Teledyne 9700 instruction manual Detector

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2 Theory of Operation

Model 9700

 

 

 

 

An optional CAUTION alarm circuit utilizes potentiometer P4 to establish the setpoint. When the setting of P4 is exceeded. transistor Q2 is turned on and relay K1 is energized, resulting in an alarm.

The optional FAILURE alarm circuit is set up so that if the detector opens up, an alarm comparator will trip and turn off a relay, which is normally energized, i.e., during the non-alarm condition, the normally open contact will be closed and the normally closed contact will be open.

The power supply circuitry includes transformer T1 which is a 40-volt center-tapped unit. Two sets of rectifiers are used to supply two regulated power circuits and +/-24 VDC unregulated. The circuit that includes Zener diodes ZD2 and ZD3 supplies +/-15 VDC regulated. Regulator VR2 is the current regulator for the detector. This regulator is set up so that current through the detector is determined by resistors R4 and R5. Current output of 0.3A can be measured at a pair of test points. Capacitor C9, connected across the input, gives protection from line transients, high voltage spikes, etc.

2. 3 Detector

The basic elements of the combustible gas detector are shown in Figure 5. The two beads each consist of a very small coil of wire coated with an appropriate material. The active (or measuring) bead coating is a mixture of a catalytic material with an inert binder. This catalytic material is selected to enhance the oxidation of combustible gases. The reference bead coating is an inert material having similar thermal properties to the other bead.

Upon exposure of the detector to an atmosphere containing com- bustible gases and oxygen, these will combine at the surface of the measur- ing bead. Energy produced by this reaction will heat the active bead and cause the electrical resistance of its wire coil to change. The change in resistance of this coil is, then, for a particular gas, a measure of the reaction rate at the bead surface. The reaction rate and energy production depend strongly on the nature of the gas. By raising the temperature of the bead, the reaction rate can be increased, making the effects of different gases more nearly equal. Thus, the sensitivity of the detector is made greater and more nearly equal for different gases. This heating is accomplished by passing a constant electrical current through the wire coil supporting the bead.

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TELEDYNE BROWN ENGINEERING

Analytical Instruments

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Contents Model Flue Gas Analysis System Warranty Important NoticeTable of Contents Maintenance & Troubleshooting Introduction Flue Gas Analysis SystemOverview General Information Sample ConditioningSample Conditioning Standard Features Oxygen Analyzer SectionOxygen Analyzer Section General Information Optional Features General Information Combustible Gas Analyzer Section Combustible Gas Analyzer SectionGeneral Information Compound LEL Response Factor Operating Controls and Indicators Meter Trim Recessed Secondary ControlsAnalog Output Current MAX Load Output Impedance Theory of Operation Oxygen AnalyzerTheory of Operation Combustible Analyzer Detector Flue Gas Analysis System Theory of Operation Output Signal Voltage InstallationPower Electrical ConnectionsInterconnection Diagram Alarm and/or Control Circuitry Output Signal CurrentInstallation Preliminary OperationStartup of Oxygen Analyzer Meter ZeroingInitial Calibration and Equilibration Flue Gas Analysis System Operational Calibration Routine Operational Calibration ProcedureStartup of Combustibles Analyzer Operation Analyzer Startup Span GasSystem Startup Sample System StartupOperation Routine Maintenance Flue Gas Analysis System Maintenance & TroubleshootingMaintenance Oxygen Cell ReplacementCell Warranty Filter Condensate Trap Spray NozzleWater Strainer Combustible SensorPump TroubleshootingGeneral Oxygen Analyzer .2.2.1 Inability to Calibrate Combustible Analyzer Section Inability to CalibrateNo Alarm With High Gas Level Lamp Failure Specifications AppendixAppendix Model Oxygen Analysis SectionRecommended Spare Parts List Model 9700 System Standard Unit OnlyReference Drawings Response of Combustible Sensor to Various Gases Appendix Model Supporting Equipment for Flue Gas Analysis Systems Figure A-1 Typical Dry Probe Maintenance General Maintenance for CC-2B Series PumpsRepair Appendix Model Flue Gas Analysis System Figure A-3 Pump Assembly Flue Gas Analysis System Replacing the Liner in the Flex-I-Liner Pump Figure A-4 Replacing Flex-I-LinerFlue Gas Analysis System