ultrasonic waves to make the trip from Go! Motion to an object and back. Using
this time and the speed of sound in air, the distance to the nearest object is
determined.
Note that Go! Motion will report the distance to the closest object that produces a
sufficiently strong echo. Go! Motion can pick up objects such as chairs and tables
in the cone of ultrasound.
The sensitivity of the echo detection circuitry automatically increases, in steps,
every few milliseconds as the ultrasound travels out and back. This change in
sensitivity enables the detection of weaker signals.
Troubleshooting
The most frequently reported problems with a motion detector are that the motion
does not work beyond a certain distance or that the graph is very noisy. There are
a number of ways to troubleshoot these situations, and they are described below.
1. See if the Sensitivity Switch makes a difference. Simply set the Sensitivity
Switch to the other position and retry the experiment. This change may solve
the problem.
2. If the Go! Motion does not work beyond a certain distance (e.g., it does not
detect anything beyond 1.2 m), here are some things to check if you have this
problem:
Check for movable objects (textbooks, ring stands, etc.) in the cone of the
ultrasound. If possible, move these objects out of the measurement cone. It
may not take a very large object to cause problems.
Check for a stationary object (chair, table, etc.) in the cone of the
ultrasound. This object may be detected when you are trying to study an
object farther away. It may not take a very large object to cause problems.
If you have trouble with a stationary object causing unwanted echoes, try
setting the equipment up so that the objects are not in the cone or placing
a cloth over the object. This minimizes the ultrasound reflection.
Also note that the cone of ultrasound extends downward from the center
line. This can cause problems if you are using the Go! Motion on a hard,
horizontal surface. In these cases, try pivoting the head of the Go! Motion
to aim it slightly upward.
3
3. Noisy or erratic data may have a number of causes. Here are some tips.
Sometimes other sound sources can cause problems. If there is another
source of ultrasonic waves in the same frequency range, this will cause
erroneous readings. Examples include motors and fans, air track blowers,
the sound made by the air exiting the holes on an air track, etc. Try to
eliminate these sources of noise. If you are using an air track, try changing
the air flow volume.
Make sure that the Go! Motion is not placed close to a computer or
computer monitor.
If the room in which the Go! Motion is being used has a lot of hard,
sound-reflecting surfaces, you can get strange effects caused by the
ultrasound bouncing around the room. Standing waves can be set up
between the Go! Motion and a sound reflector. Try placing a cloth
horizontally just in front of and below the Motion Detector. This
sometimes helps eliminate ultrasound that is “skipping” into the
Go! Motion.
Try changing the data-collection rate. Sometimes motion detectors work
better at one data rate than another. Rates above 30 Hz do not work well in
acoustically live rooms.
If you are studying people moving, have them hold a large, flat object (e.g.,
a large book or a pizza box) as a reflector. If you have an irregular
reflecting surface, sometimes the waves will be reflected back to the
transducer, and sometimes not. The results will seem erratic.
An excellent discussion of motion detector theory and operation can be found in
“Physics and Technical Characteristics of Ultrasonic Sonar Systems”, Dan
MacIsaac and Ari Hamalainen,
The Physics Teacher
40, 39–46 (January 2002).
For additional troubleshooting tips and FAQs, see
www.vernier.com/til/2115
Repair Information
If you have watched the related product video(s), followed the troubleshooting
steps, and are still having trouble with your Go! Motion, 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
Digital Sensor Cable
MDC-BTD
Digital Extension Cable
EXT-BTD
Motion Detector Clamp
MD-CLAMP
4
