(ak sel, ∂ rom’ i t∂r) 1. A transducer whose output is proportional to ground acceleration. Accelerometers are used with shipboard-gravimeter and inertial-navigation systems. 2. A seismometer whose output is proportional to the acceleration to which it is subjected. For example, a geophone with velocity response proportional to frequency and a 90° phase shift (as may be the case below the natural frequency) operates as an accelerometer.