Tube 1, to be tested, is connected to the cylinder of pressure device 2. The movable end of tube 1 is connected through flexible link 3 to pulley 4 which turns about a fixed axis. Pulley 4 is mounted on and turns with an axle. Also mounted on this axle is mirror 5 on which light from lamp 6 falls after passing through collimator tube 7. The beam of light is reflected by mirror 5 onto scale 8. When the pressure is increased by pressure device 2, tube 1 tends to straighten out and the motion of its free end turns pulley 4 and mirror 5. Increasing the pressure by equal intervals and noting the corresponding displacement of the beam of light, the pressure can be found, beyond which the increment in the readings noticeably increases, deviating from a linear law. The pressure corresponding to this point is the sought limit of proportionality of the Bourdon tube.
$4075$EHP,M$