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BT11i High g Accelerometer User’s Guide
Short description
The CMA High g Accelerometer BT11i measures acceleration in the range between
-‐25.0 g
1
(-‐245.0 m/s
2
) to 25.0 g (245.0 m/s
2
). The sensing element of the sensor is
mounted inside the round box and the arrow on the label of this box marks the
direction in which acceleration is measured. If the sensor is at rest and oriented with
the arrow pointing down its acceleration value is -‐1.0 g (-‐9.8 m/s
2
). When the arrow
points up the measured acceleration value is 1.0 g (9.8 m/s
2
). When the axis arrow is
held horizontally the measured acceleration value is zero.
The measurement range of the High g Accelerometer allows measuring accelerations
produced during collisions experiments but dropping the Accelerometer on a hard
surface from even a few centimeters can produce acceleration of a hundred g’s.
Accelerations above ± 50 g will damage the sensor.
The High g Accelerometer is delivered with two pieces of Velcro tape, which can be
used to mount the round box of the Accelerometer on a moving object.
The High g Accelerometer can be directly connected to analog BT inputs of the CMA
interfaces. The sensor cable BT -‐ IEEE1394 needed to connect the sensor to an
interface is not supplied with the sensor and has to be purchased separately (CMA
Article BTsc_1).
Sensor recognition
The High g Accelerometer has a memory chip (EEPROM) with information about the
sensor: its name, measured quantity, unit and calibration. Through a simple protocol
(I
2
C) this information is read by the CMA interfaces and the sensor is automatically
recognized when it is connected to these interfaces. If your High g Accelerometer is
not automatically detected by an interface you have to manually set up your sensor
by selecting it from the Coach Sensor Library.
Calibration
The CMA High g Accelerometer BT11i is supplied calibrated. The output of the
Accelerometer is linear with respect to the acceleration. The supplied calibration
function is:
a(m/s
2
) = 178.1818*V
out
(V) – 445.4545.
The Coach 6 program allows selecting the calibration supplied by the sensor memory
(EEPROM) or the calibration stored in the Coach 6 Sensor Library. For better
accuracy the pre-‐defined calibration can be shifted.
For even more accurate measurements a new user calibration can be performed
using the acceleration due to gravity.
To calibrate the sensor:
1
1 g is the acceleration due to gravity at the earth’s surface and is equal to 9.8 m/s
2
.
