Ametek CEM/Humox, Руководство пользователя

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1-2 | Thermox CEM/Humox Analyzer
Basic Elements of the Sensor
The CEM/Humox analyzer consists of the following basic system.
The Plumbing
All inlet and outlet tubing (cell housing), the sensing cell, and the sensing cell
fitting.
The Measuring System
The sensing cell, interconnecting wiring, and the control unit.
The Temperature System
The electrical cell heater (furnace), the type “K” thermocouple (monitors cell
operating temperature), and the sensor board containing cold junction thermo -
couple compensation. The sensing cell operates at a constant temperature. The
circuit board in the sensor terminal box switches power to the furnace from the
AC mains connected to the sensor
The Oxygen Measuring Cell
To get a percent moisture reading, the system calculates the difference between a
wet sample and a dry, conditioned sample. Both are measured using zirconium
oxide cells. The customer provided cooler dries the sample. Knowing the cooler
temperature setpoint or using the Platinum 100 ohm RTD provided to measure
the cooler exhaust temperature, the residual moisture contained in the gas stream
after the cooler can be calculated and added to the moisture calculated from the
wet and dry O
2
readings.
The sensing element itself is a closed-
end tube or disk made from ceramic
zirconium oxide stabilized with an oxide
of yttrium or calcium. Porous plati -
num coatings on the inside and outside
serve as a catalyst and as electrodes.
At high temperatures (generally above
1200°F/650°C), oxygen molecules
coming in contact with the platinum
electrodes near the sensor become ionic.
As long as the oxygen partial pressures
on either side of the cell are equal, the
movement is random and no net flow of
ions occurs. If, however, gases having
different oxygen partial pressures are on
either side of the cell, a potentiometric
voltage is produced (See Figure 1-1).
The magnitude of this voltage is a func -
Figure 1-1.
Zirconium oxide cell
principle of operation.