🔍 Key Concepts

• engine indicator cards and what they normally plot on the horizontal axis (time/crank angle vs. piston travel/volume) • how a drum motion (rotating vs. oscillating) affects the shape of the trace on the card • how a balanced-diaphragm indicator records pressure changes when there is little or no reciprocating motion available

💭 Think About

• Look at the indicator card: does it show a closed loop (like a classic P–V diagram) or an open, repeated trace over several cycles? What does that tell you about what is on the horizontal axis? • Ask yourself which device in the choices would naturally give you a continuous motion in one direction (producing a loop) versus a back-and-forth motion (producing a repeated, open trace like the one shown). • Think about which option is an actual pressure‑sensing element and which are motion‑producing mechanisms; which combination matches a diagram that shows pressure vs. crank angle or time, as in the illustration?

✅ Before You Answer

• Verify whether the diagram is open or closed and if it represents P–V or P–θ/time. • Check which of the listed devices is used to give the indicator drum a back‑and‑forth (oscillating) motion instead of continuous rotation. • Confirm in your study material which type of indicator card (P–V vs. pressure‑time/angle) is associated with a balanced‑diaphragm indicator before choosing your answer.