Data acquisition
Encyclopedia
Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems (abbreviated with the acronym DAS or DAQ) typically convert analog waveforms into digital values for processing. The components of data acquisition systems include:
Data acquisition applications are controlled by software programs developed using various general purpose programming languages such as BASIC
, C
, Fortran
, Java
, Lisp, Pascal
.
Specialized software tools used for building large-scale data acquisition systems include EPICS
. Graphical programming environments include ladder logic
, Visual C++
, Visual Basic
, and LabVIEW
.
to be measured. Examples of this include temperature, light intensity, gas pressure, fluid flow, and force. Regardless of the type of physical property to be measured, the physical state that is to be measured must first be transformed into a unified form that can be sampled by a data acquisition system. The task of performing such transformations falls on devices called sensors.
A sensor
, which is a type of transducer
, is a device that converts a physical property into a corresponding electrical signal (e.g., a voltage or current) or, in many cases, into a corresponding electrical characteristic (e.g., resistance or capacitance) that can easily be converted to an electrical signal.
The ability of a data acquisition system to measure differing properties depends on having sensors that are suited to detect the various properties to be measured. There are specific sensors for many different applications. DAQ systems also employ various signal conditioning
techniques to adequately modify various electrical signals into voltage that can then be digitized using an Analog-to-digital converter
(ADC).
(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 being used. The signal may need to be amplified, filtered or demodulated. Various other examples of signal conditioning might be bridge completion, providing current or voltage excitation to the sensor, isolation, linearization.
For transmission purposes, single ended
analog signals, which are more susceptible to noise can be converted to differential signals
. Once digitized, the signal can be encoded to reduce and correct transmission errors.
, serial
, USB, etc.) or cards connected to slots (S-100 bus
, AppleBus, ISA, MCA
, PCI, PCI-E, etc.) in the motherboard
. 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 can be expensive due to the many wires, and the required shielding.
DAQ cards often contain multiple components (multiplexer, ADC, DAC, TTL-IO, high speed timers, RAM). These are accessible via a bus
by a microcontroller
, which can run small programs. A controller is more flexible than a hard wired logic, yet cheaper than a CPU so that it is permissible 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.
Many times reconfigurable logic is used to achieve high speed for specific tasks and digital signal processor
s are used after the data has been acquired to obtain some results.
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.
Not all DAQ hardware has to run permanently connected to a PC, for example intelligent stand-alone loggers and oscilloscopes, which can be operated from a PC, yet they can operate completely independent of the PC.
. These expensive specialized systems were surpassed in 1974 by general purpose S-100 computers and data acquisitions cards produced by Tecmar
/Scientific Solutions Inc. In 1981 IBM introduced the IBM Personal Computer and Scientific Solutions introduced the first PC data acquisition products.
- Sensors that convert physical parameters to electrical signals.
- Signal conditioning circuitry to convert sensor signals into a form that can be converted to digital values.
- Analog-to-digital converters, which convert conditioned sensor signals to digital values.
Data acquisition applications are controlled by software programs developed using various general purpose programming languages such as BASIC
BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
, C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, Fortran
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...
, Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
, Lisp, Pascal
Pascal (programming language)
Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...
.
Specialized software tools used for building large-scale data acquisition systems include EPICS
EPICS
The Experimental Physics and Industrial Control System is a software environment used to develop and implement distributed control systems to operate devices such as particle accelerators, telescopes and other large experiments. EPICS also provides SCADA capabilities...
. Graphical programming environments include ladder logic
Ladder logic
Ladder logic is a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay logic hardware. It is primarily used to develop software for programmable logic controllers used in industrial control applications...
, Visual C++
Visual C++
Microsoft Visual C++ is a commercial , integrated development environment product from Microsoft for the C, C++, and C++/CLI programming languages...
, Visual Basic
Visual Basic
Visual Basic is the third-generation event-driven programming language and integrated development environment from Microsoft for its COM programming model...
, and LabVIEW
LabVIEW
LabVIEW is a system design platform and development environment for a visual programming language from National Instruments. LabVIEW provides engineers and scientists with the tools needed to create and deploy measurement and control systems.The graphical language is named "G"...
.
Source
Data acquisition begins with the physical phenomenon or physical propertyPhysical property
A physical property is any property that is measurable whose value describes a physical system's state. The changes in the physical properties of a system can be used to describe its transformations ....
to be measured. Examples of this include temperature, light intensity, gas pressure, fluid flow, and force. Regardless of the type of physical property to be measured, the physical state that is to be measured must first be transformed into a unified form that can be sampled by a data acquisition system. The task of performing such transformations falls on devices called sensors.
A sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
, which is a type of transducer
Transducer
A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
, is a device that converts a physical property into a corresponding electrical signal (e.g., a voltage or current) or, in many cases, into a corresponding electrical characteristic (e.g., resistance or capacitance) that can easily be converted to an electrical signal.
The ability of a data acquisition system to measure differing properties depends on having sensors that are suited to detect the various properties to be measured. There are specific sensors for many different applications. DAQ systems also employ various signal conditioning
Signal conditioning
In electronics, signal conditioning means manipulating an analog signal in such a way that it meets the requirements of the next stage for further processing...
techniques to adequately modify various electrical signals into voltage that can then be digitized using an Analog-to-digital converter
Analog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
(ADC).
Signals
Signals may be digitalDigital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
(also called logic signals sometimes) or analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
depending on the transducer used.
Signal conditioning may be necessary if the signal from the transducer is not suitable for the DAQ hardware being used. The signal may need to be amplified, filtered or demodulated. Various other examples of signal conditioning might be bridge completion, providing current or voltage excitation to the sensor, isolation, linearization.
For transmission purposes, single ended
Single-ended signalling
Single-ended signaling is the simplest and most commonly used method of transmitting electrical signals over wires. One wire carries a varying voltage that represents the signal, while the other wire is connected to a reference voltage, usually ground....
analog signals, which are more susceptible to noise can be converted to differential signals
Differential signaling
Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analog signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, Ethernet , PCI Express and USB...
. Once digitized, the signal can be encoded to reduce and correct transmission errors.
DAQ hardware
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 (parallelParallel port
A parallel port is a type of interface found on computers for connecting various peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port...
, serial
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
, USB, etc.) or cards connected to slots (S-100 bus
S-100 bus
The S-100 bus or Altair bus, IEEE696-1983 , was an early computer bus designed in 1974 as a part of the Altair 8800, generally considered today to be the first personal computer...
, AppleBus, ISA, MCA
Micro Channel architecture
Micro Channel Architecture was a proprietary 16- or 32-bit parallel computer bus introduced by IBM in 1987 which was used on PS/2 and other computers through the mid 1990s.- Background :...
, PCI, PCI-E, etc.) in the motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
. Usually the space on the back of a PCI card is too small for all the connections needed, so an external breakout box
Breakout box
A breakout box is an electrical device, usually housed in a box, in which a compound electrical connector is separated or "broken out" into its component connectors. Compound connectors are used where sufficient space for connections is unavailable...
is required. The cable between this box and the PC can be expensive due to the many wires, and the required shielding.
DAQ cards often contain multiple components (multiplexer, ADC, DAC, TTL-IO, high speed timers, RAM). These are accessible via a bus
Bus
A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...
by a microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
, which can run small programs. A controller is more flexible than a hard wired logic, yet cheaper than a CPU so that it is permissible 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.
Many times reconfigurable logic is used to achieve high speed for specific tasks and digital signal processor
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
s are used after the data has been acquired to obtain some results.
The fixed connection with the PC allows for comfortable compilation
Cross compiler
A cross compiler is a compiler capable of creating executable code for a platform other than the one on which the compiler is run. Cross compiler tools are used to generate executables for embedded system or multiple platforms. It is used to compile for a platform upon which it is not feasible to...
and debugging
Debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...
. Using an external housing a modular design with slots in a bus can grow with the needs of the user.
Not all DAQ hardware has to run permanently connected to a PC, for example intelligent stand-alone loggers and oscilloscopes, which can be operated from a PC, yet they can operate completely independent of the PC.
DAQ software
DAQ software is needed in order for the DAQ hardware to work with a PC. The device driver performs low-level register writes and reads on the hardware, while exposing a standard API for developing user applications. A standard API such as COMEDI allows the same user applications to run on different operating systems, e.g. a user application that runs on Windows will also run on Linux.History
In 1963, IBM produced computers which were specialized for data acquisition. These include the IBM 7700 Data Acquisition System and its successor, the IBM 1800 Data Acquisition and Control SystemIBM 1800
The IBM 1800 Data Acquisition and Control System was a process control variant of the IBM 1130 with two extra instructions , extra I/O capabilities, 'selector channel like' cycle-stealing capability and three hardware index registers....
. These expensive specialized systems were surpassed in 1974 by general purpose S-100 computers and data acquisitions cards produced by Tecmar
Tecmar
Tecmar was an American manufacturer of PC enhancement products based in Solon, OH. The company was founded in 1974 and their first products were data acquisition boards for the first generation of microcomputers. Popular products included the Scientific Solutions LabMaster series of boards for...
/Scientific Solutions Inc. In 1981 IBM introduced the IBM Personal Computer and Scientific Solutions introduced the first PC data acquisition products.
See also
- Signal processingSignal processingSignal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
- Data analysisData analysisAnalysis of data is a process of inspecting, cleaning, transforming, and modeling data with the goal of highlighting useful information, suggesting conclusions, and supporting decision making...
- Test methodTest methodA test method is a definitive procedure that produces a test result.A test can be considered as technical operation that consists of determination of one or more characteristics of a given product, process or service according to a specified procedure. Often a test is part of an experiment.The test...
- Input devices:
- 3D scanner3D scannerA 3D scanner is a device that analyzes a real-world object or environment to collect data on its shape and possibly its appearance . The collected data can then be used to construct digital, three dimensional models....
- Analog to digital converter
- Time to digital converterTime to digital converterIn electronic instrumentation and signal processing, a time to digital converter is a device for converting a signal of sporadic pulses into a digital representation of their time indices. In other words, a TDC outputs the time of arrival for each incoming pulse...
- 3D scanner
- Hardware:
- CAMAC - Computer Automated Measurement and Control
- Industrial EthernetIndustrial EthernetIndustrial Ethernet refers to the use of the Ethernet family of computer network technologies in an industrial environment, for automation and process control. A number of techniques are used to adapt Ethernet for the needs of industrial processes, which require real time behavior...
- Industrial USBIndustrial USBIndustrial USB is the name given to the use of the USB protocol in an industrial environment, for data acquisition, automation, and production machine control....
- LAN eXtensions for Instrumentation
- NIMNIMThe Nuclear Instrumentation Module standard defines mechanical and electrical specifications for electronics modules used in experimental particle and nuclear physics...
- PowerLabPowerLabPowerLab is a data acquisition system developed by ADInstruments comprising hardware and software and designed for use in life science research and teaching applications...
- PCI eXtensions for Instrumentation
- VMEbusVMEbusVMEbus is a computer bus standard, originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on Eurocard sizes, mechanicals and connectors , but uses its own signalling system,...
- VXIVXIThe VXI bus architecture is an open standard platform for automated test based upon VMEbus. VXI stands for VME eXtensions for Instrumentation, defining additional bus lines for timing and triggering as well as mechanical requirements and standard protocols for configuration, message-based...
- Software:
- EPICSEPICSThe Experimental Physics and Industrial Control System is a software environment used to develop and implement distributed control systems to operate devices such as particle accelerators, telescopes and other large experiments. EPICS also provides SCADA capabilities...
- LabChart
- LabVIEWLabVIEWLabVIEW is a system design platform and development environment for a visual programming language from National Instruments. LabVIEW provides engineers and scientists with the tools needed to create and deploy measurement and control systems.The graphical language is named "G"...
- IOXIox acquisition softwareiox is a data acquisition software developed by emka TECHNOLOGIES SA, based in Paris, France, especially adapted to safety pharmacology and toxicology studies in small and large animals including rodents, dogs, and non-human primates.-Background:...
- EPICS