Understanding the Sigma Comparator Classification

The question asks about the type of comparator that a Sigma comparator belongs to. Comparators are essential instruments in metrology, used to compare the dimension of a workpiece with a standard or master gauge, and thus determine the deviation from the standard.

What is a Sigma Comparator?

The Sigma comparator is a specific type of comparator known for its robust design and high magnification achieved through mechanical means.

It works by utilizing a system of levers and linkages to amplify small movements detected by a stylus contacting the workpiece surface. This magnified movement is then indicated on a dial.

Types of Comparators

Comparators are broadly classified based on the principle they use for magnification:

• Mechanical Comparators: Use mechanical linkages like levers, gears, or reeds to magnify the displacement.
• Electrical Comparators: Convert displacement into a change in electrical resistance or inductance, which is then measured.
• Electronic Comparators: Use electronic circuits to amplify the signal from a transducer (like LVDT or capacitance probe).
• Optical Comparators: Use optical principles (like light beams and lenses) for magnification.
• Pneumatic Comparators: Use changes in air pressure or flow caused by the workpiece dimension to indicate deviation.

Classifying the Sigma Comparator

As discussed, the Sigma comparator employs a system of mechanical levers and linkages to achieve magnification of the workpiece's dimensional deviation. It relies purely on the mechanical advantage provided by these components to amplify the small displacement of the stylus into a larger movement of the indicator needle.

Therefore, based on its working principle, the Sigma comparator is classified as a mechanical comparator.

Comparing this with the given options:

• Electrical: Incorrect, it doesn't use electrical resistance or inductance changes as the primary magnification method.
• Electronic: Incorrect, it doesn't rely on electronic circuits for amplification.
• Mechanical: Correct, it uses a mechanical lever system for magnification.
• Optical: Incorrect, it doesn't use light or lenses for magnification.

Thus, the Sigma comparator falls under the category of mechanical comparators due to its use of mechanical linkages to achieve magnification.

Revision Table: Sigma Comparator Basics

Additional Information: Advantages of Mechanical Comparators

Mechanical comparators, like the Sigma comparator, offer several advantages:

• Simple and robust construction.
• Generally less expensive than electronic or optical types.
• Do not require external power supply (except for lighting in some specific designs, but not for the measurement principle itself).
• Relatively easy to operate and maintain.

However, they can be susceptible to friction and inertia in the moving parts, which can affect accuracy at very high magnifications compared to some other types.