Texas Instruments CBR 2 manual Hints for effective data collection cont, The clear zone

Hints for effective data collection (cont.)

The clear zone

The path of the CBR 2™ motion detector beam is not a narrow, pencil-like beam, but fans out in all directions up to 15° from center in a 30° cone-shaped beam.

To avoid interference from other objects in the vicinity, try to establish a clear zone in the path of the CBR 2™ motion detector beam. This helps ensure that objects other than the target do not get recorded by the CBR 2™ motion detector. The CBR 2™ motion detector records the closest object in the clear zone.

30°

15 centimeters

Reflective surfaces

Some surfaces reflect pulses better than others. For example, you might see better results with a relatively hard, smooth surfaced ball than with a tennis ball. Conversely, samples taken in a room filled with hard, reflective surfaces are more likely to show stray data points. Measurements of irregular surfaces (such as a toy car or a student holding a calculator while walking) may appear uneven.

A Distance-Time plot of a nonmoving object may have small differences in the calculated distance values. If any of these values map to a different pixel, the expected flat line may show occasional blips. The Velocity-Time plot may appear even more jagged, because the change in distance between any two points over time is, by definition, velocity.

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