Do you sell a Goniometer or Tilt Angle Sensor?

Yes, Vernier does sell a Goniometer, order code GNM-BTA, $159.

However, if you already have a Low-g Accelerometer, order code LGA-BTA, $89, you can use to report tilt angle using Logger Pro.

The JointAngleSensorLowG.cmbl Logger Pro experiment file is already configured to use the accelerometer in this way. Using this file, LoggerPro will report an angle of 90 degrees when the LG-BTA is resting flat. As the low G accelerometer is tilted is will report a decrease in angle.

To create your own file in Logger Pro, you need to create a calculated column that takes the ArcCos of Acceleration / the force of gravity. Make sure that Logger Pro is using degrees for all trigonometric calculations. The default condition is radians. See 'settings for file' under the the FILE drop down menu. Sampling at 10 samples a second works fine and some smoothing should be used as well.

Vernier also sells a Rotary Motion Sensor Rotary Motion Sensor, order code RMV-BTD, $169 that can be used as a goniometer. You will need to attach a rod to the Rotary Motion Sensor and then place the Sensor to the joint of interest. Once again, you will need to make sure that you are using degrees for all trigonometric calculations.