Last week, I ran into an engineer who had recently designed a wireless vibration sensor using MEMS chips as the vibration sensing source. During our conversation, he explained that he had gone to great lengths to get the MEMS vibration chip to meet the performance stated on the data sheet. The MEMS manufacturer had even admitted that they are not able to realize the datasheet performance of this MEMS chips in an actual sensor and asked how he had achieved this. I suspect this is something he wasn\u2019t willing to share.<\/p>\n
He went on to share his frustration that, after all of his work to get stated performance out of the MEMS chip, the design was still more expensive than the existing piezoelectric wireless sensing elements the company is using today. So, his design was shelved and his hard work may never reach the market.<\/p>\n
I got the sense this was a learning moment for him: piezoelectric accelerometers still have better performance, are easier to integrate into the mechanical packaging, and are still lower cost. While MEMS may be easy to integrate to the electronics of a wireless radio or personal activity monitor, it can be very difficult to integrate a MEMS chip into the mechanical packaging of a sensor and achieve the vibration coupling necessary for early detection of bearing or gearing faults. I wondered how many others have fallen into a false sense of simplicity when integrating MEMS into wireless or wired vibration products?<\/p>\n
Ultimately, this engineer concluded that, for effective machinery health monitoring, MEMS vibration chips are still more expensive for the same or less performance than piezoelectric based accelerometers.<\/p>\n
MEMS may seem easier to integrate, but there are significant challenges to achieve the stated datasheet performance, and the overall product cost is higher than their piezo equivalents.<\/em><\/h3>\n
Knowing that didn\u2019t solve his design challenge. For the wireless vibration sensors that are the future of his \u2013 and many other \u2013 companies, it\u2019s not as simple as \u201cMEMS or piezo.\u201d Like MEMS, piezoelectric accelerometers have their limitations:<\/p>\n
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Piezoelectric sensing elements are often larger and take up more physical space in a wireless vibration sensor.<\/li>\n
Piezo typically has higher power requirements and often has a longer startup and settling period than equivalent MEMS chips<\/li>\n<\/ul>\n