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.
- 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.
- 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.
- 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