083730300A DCN8101 ix
5.7.14 Subsystem Checkout .....................................................................................................................128
5.7.14.1 AC Mains Configuration...................................................................................................128
5.7.14.2 DC Power Supply ............................................................................................................128
5.7.14.3 I
2
C Bus .............................................................................................................................129
5.7.14.4 Touchscreen Interface .....................................................................................................129
5.7.14.5 LCD Display Module ........................................................................................................129
5.7.14.6 Relay Board .....................................................................................................................130
5.7.14.7 Sync/Demodulator Assembly ..........................................................................................130
5.7.14.8 Opto Pickup Assembly ....................................................................................................131
5.7.14.9 GFC Wheel Drive ............................................................................................................131
5.7.14.10 IR Source ....................................................................................................................131
5.7.14.11 Pressure/Flow Sensor Assembly ................................................................................132
5.7.15 Motherboard ...................................................................................................................................132
5.7.15.1 A/D Functions ..................................................................................................................132
5.7.15.2 Status Outputs .................................................................................................................133
5.7.15.3 Control Inputs – Remote Zero, Span ...............................................................................133
5.7.16 CPU ................................................................................................................................................133
5.7.17 RS-232 Communications ...............................................................................................................134
5.7.17.1 General RS-232 Troubleshooting ....................................................................................134
5.7.18 The Optional CO
2
Sensor ..............................................................................................................134
5.8 Repair Procedures .....................................................................................................................................135
5.8.1 Repairing Sample Flow Control Assembly .....................................................................................135
5.8.2 Removing/Replacing the GFC Wheel ............................................................................................136
5.8.3 Checking and Adjusting the Sync/Demodulator, Circuit Gain (CO MEAS) ..................................138
5.8.3.1 Checking the Sync/Demodulator Circuit Gain .................................................................138
5.8.3.2 Adjusting the Sync/Demodulator, Circuit Gain ................................................................139
5.8.4 Disk-On-Module Replacement .......................................................................................................140
5.9 Frequently Asked Questions .....................................................................................................................141
5.10 Technical Assistance .....................................................................................................................142
6. Theory of Operation ................................................................................................................ 143
6.1 Measurement Method ................................................................................................................................143
6.1.1 Beer’s Law......................................................................................................................................144
6.2 Measurement Fundamentals .....................................................................................................................144
6.1.2 Gas Filter Correlation .....................................................................................................................145
6.1.2.1 The GFC Wheel ...............................................................................................................145
6.1.2.2 The Measure Reference Ratio ........................................................................................146
6.1.2.3 Interference and Signal to Noise Rejection .....................................................................147
6.1.2.4 Summary Interference Rejection .....................................................................................148
6.3 Pneumatic Operation .................................................................................................................................148
6.3.1 Flow Rate Control ..........................................................................................................................149
6.3.1.1 Critical Flow Orifice ..........................................................................................................149
6.3.2 Particulate Filter .............................................................................................................................150
6.3.3 Pneumatic Sensors ........................................................................................................................150
6.3.3.1 Sample Pressure Sensor.................................................................................................151
6.3.3.2 Sample Flow Sensor .......................................................................................................151
6.4 Electronic Operation ..................................................................................................................................151
6.4.1 CPU ................................................................................................................................................153
6.4.1.1 Disk-On-Module (DOM) ...................................................................................................153
6.4.1.2 Flash Chip .......................................................................................................................153
6.4.2 Optical Bench & GFC Wheel..........................................................................................................154
6.4.2.1 Temperature Control .......................................................................................................154
6.4.2.2 IR Source .........................................................................................................................154
6.4.2.3 GFC Wheel ......................................................................................................................155
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