Campbell Scientific CR1000 Measurement and Control System - Manual (Page 13)

Table of Contents
13
8.1.2.8.2 Measuring the Necessary Settling Time ................... 287
8.1.2.9 Self-Calibration.................................................................. 289
8.1.2.10 Time Skew Between Measurements ................................ 294
8.1.3 Resistance Measurements............................................................ 295
8.1.3.1 ac Excitation....................................................................... 297
8.1.3.2 Accuracy of Ratiometric-Resistance Measurements.......... 298
8.1.3.3 Strain Calculations ............................................................. 300
8.1.4 Thermocouple.............................................................................. 301
8.1.4.1 Error Analysis .................................................................... 302
8.1.4.1.1 Panel-Temperature Error .......................................... 302
8.1.4.1.2 Thermocouple Limits of Error.................................. 304
8.1.4.1.3 Thermocouple Voltage Measurement Error ............. 305
8.1.4.1.4 Ground Looping Error.............................................. 309
8.1.4.1.5 Noise Error ............................................................... 309
8.1.4.1.6 Thermocouple Polynomial Error .............................. 309
8.1.4.1.7 Reference-Junction Error.......................................... 310
8.1.4.1.8 Thermocouple Error Summary................................. 310
8.1.4.2 Use of External Reference Junction ................................... 311
8.1.5 Pulse ............................................................................................ 312
8.1.5.1 Pulse-Input Channels (P1 - P2) .......................................... 314
8.1.5.1.1 High-frequency Pulse (P1 - P2)................................ 315
8.1.5.1.2 Low-Level ac (P1 - P2) ............................................ 315
8.1.5.1.3 Switch Closure (P1 - P2) .......................................... 315
8.1.5.2 Pulse Input on Digital I/O Channels C1 - C8..................... 315
8.1.5.2.1 High Frequency Mode.............................................. 316
8.1.5.2.2 Low-Frequency Mode .............................................. 316
8.1.5.3 Pulse Measurement Tips .................................................... 317
8.1.5.3.1 Frequency Resolution............................................... 318
8.1.5.4 Pulse Measurement Problems ............................................ 320
8.1.5.4.1 Pay Attention to Specifications ................................ 320
8.1.5.4.2 Input Filters and Signal Attenuation......................... 320
8.1.5.4.3 Switch Bounce and NAN ......................................... 322
8.1.6 Period Averaging......................................................................... 322
8.1.7 SDI-12 Recording........................................................................ 323
8.1.8 RS-232 and TTL.......................................................................... 323
8.1.9 Field Calibration.......................................................................... 324
8.1.10 Cabling Effects .......................................................................... 324
8.1.10.1 Analog Sensor Cables ...................................................... 324
8.1.10.2 Pulse Sensors ................................................................... 324
8.1.10.3 RS-232 Sensors................................................................ 325
8.1.10.4 SDI-12 Sensors ................................................................ 325
8.1.11 Synchronizing Measurements.................................................... 325
8.2 Measurement and Control Peripherals .................................................. 326
8.2.1 Analog-Input Expansion Modules............................................... 327
8.2.2 Pulse-Input Expansion Modules .................................................. 327
8.2.3 Serial-Input Expansion Modules ................................................. 327
8.2.4 Control Outputs ........................................................................... 327
8.2.4.1 Digital I/O Ports................................................................. 327
8.2.4.2 Relays and Relay Drivers................................................... 328
8.2.4.3 Component-Built Relays.................................................... 328
8.2.5 Analog Control / Output Devices ................................................ 329
8.2.6 TIMs ............................................................................................ 329
8.2.7 Vibrating Wire............................................................................. 330
8.2.8 Low-level ac ................................................................................ 330
8.3 Memory and Final Data Storage ........................................................... 330
8.3.1 Storage Media.............................................................................. 330