Vernier Software and Technology
Vernier Software & Technology
Tech Info Library

Is there a way to calibrate the Motion Detector?

In most cases, calibration is unnecessary. Only the Go Direct Motion Detector can be calibrated for better accuracy, by using the Motion channel and performing a 1-point calibration based on a measured distance.

You can zero the motion detector by placing the target at the desired origin, and choosing zero within the software. In Logger Pro, the zero option is in the experiment menu. In LabQuest and Graphical Analysis 4, click or tap the meter. In EasyData on TI calculators, zero is in the Setup menu. In DataQuest, on the TI-nspire, Zero is found in Setup Sensors, in the Experiment menu.

The direction of the coordinate system can be reversed so that values increase as a target moves toward the motion detector instead of away. Do this in Logger Pro by choosing Set Up Sensors > Show All Interfaces, and then click the icon of the Motion Detector in DIG 1 or DIG 2. The resulting popup menu includes Reverse. In LabQuest, tap the meter display to access Reverse. In LabQuest App and Graphical Analysis 4, click or tap the meter. In DataQuest, on the TI-nspire, Reverse is found in Setup Sensors, in the Experiment menu. Reverse is not available for EasyData on TI calculators.

Using the combination of zero and reverse allows you to do things like measure motion from a point not at the detector. For example, you can point the detector downward toward the floor. Reverse and zero with nothing between the detector and the floor. Now, the detector will report position above the floor, with up as positive and zero at the floor.

There is an offset in motion detector readings that varies by interface. Typically it is only 1-2 cm. If this is a problem, in Logger Pro you can also add an offset value using the menu in Sensor Setup. On LabQuest and Graphical Analysis 4, you can use a calculated column.

All motion detectors have a minimum working distance. The models currently available have a 15 cm minimum working distance, in that the sensor gives unreliable data if the target is closer than this distance.

Logger Pro allows you to correct motion detector readings for the ambient temperature. Since the speed of sound is temperature-dependent, motion readings will vary slightly by temperature. This is a very small correction, and is almost never important. When using a Go!Motion or Calculator Based Ranger connected directly by USB cable, temperature compensation is automatic. The Go Direct Motion has a temperature-compensated channel, called Motion with TC.

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