Data Acquisition

More documents

Recommendations

Info

Figure 5.20Many aliases combined with a speech signalIt could be assumed that aliasing is a phenomenon associated with high frequencies, andthat low frequencies (such as thermocouple temperature signals) are immune to this effect.Temperature changes so slowly that the input signal is almost DC; it seems therefore reasonableto sample it extremely slowly and not be concerned with frequency analyses.However, if the input signal contains a noise spike as shown in Figure 5.21(a), the resultingspectrum results in a noise floor around –60 dB, shown in Figure 5.21(b). This is because animpulse spike in the time domain spreads itself out evenly in the frequency domain. Thus,when sampled at a low frequency, the high-frequency components of the noise spike aliasdown and add to the low frequency components. The extra energy of these added frequenciescauses the temperature application to oscillate. If a low pass filter is used, the spike – with itsequivalent high-frequency components – is removed (as shown in the time domain in Figure5.21(c). The spectrum corresponding to this (Figure 5.21(d)) now has a noise floor of –80 to–90 dB, which does not affect the readings obtained by the A/D board.
Figure 5.21A spike causes wideband aliasingThese techniques are discussed in the following sections:• Continuous channel scanning• Simultaneous sampling• Block mode operations5.6.1 Continuous channel scanningThe method of sampling that facilitates the connecting of the required input channel to theA/D converter at a constant rate is known as continuous channel scanning. Continuouschannel scanning allows channels to be sampled in a pre-determined and arbitrary order (e.g.channel 5, channel 1, channel 11), as well as at different sampling rates. An example of thiswould be the sampling of three channels in the following order (channel 5, channel 1, channel11, channel 1). Channel 1 is being sampled at twice the rate as channels 5 & 11, which for anA/D board with throughput of 100 kHz represents a sampling rate of 50 kHz. Channels 5 &11 are sampled at 25 kHz. There are two methods of continuous channel scanning, eitherunder software control or by on-board hardware control.Software channel scanningWhere continuous channel scanning is performed by software the address of the channel to besampled is written to the multiplexer and the gain setting sent to the programmable gainamplifier (PGA), where one is fitted. Once the signal is settled, an A/D conversion is
Page 2 and 3:
Practical Data Acquisition forInstr
Page 4 and 5:
Practical Data Acquisition forInstr
Page 6 and 7:
In less than a decade, the PC has b
Page 8 and 9:
PrefaceContentsxvii1 Introduction 1
Page 10 and 11:
Contents vii4.2.1 Hardware interrup
Page 12 and 13:
Contents ix6.2.3 Functional descrip
Page 14 and 15:
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 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
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 66 and 67:
ThermocouplesDigitalTransmitterDigi
Page 68 and 69:
Examples of floating signal sources
Page 70 and 71:
espect to the measurement system gr
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
Page 78 and 79:
field or if the field is caused by
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
Page 92 and 93:
available to the expansion bus. A l
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
Page 102 and 103:
ferring samples until the counter r
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
Page 114 and 115:
Figure 4.15Timing chart of an exten
Page 116 and 117:
4.7.2 Expanded memory system (EMS)E
Page 118 and 119: The IBM PC and early versions of th
Page 120 and 121: Figure 4.17ISA signal mnemonics, si
Page 122 and 123: data bus. An example of this happen
Page 124 and 125: NOWSThe /NOWS (NO wait state) signa
Page 126 and 127: interrupt lines (1RQ13, 8, 2, 1 and
Page 128 and 129: one application at a time, it is ne
Page 130 and 131: The need for PCs to exchange data w
Page 132 and 133: Figure 4.198-bit 21-line I/O board4
Page 134 and 135: Address decoding on the 24-line pro
Page 136 and 137: The write cycle is considered in th
Page 138 and 139: data acquisition and control system
Page 140 and 141: Adjustable on-board fixed gain ampl
Page 142 and 143: level applied at the input. When a
Page 144 and 145: Each step effectively divides the r
Page 146 and 147: The operation of a dual slope integ
Page 148 and 149: Code widthThis is the fundamental q
Page 150 and 151: (a) Unipolar offset error(b) Bipola
Page 152 and 153: Changes in temperature result in a
Page 154 and 155: 1 LSB. Therefore, an ideal A/D conv
Page 156 and 157: • The source and level of interru
Page 158 and 159: 5.3.3 Differential inputsTrue diffe
Page 160 and 161: A/D board can divide the input rang
Page 162 and 163: a) DC alias caused by sampling at h
Page 164 and 165: Figure 5.15Frequency spectrum of or
Page 166 and 167: ate be a minimum of about five time
Page 170 and 171: initiated. The data is subsequently
Page 172 and 173: Figure 5.22Time skew between channe
Page 174 and 175: For each burst trigger, the A/D boa
Page 176 and 177: Analog output D/A boardsUnlike high
Page 178 and 179: Like the weighted-current source ne
Page 180 and 181: The generation of high frequency si
Page 182 and 183: • The plug-in connector, which pr
Page 184 and 185: Latched digital I/OFor applications
Page 186 and 187: y increasing the resistance of R x
Page 188 and 189: One advantage of this type of relay
Page 190 and 191: Figure 5.36Waveforms showing genera
Page 192 and 193: When a counter is configured to ena
Page 194 and 195: 6The standardization of the RS-232
Page 196 and 197: A duplex system is designed for sen
Page 198 and 199: Some examples of the HEX and BIN va
Page 200 and 201: In summary, the optional settings f
Page 202 and 203: At the RS-232 receiver the followin
Page 204 and 205: 110 850300 800600 7001200 5002400 2
Page 206 and 207: • Pin 7: Signal ground (common)Th
Page 208 and 209: 6.2.5 Examples of RS-232 interfaces
Page 210 and 211: terminating resistors, approximatel
Page 212 and 213: Another commonly used technique, ba
Page 214 and 215: • Line controlThis applies to hal
Page 216 and 217: The calculation of the block checks
Page 218 and 219:
The mechanism of operation of the C
Page 220 and 221:
Figure 6.18, has appropriate intern
Page 222 and 223:
77.1 IntroductionAs with other form
Page 224 and 225:
inserted in the device. This is its
Page 226 and 227:
How frequently logged data is uploa
Page 228 and 229:
The following hardware components d
Page 230 and 231:
In a typical stand-alone data acqui
Page 232 and 233:
The maximum battery life that can b
Page 234 and 235:
Input termination resistors, typica
Page 236 and 237:
Figure 7.13 shows the standard conn
Page 238 and 239:
interface, even at high speed, the
Page 240 and 241:
• Use different data formats so t
Page 242 and 243:
Command errors are reported immedia
Page 244 and 245:
• Channel scalingThis automatical
Page 246 and 247:
The channel scan for this type of s
Page 248 and 249:
Data is logged in a fixed non-ASCII
Page 250 and 251:
7.9 Stand-alone logger/controllers
Page 252 and 253:
88.1 IntroductionThe communications
Page 254 and 255:
Figure 8.2GPIB connector (IEEE 488)
Page 256 and 257:
• TalkersA talker is a one-way co
Page 258 and 259:
controller in charge (CIC). The IFC
Page 260 and 261:
Each device connected to the GPIB h
Page 262 and 263:
One of the additional features that
Page 264 and 265:
• The controller temporarily conf
Page 266 and 267:
Table 8.4IEEE 488.2 commandsThe SCP
Page 268 and 269:
Figure 8.9SCPI instrument modelThe
Page 270 and 271:
99.1 Ethernet and fieldbuses for da
Page 272 and 273:
cabling tray etc and the transceive
Page 274 and 275:
transceiver in the MAU and this is
Page 276 and 277:
Advantages of the system include:
Page 278 and 279:
of a cell as well, but these are ig
Page 280 and 281:
Figure 9.8CSMA/CD collisionsAssume
Page 282 and 283:
• PreambleThis field consists of
Page 284 and 285:
of this figure. Some manufacturers
Page 286 and 287:
Grounding has safety and noise conn
Page 288 and 289:
Just as with any technology, each o
Page 290 and 291:
information. The packet is then pla
Page 292 and 293:
There are two types of connectors,
Page 294 and 295:
HOSTClient SoftwareManages Interfac
Page 296 and 297:
Figure 10.6USB connector pinsThere
Page 298 and 299:
The idle states for low- and high-s
Page 300 and 301:
The interrupt transfer type is used
Page 302 and 303:
than in spending a lot of time and
Page 304 and 305:
• The sensitivity of the output/i
Page 306 and 307:
term error (m) in the system and ad
Page 308 and 309:
11.2 Capturing high speed transient
Page 310 and 311:
12IntroductionThe PCMCIA (PCMCIA st
Page 312 and 313:
adapter on a full size computer has
Page 314 and 315:
Pager cards are used in offices and
Page 316 and 317:
Size 85.6 mm × 54.0 mmType I 3.3 m
Page 318 and 319:
The memory only interface is conver
Page 320 and 321:
The AIMS interface supports large d
Page 322 and 323:
12.8 FutureThe card information str
Page 324 and 325:
A/D conversion timeAddressAddress r
Page 326 and 327:
Back-planeBand pass filterBandwidth
Page 328 and 329:
BufferBusBWCache memoryCCDCCIRCCITT
Page 330 and 331:
pixel is subjected to a mathematica
Page 332 and 333:
data between the computer memory an
Page 334 and 335:
FrameFrame grabberFringingFull dupl
Page 336 and 337:
so that they interlock. The PAL sta
Page 338 and 339:
Lux-secondSI unit of light exposure
Page 340 and 341:
NTSCNull modemNumber of channelsNyq
Page 342 and 343:
PortPPIPre-triggerProgram I/OProgra
Page 344 and 345:
whereby the first gray level of eac
Page 346 and 347:
allowing the user to control basic
Page 348 and 349:
input.TrunkUARTUnipolar inputsUnloa
Page 350 and 351:
Appendix BThe information in this s
Page 352 and 353:
Table B.4Controller 2: 16-bit (AT o
Page 354 and 355:
B.5 8253/8254 Counter/timer
Page 356:
Table B.8Memory map for PC/XT/AT
Page 359 and 360:
Table B.10BIOS data area
Page 361 and 362:
Table B.15ROMTable B.16AT extended
Page 363 and 364:
← ↔ ← ← ← ↔
Page 365 and 366:
Figure B.1Card dimensions for PC/XT
Page 367 and 368:
Appendix CThis section contains bri
Page 369 and 370:
the control register of the 8255. T
Page 371 and 372:
The bits A7 (MSB) down to A0 (LSB)
Page 373 and 374:
Table C.6Instructions for reading o
Page 375 and 376:
The program could also enable the I
Page 377 and 378:
Group AConfiguration Informationto
Page 379 and 380:
C.11 Single-bit set/resetAny of the
Page 381 and 382:
Figure C.15Bi-directional bus (mode
Page 383 and 384:
Figure D.18254 Block diagramFigure
Page 385 and 386:
Figure D.3TCCTRL registerThe functi
Page 387 and 388:
This is the data register of the fi
Page 389 and 390:
• A simple read operation• A co
Page 391 and 392:
The null count bit indicates if the
Page 393 and 394:
For even counts: the output is init
Page 395 and 396:
Appendix EThe IPTS-68 standard defi
Page 397 and 398:
Number of ranges = 2Range #1 -270 t
Page 399 and 400:
Page 401 and 402:
Range #2 0 to 1372°COrder of polyn
Page 403 and 404:
Number of Ranges = 4Range #1 -50 to
Page 405 and 406:
Page 407 and 408:
Appendix FF.1 IntroductionAll activ
Page 409 and 410:
Table F.3 gives the conversion betw
Page 411 and 412:
The conversion between binary and h
Page 413 and 414:
F.8 Internal representation of info
Page 415 and 416:
12 which is equivalent to: 1100-4 S
Page 417 and 418:
DCDCASDCISDCLDDDIODTDTASDTISENDEOIE
Page 419 and 420:
STBSTRSSWNST(T)TETACSTADSTAGTCATCST
Page 421 and 422:
404 IndexDuplex:full duplex 178half
Page 423 and 424:
406 IndexOpen loop control 285see a
Page 425:
THIS BOOK WAS DEVELOPED BY IDC TECH
show all

Data Acquisition

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?