Delta F Non-Depleting Coulometric

Zirconium Oxide

Paramagnetic

Polarographic

Delta F Non-Depleting Coulometric

Principle of Operation
The continuing growth of the process control industry was accompanied by ever-increasing demands for improved measurement accuracy and stability in analytical instruments.  These demands were answered in 1973 with the introduction of the newest development in electrochemical oxygen analysis - the non-depleting coulometric sensor.

Unlike galvanic oxygen sensors, the non-depleting sensor does not require periodic replacement.  The sensor operates on a coulometric process whereby oxygen in the sample gas is reduced in an electrochemical cell. Sample gas diffuses through a simple gas diffusion barrier to the cathode, which is in contact with an electrolyte solution.  Oxygen is reduced at this electrode to hydroxyl ions.  Assisted by a potassium hydroxide electrolyte, the ions migrate to the anode, where they are oxidized back to oxygen.  The chemical reaction at the cathode is:

The reaction at the anode is:

Unlike replaceable galvanic electrochemical sensors that use a consumable lead anode as the driving mechanism for the reaction, an external EMF of 1.3 VDC drives the reaction in this sensor.  The resulting cell current is directly proportional to the oxygen concentration in the gas stream and is amplified accurately by solid-state circuitry, and is displayed as either percent, parts per million, or parts per billion of oxygen. The essential configuration of this sensor cell is illustrated on our Sensor Technology page.

Advantages and Disadvantages

The non-depleting coulometric sensor electrodes are, as stated in the name, "non-depleting."  Therefore, neither electrode undergoes chemical changes as oxygen is being measured. As a result, the output of the analyzer is inherently much more stable than galvanic sensors.  Also, periodic sensor replacement is eliminated, as are false low oxygen readings associated with replaceable galvanic sensors. Since there is no requirement for warm-up, pre-purging, or other preconditioning steps, most analyses can be obtained in minutes.  The non-depleting coulometric oxygen cell responds instantaneously to changes in oxygen concentrations and is not susceptible to "oxygen shock."  It recovers from high levels of oxygen (air) to ppm levels within minutes, due in part to the fact that it does not use a membrane to diffuse oxygen into the sensor cell.

The non-depleting coulometric is not recommended for oxygen concentrations above 25%.

Typical Usage

Analyzers using the non-depleting coulometric sensor are made exclusively by Delta F Corporation in Woburn, Massachusetts.  The analyzers are used widely in many  industries where precise measurement and monitoring of oxygen levels is critical.  Common use is for applications where frequent calibration is either impossible or undesirable.  Some typical examples include industrial gas manufacturing; petrochemical, chemical, and pharmaceutical operations; semiconductor manufacturing; glass processing furnaces; steel and aluminum heat-treating furnaces; inert gas welding ; and natural gas transmission.