|Object Name:||Air Data System, Capsule Sensor, Cam-Corrector Mechanism|
|Year of Manufacture:||circa 1960|
|Location:||Main Object Store|
This is an item from the original Marconi Collection (Ref: 2040) and is the cam correction mechanism from a Static or Pitot-Static Capsule unit.
The Differential Pressure Transducer contains two aneroid capsules, or diaphragms, which expands and contracts with the pressure input from the pitot tube. The case around the diaphragm is airtight and is vented to the static port. Some units will have multiple aneroid capsules to multiply the movement. The difference between the pitot pressure and the static pressure is called dynamic pressure. The greater the dynamic pressure, the higher the airspeed.
The non-linear relationship between the capsule expansion and airspeed is mainly linearised by the design of the mechanical linkage that couples the offset arrangement of input and output shafts (see side view). This non-linearity is fine-tuned by a cam follower arm in the linkage as it moves around the arc of a cam strip (see top view), the profile of which can be adjusted by two rows of fifteen grub screws.
Within the casing is a wire wound potentiometer driven by the cam correction mechanism's output shaft to give an electrical output of airspeed.