MEMS vs. Geophone

For many years, vibration monitoring sensors in the construction sector were predominantly based on geophone technology. In recent years, the introduction of MEMS-based sensors has revolutionized the industry. Gradually, a shift is being made to use these compact and user-oriented devices based on MEMS technology. However, in some cases, the preference for geophones remains, and using MEMS-based sensors in construction is frowned upon or rejected. In this article, we impugn those 'common beliefs' and present evidence from a Dutch scientific research paper where MEMS accelerometers and geophones are compared. 

Vibration monitoring is a rapidly evolving field, and its development in the Netherlands has been particularly notable. Because a Dutch monitoring specialist wrote the research article about the Dutch market, we will explore how vibration monitoring systems have advanced over time to meet the needs of Dutch businesses specifically.

MEMS is an abbreviation for 'microelectromechanical systems.' MEMS technology allows for the manufacturing of microscale devices such as sensors. Various sectors apply this technology, from aircraft and automotive to even the pharmaceutical industry. MEMS technology revolutionized the sensor market. The miniature devices manufactured on silicon chips are highly reliable and rapidly responding. 

Myths about MEMS technology

Still, in the vibration monitoring sector, it is sometimes believed that MEMS-based sensors are inferior to geophones. Some claim that at low vibration levels, MEMS' measurements are not as precise as geophones' and that very high vibration levels are registered by MEMS at high frequencies, compared to a geophone.

This is simply not true. Such discrepancies might have existed in the past, but MEMS-based sensors have evolved significantly since then, and their present performance is equivalent to geophones. MEMS-based sensors surpass geophones in many ways. Because of the lightweight, compact size and the fact that MEMS technology does not require manual leveling, it offers a fantastic basis for developing incredibly easy-to-use vibration monitoring systems. In contrast, the installation of geophones often includes complicated procedures and tiresome training sessions, making it nearly impossible to perform for a non-specialist.

Some vibration monitors are specifically designed for construction vibration monitoring. Others have a different focus (e.g., machine health monitoring) and are less or even unsuitable for the construction environment. It is, therefore, crucial that the sensor you choose is suitable for the activity and specific situation related to your project. There is no one-size-fits-all solution. Construction vibration monitoring devices are designed to follow certain regulations. Vibration limits are hardly ever set by law; they are generally set by regulations, guidelines, industry standards, and specifications. Often, they differ per country or even per state. In the USA, there is no national standard; therefore, European standards are often applied instead.

For this article, the Dutch standard SBR-A is evaluated. SBR-A includes the following requirements: 

Vibration monitoring sensors must have the means to register velocities between 0.2mm/s and 50 mm/s over the entire frequency range of 1 to 100 Hz. For accelerometers, those values have to be between 1 mm/s2 and 30 m/s2. 

This standard allows for an accuracy of 10% (which equates to 1dB) over the entire frequency range. A sensor is approved when it complies with those parameters. 

In 2018, research conducted by Martijn van Delft (Allnamics) and Carel Ostendorf (Cauberg-Huygen) put an end to the skepticism surrounding the use of MEMS for construction vibration monitoring. The vibration monitors Axilog II, Vibra, Infra C22 (geophone technology), and SWARM (MEMS technology) were compared on measurements of two types of vibrations: