Data acquisition and storage
After the last amplification stage, the output electric signal of the detector is carried with a 20m long shielded coaxial cable to a 23bit-10MHz ADC board on a VXI bus.
The ADC control is provided from the acquisition workstation by hardware Interrupt Requests (IRQ), which have a slow intrinsic time jitter of the order of 0.1µs. Each time new data are ready in the ADC internal memory, an IRQ is sent from the ADC to the GPS clock, that answers back a synchronization time label to the acquisition workstation through an RS232 port. In this way the achieved timing precision is of the order of 0.1µs.
The acquisition software collects the data from the ADC, add to them the time label, setup parameters and other informations organized in a binary frame. Then the frame can be stored on disk, stored on tape, sent by ethernet TCP to the analysis workstations or just used ‘on the fly’ by monitoring software.
The acquisition of the detector signal can be done along with auxiliary informations, e.g. from sysmometers, thermometers, analog lock-ins, and so on. These data are digitized with a multiplexed 24 channels 16bit ADC board, or acquired through the GPIB port. The latter port can provide control signals for instrumentations as well.
------FIGURA SCHEMA ACQUISIZIONE IN INGLESE
AURIGA data acquisition schematics-----
The ADC board is a Hewlett-Pakard E1430A VXI 10 MSa/s 23-bit Digitizer with DSP and Local Bus.
The main features of the HP E1430A board are:
------------ FIGURA -------------
Details: The HP E1430A high-resolution digitizer is a C-size, one-slot, register-based VXI module that can analyze spectra or capture transients, digitize IFs or record waveforms. The module includes DSP-based real time digital filtering with digital LO and large FIFO memories.
The digitizer used in this module is a two-pass (or sub-ranging) type that provides 23 bits of raw resolution. The digitizer in the E1430A has low distortion with a noise density of -136 dBfs/Hz and a noise figure of 15 dB.
The module comes with multistage digital filters built in with a maximum information bandwidth of 4 MHz. A high-speed 8 MB memory captures transients or acts as a FIFO for continuous digitizing during the block-mode data transfers used by some DSP algorithms. Data transfer is over the VXI data path and the high speed Local Bus (40 Mbytes/sec).
The VXI (VME eXtension for Instrumentation) is an enhanced version of VME (Versa Module Eurocard) bus, and is made up of control and syncronization lines between digital boards (with TTL or ECL signals) that are capable of up to 100MB/s data transfer rate and IRQ generation and transmission with a time jitter of 100ns.
Standard serial communication port for workstations and PC.
Multisystem eXtension Interface: it is a 8MB/s bus for connection of up to 8 digital devices and expansion boards.
Computer Aided Software Engineering: a set of utilities/compilers/editors to manipulate a software source code at block-diagram level.
A CASE by Artis Software, to help in designing event driven software, with visual modelling facilities and tools, equipped with simulation and debug modules. Artifex can generate the C-code of the project for a vast number of hardware architecture, which greatly simplify portability of the code. For more details see http://www.artis.it
BANNER + SCREENCAPTURES
The data acquisition workstation is a Sun Sparc 10, provided with RS232, GPIB and MXI interfaces. A special MXI-VXI adapter cable is required to bridge between the two buses.
The Global Positioning Sistem is a method to determine geographical coordinates and local time coordinate on Earth using calibrating signals from a network of satellites. It is based on the knowledge of the orbits of the satellites and the measured phase shifts of their signals at the receiver. The precision of this measure is of ~100m in position and ~1µs in time.
The main tool for writing acquisition software is the CASE Artifex, by Artis Software. The output code is standard ANSI C, and is compiled under Sun/OS® and Solaris®. The processes involved in acquisition are
The data and informations collected by the acquisition software are stored in sets of binary files, each one several 105 bytes long, corresponding to a few hours of acquisition at 5 kHz. The informations inside the file are organized in smaller units or frames of different kinds: buffers of acquired data from the ADC, setup informations (input voltage range, sampling frequency, etc.), slow channels or GPIB channels.
Monitor and setup GUI
The grafical user interface for control and monitor of the acquisition processes is realized with National Instruments LabView® software. The main interface lets the user chose which task are to be activated (bare acquisition, data storing to disk, backup to tape, auxiliary channels acquisition, ....) and set-up the acquisition parameters. In addition it provides a graphical (through very low-level) interface to monitor the data while they are acquired, that works just with the bare acquisition process on.
The present hard disk storage is 1.7GB, that provide for 10÷20 hours of buffer in case of failure of the primary tape storage.
The tape backup for long-term storage and offline analysis uses ¼" 4.5GB ExaByte® cassettes or ½" 35 GB DLT tapes.