4
Accelerometer
The accelerometer is a microelectromechanical device (MEMS device)
consisting of a cantilever and a test mass. As the mass is accelerated, the
cantilever bends, generating a signal proportional to the acceleration. Three
orthogonal axes provide three channels of acceleration information.
Additional Information about Acceleration
Since the accelerometer is sensitive to both acceleration and the Earth’s
gravitational field, interpreting accelerometer measurements is complex. A useful
model for understanding accelerometer measurements is a spring-based scale
with a reference mass (or object) attached to the scale. If the scale is pointing
upward (the usual orientation for such a device) the weight of the mass causes
the spring to compress, and you get a non-zero reading. If you were to turn the
scale upside down, the spring will be extended, instead of compressed, and we
get a reading of the opposite sign. If you turn the scale so it points sideways,
and keep it motionless, then the spring will just be at its relaxed length, and the
reading will be zero. If you accelerated the scale toward the mass, then the
spring would compress. If you accelerate the scale away from the mass the
spring would stretch. In each case the scale is reading a value corresponding to
the normal force on the mass. This reading can be made relative by dividing out
the mass, giving units of N/kg, which is the same as m/s
2
.
Troubleshooting
For troubleshooting and FAQs, see
www.vernier.com/til/4131
Repair Information
If you have followed the troubleshooting steps, and are still having trouble with
your Go Direct Sensor Cart, contact Vernier Technical Support at
[email protected] or call 888-837-6437. Support specialists will work with
you to determine if the unit needs to be sent in for repair. At that time, a Return
Merchandise Authorization (RMA) number will be issued and instructions will
be communicated on how to return the unit for repair.
Accessories/Replacements
Item
Order Code
Sensor Cart Accessory Kit
GDX-CART-AK
Dynamics Cart and Track System with Go
Direct Sensor Carts
DTS-GDX
Dynamics Cart and Track System with Go
Direct Sensor Carts and Long Track
DTS-GDX-LONG
Replacement Battery
GDX-BAT-650
Micro USB Cable
CB-USB-MICRO
USB-C to Micro USB Cable
CB-USB-C-MICRO
Warranty
Vernier warrants this product to be free from defects in materials and
workmanship for a period of five years from the date of shipment to the
Care and Maintenance
Battery Information
The Go Direct Sensor Cart contains a small lithium-ion battery. The system is
designed to consume very little power and not put heavy demands on the
battery. Although the battery is warranted for one year, the expected battery life
should be several years. Replacement batteries are available from Vernier (order
code: GDX-BAT-650).
Storage and Maintenance
To store the Go Direct Sensor Cart for extended periods of time, put the device
in sleep mode by holding the button down for at least three seconds. The red
LED will stop flashing to show that the unit is in sleep mode. Over several
months, the battery will discharge but will not be damaged. After such storage,
charge the device for a few hours, and the unit will be ready to go.
Exposing the battery to temperatures over 35°C (95°F) will reduce its lifespan. If
possible, store the device in an area that is not exposed to temperature extremes.
Water Resistance
The Go Direct Sensor Cart is not water resistant and should never be immersed
in water.
If water gets into the device, immediately power the unit down (press and hold
the power button for more than three seconds). Disconnect the sensor and
charging cable and remove the battery. Allow the device to dry thoroughly
before attempting to use the device again. Do not attempt to dry using an
external heat source.
How the Sensor Works
Position
The position channel uses an optical encoder system. As the sensing wheel
rotates, the position of attached disc with radial markings is detected by a pair
of optical sensors. From counting the events and their sequence, the angle
turned as well as its sense of rotation can be determined. The angle is converted
to a change in position using the diameter of the sensing wheel. Since the wheel
does not turn if the cart is not on a surface, the reading will not change if the
cart is repositioned by lifting.
A result of the design is that there is no natural zero for the sensor. The position
when the cart is first connected to software is thus used as a zero. The position
channel can be zeroed in software as desired.
Velocity and acceleration are calculated in software from the position and time
data.
Force
The force channel uses strain gauge technology to measure force based on the
bending of a beam in a load cell.
