Sensors & transducers
-135 °C to -70 °C and the Martian surface layer along its equator achieves positive temperatures during the day time. Considering the temperature and low pressure of the atmosphere on Mars, it was previously estimated that liquid water could not be present on Mars. However, in May 2015, supported by the measurements made by FMI and Vaisala technology, combined with numerical models, the first evidence of ancient liquid water on Mars was confirmed. Curiosity’s mission was to determine whether Mars has ever had the right environmental conditions to support microbial life forms. The discovery of traces of ancient liquid water was therefore a major success, and led to the mission objective for Perseverance: to search for signs of ancient microbial life. For the latest updates visit
https://mars.nasa.gov/mars2020/news/
ENVIRONMENTAL MONITORING ON EARTH
Meteorological and aviation measurements rely on the same pressure and humidity technologies that are deployed on Mars. However, terrestrial applications also include building management systems and industrial monitoring where products are dried or moistened, or where process measurements, such as gas levels, require compensation. On Mars, sensor service and calibration is not possible for obvious reasons, but on Earth it is relatively simple to perform. However, terrestrial customers are also looking for sensors with high levels of accuracy and stability, long life expectancy and extended periods between service or calibration. This is important because unreliable measurements could have catastrophic consequences and because frequent service and calibration would interrupt production and increase operational costs. Despite the long-term stability of the
Vaisala sensors, it is still necessary to conduct regular calibration in order to check that the instrument is within specification and capable of producing valid data. Unless required by regulation, it may be possible to extend the period between calibrations as an instrument is proven to be stable.
Instrumentation Monthly February 2023
HUMIDITY MONITORING TECHNOLOGY Vaisala’s HUMICAP humidity sensors employ a capacitive thin-film polymer sensor consisting of a substrate (typically glass or ceramic) on which a film of polymer is deposited between two electrodes. The polymer either absorbs or releases water vapour as the relative humidity of the ambient air rises or falls, which changes its dielectric properties, and thereby the capacitance of the sensor, which is measured and converted to a humidity reading.
PRESSURE MONITORING TECHNOLOGY Utilising a single-crystal silicon material, Vaisala’s BAROCAP is a micromechanical pressure sensor that measures dimensional changes in its silicon membrane. As the surrounding pressure increases or decreases, the membrane bends, thereby increasing or decreasing the height of the vacuum gap inside the sensor. Opposite sides of the gap act as electrodes, and as the distance between them alters, the sensor capacitance changes, which is measured and converted to pressure readings.
SUMMARY
While participation in projects such as the Mars missions is an exciting and challenging diversion from the daily business, Vaisala’s engineers are keen to point out that invitations to be involved in such work only come when product development aims for ‘best in class’. Torri says: “Our sensors have become the industry standard for three main reasons. Firstly, we focus intensely on the voice of the customer; listening to their needs and driving our R&D to meet and exceed expectations. Secondly, as part of our constant drive for improvement, we seek and encourage innovation in everything we do. Thirdly, the Vaisala brand stands for quality and reliability, so before any product can be awarded the Vaisala logo, it has to earn that right by passing a rigorous and demanding performance test program.”
Vaisala
www.vaisala.com 31
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