Teledyne 9060L - Zirconium oxide flue gas oxygen analyzer - Manual (Page 19)

Percent Oxygen Analyzer Operational Theory
Teledyne Analytical Instruments 19
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:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
Outside ) (PO
Inside ) (PO
log
4F
RT
ts) E(millivol
2
2
e
where T is the temperature (K) at the disc (>650°C (1200°F)), R is the
gas constant. F is the Faraday constant and (PO
2
) Inside and (PO
2
)
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:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
× = −
Outside ) PO (
21 . 0
log T 10 154 . 2 ts) E(millivol
2
e
2
Transposing this equation:
⎟
⎠
⎞
⎜
⎝
⎛
=
T
46.421E -
EXP 0.21 (ATM) Outside ) %O (
2
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