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Basics of Data Acquisition Systems Dr inż. Zdzisław Pólkowski Badea George-Cosmin http://www.geo-integration.com/products/G001.htm Content • • • • • • • • • • • • • • Definition A data acquisition system consists Block Diagram Transducer Converters U/I and I/U Converters R/U Converters C/U AO- amplifier Amplifiers with modulation-demodulation Differentiator and Integrator Circuits Logarithmic and exponential amplifiers Multiplexer / Demultiplexer Conversion circuits analog and digital signals Conclusion Definition • 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 easy processing. http://www.ni.com/data-acquisition/what-is/ A data acquisition system consists: 1. Sense of physical variables (transducers); 2. Signal Conditioning for electrical signal to make it readable by an A/D board; 3. Convert the signal into a digital format acceptable by a computer (DAQ device); 4. Process, analyze, store and display the acquired data with the help of software. http://www.slideshare.net/amoldude/data-acquisition-system-33836067?qid=d49e6c85-1fa7-4a71-ac861ff0db642725&v=default&b=&from_search=2 Block Diagram Physical System Transducer Sensor Signal Conditioning Noisy Electrical Signal Physical Variable: Temperature Pressure Motion Flow A/D Converter Computer Digitized Signal Filtered And Amplified Signal 8-Bit Binary Code http://www.slideshare.net/sumeetpatel21/data-acquisition-system-40835631?related=2 Block Diagram Physical System Physical System/Conditions: • Physical condition that can be used as input of DAS or which can be represented in Digital form are as under… Temperature; Pressure; Light; Force; Displacement; Level; Electric signals; ON/OFF switch. http://www.slideshare.net/sumeetpatel21/data-acquisition-system-40835631?related=2 Block Diagram Transducer Transducers: Sensor • A transducer converts temperature, pressure, level, length, position, etc. into voltage, current, frequency, pulses or other signals. • A transducer thus converts the physical conditions in electrical waveform for easy signal processing http://www.thomasnet.com/articles/engineering-consulting/transducer-signals Block Diagram Signal Signal Conditioning: Conditioning • Signal conditioning circuits improve the quality of signals generated by transducers before they are converted into digital signals by the PC’s data acquisition hardware. • Most common signal conditioning functions are amplification, linearization, cold-junction compensation, filtering, attenuation, excitation, common-mode rejection, and so on. http://www.ni.com/white-paper/4084/en/ Block Diagram A/D Converter Analog Digital (A/D) converter: • Analog to digital (A/D) conversion changes analog voltage or current levels into digital information. • The conversion is necessary to enable the computer to process or store the signals. • A/D converters are electrical circuits that have the following characteristics: 1. The input to the A/D converter is a voltage; 2. The output of the A/D converter is a binary signal. http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Interfaces/ConvAD.html Transducer • • Converts a physical phenomenon into a measurable electrical signal. Variety of transducers: Phenomena Transducer Temperature Thermocouples Resistance temperature detectors Light Vacuum tube photo sensors Photoconductive cells Sound Microphones Force and pressure Strain gages and load cells Position (displacement) Potentiometers Optical encoders Fluid flow Head meters Rotational and ultrasonic flowmeters pH pH electrodes https://www.futek.com/DataAcquisitionHowto.aspx Converters U/I and I/U Source: http://www.mediacollege.com/glossary/q/quantization.html Converters U/I and I/U 1. Converters voltage-current: • Voltage-current converters are common functional blocks in the structure measuring and control electronic equipment. • Voltage-current converters can generate unidirectional current (of one polarity) or bidirectional (both polarities): a) Unidirectional voltage-current converters come from constant power generators with bipolar transistor or field effect voltage reference being replaced by a variable control voltage. b) The easiest bidirectional voltage-current converter for floating tasks can be achieved by connecting the load impedance intrareieşire reaction resistance instead of an operational amplifier in inverting assembly. http://media1.wgz.ro/files/media1:4b51fa8487a9d.pdf.upl/Ccsm2.pdf Converters U/I and I/U 2. Converters current-voltage: • Current-voltage converters are widely used in instrumentation control structure, which ranks among basic blocks, along with amplifiers, multipliers, memory-sampling circuits, voltage-current converters, analog-digital or digital-to-analog and so on. • The simplest current-voltage converter is a resistance cuadripolară called when the shunt used to measure current. The converter with which receives the voltage across the shunt should have a much higher input resistance than the shunt to not introduce unacceptable errors. • Shunt current-voltage converters with high current is not used as input current is closed by power sources and output operational amplifiers used, increasing power dissipation. http://media1.wgz.ro/files/media1:4b51fa8487a9d.pdf.upl/Ccsm2.pdf Converters R/U • Converters Resistance to Voltage: • Many sensors exhibit a change electrical resistance in response to the quantity that they are trying to measure. • There are two ways to convert resistance of a sensor to a voltage. The first, and simplest way is to apply a voltage to a resistor divider network composed of a reference resistor and the sensor as shown: • The voltage that appears across the sensor is then buffered before being sent to the ADC. The output voltage is given by: http://soundlab.cs.princeton.edu/learning/tutorials/sensors/node17.html Converters C/U • Converters Capacitance to Voltage: • We have seen that the electrical property of capacitance has been the main physical principle behind many of the sensors that we have discussed. • This has made it a useful tool in measuring small vibrations. Capacitance can also be used to measure much greater distances than we have seen so far. • Capacitance can be measured in the same two ways discussed previously for measuring resistance - a voltage divider or a bridge circuit. Instead of using resistors, capacitors are used. • The output voltage can be written as: http://soundlab.cs.princeton.edu/learning/tutorials/sensors/node18.html AO- amplifier A method of amplifying: • It is necessary that . It appears a indeterminate: • It can be maintained at 0 by connecting impedance outside a configuration AO negative reaction. These impedances with AO maintain at zero and determine the output voltage http://www.bel.utcluj.ro/dce/didactic/de/12_AO_amplificatoare.pdf Amplifiers with modulation-demodulation • Block diagram of a modulation-demodulation amplifier is shown below: FTJ1 = input filter M = modulator Aca = amplifier c.a. D = demodulator FTJ2 = output filter O = oscillator http://iota.ee.tuiasi.ro/~czet/Curs/Masurari/C10%20Instrumente%20si%20dispozitive%20de%20masurare%20analogice.pdf Differentiator and Integrator Circuits 1. Differentiator: • The right-hand side of the capacitor is held to a voltage of 0 volts, due to the virtual ground effect. Therefore, current through the capacitor is solely due to change in the input voltage. A steady input voltage won’t cause a current through C, but a changing input voltage will • The formula for determining voltage output for the differentiator is as follows: http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/differentiator-integrator-circuits/ Differentiator and Integrator Circuits 2. Integrator: • As before, the negative feedback of the op-amp ensures that the inverting input will be held at 0 volts. If the input voltage is exactly 0 volts, there will be no current through the resistor, therefore no charging of the capacitor, and therefore the output voltage will not change. •The formula for determining voltage output for the integrator is as follows: http://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/differentiator-integrator-circuits/ Logarithmic and exponential amplifiers 1. Amplifier logarithmic: • • Circuit limitations: the range of variation of the output voltage is reduced by a few tens mV; the temperature dependence of the output voltage by and . http://www.bel.utcluj.ro/dce/didactic/cef/17_aplicatii_cu_AO.pdf Logarithmic and exponential amplifiers 2. Amplifier exponential: http://www.bel.utcluj.ro/dce/didactic/cef/17_aplicatii_cu_AO.pdf Multiplexer / Demultiplexer • The basic function of the Multiplexer (MUX); • The typical application of a MUX; • The basic function of the Multiplexer (DEMUX); • The typical application of a DEMUX; http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf Multiplexer / Demultiplexer 1. Multiplexer (MUX): • A MUX is a digital switch that has multiple inputs and a single output. • The select lines determine which input is connected to the output. • MUX Types: a. 2-to-1 (1 select line); b. 4-to-1 (2 select lines); c. 8-to-1 (3 select lines); d. 16-to-1 (4 select lines). http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf Multiplexer / Demultiplexer 1. Typical application of a MUX: http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf Multiplexer / Demultiplexer 2. Demultiplexer (DEMUX): • A DEMUX is a digital switch with a single input and a multiple outputs. • The select lines determine which output the input is connected to • DEMUX Types: a. 1-to-2 (1 select line); b. 1-to-4 (2 select lines); c. 1-to-8 (3 select lines); d. 1-to-16 (4 select lines). http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf Multiplexer / Demultiplexer 2. Typical application of a DEMUX: http://student.rdias.ac.in/uploads/piyush.dua/unit1-1%28multiplexer,demultiplexer,decoder%29.pdf Conversion circuits analog and digital signals http://www3.eng.cam.ac.uk/DesignOffice/mdp/electric_web/Digital/DIGI_13.html Conversion circuits analog and digital signals 1. Digital-to-analog: • Digital-to-analog conversion is a process in which signals having a few defined levels or states are converted into signals having a theoretically infinite number of states. • A common example is the processing, by a modem, of computer data into audio-frequency (AF) tones that can be transmitted over a twisted pair telephone line. The circuit that performs this function is a digital-toanalog converter (DAC) • But when a DAC is used to decode the binary digital signals, meaningful output appears. This might be a voice, a picture, a musical tune, or mechanical motion. http://whatis.techtarget.com/definition/digital-to-analog-conversion-DAC Conversion circuits analog and digital signals 1. Analog-to-digital : • Analog-to-digital conversion is an electronic process in which a continuously variable signal is changed, without altering its essential content, into a multi-level signal. • The input to an analog-to-digital converter (ADC) consists of a voltage that varies among a theoretically infinite number of values. • Digital signals propagate more efficiently than analog signals, largely because digital impulses, which are well-defined and orderly, are easier for electronic circuits to distinguish from noise, which is chaotic http://whatis.techtarget.com/definition/analog-to-digital-conversion-ADC Conclusion Data acquisition systems typically convert analog physical condition into digital values for easy processing; DAS is advantageous as we can store a lot of physical condition data in digitized form; DAS helps in easy processing of data as well as easy comparison can be done; Today DAS is used in almost every field, industry and companies. http://www.slideshare.net/sumeetpatel21/data-acquisition-system-40835631?related=2