OXITEC® In Situ Oxygen Analyser Systems - ENOTEC - #2

Theory = Practice

ENOTEC goes for it with Nernst

Measuring oxygen using the zirconium oxide principle has been re­cognised a million times over as a simple and cost-efficient method for measuring oxygen in flue gases.

Configuration of the measuring cell

The technological and structural design of the OXITEC® zirconium oxide measuring cell guarantees permanent gas-tight separation

of process gas from reference gas.

ENOTEC has resolutely put the Nernst equation

into practice for the user's benefit.

The Nernst equation and its "leak-tight fraction line".

A process gas (A) with an unknown oxygen (0₂) concentration flows around the outside of a measuring probe which is sealed off to the process gas by means of a heated zirconium-oxide measuring cell (B). A reference gas (C), with a known oxygen (0₂) concentration, flows to the inside of the measuring cell.

At an optimum temperature a voltage (U) in mV is created between the two surfaces of the cell. At a constant temperature in the cell this voltage is dependent only on the ratio of the oxygen concen­trations (partial pressures) in (A) and (C). Using air (oxygen content at constant 20.95%) as a reference gas, the measured voltage is a direct measure of the oxygen concentra­tion in the process gas (A), provided that the isolation between the process gas and the reference gas is absolutely gas-tight, thus ruling out distortion of the resulting measured value.

Ion-migration

Solder

Zirconium--oxid (B)

Heating Electrodes

Thermo­couple

Reference gas n (Air)(C) 1}

Only probes manufactured by ENOTEC truly comply with the Nernst equation.

U = measurable voltage (mV)

K = natural constant

T = temperature (measuring cell)

P1 = 0₂ - partial pressure in the reference gas

P2 = 0₂ - partial pressure in the process gas

C = constant offset

With a "leak-tight fraction line" and air as the reference gas, all parameters in the Nernst equation - except for P2 - are constant. This means that the mV signal is dependent only on the 0₂ partial

pressure (P2) in the process gas.

Thanks to the special soldering technique used in their manufacture, only OXITEC® probes guarantee the leak-tight fraction line.