Motus Bioengineering Inc.

Sensor Comparison

Gyroscope - The best approach

• Measures rotational motion -- human motion is rotational about joints.
• Not influenced by gravity.
• Both frequency & magnitude information accurate down to DC (zero frequency).
• Only a single integration is needed to obtain angular displacement.
• High signal to noise ratio.
• High dynamic range.
• Solid state gyros (with no spinning wheels) do not influence motion of subject being measured.
• No intimate electrical contact with subject.
   
   

• Measures linear motion & gravity concurrently. Results cannot be decoupled without gyros. Does not measure human rotational motion.
• Signal magnitude corrupted by gravity.
• Frequency data good but bandwidth often not down to DC.
• Difficult second integration required to obtain displacement.
• Low signal to noise ratio piezoelectric accels. High for servo accels but includes gravity component.
• High dynamic range.
• Piezoelectric accels can be very small with no influence; servo accels much larger.
• No intimate electrical contact with subject.

• Measures electrical current associated with muscular action. Does not measure movement directly.
• Not influenced by gravity.
• Frequency information good but magnitude less repeatable.  Contact resistance is a significant variable.
• Displacement, velocity and power cannot be obtained.
• Low signal to noise ratio. Sensitive to remote muscle activity and interference.
• Low dynamic range.
• Small sensing elements available with no influence on motion.
• Intimate electrical contact with subject required.