1. Mechanical spring Devices
   1. Cantilever
   2. Closed-coiled Helical spring
   3. Flat spiral spring
   4. when subjected to Compressive force the displacement is given by
   5. when subjected to torque τ, the deflection angle in radians is given by
   6. Convents force into displacement, deflection of free end is given by
2. Pressure Sensitive primary Devices
   1. Diaphragms
      1. whole series of mechanical devices that change shapes when force (pressure) applied to it
         1. Flat
         2. Corrugated
         3. deflection ≈ 2% of diameter
   2. Bellows
   3. Bourden tubes
3. Flow-rate sensing Elements
   1. Differential Pressure meters
      1. orifice plate
      2. Venturi tube
      3. flow nozzle