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Data Acquisition Data acquisition , also referred to as DAQ or DAS , is the process of conversion of real world events into machine-analyzable Signals. Data acquisition process involves gathering Signals from test objects and subsequently processing these Signals to derive the required information . A data acquisition system consists of Sensors, which perform the function of converting any measurement parameter into an electrical signal; the electric signal , in turn serves as an input for data acquisition Hardware. The signal is digitized for display , analysis and storage on a PC . PC-based data acquisition was invented in 1981 by Scientific Solutions. Data acquisition (DAQ) systems are marketed in numerous PC technology Platforms to enable greater flexibility . Engineers and scientists can use either of PCI , PXI , PXI Express , PCI Express , USB , IEEE 1394 , PCMCIA , parallel or serial Ports for data acquisition in measurement , test and automation applications . Data Acquisition Process The vital aspect in data acquisition process is the physical property of an object that is to be measured . This physical property can be either the temperature in a room , force exerted on an object , pressure within a chamber , the intensity variation of a light source , or any other property . An ideal data acquisition system is one which is capable of measuring all the above as well as other physical properties . Five components are taken into consideration while building a basic Data Acquisition system: Transducers and Sensors Signals Signal conditioning DAQ Hardware Driver and application Software Transducers and Sensors A transducer serves the purpose of converting a physical property into a determinable electrical signal , such as current or voltage . The ability of the transducer to convert diverse physical phenomena into an output measurable by the DAQ Hardware is an indication of the efficiency of Data Acquisition Systems. In Data Acquisition Systems Transducers are synonymous with Sensors. Specific Transducers are employed to correspond to the type of application; thus different Transducers are used for applications such as temperature measurement , fluid flow , force and pressure measurement . Transducers differ in their requirements to produce an output signal . While some Transducers necessitate excitation in the form of current or voltage , some Transducers necessitate the usage of additional components and even resistor Networks to generate a signal . Signals Signals can be digital or analog depending upon the nature of the transducer used . The digital or analog nature of a signal is significant since each of these is measured in a different way . Analog Signals An analog signal can take any value at a given point of time . Temperature , voltage , sound , pressure , load are some examples of analog Signals. Level , shape and frequency are three significant characteristics of an analog signal . Each of these attributes provide significant information in signal analysis . A data acquisition system that provides optimal accuracy is preferred in analog level measurements . The shape of an analog signal gives information on the signal’s DC values , peak values and slope . Unlike the level and shape , the frequency of an analog signal cannot be measured directly . Software is used for the frequency analysis of a signal . Digital Signals Digital Signals cannot assume any value with respect to time . It has two states - high and low . State and rate of a digital signal are two important attributes to be measured . Signal Conditioning Signal conditioning may be necessary if the signal outputted by the transducer is not compatible with the data acquisition (DAQ) Hardware. Such Signals may require amplification , reduction or filtration of components . Signal conditioning ensures maximum accuracy of a system; allows for proper sensor operation and guarantees safety . Selection of the right Hardware is essential for signal conditioning . Signal conditioning is offered in both integrated and modular forms . DAQ Hardware DAQ Hardware is an interface between the output signal and a PC . DAQ Hardware can be either Modules connectable to the computer’s Ports (USB , parallel , serial , etc . ) or Cards connected to slots in the mother board . Quite often multiple components (high-speed Timers, multiplexer , DAC , TTL-IO , ADC , RAM) are contained in DAQ-cards . These components are accessible via a bus by a micro-controller capable of running small programs . The controller despite being more flexible than a hard-wired logic is cheaper than a CPU . It is also easier to block the controller with simple polling loops . Driver Software Driver Software usually accompanies the DAQ Hardware, or can be acquired from vendors . Driver Software is the intermediate layer that enables an easy communication with the Hardware by specifying the communication standards between the operating system and DAQ Hardware. The driver Software allows easy access of Signals being read by the DAQ Hardware. Application Software Application Software customizes the data provided by Driver Software and makes it suitable for analysis . There are many real-time application Software for DAQ Modules wherein data is fed on a continual basis . The decision to control an application is taken based on the data presented by the Application Software. Applications of Data Acquisition (DAQ): Specific applications of data acquisition (DAQ) systems include: Testing of jet engine and satellite structures Missile and rocket payload simulations Helicopter engine Manufacturing plant monitoring Pulmonary research |
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