Campbell Scientific CR800 and CR850 Measurement and Control Systems User Manual
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Table of Contents
12
7.8.13.8 Formatting String Hexadecimal Variables ....................... 241
7.8.14 Data Tables ................................................................................ 241
7.8.15 PulseCountReset Instruction...................................................... 242
7.8.16 Program Signatures.................................................................... 243
7.8.16.1 Text Signature .................................................................. 243
7.8.16.2 Binary Runtime Signature................................................ 243
7.8.16.3 Executable Code Signatures............................................. 243
7.8.17 Advanced Programming Examples............................................ 244
7.8.17.1 Miscellaneous Features .................................................... 244
7.8.17.2 Running Average and Total of Rain................................. 247
7.8.17.3 Use of Multiple Scans ...................................................... 247
7.8.17.4 Groundwater Pump Test................................................... 248
7.8.17.5 Scaling Array ................................................................... 251
7.8.17.6 Conditional Output........................................................... 252
7.8.17.7 Capturing Events.............................................................. 253
7.8.18 PRT Measurement ..................................................................... 254
7.8.18.1 PRT Calculation Standards .............................................. 254
7.8.18.2 Measuring PT100s (100-Ohm PRTs)............................... 258
7.8.18.2.1 Self-Heating and Resolution................................... 258
7.8.18.2.2 PT100 in Four-Wire Half-Bridge ........................... 258
7.8.18.2.3 PT100 in Three-Wire Half-Bridge.......................... 260
7.8.18.2.4 PT100 in Four-Wire Full-Bridge ............................ 262
7.8.19 Running Average ....................................................................... 264
Section 8. Operation .....................................................269
8.1 Measurements ....................................................................................... 269
8.1.1 Time............................................................................................. 269
8.1.1.1 Time Stamps ...................................................................... 269
8.1.2 Voltage ........................................................................................ 270
8.1.2.1 Input Limits........................................................................ 271
8.1.2.2 Reducing Error................................................................... 272
8.1.2.3 Measurement Sequence...................................................... 273
8.1.2.4 Measurement Accuracy...................................................... 274
8.1.2.5 Voltage Range.................................................................... 276
8.1.2.5.1 AutoRange................................................................ 276
8.1.2.5.2 Fixed Voltage Ranges............................................... 277
8.1.2.5.3 Common Mode Null / Open Input Detect................. 277
8.1.2.6 Offset Voltage Compensation ............................................ 278
8.1.2.6.1 Input and Excitation Reversal................................... 278
8.1.2.6.2 Ground Reference Offset Voltage ............................ 279
8.1.2.6.3 Background Calibration............................................ 279
8.1.2.7 Integration .......................................................................... 279
8.1.2.7.1 ac Power Line Noise Rejection................................. 280
8.1.2.8 Signal Settling Time........................................................... 282
8.1.2.8.1 Minimizing Settling Errors ....................................... 283
8.1.2.8.2 Measuring the Necessary Settling Time ................... 283
8.1.2.9 Self-Calibration.................................................................. 285
8.1.2.10 Time Skew Between Measurements ................................ 290
8.1.3 Resistance Measurements............................................................ 291
8.1.3.1 ac Excitation....................................................................... 293
8.1.3.2 Accuracy of Ratiometric-Resistance Measurements.......... 294
8.1.3.3 Strain Calculations ............................................................. 296
8.1.4 Thermocouple.............................................................................. 297
8.1.5 Pulse ............................................................................................ 297
8.1.5.1 Pulse-Input Channels (P1 - P2) .......................................... 299