An indicator diagram traces out the pressure and volume relationships in the cylinder of an engine on rectangular axes, and it can be used to estimate the work done by the engine per cycle. The indicator must move a vertical distance proportional to the pressure in the
An indicator diagram traces out the pressure and volume relationships in the cylinder of an engine on rectangular axes, and it can be used to estimate the work done by the engine per cycle. The indicator must move a vertical distance proportional to the pressure in the cylinder and the drum, as it rotates, provides a horizontal motion proportional to the change in cylinder volume.
The indicator is connected to a screwed cock which is in connection with the combustion chamber of the cylinder being monitored. When the engine cock is opened, the cylinder pressure also acts on the piston in the indicator cylinder, causing it to rise. This vertical movement is resisted by a spring, the strength of which is chosen to obtain a diagram illustrating the part of the cycle being investigated. The vertical movement of the piston is transferred to the pen mechanism by a parallel motion linkage.
The indicator card is held onto drum with spring clips. The drum is rotated against an internal sp