Vernier 3D-BTA User Manual

3-Axis Accelerometer

(Order Code 3D-BTA)

The 3-Axis Accelerometer consists of three –5 to
+5 g accelerometers mounted in one small block.
Using the appropriate data collection hardware and
software, you can graph any of these components, or calculate the magnitude of the
net acceleration. The 3-Axis Accelerometer can be used for a wide variety of
experiments and demonstrations, both inside the lab and outside.
There are sample data collected with the 3-axis Accelerometer

A 3-Axis Accelerometer was used to collect data during a bungee jump. The first
three graphs show the three component accelerations. The next graph shows the net
acceleration calculated as the square root of the sum of the squares of the component
accelerations.

Bungee jump accelerations

Net acceleration

Below is a sample graph made using the 3-Axis Accelerometer mounted on a
pendulum. The pendulum is swinging through a wide angle, so the angle of the
accelerometer is changing significantly. A simple, one-dimensional accelerometer
would not have done this job as well. In this case, only the net acceleration is

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graphed. (See the April 1995 issue of The Physics Teacher for a discussion of the
acceleration of a pendulum.)

Acceleration of a pendulum bob

The graph below shows data collected on a ride called the Vortex. A 3-Axis
Accelerometer and a Barometer were used in this experiment. A video taken during
data collection can be viewed in the Sample Movies folder of Logger Pro 3. These
data were collected by Clarence Bakken. For more information on data collection in
an amusement park visit our web site, www.vernier.com/cmat/datapark.html, and
download the Data Collection at the Amusement Park manual.

Data collected on the Vortex

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Collecting Data with the 3-Axis Accelerometer

This sensor can be used with the following interfaces to collect data:

• Vernier LabQuest

®

as a standalone device or with a computer

• Vernier LabQuest

®

Mini with a computer

• Vernier LabPro

®

with a computer, TI graphing calculator, or Palm® handheld

• Vernier SensorDAQ

TM

• CBL 2

TM

Here is the general procedure to follow when using the 3-Axis Accelerometer:

1. Connect the 3-Axis Accelerometer to the interface.

2. Start the data-collection software1.

3. The software will identify the 3-Axis Accelerometer and load a default data­collection setup. You are now ready to collect data.

Data-Collection Software

This sensor can be used with an interface and the following data-collection software.

• Logger Pro 3 This computer program is used with LabQuest, LabQuest Mini,

LabPro, or Go!Link.

• Logger Pro 2 This computer program is used with ULI or Serial Box Interface.

• Logger Lite This computer program is used with LabQuest, LabQuest Mini,

LabPro, or Go!Link.

• LabQuest App This program is used when LabQ uest is used as a stand-alone

device.

• EasyData App This calcu lator application for the TI-83 Plus and TI-84 Plus can

be used with CBL 2, LabPro, and Vernier EasyLink. We recommend version

2.0 or newer, which can be downloaded from the Vernier web site,
www.vernier.com/easy/easydata.html, and then transferred to the calculator.
See the Vernier web site, www.vernier.com/calc/software/index.html for more
information on the App and Program Transfer Guidebook.

• DataMate program Use DataMate with LabPro or CBL 2 and TI-73, TI-83,

TI-84, TI-86, TI-89, and Voyage 200 calculators. See the LabPro and CBL 2
Guidebooks for instructions on transferring DataMate to the calculator.

• Data Pro This program is used with LabPro and a Palm handheld.

• LabVIEW National Instruments LabVIEW™ software is a graphical

programming language sold by National Instruments. It is used with
SensorDAQ and can be used with a number of other Vernier interfaces. See
www.vernier.com/labview for more information.

NOTE: This product is to be used for educational purposes only. It is not
appropriate for industrial, medical, research, or commercial applications.

1

If you are using Logger Pro 2 with either a ULI or SBI, the sensor will not auto-ID. Open an

experiment file for the 3-Axis Accelerometer in the Probes & Sensors folder.

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Specifications

Power: 30 mA @ 5 VDC
For each axis:
Range: ±49

m/s

2

(±5 g)

Accuracy: ±0.5

m/s

2

(±0.05 g)
Frequency Response: 0–100 Hz
Resolution
13-bit (with SensorDAQ) 0.018

m/s

2

12-bit (with LabPro LabQuest,
LabQuest Mini, Go!

Link, ULI, or SBI) 0.037 m/s2

10-bit (with CBL 2) 0.15

m/s

2

Stored calibration information:
Slope 30.46 m/s

2

/V

Intercept –72.62 m/s

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How the Accelerometer Works

The 3-Axis Accelerometer contains three acceleration-sensing integrated circuits
(IC’s), along with the associated electronics. It is functionally equivalent to three of
our Low-g Accelerometers (LGA-BTA) mounted in a small block at orthogonal
angles. Each of the accelerometers measures acceleration along one line and
produces a signal on one of the three outputs. These three axes and three outputs are
labeled X, Y, and Z. The IC sensors are similar to those originally designed to
control the release of air bags in an automobile. This IC is micro-machined with very
thin “fingers” carved in silicon. These fingers flex when accelerated. They are
arranged and connected like the plates of a capacitor. As the fingers flex, the
capacitance changes, and a circuit included in the IC monitors the capacitance,
converting it into a voltage. An op-amp circuit amplifies and filters the signal from
the IC. The net result is that the voltage varies in a linear way with acceleration.

Each of the outputs is labeled with X, Y, or Z. This corresponds with the directions
shown on the label on the sensor. Accelerations are normally measured in either
meters per second per second (m/s

2

) or g’s. One g is the acceleration due to gravity

at the Earth’s surface, or 9.8 m/s

2

. This accelerometer will measure accelerations in

the range of –5 g (–49 m/s

2

) to +5 g (+49 m/s2) in each direction.

This is a range of accelerations which a human body could experience without
damage. Many collisions will produce much larger accelerations. In fact, dropping
the Accelerometer on a hard surface from even a few centimeters can produce
accelerations of a hundred g’s. The 3-Axis Accelerometer will not be damaged by
accelerations up to 1000 g’s.

When properly calibrated, when the arrow representing an axis points upward, that
channel reads +9.8 m/s

2

. When an axis arrow points down, that channel should read

–9.8 m/s

2

. When an axis arrow is held horizontally, that channel will read zero. In
most cases, data collection software can be used to create a New Column to calculate
the square root of the sum of the squares of the accelerations. It will be equal to

9.8 m/s

2

when the 3-Axis Accelerometer has no acceleration, and zero when it is in
free fall. The orientation of the 3-Axis Accelerometer does not matter. To understand
how this works, try holding the 3-Axis Accelerometer in your hand and very slowly