In general a pneumatic transmitter senses a variable, such as differencial fluid pressure existing at a primary device, and transmits a pneumatic signal proportional thereto a remote location. This is achieved in the case of the devices disclosed by providing a differential pressure unit (d.p.u) with fluid connections to the primary device. Such a d.p.u commonly includes a bellows assembly embodying a pair of fluid fill bellows to which the different pressures are applied. The pressure differential causes the bellows to move a proportional distance and their movement is mechanically transmitted by a torque tube assembly to rotational movement of an output shaft.