Research Proves MEMS Accelerometers Effective
in Blast-Induced Shock and Vibration Monitoring
Introduction: The Evolution of Vibration Monitoring in the Explosives Industry
The need to monitor vibration levels, primarily because of the environmental impact of blasting operations, has always been paramount in the explosives industry. Traditional methods employed the use of geophones. While these have been the industry standards for decades, they were not without challenges. In addition to being large and unwieldy to install, they typically required the installation of several accessories to operate (modem, antenna, battery, etc.). As well, geophones operating below their inherent natural frequency (typically in the range of 4 to 10 Hz) can experience “roll-off”, a distortion of the vibration signal phase, and a limitation first detailed by Farnfield (1996). Though modern geophones use amplifiers to bypass this concern, the evolution of an alternative that produces reliable vibration monitoring data without these challenges would be welcome.
The Advent of MEMS in Vibration Monitoring
Enter MEMS (Micro-electromechanical systems) accelerometers. Historically, the adoption of accelerometers in the explosives industry was infrequent because high costs and the need for charge amplifiers made them less appealing. However, the development and ubiquity of MEMS technology in recent years marked a turning point for vibration monitoring in the explosives industry.
MEMS technology is transformative. It enables the creation of diminutive devices that seamlessly merge both mechanical and electronic elements onto a singular circuit. With real-life applications already evident (e.g., the accelerometers triggering airbag deployment in vehicles, or the ones in smartphones detecting movement), MEMS technology promised innovation and efficiency. The economies of scale brought about by the extensive use of MEMS accelerometers in consumer electronics, like smartphones, have driven costs down, making them more accessible for industrial applications.
Shaking Table Validation: MEMS Accelerometer Vibration Monitoring Accuracy Test
But are MEMS accelerometers a reliable alternative for explosive industry applications? A 2022 research study set about to answer this question. The first step was to conduct a test to compare MEMS performance against a calibration standard via a series of shaking table tests. This test used a rig that housed both an embedded MEMS accelerometer and a calibration accelerometer (the Bruel & Kjaer type 4370).
Following a zero Hz frequency static calibration, the data captured underwent an FFT conversion into the time domain. This extraction process gave two crucial insights: amplitude and phase response.
In both cases, the results indicate the accurate and reliable performance of the MEMS device at measuring vibratory events well within ISEE standards.
Fig. 1: Amplitude response compared to the ISEE Standard
Fig. 2: Phase response compared to the ISEE Standard
Field Testing: MEMS Accelerometers Pass Test to Measure Ground Vibration
Following these successful validations, a prototype MEMS accelerometer was developed and placed in field trials against two of the industry's widely accepted seismographs known for compliance with ISEE standards. A total of 55 events were monitored with resultant PPV values ranging from 0.8 mm/s (0.03 i.p.s) to 58.5 mm/s (2.3 i.p.s).
The following graph shows the data from these trials with the resultant PPV values from the standard seismographs plotted against that recorded with the accelerometer-based prototype.
The correlation coefficient between the data sets is 0.992.
Figure 3: Comparison between prototype PPV data and that from
a ‘standard’ seismograph
Conclusion: MEMS Accelerometers Proven Effective for Vibration Monitoring in the Explosives Industry
It is evident that MEMS accelerometers, with their precision, economic viability, and adaptability, are primed to redefine vibration monitoring in the explosives industry. With their proven ability to deliver reliable, accurate vibration monitoring results within ISEE standards, MEMS accelerometers could be poised to become the new gold standard in vibration monitoring for the explosives industry.
To read the full study and request a copy, please click the link below:
For additional information regarding MEMS technology, please click the links below:
Blog post: MEMS vs. Geophones: The Evolution of Construction Vibration Monitoring
White paper: The Use of MEMS Accelerometers in Vibration Monitoring
What Sets MEMS Technology Apart from Traditional Geophones?
MEMS accelerometers can function in any orientation without losing accuracy. In contrast, geophones are required to be reasonably level and are split into two primary versions, horizontal and vertical.
MEMS accelerometers are more accurate at lower frequencies (<4 Hz) than geophones; in fact, MEMS accelerometers can be DC coupled, which allows them to reliably measure down to 0Hz (something impossible with geophones).
The need for accessories to be installed on geophone-based seismographs creates multiple potential points of failure which fully integrated MEMS devices do not have.
A geophone-based seismograph's need for additional components can increase the inherent potential for noise created by the device. Fully integrated MEMS devices do not have this issue.
MEMS accelerometer sensors are smaller, lightweight, easier to install and activate, and many come with battery, cell service, and cloud integration fully enabled.