Manual Number: 32650
Manual Revision: C
ECR Number: 36283
3710 series DC Accelerometer Operating Guide
1
1.0
Introduction
This operating guide contains information that will familiarize
the user with the basic operation and installation of the 3710
Series MEMS DC Accelerometers. However, it is not
intended to cover all of the specific measurement challenges
that one may encounter while using the device. Therefore, if
you have detailed questions or are unsure of how to properly
operate the sensor after reading this “Operating Guide”, please
contact a PCB Application Engineer using our 24-Hour
SensorLine
TM
at 716-684-0001.
2.0
Common Applications and Features
The 3710 Series MEMS DC Accelerometers achieve true DC
response for measuring uniform (or constant) acceleration and
low-frequency vibration. For this reason, they are often used
to:
•
Perform
ride
quality
assessments
of
elevators,
automobiles, trains, and amusement park rides.
•
Analyze the low frequency characteristics of buildings,
bridges, and large aerospace objects.
•
Acquire tilt and orientation data for feedback control and
stabilization purposes.
Because of the critical nature of these and similar test
applications, all 3710 series MEMS DC Accelerometers have
been designed and manufactured with the following common
characteristics:
•
Rugged, all-welded titanium housing insures reliability
and durability in demanding applications and environ-
ments.
•
Built-in microelectronics provide conveniently standard-
ized sensitivities and low-noise output signals unmatched
by similar sensing technologies.
•
Internal voltage regulator allows sensor to be powered
from virtually any unregulated DC voltage source, such as
a bench-top power supply or portable battery source.
•
Gas damping extends the upper frequency range, atten-
uates unwanted high-frequency vibration, and provides
stable performance over the entire operating temperature
range.
•
Hermetic, multi-pin connector provides a reliable connec-
tion even under the harshest environmental conditions.
3.0
Principle of Operation
The sensor element of the 3710 series features a proof mass,
ring frame, and attachment system between the two. These
features are bulk micro machined from the same single-crystal
silicon wafer. The movement of the proof mass is directly
affected by acceleration applied in the axis of sensitivity.
The sensor element is connected as a bridge element in the
circuit. The electrical characteristics of one portion of the
bridge, increases in value, while the other decreases when
exposed to acceleration. This approach minimizes common
mode errors and improves non-linearity.
A selection of full scale measurement ranges are attained by
modifying the stiffness of the suspension system of the proof
mass. A high natural frequency is accomplished through the
combination of a lightweight proof mass and suspension stiff-
ness.
Ruggedness is enhanced through the use of mechanical stops
on the two outer wafers to restrict the travel of the proof mass.
Damping is used to mitigate high frequency inputs.
The sensor elements use squeeze-film gas damping that is
nominally 0.7 critical. This is the result of the movement of the
proof mass pressing on the gas in the gap between it and the
outer sensor layer. Damping helps prevent the output of the
accelerometer from becoming saturated, as would happen
when the resonance of an accelerometer with no damping is
excited by random vibration. The advantage of gas damping
over liquid damping is that it is minimally affected by tem-
perature changes.
The 3710 series accelerometers contain conditioning circuitry
that provides a high sensitivity output. This IC also provides
compensation of zero bias and sensitivity errors over tempera-
ture using a continuous piecewise straight line correction en-
gine.
An on-board voltage regulator allows a typical excitation
range of 6 to 30 VDC with <10 mA current draw. The 3710
series features a ± 2 V Full Scale zero based output referenced
to power ground. A negative voltage generator provides a
sufficient signal swing for negative acceleration outputs with a
positive voltage swing of +4.0 V accommodating positive
accelerations.
An automated calibration step is conducted at the completion
of the accelerometer assembly at discrete temperatures over
the specified operating temperature range. The IC features an
on-chip temperature sensor for accurate thermal corrections.
