Which instrument is often used to check the alignment of two shafts?

• A. Micrometer
• B. Dial indicator
• C. Manometer
• D. Sling psychrometer

Answer: (B)

The key idea is measuring small relative displacements to detect misalignment between two shafts. When two shafts aren’t perfectly co-linear, even tiny offsets or angular differences show up as deflection as the shafts rotate. A dial indicator is designed to translate those tiny linear movements into a readable dial reading with very high precision. By mounting the indicator so its plunger rides on a reference surface and rotating the shafts (or using a bar that spans both shafts with the indicator(s) contacting it), you can see how much and in which direction the alignment deviates. This lets you quantify parallel misalignment, angular misalignment, and runout, and then you adjust the system to bring the shafts into alignment.

A micrometer, while precise for measuring a single dimension at a fixed point, doesn’t track relative movement between two rotating components. A manometer is used for measuring pressure, and a sling psychrometer for humidity—neither relates to shaft alignment.