Metal oxide moisture sensors have been on the market for years. Since their introduction in the 1960s, there have been many developments in trace moisture sensing technologies for industrial processes. And let’s face it – many of these appear to be a lot more exciting than the humble dew-point transmitter. But although employing lasers to monitor moisture in your process sounds cutting edge, they are not always the best choice for every application.
At Process Sensing Technologies, we offer the widest range of moisture sensing technologies for trace moisture in process applications. From the tunable diode laser technology of the Michell OptiPEAK TDL600 to the Quartz Crystal Microbalance sensor of the QMA601 among others, we understand that different applications benefit from specific technologies. In this post, we explain six key benefits of metal oxide moisture sensors.
One of the reasons for the longevity of the metal oxide moisture sensing technology is its versatility, which makes it suitable for many processes.
The measurement range covers both wet as well as very dry conditions. In terms of moisture content the range is from 23,000 ppmV down to less than 10 ppbV. That’s a dynamic measurement range over nine orders of magnitude, with just one sensor. No other technology does it with one sensing element.
Many contractual agreements for natural gas suppliers require actual dew-point measurements at pipeline pressure. Unlike other moisture measurement technologies, aluminum oxide sensors are able to measure dew-point at pressures up to 900 barg. This is more than enough for standard gas pipelines, which operate at pressures between 14 and 100 barg and makes the Michell moisture sensors ideal for applications like hydrogen monitoring in hydrogen filling stations.
The ability to take moisture readings at line pressure is an advantage for many other applications, including compressed air, given that it allows measurements which are representative of the actual sample conditions, without relying calculating values to another pressure.
Aluminum oxide is considered to be an ‘old’ technology. In part this is true as the earliest AlOx sensors were introduced in the 1960s. But just like the microprocessor (first developed in 1969), aluminum oxide sensor design has been continually refined and developed, and the sensors in production today are far in advance of the original 1960’s designs.
The improvements made include the introduction of two-wire transmitters, which are easier to install than the three-wire versions. The availability of new materials and production techniques has led to more robust sensors, which are resistant to sudden changes in pressure.
For moisture measurements in hydrocarbon liquids, aluminum oxide moisture transmitters are the only effective sensing method which allows measurement of moisture with the sample in liquid phase. With other technologies, the sample would need to be vaporized for the measurement to be made, adding to the process costs and introducing the possibility of errors.
Most commonly found in refineries and polymer production plants, moisture in liquids is an important measurement capability. Typical examples include monitoring moisture in benzene for styrene manufacture and naphtha feedstock to isomerization catalyst.
Aluminum oxide sensors are very affordable to maintain. Parts are easy to obtain and most moisture transmitters based on aluminum oxide sensors are ‘plug and play’. This simplicity means that routine maintenance doesn’t require someone with specialist skills or years of experience. Replacing the sensor takes less than five minutes and can be carried out successfully after minimal training.
Aluminum oxide sensors are extremely cost-effective to buy and install, with a low lifetime cost. Routine maintenance is easy to carry out and requires no specialist knowledge.
All measurement technologies require regular service and recalibration to ensure continued reliability. The affordability and ease of maintenance for aluminum oxide sensors gives them an advantage over many other moisture technologies: the sensor can be replaced in less than five minutes by anyone after minimal training.
Process Sensing Technologies offers a sensor exchange program, which effectively works as a lifetime warranty. Find out how it works.
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