Data acquisition
From Wikipedia, the free encyclopedia
Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer. Sometimes abbreviated DAQ or DAS, data acquisition typically involves acquisition of signals and waveforms and processing the signals to obtain desired information. The components of data acquisition systems include appropriate sensors that convert any measurement parameter to an electrical signal, which is acquired by data acquisition hardware.
Acquired data is displayed, analyzed, and stored on a computer, either using vendor supplied software, or custom displays and control can be developed using various text-based programming languages such as BASIC, C, Fortran, Java, Lisp, Pascal. EPICS is used to build large scale data acquisition systems. Comedi is an open source project that defines an application programming interface and driver structure. It is a standard programming method to access data acquisition hardware. LabVIEW offers a graphical programming environment optimized for data acquisition. MATLAB provides a programming language but also built-in graphical tools and libraries for data acquisition and analysis.
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[edit] How data is acquired
Data acquisition begins with the physical phenomenon or physical property of an object (under investigation) to be measured. This physical property or phenomenon could be the temperature or temperature change of a room, the intensity or intensity change of a light source, the pressure inside a chamber, the force applied to an object, or many other things. An effective data acquisition system can measure all of these different properties or phenomena.
A transducer is a device that converts a physical property or phenomenon into a corresponding measurable electrical signal, such as voltage or current. The ability of a data acquisition system to measure different phenomena depends on the transducers to convert the physical phenomena into signals measurable by the data acquisition hardware. Transducers are synonymous with sensors in DAQ systems. There are specific transducers for many different applications, such as measuring temperature, pressure, or fluid flow.
Signals may be digital (also called logic signals sometimes) or analog depending on the transducer used.
Signal conditioning may be necessary if the signal from the transducer is not suitable for the DAQ hardware to be used. The signal may be amplified or deamplified, or may require filtering, or a lock-in amplifier is included to perform demodulation.
Analog signals tolerate almost no cross talk and so are converted to digital data, before coming close to a PC or before traveling along long cables. For analog data to have a high signal to noise ratio, the signal needs to be very high, and sending +-10 Voltags along a fast signal path with a 50 Ohm termination requires powerful drivers. With a slightly mismatched or no termination at all, the voltage along the cable rings multiple time until it is settled in the needed precision. Digital data can have +-0.5 Volt. The same is true for DACs. Also digital data can be send over glass fiber for high voltage isolation or by means of Manchester encoding or similar through RF-couplers, which prevent net hum. Also as of 2007 16bit ADCs cost only 20 $ or €.
DAQ hardware is what usually interfaces between the signal and a PC. It could be in the form of modules that can be connected to the computer's ports (parallel, serial, USB, etc...) or cards connected to slots (PCI, ISA) in the mother board. Usually the space on the back of a PCI card is too small for all the connections needed, so an external breakout box is required. The cable between this Box and the PC is expensive due to the many wires and the required shielding and because it is exotic. DAQ-cards often contain multiple components (multiplexer, ADC, DAC, TTL-IO, high speed timers, RAM). These are accessible via a bus by a micro controller, which can run small programs. The controller is more flexible than a hard wired logic, yet cheaper than a CPU so that it is alright to block it with simple polling loops. For example: Waiting for a trigger, starting the ADC, looking up the time, waiting for the ADC to finish, move value to RAM, switch multiplexer, get TTL input, let DAC proceed with voltage ramp. As 16 bit ADCs and DACs and OpAmps and sample and holds with equal precision as of 2007 only run at 1 MHz, even low cost digital controllers like the AVR32 have about 100 clock cycles for bookkeeping in between. Reconfigurable computing may deliver high speed for digital signals. Digital signal processors spend a lot of silicon on arithmetic and allow tight control loops or filters. The fixed connection with the PC allows for comfortable compilation and debugging. Using an external housing a modular design with slots in a bus can grow with the needs of the user. High speed binary data needs special purpose hardware called Time to digital converter and high speed 8 bit ADCs are called oscilloscope#Digital storage oscilloscope, which are typically not connected to DAQ hardware, but directly to the PC.
Driver software that usually comes with the DAQ hardware or from other vendors, allows the operating system to recognize the DAQ hardware and programs to access the signals being read by the DAQ hardware. A good driver offers high and low level access. So one would start out with the high level solutions offered and improves down to assembly instructions in time critical or exotic applications.
[edit] History
Scientific Solutions -->link Scientific Solutions invented the PC based data acquisition in 1981 with the introduction of the LabMaster, BaseBoard,DADIO,LabTender, IEEE-488 hardware and LabPac software. Scientific Solutions was formally a part of Tecmar.
[edit] See also
- Signal processing
- Data acquisition system
- Data analysis
- Test method
- Input devices:
- Hardware:
- Software:
[edit] References
[edit] Books on data acquisition
- Charles D. Spencer (1990). Digital Design for Computer Data Acquisition. Cambridge University Press. ISBN 0-521-37199-6.
- B.G. Thompson & A. F. Kuckes (1989). IBM-PC in the laboratory. Cambridge University Press. ISBN 0-521-32199-9.
- W. R. Leo (1994). Techniques for Nuclear and Particle Physics Experiments. Springer. ISBN 3-540-57280-5.
[edit] Articles on data acquisition
[edit] Articles about generic data acquisition systems
- E. T. Subramaniam, Kusum Rani, B. P. Ajith Kumar, and R. K. Bhowmik (Sept 2006). "Ethernet based list processing controller for high speed data acquisition systems". Review of Scientific Instruments 77: 096102. AIP. doi:10.1063/1.2338300.
- Robson CCW, Bousselham A, Bohm C (Aug 2006). "An FPGA-based general-purpose data acquisition controller". IEEE Transactions on Nuclear Science 53 (4): 2092-2096. IEEE. doi:10.1109/TNS.2006.878698.
- Xia YP (July 2004). "Serial port controls 16 independent output lines". Electronics World: 41.
- Mason G (Nov 2002). "A handheld data acquisition system for use in an undergraduate data acquisition course". IEEE Transactions on Education 45 (4): 388 - 393. IEEE. doi:10.1109/TE.2002.804402.
- Fullem TZ, Spencer CD (Sep 2002). "A Universal Serial Bus interface for electronics projects and instruments". American journal of physics 70 (9): 972-974. AAPT. doi:10.1119/1.1477436.
- Spencer CD (Oct 2000). "A capable voltage logger for the PCI bus". American journal of physics 68 (10): 966-968. AAPT. doi:10.1119/1.1286854.
GK: Josh Keene twirp D: Sam Holden, Joe Mason M: Rob Rothon, Goof Rothon S: Rowan Douglas
Subs: subs varely on a weekly basis and are often even more unheard of
[edit] Articles about how to teach a course on data acquisition
- Antler M, Salin E, Wilczek-Vera G (Mar 2005). "Teaching data acquisition - An undergraduate experiment in the advanced analytical chemistry laboratory". Journal of Chemical Education 82 (3): 425-427. ACS.
- Moriarty PJ, Gallagher BL, Mellor CJ, Baines RR (Oct 2003). "Graphical computing in the undergraduate laboratory: Teaching and interfacing with LabVIEW". American Journal of Physics 71 (10): 1062-1074. AAPT. doi:10.1119/1.1582189.
- Hubin WN (Jan 2002). "A course in computer-based data acquisition". American Journal of Physics 70 (1): 80-85. AAPT. doi:10.1119/1.1410951.
- J. Maps (Jul 1993). "A computer-based data acquisition laboratory for undergraduates". American Journal of Physics 61 (7): 651-655. doi:10.1119/1.17175.
- Carl A. Kocher (Mar 1992). "A laboratory course in computer interfacing and instrumentation". American Journal of Physics 60 (3): 246-251. doi:10.1119/1.16903.
- Seligmann P, Spencer CD (April 1985). "Two freshman courses which introduce digital electronics, programming, computers, and interfacing". American Journal of Physics 53 (4): 343-345. doi:10.1119/1.14163.
[edit] Articles about data acquisition systems for specific applications
- Fanti, V. Marzeddu, R. Piredda, G. Randaccio, P. (October 2006). "A Portable Acquisition System Based on USB Standard for the Medipix2 X-Ray Detector". IEEE Transactions on Nuclear Science 53 (5 Part 1): 2578-2583. IEEE. doi:10.1109/TNS.2006.877153.
- DeSerio R (April 2004). "Synchronous analog I/O for acquisition of chaotic data in periodically driven systems". American journal of physics 72 (4): 553-558. AAPT. doi:10.1119/1.1648330.
- Ochoa OR, Kolp NF (Nov 1997). "The computer mouse as a data acquisition interface: Application to harmonic oscillators". American Journal of Physics 65 (11): 1115-1118. AAPT. doi:10.1119/1.18732.
- Spencer CD, Paul SR (Jan 1997). "Hardware and software for a pulse height analyzer linked to a personal computer". Computers in Physics 11 (1): 101-109. doi:10.1063/1.168598.