Zirconium Oxide Detection technology comes of age

Historically, there have been three different technologies employed for oxygen detection in process and regulatory applications:

• Electrochemical cells are the most inexpensive, and are often used for a temporary measurement, but suffer limitations in both survivability and performance in continuous monitoring applications.
• Zirconium Oxide cells, a high-temperature, solid-state electrochemical approach, have been used for decades in demanding applications. They are the most robust, but previous implementations suffered because the output was inherently logarithmic and there were thermal drift issues with many designs.
• Paramagnetic sensors, exploiting the inherent paramagnetic nature of oxygen, have long been recognized as the most accurate practical oxygen detection method, but they are also somewhat expensive and delicate and require a very clean, dry sample.

The best of all three:

Now, with our implementation of our next-generation zirconium oxide sensor technology, it is no longer necessary to compromise on ruggedness, performance, expense, or the ability to make measurements on a wet basis.

Traditional Zirconium Oxide Oxygen Sensors

At the most fundamental level Brand-Gaus oxygen sensors operate the same as traditional zirconium oxide sensors, but there are some important differences in our implementation.

As with all zirconium oxide sensors, the principle of operation is based on the Nernst relation. At approximately 700 C, zirconium oxide becomes selectively conductive to oxygen ions. This property is used to make a gas/solid/gas electrochemical cell, where the potential difference between two electrodes plated on a solid piece of zirconium oxide will be related to the difference in oxygen concentration on each side. If one side is exposed to atmospheric conditions, and the other to a gas stream of interest, that voltage difference will be proportional to the logarithm of the ratio of the two oxygen concentrations (the Nernst relation).

Because this dependence is logarithmic, traditional zirconium oxide sensors may be employed to measure concentration over several orders of magnitude, for example from PPM levels to percent levels. However, because the response is inherently nonlinear, the resulting voltage must be exponentiated to calculate the concentration. Although tractable, there is several notable complications to this scheme: The logarithm of zero is (negative)infinity, so straight logarithmic sensors cannot measure gas at zero concentration. As such, it is necessary to use a low gas value other than zero concentration to calibrate the lower end of the analyzer range. Also, the calibration of "zero" and span are inherently interrelated making calibration more difficult and less dependable. Finally, the logarithmic response becomes very flat at concentrations levels between 10 and 21%, which makes it difficult to extract the correct oxygen level in the presence of even the smallest amount of noise and drift.

Brand-Gaus Zirconium Oxide Innovations

The first implementation advantage in Brand-Gaus analyzers over traditional zirconium oxide analyzers is in the thermal design of the sensor. Instead of a bulky oven, our sensors are very compact and the heater is tightly integrated with the cell itself, resulting in small size, excellent thermal stability, low power dissipation, and an extraordinarily rugged design. The physical construction and packaging of these sensors are similar to those used in punishing automotive applications, where they must endure extreme thermal and mechanical shock, as well as other harsh environmental challenges.

Secondly, we offer an innovative detection scheme that gives a truly linear response. By placing two Zirconium cells back-to-back, and fixing the concentration in the primary cell, the second cell may be inverted and used as a source of oxygen to null the signal from the first cell. While the details of implementation are proprietary, the measurement of the amount of oxygen pumped through the second cell to keep the first cell at equilibrium is linearly related to the concentration of the gas in the measurement stream. Furthermore, this linear response allows measurement at zero, and a non-interacting zero/span calibration algorithm.

Brand-Gaus offers both logarithmic sensors for PPM applications as well as linear sensors for applications in percent ranges. The fundamental sensor design is so highly-engineered and robust that the resulting analyzers are extraordinarily simple, reliable, rugged, versatile...and very high performance too.

High-performance replacement for paramagnetic and conventional zirconium oxide analyzers

In fact, the accuracy and stability of the Brand-Gaus Linear Zirconium Oxide analyzers often surpass those of paramagnetic analyzers, thus making them a simpler, more cost-effective replacement, without any sacrifice in performance.

Those who have experienced older zirconium oxide designs may find this hard to believe, but we cannot stress enough how much of an engineering advancement our next-generation analyzers are. Ultimately, the proof is in how they perform in real applications in the field. We invite you to take advantage of our try before you buy program so you can quickly see just how simple, reliable, and accurate oxygen measurement can be. Please contact us for more details.