Which of the following can be used for angular measurements?

Explanation:

Autocollimator:

• An autocollimator is an optical instrument that is used to measure small angles with very high sensitivity.
• The autocollimator has a wide variety of applications including precision alignment, detection of angular movement, verification of angle standards, and angular monitoring over long periods.
• An autocollimator is essentially an infinity telescope and a collimator combined into one instrument.

Additional Information 

Types of Autocollimators:

1) Visual Autocollimator:

• In a visual autocollimator, the angle of tilt of the reflecting surface is measured by viewing a graduated scale through an eyepiece. As the focal length of the visual autocollimator increases, the angular resolution increases and the field of view decreases.

2) Digital Autocollimator:

• In a digital autocollimator, the micrometer adjustment is provided for the setting but the coincidence of setting graticule and the target image is detected photo-electrically.
• This autocollimator is used in the lab.
• It has very high precision, provides real-time measurements, and is very user friendly.

Applications of Autocollimator:

1. Checking the straightness of machine tool slideways.
2. Measuring very small angles.
3. Checking parallelism.
4. Checking squareness of column to base.
5. Checking the flatness of bed plates and surface tables.
6. Measuring very small displacements.
7. Checking small linear displacements.

Advantages of Autocollimators:

1. It has very high accuracy.
2. It can measure wide range angle.
3. It is very easy to set up and operate.
4. Calibration traceable to international standards.
5. It can be used to see the result visually or electronically i.e on a computer screen.
6. Wide range of accessories and levels available.

Disadvantages of Autocollimator:

1. Maintenance is required regularly.
2. It is time-consuming.
3. It requires sample cutting and processing for tracing by the detector.