Senior Inspector (SR from SC/ST) / Inspector of Legal Metrology — 2023 — Official Paper — Kerala PSC PYQ Practice with Answers

Correct answer (Option D):\nResolution is the smallest change in a physical variable that an instrument can detect and respond to.\n\nWhy others are wrong:\nOption A: Sensitivity is the ratio of the change in output to the change in input.\nOption B: Repeatability refers to the closeness of agreement among repeated measurements.\nOption C: Precision indicates the degree of reproducibility of the measurements.\n\nStudy tip:\nAlways remember that resolution defines the lowest limit of change detection, whereas sensitivity describes the scale of response.

Correct answer (Option C):\nHysteresis represents the maximum difference in output value for a given input when the input is approached from opposite directions (loading and unloading).\n\nWhy others are wrong:\nOption A: Drift refers to a gradual shift in the instrument output over time.\nOption B: Backlash is the maximum distance or angle through which any part of a mechanical system may be moved without applying appreciable force.\nOption D: Fidelity is the ability of an instrument to faithfully reproduce an input.\n\nStudy tip:\nHysteresis loops are common in both magnetic materials and elastic bodies subjected to stress cycles.

Correct answer (Option A):\nCreep error occurs in induction type energy meters when the disc rotates slowly but continuously even when there is no load current flowing through the circuit, driven purely by the pressure coil voltage.\n\nWhy others are wrong:\nOptions B, C, and D: Wattmeters, moving iron instruments, and moving coil instruments are deflecting type instruments and do not exhibit continuous integration creep error in the absence of current.\n\nStudy tip:\nTo prevent creep error, two diametrically opposite holes are drilled in the disc of the energy meter.

Correct answer (Option B):\nThe deflecting torque in a moving iron instrument is directly proportional to the square of the operating current (θ ∝ I²). Because of this square-law relationship, the scale is crowded at the beginning and open at the upper end, making it non-uniform.\n\nWhy others are wrong:\nOption A: Moving coil instruments (PMMC) have a uniform scale because θ ∝ I.\nOption C: Logarithmic scales are used in distinct application meters like decibel meters.\n\nStudy tip:\nMoving iron instruments can measure both AC and DC quantities due to the square relationship of the deflecting torque.

Correct answer (Option A):\nMoving Coil (PMMC) instruments have a perfectly uniform and linear scale, whereas Moving Iron instruments have a crowded, non-uniform scale. Looking at the markings on the scale is the quickest visual way to distinguish them.\n\nWhy others are wrong:\nOption B: The pointer design can be identical across different meter movements.\nOption C: Terminal connections look similar from the exterior.\nOption D: The external housing shape can be customized and doesn't specify the internal mechanism.\n\nStudy tip:\nPMMC instruments measure only DC, while Moving Iron instruments can measure both DC and AC.