Sine bars

The entrance and exit slits of a monochromator isolate narrow portions of the light beam and direct them on to the grating. The slit width may be varied automatically by instruments to increase or decrease radiant power reaching the sample and detector. The grating is automatically driven by what is called a sine-bar mechanism, in which the bar that holds the grating is attached to a stepper motor-driven micrometer screw. Thus, the instrument covers a range of approximately 200-900 nm, with wavelength variation of 0.2 nm. 

Gauge blocks are also widely used in conjunction with sine bars and with calibrated steel balls and rollers, as well as for checking straightness and squareness. They are also used in conjunction with a range of accessories. 

The measurement of angles can be simply carried out by using a protractor, but the degree of accuracy obtainable is, at best, 5 minutes using a vernier instrument. Greater accuracy can be obtained by using a sine bar in conjunction with gauge blocks. 

A number of different designs of sine bar are available and are covered by BS 3064 1978, which also specifies three lengths - 100, 200 and... 

A 200mm sine bar is used to check an angle of 30° 12. Calculate the size of gauge blocks necessary, (ans. 100.604mm). 

A number of different designs of sine bar are available and are covered by BS 3064 1978, which also specifies three lengths - 100, 200 and 300 mm - these being the distances between the roller axes. The more common type of sine bar is shown in Fig. 5.14 the body and rollers being made of high-quality steel, hardened and stabilised, with all surfaces finished by lapping or fine grinding to the tolerances specified in the British Standard. 

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