medium range of about ±30 g.
For the most aggressive types of
movement, devices with a high range
are also available like the STMicroelec-
tronics H3LIS331DL, capable of sensing
±400 g. Often, devices are available in
families encompassing varying rang-
es. For instance, the Analog Devices
ADXL344 family offers ±2-g, 4-g, 8-g,
and 16-g options. A rough rule of thumb
is to choose a range more than twice the
maximum acceleration expected to allow
for unexpected conditions.
Sensing range should not be confused
with the accelerometer’s shock range.
Operating outside of the sensing range
results only in distortion or clipping of
the output signal. The shock range is the
maximum acceleration that the device
can experience without being damaged.
The accelerometer’s packaging and
mounting style are a third key functional
choice for designers to make. Many accel-
erometers are available in chip form for
mounting on a circuit board. Single-axis
accelerometers can have the sensing di-rection either in the chip’s mounting plane
or normal to it. Two-axis devices typically
sense in the mounting plane only.
Another mounting style available is
the encased accelerometer that me-
chanically attaches to a non-electronic
supporting surface such as machinery
housing. Such devices can be attached
using bolts, screws, adhesives, magnets,
or clamps or simply be hand-held.
The mounting style chosen has an
important effect on an accelerometer’s
frequency response. As with any kind
of sensor, accelerometers have limits
on how rapidly they can respond, and
as with any mechanical system, they
can resonate with vibration at the right
frequency. The key performance param-
eters to consider, then, are the sensor’s
bandwidth and resonant frequency.
Bandwidth is the frequency range
over which the sensor’s measurements
will be consistent (i.e., a “flat” response)
and is usually specified as a tolerance
band in terms of percentage deviation
from the accelerometer’s performance ata reference frequency — often 100 Hz.
To get a full picture of a device’s behavior,
however, designers should look for a fre-
quency response curve in the data sheets.
For many applications, it is essen-
tial that the accelerometer’s frequency
response extends all the way to DC.
This is essential for applications that are
measuring orientation using gravity to
determine which way is “down.” It is also
important for those applications that are
integrating acceleration to determine
velocity or movement.
There are numerous other perfor-
mance parameters for designers to
explore as well. These include:- Sensitivity. This is a measure of how
strong a signal the accelerometer
generates for a given acceleration,
often measured in mV/g for analog
devices or as the number of bits
representing 1 g in a digital device.
Sensitivity and range often go hand
in hand, with a greater range typi-
cally implying reduced sensitivity.
This parameter is not to be confused
Vendor Accelerator Types Catalog URLAnalog Devices Chip https://www.analog.com/en/parametricsearch/
Dytran Instruments Encased https://www.dytran.com/Accelerometers/Epson Encased https://www.epson-electronics.de/electronics/cms/index/
First Sensor Chip/module https://www.first-sensor.com/en/products/inertial-sensors/Honeywell Encased https://aerospace.honeywell.com/en/products/navigation-and-sensors/accelerometers
IDS Innomic Enclosed https://www.innomic.com/en/products/piezoelectric _vibration_transducers/accelerometers.htmlKionix Chip https://www.kionix.com/parametric/Accelerometers
Murata Chip https://www.murata.com/products/sensor/accelNXP Chip https://www.nxp.com/products/sensors/motion-sensors:MOTION-SENSORS
PCB Piezotronics Encased http://www.pcb.com/products/productfinder.aspx?tx=Rieker Encased https://www.riekerinc.com/product-category/electronic-sensors/accelerometers/
SAFRAN Colibrys Chip (mil/aero) https://www.colibrys.com/pro-cats/inertial-sensor/Silicon Sensing Chip/module https://www.siliconsensing.com/products/accelerometers/
STMicroelectronics Chip https://www.st.com/en/mems-and-sensors/accelerometers.html?querycriteria=productId=SCTDK Chip https://product.tdk.com/en/search/sensor/sensor/motion/list#pn=*&psts%5B%5D= 0&psts%5B%5D=-20&psts%5B%5D=-10&_l=20&_p=1&_c=part_no-part_no&_d=TE Connectivity Chip, Encased https://www.te.com/usa-en/products/sensors/vibration-sensors/ embedded-accelerometers.html?tab=pgp-story14 FEATURE Designer’s Guide: Accelerometers
JANUARY 2019 • electronicproducts.com • ELECTRONIC PRODUCTS