Brand-Gaus 4705 사용자 설명서 - 페이지 5

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3. Calibrate the voltage outputs

If accuracy of the voltage outputs is critical, calibration may be performed. There are

trim potentiometers and the back of the large blue output module on the display board,

accessible by removing the top cover. Flow zero and span concentrations to the analyzer,

verify the display reads the proper value, and adjust the zero and span pots to calibrate

the analog output to correspond with the display values.

Theory of Operation

Zirconium Oxide Measurement of O2

The oxygen measurement makes use of the fact that zirconium oxide conducts oxygen

ions when heated above 600 °C. Platinum electrodes on the interior and exterior of a

zirconium oxide tube provide a catalytic surface for the exchange of oxygen molecules

and oxygen ions. As molecules encounter the platinum electrodes, they become ionized

and are transported through the body of the zirconium oxide. This charge transport

ultimately sets up an electric potential across the electrodes that is proportional to the log

of the ratio of oxygen concentrations on each side of the oxide. Thus, if a reference gas

(usually instrument air at 20.9 %O2) flows across the inner electrode, the concentration

of sample gas flowing across the outer electrode can be determined. In a conventional

zirconium-oxide oxygen analyzer, this voltage is exponentiated to determine the

concentration.

In the Brand-Gaus Model 4705, a second zirconium-oxide cell is ganged together to

pump oxygen into the first cell, which is maintained at a constant voltage. The amount of

oxygen needed to maintain the primary cell at the operating point is a more sensitive

measurement of sample concentration, and allows for measurement at zero oxygen. This

pump signal is carefully measured and related back to the sample concentration.

Brand-Gaus Oxygen Analyzer User's Manual

Warning: This operation should only be performed by qualified

service personnel. Some internal analyzer components

are at high temperature and/or at lethal line voltage.

Theory of Operation