Page 43 - EngineerIt May 2021

MEASUREMENT AND INSTRUMENTATION

the same time, the ADXL100x family of MEMS accelerometers,
shown in Table 14, are being installed on highly critical assets,
which is unprecedented for MEMS accelerometers. At Analog
Devices, we’ve made it simple to attach our CbM sensors to
assets (XLMOUNT1, ADcmXL3021). It is also very easy to
replace piezo-electric sensors with MEMS due to our conversion
reference designs (MEMS to IEPE or 4 mA to 20 mA).
Our CbM reference designs, evaluation systems, development
platforms and system solutions are all aimed at enabling our
customers to develop the best CbM and PdM systems to keep
assets and factories running. We have addressed and solved
most of the pain points experienced by CbM designers using
not only MEMS but piezoelectric accelerometers too, and we will
continue to invest in industry-leading CbM solutions. The next
section discusses one such example of a high fidelity, high speed
data acquisition pipeline that enables CbM system developers
to detect and save vital vibration data into their machine learning
Figure 9: Frequency response of the ADXL1002 with IEPE development environment (Python, TensorFlow, MathWorks, etc.).
interface.

The sensor PCB was designed a little thicker (3 mm), and
specific solder paste was used to aid in preserving the data
sheet frequency response of the MEMS sensor while mounted
to an asset.
The reference design PCB shown in Figure 8 converts
MEMS accelerometer data to IEPE format. It powers the MEMS
accelerometer from an existing IEPE setup and outputs data in
IEPE format, allowing seamless and simple integration of MEMS
accelerometers into new or existing IEPE infrastructure.
Analog Devices has a long history of integrating industry-
leading sensors, signal conditioning, and processing into
modules. The latest CbM modules are ADcmXL1021 and
ADcmXL3021, single or triaxial (1× or 3× ADXL1002)
accelerometer-based SPI output solutions capable of being
mounted directly to assets. They have a mechanical package Figure 10: ADcmXL3021 wide bandwidth, low noise, triaxial
resonance above 50 kHz, well above the bandwidth of interest vibration sensor.
at 10 kHz.
The mounting holes accept M2.5 screws to hold the module
in place. Stainless steel screws torqued to about 25 inch-pounds
are used for many of the characterisation curves shown in the
ADcmXL3021 data sheet. In some cases, when permanent
mounting is an option, industrial epoxies or adhesives, such as
cyanoacrylate adhesive, in addition to the mounting screws, can
be used to enhance mechanical coupling.
We have already seen that ADXL100x MEMS accelerometers
have similar levels of performance as piezo-electric
accelerometers, with several distinct advantages that are now
enabling CbM and PdM to be applied to less critical assets. At Figure 11: CN-0549 block diagram and image

Table 14. ADXL100x family of CbM accelerometers

Part Number Number of Axes Accelerometer Noise Density BW (typical) Hz Is (typical) A Vs+ (min) V Vs+ (max) V
Range (typical) g/√Hz
ADXL1001 1 100 g 0.00003 11,000 0.001 3.3 5.25
ADXL1002 1 50 g 0.000025 11,000 0.001 3.3 5.25
ADXL1003 1 200 g 0.000045 15,000 0.001 3 5.5
ADXL1004 1 500 g 0.000125 24,000 0.001 3.3 5.25
ADXL1005 1 100 g 0.000075 23,000 0.001 3 5.25

EngineerIT | May 2021 | 41