Mechanical Measurement and Metrology - Dec 2011

Mechanical Engineering (Semester 3)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) Sketch and explain the following :
Imperial standard yard and international prototype meter.(8 marks) 1 (b) Compare line and end standards of measurements.(6 marks) 1 (c) Three 100mm end bars are measured on a level comparator by first wringing them together and comparing with a 300 mm bar. The 300 mm bar has a known error of +40 ?m and the three bars together measure 64 ?m less than the 300 mm bar. Bar A is 18 ?m longer than bar B and 23 ?m longer than bar C. FInd the actual length of each bar.(6 marks) 2 (a) Explain
(i) Interchangeable manufacturing.
(ii) Selective assembly of machine parts.(5 marks) 2 (b) Design a general type GO and No GO guages for a hole and shaft pair designated as 450 H₈e₉ with following details:
(i) 450 mm dia lies in 400-500 mm step.
(ii) The standard tolerance unit i is given by the formula $$ i=0.45 \ \sqrt[3]{D}+0.001D $$ microns (D is in mm).
(iii) IT8=25i, IT9=40i
(iv) The fundamental deviation for an e type shaft=-11D^0.41 microns.
Sketch the layout indicating the various tolerance on both holes and shaft and their respective guages.(15 marks) 3 (a) What is a comparator, what are the needs and characteristics of comparator?(6 marks) 3 (b) Explain with a neat sketch the working principle of Johansson Mikrokator.(10 marks) 3 (c) List the advantages and disadvantages of mechanical comparators.(4 marks) 4 (a) With a neat sketch, explain the working principle of an auto collimator.(6 marks) 4 (b) Mention the nominal angles of a standard set of angle guages and indicate how the following angles can be built using angle guages (i) 33°16'12"; (ii)57°34'9"(6 marks) 4 (c) Define "effective diameter" and "best size wire". Derive an expression to determine the best size wire diameter.(8 marks) 5 (a) Define measurement with the aid of a block diagram, explain the three stages of a generalized measurement system with suitable example.(10 marks) 5 (b) Define error in measurement. Give classification of errors.(4 marks) 5 (c) Define the following :
(i) Accuracy
(ii) Precision
(iii) Sensitivity.(6 marks) 6 (a) What is a transducer? Differentiate between
(i) Primary and secondary transducers
(ii) Active and passive transducers.(6 marks) 6 (b) With a neat block diagram, explain the working principle of CRO (10 marks) 6 (c) State the advantages of electrical signal conditioning elements(4 marks) 7 (a) Explain with a neat sketch the working principle of McLeod guage.(8 marks) 7 (b) Explai with a neat sketch the working principle of a Pirani guage.(6 marks) 7 (c) Explain with suitable diagram the working of hydraulic dynamometer.(6 marks) 8 (a) What is a thermo couple? State the laws of thermocouple and explain the same.(6 marks) 8 (b) Derive an expression for guage factor of a strain guage. Why guage factor is at least two for most of the materials?(6 marks) 8 (c) Explain the working principle of optical pyrometer, with a neat sketch.(8 marks)