Ex. No: Date: Straightness Measurement using Autocollimator

Ex. No: Date: Straightness Measurement using Autocollimator

 Ai  A i m: To measure, straightness of a beam /given surface with the use of AutoCollimator.

 Ap  A ppar atus R equire uir ed: Autocollimator, Reflector, Straight edge

P r elab Questi Questi ons: 1.  Spe  Specify the auto utocollim collima ator .

 2. Wh What at i s the least least count count of mi crom cr ome eter ter head head in in autocolli autocollim mator ator??

Theory: Tests for straightness can be carried out by using spirit level or auto-collimator. The straightness of any surface could be determined by either of these instruments by measuring the relative angular positions of number of adjacent sections of the surface to  be tested.

Set up diagram

F ormula : Tan ө= h/l  Tan ө- angular tilt in sec h= Tan ө*l*1000 microns l= length of the base of reflector in mm h= rise/fall of current position with respect to previo us position in microns

Graph:

Description : Auto-collimators are sensitive and inherently very accurate optical instruments for the measurement of small angular deviations of a light reflecting flat surface. The autocollimator has its own target which is projected by collimated light beams on a remotely  placed surface and the reflected target image is observed in the ocular of the instrument.

Procedure: 1. Clean the surface plate or table. 2. Position the auto-collimator in line with the reflector. Switch on the lamp in the autocollimator, the alignment between the auto-collimator and reflector should be checked at both extremes of the operational distance to make certain that the target graticule is contained within the eyepiece field. 3. Fix a guide strip to control the horizontal displacement of the reflector and minimize the movement of the target graticule 4. Mark off the positions along the surface plate equal to the pitch positions on the reflector base (in this case 100 mm). 5. At the initial position, Make the target graticule and reflected graticule(green in colour) to get coincide by physical adjustment( adjusting leveling screw and collimator) and note down the reading on both micrometers ( for x and Y axis) 6. Move the carriage (reflector) to the next position and adjust the micrometers to make the reflected graticule to coincide with target graticule. Note down both micrometers the reading for position 2. 7. This method is to continue until the final outward position is recorded(Forward method ‘F’) 8. To improve on the accuracy and ensure no errors have been introduced, readings should also be taken on the inward run.( Backward method ‘B’) If this exercise is followed then the average of the two readings is to be shown in avg column .

Tabulation for Straightness measurement using autocollimator: Rise or fall

Position

Mean reading

Difference

in the

of

from first

interval of

Cumulative

Adjustment to

Autocollimator

readings

length l

rise or fall

 bring both ends

Errors from

(sec)

(sec)

(mm)

mm

zero

straight line(mm)

X axis

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Y axis

X

Y

X

Y

X

axis

axis

axis

axis

axis

Y axis X axis Y axis

X axis

Y axis

Post lab Questions Plot the straightness graph in excel.

Result: The straightness error of the given surface found to be-------

microns