Electronic Products - January 2019

Fig. 2: Their inclusion in consumer devices

such as smartphones and automobiles has

dropped the size and price of three-axis

accelerometer chips such as this IAM-

from TDK/InvenSense.

Stud

Mounting

Insulating

Flange

Magnetic

Base

Adhesive

Pad

Direct

Adhesive

Tr iaxial Probe

IMAGE: (TOP) TDK/INVENSENSE: (BOTTOM) IDS INNOMIC Mounting Cube

Fig. 3: Encased accelerometers are available with a variety

of mounting options, but the choice can affect the achieved

sensing bandwidth.

with transverse, or cross-axis, sensi-

tivity. Cross-axis sensitivity refers to

the amount of signal that appears in

the sensor for one dimension (say,

X) when the acceleration is strictly

orthogonal to that dimension — Y

or Z. Such signals are error sources

and should be as small as possible.

• Noise. This parameter can be
  expressed in several different ways,
  including RMS or as a spectral val-
  ue. Designers should consider noise
  specifications in conjunction with
  sensitivity.


• Linearity. This parameter indicates
  measurement consistency over
  the accelerometer’s sensing range.
  Ideally, a unit change in accelera-
  tion should produce a unit change
  in the output signal regardless of
  how strong the absolute accelera-
  tion may be. In practice, calibration
  may be required to correct some
  non-linear operation.


• Temperature sensitivity. Because
  they are mechanical systems, accel-
  erometers are susceptible to tem-
  perature, which causes dimensional
  changes as it varies. Temperature

sensitivity measures how significant

an impact a temperature change will

have on the output signal.

There is also a host of practical con-

siderations that affect an accelerometer

choice in the final design. These include

the device’s supply voltage, current

draw, package size, degree of robustness

— commercial-, industrial-, or rugge-

dized-grade — and the like. Sensors

may generate an analog output signal or

include an integrated ADC to provide a

digital signal. The digital signal interface

may conform to an industry standard

such as I^2 C or SPI or, in rare cases, pro-

duce a pulse-width modulated (PWM)

output. The accelerometer may be a raw

sensor or an integrated device with signal

conditioning and controls built in.

With all of these parameters and

variations to consider, it should come as

no surprise that there are many vendors

offering accelerometers, often focusing

on a few types and application spaces.

The table above provides a partial list of

representative vendors that developers

can use to jumpstart their search for the

best match to their needs.

Many of the above vendors offer di-

rectly comparable products for common

applications, while others specialize in

niche devices for which there are few

competitors. Regardless, the right choice

of accelerometer is so highly applica-

tion-dependent that developers should

consider enlisting help in making a final

selection once the essential needs are

well-defined and the choices narrowed

down. The vendor’s support can prove an

essential final factor in choosing the right

accelerometer for a design. ☐

ELECTRONIC PRODUCTS • electronicproducts.com • JANUARY 2019