NT while for the real timeapplications an I/O card with a dedicated CPU on board isused. The PXI-1000B mainframe is the physical supportfor the controller and the I/O boards. It is fully compatiblewith PXI and CompactPCI modules and it is a compact3U-sized unit with an 8-slot chassis. The PXI-8156B PXIembedded computer is the high-performance PXI systemcontroller with the entire standard I/O features built in.This computer has on-board PCI video and is still able toconnect to the PXI bus without the need of a PCI-to-PCIbridge. Therefore it preserves the full 132 Mbytes/s PCIbandwidth for other PXI boards. In addition, the PXI-8156B supports masters in all seven available PXI slots.The package provides also an USB port, a 10BaseTEthernet port and an IEEE 488.2 (GPIB) interface.3.2 The CompactPCI and PXI BusesThe CompactPCI bus combines PCI (PeripheralComponent Interface) electrical specifications withEurocard mechanics and high-performance connectors todefine a core architecture that can be used to build varioustypes of industrial systems [3]. Besides the PXI (PCIeXtension for Instrumentation) extends CompactPCI formeasurements and automation while it maintainsinteroperability with ComapctPCI [4]. The PXIspecifications are of three kinds: electrical, mechanical andsoftware. The first defines timing and triggeringextensions that bring high-performance instrumentationcapabilities to CompactPCI systems.Figure 2: The PXI products from National Instruments.The second adds requirements for environmental testing,electromagnetic compliance, and safety testing. Activecooling with fans is also required and controller locationsare more rigidly defined to improve interoperability. Thelatter defines minimum software driver requirements thatPXI modules must meet for operation in system usingMicrosoft Windows.3.3 The I/O BoardsThe PXI hardware platform fully supports also anyCompactPCI board. Therefore, a great number of I/Oboards are available on the market suitable for any kind ofdata acquisition application. We consider three particularboards that allow us to cover our specifications: the PXI-6030E and the PXI-7030E from National Instruments andthe cADC64 from Innovative Integration. The first is amultifunction I/O board with 16 single-ended inputs at 16bits, 2 analog outputs at 16 bits, 8 TTL digital I/O linesand 2 counters at 24 bits. The second is a stack of twoboards: a PXI-6030E and a dedicated CPU card optimisedfor fast and deterministic I/O acquisition. The DAQdaughter board resides on the embedded PCI bus of thecontroller board. The RT board communicates to the hostcomputer in which it resides through shared memory onthe 7030 processor board. Both the host computer and theembedded processor have access to the shared memory.The memory is allocated for various tasks. For example,LabVIEW RT uses part of the shared memory fordownloading software on the board. There is also somememory space allocated to the user for passing databetween the host PC and the processor board. Moreover,it is suitable for real-time applications while it maintainsthe plug-and-play property. This allows an easyapplication programming without the low-level drivercoding. Finally the cADC64 board, from InnovativeIntegration, supports an on board Texas Instruments DSPand 64 single-ended multiplexed analog inputs [5]. Thisboard needs also a development system for the DSPprogramming. However, it is suitable for those fast real-time applications that need the direct control of the lowlevel software operations. The development toolsavailable are a C cross-compiler, the assembler and a setof libraries. The DSP is a high performance TMS320C3232-bit floating-point capable of up to60MFLOPS/30MIPS. On-chip peripherals include twoflexible 32-bit counter/timers, 2 prioritised DMAcontrollers, a bi-directional sync serial port, 2Kbyte ofdual-access SRAM and a prioritised interrupt controller.The analog input chain employs eight 16-bit,instrumentation-grade A/D converters addressable as pairsby the DSP via four memory mapped-locations. EachA/D features an analog input simultaneously sampledupon receipt of a DSP software command or an externalTTL trigger. Each of the native analog inputs is routedthrough a differential instrumentation amplifier into a six-pole (120 dB/decade) anti-alias filter. A simple, highspeed, memory-mapped 16-bit latch is available tosupport general purpose digital I/O. The port may besoftware or externally clocked at rates to 5 MHz and eachbit on the port is capable of sourcing 40 mA.3.4 The DSP SystemThe Compact PCI interface supports bus mastering,directed by the DSP, capable of bursts of 132 Mbytes/secand sustained transfers of 20 Mbytes/sec on mostplatforms. This provides superior connectivity with419transfer rates well above competing 'C32 offeringsfeaturing awkward, register-based interfaces suitable onlyfor object code downloading. Multiple cards may beinstalled in systems with full driver support underWindows 95 and NT. The cADC64 may be programmedin C or Assembler using the tools available in thedevelopment package. The Windows device driver andDDL provided support host PC application developmentin Visual C or Basic, and any other environment capableof linking to a standard Windows DLL. Alternately, theboard is compatible with a number of packages includingLabVIEW for users seeking a turnkey data acquisition andanalysis solution. Additionally, the Ventura libraryprovides full-bandwidth access to the extensive hardwarecomplement of the cADC64 without any DSPprogramming.Figure3: The CompactPCI I/O card, from InnovativeIntegration, with a TMSC32 DSP on board.3.5 The Software ToolsThe Windows NT operating system allows using severalhigh level programming languages and software toolswhich are available on the market. An easy start-up of thedata acquisition and control system has been implementedin LabVIEW. LabVIEW RT [6] is the particular releasethat we adopt. This extension allows real-timeapplications using dedicated boards as PXI-7030E.Moreover the most performance demanding applicationshave been developed in C and/or Assembler and run on theDSP boards available. Any application may be alsowritten in C (e.g. VisualC) or CVI from NationalInstruments. Another interesting environment is theLinux OS. In particular the novel LinuxRT may representan improvement of the conventional Windows OS. Thewhole HW set-up is fully compatible with a future OSupgrade to LinuxRT. An Unix-like real-time operativesystem will add further features to this compact embeddedcontrol system, like multitasking and multithreadscapability, a full determinism of the system and theremote logging and control.4 A COMPACT CONTROL SYSTEMThe control system main tasks are the following: themanipulator movements, the vacuum and cooling systemmonitoring, the instrumentation control via GPIBinterface and the beamline and machine control systemslinks via Ethernet. The manipulator permits threemovements through stepping motors. The positions arecontrolled by optical encoders with a precision up 1 µm.Each stepper is driven with digital I/O and its movementsare controlled through a closed feedback loop with theoptical encoder. The vacuum devices and the coolingsystem are controlled through serial interfaces. Theselinks provide low speed information on the UHV chamberstatus. The most critical instrumentation is controlled viaIEEE 488.2 parallel interface. A complex system offloating HV power supplies is one of them. It polarisesthe electrodes of the detector up to some kV with 16-bitaccuracy. Another example is the electronics for the dataacquisition in counting mode. A 16 channels intelligentsystem provides the 16-bit counters necessary for the datacollection. A local CPU with a real-time OS on boardprovides a GPIB high level interface for the data transferto the host. The PXI controller with its on board Ethernetinterface allows the connection with the main controlsystems of Elettra. Besides, the link with the BeamlineControl System (BCS) provides bi-directional data flow.The main machine parameters, the beamline status and theremote control of the insertion device may be available bya TCP/IP simple client and server application. The PXImodularity allows a further expansion of the systemadding other mainframes for supporting more I/O devices.5 CONCLUSIONSA new interesting solution for small and medium sizeexperimental set-up controls has been presented. Aninnovative HW and SW platform based on standard PCcomponent has been analysed. The performing PCI busenclosed in an industrial extension system called PXI hasbeen introduced in a harsh experimental physicsenvironment. Flexibility, modularity, reliability andmaintainability represent its most interesting features. Animplementation of a control and data acquisition systemof an experimental apparatus has been realised. Thecombination of the standard-de-facto low cost Windows orLinux environments and the high level deterministic real-time capability seem to be very attractive for the mostdemanding experimental physics control system.6 ACKNOWLEDGEMENTSThe authors would like to thank G. Cautero, C. Fava, L.Gori, R. Tommasini, P. Tosolini for their technical skilland friendly collaboration.REFERENCES[1] A. Galimberti et al., Proc. 18th PAC, New York,NY, USA (1999).[2] A. Galimberti et al., to be published on Nucl. Instr.and Meth. as Proc. 5th PSD Conf., London, UK,1999.[3] PICMG 2.0 R2.1 CompactPCI Specification[4] PXI Specification, National Instruments, Rev 1.0,August 20, 1997.[5] cADC64 Data Sheet, Innovative Integration.[6] PCI/PXI-7030 and LabVIEW RT User Manual,National Instruments, 1999.420

A Control And Data Acquisition System Based On The PXI Bus For The New Photon Beam Position Monitor Prototype

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