Indicator diagrams taken using mechanical equipment are limited by the speed of the engine and the skill of the operator. Normally it is not possible to obtain an accurate powercard on engines running above 120rpm because of vibrations in the equipment. Draw cards are reliant on the operators skill. It is possible to take drawcards on engines running up to about 450 rpm.
Modern methods allow the computer to generate indicator diagrams and calculate the power developed in the cylinder for engines running at any speed.
From the crank angle diagram, faults in the injection process can be determined:
It should be noted that some slow speed two strokes (MAN B&W MC engines) combustion is delayed until 2-3° after TDC to limit the pressure rise to 35 bar, to prevent overloading of the crosshead bearing. This will give a slight dip in the pressure after TDC, which should not be construed as a fault.