Data Acquisition

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ThermocouplesDigitalTransmitterDigitalTransmitterDigitalTransmitterRS-485 InterfaceBoardHost ComputerDigitalTransmitterDigitalTransmitterStrain gaugeRelayFigure 3.17Distributed I/O signal conditioning network using individual digital transmitter modulesLike other signal conditioning modules, these devices require an external power supply.The power supply should be located to supply as many signal-conditioning modules as itsrating will allow.When measuring analog input signals from transducers, it is unfortunately not just asimple matter of wiring the transducer leads to the signal conditioning equipment or dataacquisition board, or connecting the signal conditioning equipment to the data acquisitionboard itself.Signal conditioning equipment and data acquisition boards typically provide a varietyof methods for taking measurements of input signals. When determining the wiringconnections and analog input configuration that will produce accurate and noise freemeasurements, careful consideration must be given not only to the type of signal producedby the transducer but also to the nature of the signal source.The most common electrical signal output by transducers or signal conditioningequipment is in the form of voltage. In certain situations, where the output signal fromsignal conditioning equipment must be transmitted over long distances or is particularlysusceptible to noise, it may be converted to a current or frequency signal. In most caseshowever, the signal is converted back to a voltage signal before a measurement is taken.It is therefore necessary to understand the voltage signal source and the various methodsof taking measurements of voltage signals.Two categories of voltage signal source are defined:• Grounded signal source• Floating (ungrounded) signal source
Three types of measurement are available on most signal conditioning equipment anddata acquisition boards:• Single-ended• Differential• Pseudo-differentialSince an understanding of the types of signal sources and measurement systems isnecessary to determine the best methods of taking analog signal measurements, thesetopics are discussed in the following sections.3.4.1 Grounded signal sourcesBy definition, voltage is a measurement of the potential difference between two points.Grounded signal sources have one of their signal leads connected to the system ground asshown in Figure 3.18. This is theoretically shown as earth potential, although the systemground is not necessarily at earth potential. The voltage output from the signal source isthe potential difference between the system ground and the positive signal lead of thesignal source.Figure 3.18Grounded signal sourceA common example of a grounded signal source is an instrument that is earthed via itsAC plug to the building ground.3.4.2 Floating signal sourcesFloating or ungrounded signal sources, as shown in Figure 3.19, do not have either of thesignal source leads connected to the system ground. This means that the signal source isnot referenced to any absolute reference. The potential difference, that each of the signallines may have, with respect to the system ground or earth potential between the signallines, is not indicated in anyway by the voltage potential.Figure 3.19Ungrounded signal source
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Practical Data Acquisition forInstr
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Practical Data Acquisition forInstr
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In less than a decade, the PC has b
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PrefaceContentsxvii1 Introduction 1
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Contents vii4.2.1 Hardware interrup
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Contents ix6.2.3 Functional descrip
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Contents xi9.1 Ethernet and fieldbu
Page 16 and 17: Contents xiii12.5.2 Pin assignments
Page 18 and 19: Contents xvType R thermocouple 384T
Page 20 and 21: A data acquisition and control syst
Page 22 and 23: FilteringIn noisy environments, it
Page 24 and 25: are capable of programmed I/O and i
Page 26 and 27: Plug-in expansion boards are common
Page 28 and 29: 50 mRS-232 Communication InterfaceS
Page 30 and 31: speeds are of the order of 1 Mbyte/
Page 32 and 33: 14 Practical Data Acquisition for I
Page 54 and 55: 3PC based data acquisition (DAQ) sy
Page 56 and 57: 3.2.3 FilteringIsolation performs s
Page 58 and 59: The transfer characteristics of a p
Page 60 and 61: Figure 3.7Ideal band pass filter tr
Page 62 and 63: Figure 3.11Two-stage Butterworth fi
Page 64 and 65: As individual signal conditioning m
Page 68 and 69: Examples of floating signal sources
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Page 72 and 73: Figure 3.26Opto-coupler isolation o
Page 74 and 75: • Using isolation amplifiers to i
Page 76 and 77: Figure 3.31Physical representation
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Page 80 and 81: Where the shield is grounded (i.e.
Page 82 and 83: mines the amount of noise in the ci
Page 84 and 85: For full-duplex systems using balan
Page 86 and 87: 4.1.1 DOSusually consist of a small
Page 88 and 89: With the advent of Windows as a gra
Page 90 and 91: UNIX shellSimilar to the DOS comman
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Page 94 and 95: 4.2.7 Interrupt service routinesIt
Page 96 and 97: Whichever CPU is being used, it mus
Page 98 and 99: • An I/O device requests a DMA tr
Page 100 and 101: Normal DMA using on-board FIFOThe D
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Page 104 and 105: The read or write command signals (
Page 106 and 107: Shortened 3-BCLK 8-bit memory acces
Page 108 and 109: Extended 6-BCLK 16-bit memory acces
Page 110 and 111: • A cycle which the expansion boa
Page 112 and 113: Figure 4.13Timing chart of a shorte
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4.7.2 Expanded memory system (EMS)E
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The IBM PC and early versions of th
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Figure 4.17ISA signal mnemonics, si
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data bus. An example of this happen
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NOWSThe /NOWS (NO wait state) signa
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interrupt lines (1RQ13, 8, 2, 1 and
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one application at a time, it is ne
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The need for PCs to exchange data w
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Figure 4.198-bit 21-line I/O board4
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Address decoding on the 24-line pro
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The write cycle is considered in th
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data acquisition and control system
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Adjustable on-board fixed gain ampl
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level applied at the input. When a
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Each step effectively divides the r
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The operation of a dual slope integ
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Code widthThis is the fundamental q
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(a) Unipolar offset error(b) Bipola
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Changes in temperature result in a
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1 LSB. Therefore, an ideal A/D conv
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• The source and level of interru
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5.3.3 Differential inputsTrue diffe
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A/D board can divide the input rang
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a) DC alias caused by sampling at h
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Figure 5.15Frequency spectrum of or
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ate be a minimum of about five time
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Figure 5.20Many aliases combined wi
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initiated. The data is subsequently
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Figure 5.22Time skew between channe
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For each burst trigger, the A/D boa
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Analog output D/A boardsUnlike high
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Like the weighted-current source ne
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The generation of high frequency si
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• The plug-in connector, which pr
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Latched digital I/OFor applications
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y increasing the resistance of R x
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One advantage of this type of relay
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Figure 5.36Waveforms showing genera
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When a counter is configured to ena
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6The standardization of the RS-232
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A duplex system is designed for sen
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Some examples of the HEX and BIN va
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In summary, the optional settings f
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At the RS-232 receiver the followin
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110 850300 800600 7001200 5002400 2
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• Pin 7: Signal ground (common)Th
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6.2.5 Examples of RS-232 interfaces
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terminating resistors, approximatel
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Another commonly used technique, ba
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• Line controlThis applies to hal
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The calculation of the block checks
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The mechanism of operation of the C
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Figure 6.18, has appropriate intern
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77.1 IntroductionAs with other form
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inserted in the device. This is its
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How frequently logged data is uploa
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The following hardware components d
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In a typical stand-alone data acqui
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The maximum battery life that can b
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Input termination resistors, typica
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Figure 7.13 shows the standard conn
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interface, even at high speed, the
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• Use different data formats so t
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Command errors are reported immedia
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• Channel scalingThis automatical
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The channel scan for this type of s
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Data is logged in a fixed non-ASCII
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7.9 Stand-alone logger/controllers
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88.1 IntroductionThe communications
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Figure 8.2GPIB connector (IEEE 488)
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• TalkersA talker is a one-way co
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controller in charge (CIC). The IFC
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Each device connected to the GPIB h
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One of the additional features that
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• The controller temporarily conf
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Table 8.4IEEE 488.2 commandsThe SCP
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Figure 8.9SCPI instrument modelThe
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99.1 Ethernet and fieldbuses for da
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cabling tray etc and the transceive
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transceiver in the MAU and this is
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Advantages of the system include:
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of a cell as well, but these are ig
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Figure 9.8CSMA/CD collisionsAssume
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• PreambleThis field consists of
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of this figure. Some manufacturers
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Grounding has safety and noise conn
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Just as with any technology, each o
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information. The packet is then pla
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There are two types of connectors,
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HOSTClient SoftwareManages Interfac
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Figure 10.6USB connector pinsThere
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The idle states for low- and high-s
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The interrupt transfer type is used
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than in spending a lot of time and
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• The sensitivity of the output/i
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term error (m) in the system and ad
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11.2 Capturing high speed transient
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12IntroductionThe PCMCIA (PCMCIA st
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adapter on a full size computer has
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Pager cards are used in offices and
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Size 85.6 mm × 54.0 mmType I 3.3 m
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The memory only interface is conver
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The AIMS interface supports large d
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12.8 FutureThe card information str
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A/D conversion timeAddressAddress r
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Back-planeBand pass filterBandwidth
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BufferBusBWCache memoryCCDCCIRCCITT
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pixel is subjected to a mathematica
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data between the computer memory an
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FrameFrame grabberFringingFull dupl
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so that they interlock. The PAL sta
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Lux-secondSI unit of light exposure
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NTSCNull modemNumber of channelsNyq
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PortPPIPre-triggerProgram I/OProgra
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whereby the first gray level of eac
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allowing the user to control basic
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input.TrunkUARTUnipolar inputsUnloa
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Appendix BThe information in this s
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Table B.4Controller 2: 16-bit (AT o
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B.5 8253/8254 Counter/timer
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Table B.8Memory map for PC/XT/AT
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Table B.10BIOS data area
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Table B.15ROMTable B.16AT extended
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← ↔ ← ← ← ↔
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Figure B.1Card dimensions for PC/XT
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Appendix CThis section contains bri
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the control register of the 8255. T
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The bits A7 (MSB) down to A0 (LSB)
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Table C.6Instructions for reading o
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The program could also enable the I
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Group AConfiguration Informationto
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C.11 Single-bit set/resetAny of the
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Figure C.15Bi-directional bus (mode
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Figure D.18254 Block diagramFigure
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Figure D.3TCCTRL registerThe functi
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This is the data register of the fi
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• A simple read operation• A co
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The null count bit indicates if the
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For even counts: the output is init
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Appendix EThe IPTS-68 standard defi
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Number of ranges = 2Range #1 -270 t
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Range #2 0 to 1372°COrder of polyn
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Number of Ranges = 4Range #1 -50 to
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Appendix FF.1 IntroductionAll activ
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Table F.3 gives the conversion betw
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The conversion between binary and h
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F.8 Internal representation of info
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12 which is equivalent to: 1100-4 S
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DCDCASDCISDCLDDDIODTDTASDTISENDEOIE
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STBSTRSSWNST(T)TETACSTADSTAGTCATCST
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404 IndexDuplex:full duplex 178half
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406 IndexOpen loop control 285see a
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THIS BOOK WAS DEVELOPED BY IDC TECH
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