Fisher® 546, 546S, and 546NS transducers receives a direct-current input signal and use a torque motor,
nozzle-flapper, and pneumatic relay to convert the signal to a proportional pneumatic output signal. Nozzle pressure, which operates the relay, is also piped to the torque motor feedback bellows. This provides a comparison between input signal and nozzle pressure and corrects errors in nozzle pressure.