2 Theory of Operation | Model 9700 |
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electrolysis. Only after the oxygen is reduced to a low enough concentra- tion can the cell be used to measure the flue gas sample.
The signal from the first amplification stage is connected to a non- inverting second stage (A2) which contains a thermistor in its feedback loop: the thermistor is mounted adjacent to the oxygen cell and is used to measure temperature of the cell rises and cell output increases, thermistor resistance decreases and the gain of amplifier A2 decreases in order to maintain a constant net output voltage for a given concentration of oxygen.
The signal from the first amplification stage is connected to a non- inverting second stage (A2) which contains a thermistor in its feedback loop: the thermistor is mounted adjacent to the oxygen cell and is used to measure the temperature of the cell. As temperature rises and cell output increases, thermistor resistance decreases and the gain of the amplifier A2 decreases in order to maintain a constant net output voltage for a given concentration of oxygen. Potentiometers R7 and R8 are used to correct for internal offset errors in operational amplifiers A1 and A2, respectively.
The output of
The analyzer circuitry requires 115 VAC, 50/60 Hz, single phase power which is connected through RANGE switch SW1 to the fused primary of transformer T1. Rectification, by diodes D1 through D4 con- nected across the transformer secondary, provides +/- 15 VDC unregulated to the operational amplifiers. Capacitors C7 and C8 provide a bypass for stray electrical noise picked up on the power lines, transients, and RF.
AC input power is also connected to a Triac controlled heater circuit. When temperature rises above the setpoint of thermal switch SW3, heater H1 is turned off. When the heater contacts close, the Triac is shut off.
When the temperature falls below the setpoint, the Triac and heater are turned on. The heater and thermal switch are physically located in the combustible sensor compartment.
TELEDYNE BROWN ENGINEERING |
Analytical Instruments
