Percent Oxygen Analyzer | Operational Theory | |
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require a heater. When the outside and inside of the sensor are exposed to different oxygen partial pressures, an EMF (E) is developed which obeys the Nernst equation:
| RT | ⎛ | (PO2) Inside | ⎞ |
E(millivolts) = | ⎜ | ⎟ | ||
| log e⎜ |
| ⎟ | |
4F |
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| ⎝ | (PO2) Outside ⎠ | ||
where T is the temperature (K) at the disc (>650°C (1200°F)), R is the gas constant. F is the Faraday constant and (PO2) Inside and (PO2) Outside are the oxygen partial pressures at the inner and outer electrodes respectively with the higher oxygen partial pressure being positive.
If dry air at atmospheric pressure, (21% oxygen) is used as a reference at the inner electrode, the following equations are obtained:
| − 2 | ⎛ | 0.21 | ⎞ |
E(millivolts) = 2.154 ⋅10 | ⎜ | ⎟ | ||
| T loge ⎜ |
| ⎟ | |
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| ⎝ | (PO2 ) Outside ⎠ | |
Transposing this equation: |
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⎛ - 46.421E | ⎞ | ||
(%O2 ) Outside (ATM) = 0.21 EXP ⎜ |
| ⎟ | |
T | |||
⎝ | ⎠ | ||
The 9060L transmitter solves this equation which is valid above 650°C (1200°F). Either the probe heater or the process maintains the sensor temperature at this level.
2.2.3 Heater
CAUTION: DANGEROUS VOLTAGE (120 VAC) EXISTS WITHIN THE PROBE OR HEATER AND PRESENTS AN ELECTRICAL SHOCK HAZARD TO MAINTENANCE PERSONNEL. ALWAYS DISCONNECT THE PROBE FROM THE ANALYZER BEFORE WORKING WITH THE PROBE, SENSOR, OR HEATER.
THE EARTH CONNECTION (GREEN WIRE) FROM
Teledyne Analytical Instruments | 19 |