Potentiometer calibration - standing

The signals from the potentiometers are conditioned using custom built electronic modules (pot. module) which allow the gain and offset to be set. These modules were calibrated to have a sensitivity of 10V/rad as described below. A positive angle is measured during dorsiflexion whereas a negative angle is measured during plantarflexion.

The final calibration curves for the left and right potentiometers are given below. The right potentiometer gain was set to -3.67 and the offset to -0.35. The left potentiometer gain was set to -3.59 and the offset to -0.4.

Calibration method

1. Trim the potentiometer module gain to 2. (Any known low value will do -- though a gain of 1 is not achievable on the pot module.)
2. Determine the current static sensitivity of the pot/pot-module combination. A 21-point curve of the actuator angle vs. module output was determined (black markers and curve.) A precise Mitutoyo goniometer was used to measure the angle. A X12 magnifying glass was used to read the ruled scale. The slope of the resultant calibration curve indicates a potentiometer sensitivity of 3.374 = 6.7482/2.
3. Adjust the pot-module gain to 2.964 = 10/3.374 to obtain the overall desired pot/module sensitivity.
4. Re-do the calibration, as in step 2, to confirm the sensitivity setting (magenta markers and curve.)

Last modified: 2003-08-07 Shauna Forster