The subject matter of this specification can be embodied in, among other things, a position sensor system that includes a fluid effector that includes a housing having an inner surface defining a cavity, and a moveable body having a first face and a second face opposite the first face and configured to contact the inner surface and subdivide the cavity to define a first chamber and a second chamber, an acoustic transmitter system configured to emit a first emitted waveform toward the first face, and emit a second emitted waveform toward the second face, and an acoustic receiver system configured to detect a first reflected waveform based on a first reflection of the first emitted waveform based on the moveable body, and detect a second reflected waveform based on a second reflection of the second emitted waveform based on the moveable body.