Issue link: https://resources.mouser.com/i/1512203
56 ADI | Engineering a More Sustainable Future Figure 9. Comparison of vibration sensors clustered into triaxial MEMS and IEPE and single-axis MEMS and IEPE. triaxial IEPE sensors have similar performance to triaxial MEMS sensors but at a much higher cost. For the low criticality assets cluster, it is not viable to use triaxial IEPE sensors due to their high cost, but this further highlights the point that triaxial MEMS sensors can compete with some triaxial IEPE sensors in terms of noise and bandwidth. What Sensor Was Most Suitable for the Deployable Single-Pair Ethernet Conditioning Monitoring Sensor and Why? The deployable single-pair Ethernet condition monitoring sensor was designed to house a vibration sensor, but the system architecture allows for many types of sensors such as temperature, pressure, sound, position, etc. to be used whether they be analog or digital output with minimal changes to the microcontroller firmware. The vibration sensor had to be small, digital out ( SPI or I 2 C ) with high levels of integration ( amplifiers, ADCs ) in order to meet the size and performance requirements of the deployable single-pair Ethernet condition monitoring sensor. A 3-axis, digital output MEMS accelerometer was chosen based on the specifications shown in Table 5. A low noise triaxial sensor was chosen instead of a lower noise, wider bandwidth single axis MEMS sensor in order to provide more diagnostic insights ( 3-axis vs. 1-axis ) and ease mounting challenges associated with single-axis sensors. The next key consideration is power consumption, and it is clear to see ADXL357 will produce less self-heating effects inside an IP6x module compared to the other sensors as the ADXL357 does not need an ADC or op amp, reducing the overall solution size and BOM cost. A reduced solution size ensures a small mechanical enclosure and good modal frequency performance, as explained in the section on modal analysis. Higher performance, single axis, wide bandwidth ( 11 kHz to 23 kHz ) MEMS sensors, such as the ADXL100x family with up to 14-bit resolution could be seamlessly integrated, but this would likely require an external ADC to preserve performance as most low power microcontrollers only have integrated 12-bit ADCs. However, with a suitable microcontroller, oversampling and decimation could be used to increase resolution above 12 bits, meaning a single-axis, analog output MEMS accelerometer could be integrated to the existing system with minimal effort. Please note, if you require better than 13-bit resolution, you must use an analog output MEMS or IEPE sensor, as shown in Table 7. Microcontroller and Software Architecture Choices A simple vibration sensor-based MQTT architecture is shown in Figure 10 and a high level block diagram for the deployable single-pair Ethernet conditioning monitoring sensor interfaced to a PC or Raspberry Pi is shown in Figure 11. Message Queue Telemetry Transport ( MQTT ) is a lightweight messaging protocol for the Internet of Things that allows network clients to distribute telemetry data in low bandwidth environments. MQTT is considered lightweight due to its messages having a small code footprint. The publish and subscribe messaging transport is ideal for connecting remote devices with a minimal code footprint and network bandwidth. MQTT is used in a vast array of industries from oil and gas, automotive, telecommunications, and manufacturing. 9 Adobe Stock / WilliamJu – stock.adobe.com