Indian Institute of Technology Madras (IIT-M) 2008 B.Tech Experimental Technique and Measurements, Quiz 1 - Question Paper

Department of Ocean Engineering, IIT Madras

OE 511 Experimental Technique and Measurements

Test 1

29^th Sept 2008 90 min

Answer all Questions.

(Properties of SS: E = 2 x 10¹¹ N/m² and = 0.3)

1. A stainless steel cantilever beam of length 30 mm, width 10 mm and thickness 1 mm has a 50 gm weight at the free end. Four strain gauges of equal resistances and gauge factor 2.05 are fixed at the clamped end and they form a Wheatstone bridge for maximum sensitivity. The beam is sealed in an enclosure and the cavity is filled with a viscous fluid to provide a damping ratio of 0.7 of critical.

Compute,

The frequency range for displacement and acceleration measurements.

Sensitivity in mV/g if the bridge excitation voltage is 5.0 V

Maximum acceleration measurable, if the fatigue strength is 200 MPa. (7)

2. A column has two strain gauges in the longitudinal direction and two in the transverse direction. These gauges are of 120 ohms and gauge factor 2.1 and are connected in a Wheatstone bridge form for maximum sensitivity. The bridge excitation is 5 V. When a resistance of 300 kohm was connected across one of the gauges for calibration of the measuring system, the instrument connected to the bridge has shown a displacement of 27 divisions. When the column is loaded the reading shown is 36 divisions. What is the strain in the column in m/m? (5)

3. Explain with an example the term accuracy of a measuring system. In a measuring system, individual subsystems had accuracies of 1 %, 0.5 % and 1.2 %. What would be the combined accuracy of measurement? (4)

4. Describe with neat diagrams the working of an LVDT. Explain the signal forms at various stages of the measuring system. How is the measurement made direction sensitive? (5)

5. A rectangular rosette is fixed on a model. Readings obtained for different conditions in m/m are given below. Compute ε₁ and ε_2, σ₁ and σ₂ and their direction. Material of the model is SS

ε_a ε_b ε_c

No Load 187 -205 -176

Loaded 689 -794 487 (4)