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Table of Contents Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments xiii
8. MAINTENANCE SCHEDULE & PROCEDURES .................................................................................................. 179
8.1. Maintenance Schedule ................................................................................................................................... 179
8.2. Predicting Failures Using the Test Functions ................................................................................................. 183
8.3. Maintenance Procedures ............................................................................................................................... 184
8.3.1. Replacing the Sample Particulate Filter .................................................................................................. 184
8.3.2. Rebuilding the Sample Pump ................................................................................................................. 185
8.3.3. Performing Leak Checks ........................................................................................................................ 185
8.3.4. Performing a Sample Flow Check .......................................................................................................... 186
8.3.5. Cleaning the Optical Bench .................................................................................................................... 186
8.3.6. Cleaning Exterior Surfaces of the GFC 7000TA ..................................................................................... 186
9. THEORY OF OPERATION .................................................................................................................................... 187
9.1. Measurement Method .................................................................................................................................... 187
9.1.1. Beer’s Law .............................................................................................................................................. 187
9.1.2. Measurement Fundamentals .................................................................................................................. 187
9.1.3. Gas Filter Correlation .............................................................................................................................. 188
9.1.4. Interference and Signal to Noise Rejection ............................................................................................. 190
9.2. Pneumatic Operation ...................................................................................................................................... 193
9.2.1. Sample Gas Flow ................................................................................................................................... 194
9.2.2. Flow Rate Control ................................................................................................................................... 194
9.2.3. Purge Gas Pressure Control ................................................................................................................... 196
9.2.4. Particulate Filter ...................................................................................................................................... 196
9.2.5. Pneumatic Sensors ................................................................................................................................. 196
9.3. Electronic Operation ....................................................................................................................................... 197
9.3.1. Overview ................................................................................................................................................. 197
9.3.2. CPU ........................................................................................................................................................ 199
9.3.3. Optical Bench & GFC Wheel .................................................................................................................. 200
9.3.4. Synchronous Demodulator (Sync/Demod) Assembly ............................................................................. 202
9.3.5. Relay Board ............................................................................................................................................ 205
9.3.6. Mother Board .......................................................................................................................................... 207
9.3.7. I
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C Data Bus ........................................................................................................................................... 210
9.3.8. Power Supply/ Circuit Breaker ................................................................................................................ 211
9.4. Front Panel Touchscreen/Display Interface ................................................................................................... 212
9.4.1. LVDS Transmitter Board ......................................................................................................................... 212
9.4.2. Front Panel Touchscreen/Display Interface PCA .................................................................................... 212
9.5. Software Operation ........................................................................................................................................ 213
9.5.1. Adaptive Filter ......................................................................................................................................... 213
9.5.2. Calibration - Slope and Offset ................................................................................................................. 214
9.5.3. Measurement Algorithm .......................................................................................................................... 214
9.5.4. Temperature and Pressure Compensation ............................................................................................. 215
9.5.5. Internal Data Acquisition System (DAS) ................................................................................................. 215
10. TROUBLESHOOTING & REPAIR PROCEDURES ............................................................................................ 217
10.1. General Troubleshooting Hints ..................................................................................................................... 217
10.1.1. Interpreting WARNING Messages ........................................................................................................ 218
10.1.2. Fault Diagnosis with TEST Functions ................................................................................................... 221
10.1.3. Using the Diagnostic Signal I/O Function ............................................................................................. 223
10.1.4. Internal Electronic Status LEDs ............................................................................................................ 224
10.2. Gas Flow Problems ...................................................................................................................................... 228
10.2.1. GFC 7000TA Internal Gas Flow Diagrams ........................................................................................... 229
10.2.2. Typical Sample Gas Flow Problems ..................................................................................................... 232
10.2.3. Poor or Stopped Flow of Purge Gas ..................................................................................................... 234
10.3. Calibration Problems .................................................................................................................................... 235
10.3.1. Miscalibrated ......................................................................................................................................... 235
10.3.2. Non-Repeatable Zero and Span ........................................................................................................... 236
10.3.3. Inability to Span – Touchscreen SPAN Button Not Visible ................................................................... 236
10.3.4. Inability to Zero – Touchscreen ZERO Button Not Visible .................................................................... 237
10.4. Other Performance Problems ....................................................................................................................... 238
10.4.1. Temperature Problems ......................................................................................................................... 238
10.4.2. Excessive Noise ................................................................................................................................... 240
10.5. Subsystem Checkout ................................................................................................................................... 241
10.5.1. AC Mains Configuration ........................................................................................................................ 241
10.5.2. DC Power Supply ................................................................................................................................. 241
10.5.3. I
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C Bus .................................................................................................................................................. 242