Sigma Comparator: Construction, Working Principle, Applications, Advantages, & Disadvantages [PDF]

Contents

A comparator works on the relative dimension, which means it can measure the difference between basic dimensions with the actual dimension. Sigma comparator is a type of mechanical comparator developed by the Sigma Instrument Company, USA.

Construction of Sigma Comparator:

A Sigma Comparator is constructed by the following components, and those are:

Plunger
Knife Edge
Slit Diaphragm
Sapphire Bearing Block
Moving Block
Fixed Block
Cross Strip Hinge
Y-arm
Phosphor Bronze Driving Band
Driving Drum
Pointer Spindle
Pointer
Scale

Plunger:

It is the sensing unit that senses any uneven surface texture. This component of the comparator is directly in touch with the surface.

Knife Edge:

It is a knife-edge shaped metallic strip, which is fitted with the plunger.

Slit Diaphragm:

Generally, a diaphragm is made of rubber-type material (polymer). In the Sigma comparator there are 2 slit diaphragm provided to have frictionless linear movement of the plunger.

Saphire Bearing Block:

This component is directly in touch with Knife-edge and moving block.

Moving Block:

A moving block is a moving arm or member which is directly connected with knife-edge member, and it is the bottom part of Cross Strip.

Fixed Block:

It is an upper part of Cross Strip.

Cross Strip Hinge:

It is a pivoted portion of the moving block and fixed block arms.

Y-arm:

It is a simple Y shape arm connected between the driving drum through a Phosphor Bronze driving band and moving block [Cross Strip].

Phosphor Bronze Driving Band:

This arm is made of Phosphor Bronze alloy having high spring qualities, high fatigue resistance, superior formability, and high corrosion resistance.

Driving Drum:

It used to link the pointer with the Phosphor Bronze driving band [Y-arm] with the help of pointer spindle.

Pointer Spindle:

It is used to attach the pointer with the driving drum.

Pointer:

A pointer is used for displaying the measured value on a linear scale.

Scale:

The pointer and scale are a part of the display unit, the scale can be linear or circular in shape.

diagram of sigma comparator — ^{Movement of Sigma Comparator}

Working Principle of Sigma Comparator:

The working of a Sigma Comparator is stated below:

The plunger is fitted through the slit diaphragm to give a frictionless surface.
When the plunger is pushed upward due to the uneven element it displace the knife-edge either upward or downward.
The knife-edge is fitted with the moving block using a Sapphire bearing block.
Due to the upward or downward movement of the knife-edge, the moving block respond accordingly as it is hinged.
Y-arm is directly connected with the cross-strip, so when there is a rotating movement on the cross strip that movement is transferred to the driving drum with help of Y-arm.
The driving drum is fitted with spindle and pointer.
Any movement in driving drum results in the pointer movement, and we get the magnified result on the display unit or scale.
The first magnification of this instrument depends on the Y-arm and the length of the Y-arm, and the second magnification depends on the ratio of the radius of the pointer and the radius of the spindle.

Applications of Sigma Comparator:

Sigma Comparator is used for various purposes like:

It is used in the selective assembly.
In mass production, we can see this type of instrument.

Advantages of Sigma Comparator:

Following are some advantages of Sigma Comparator:

It has a bold scale and larger indicating pointer.
Cheaper in Price
This type of comparator does not need any external source of energy to work.
It is robust, compact and easy to handle instrument.

Disadvantages of Sigma Comparator:

Following are some disadvantages of Sigma Comparator:

Design is complicated.
Due to many mechanical components, there is a chance of wear and tear.
Parallax error can occur in this type of instrument.
It is not a sensitive instrument as of mechanical or optical due to the chances of friction.

FAQ’s:

What is a Sigma comparator?

Sigma comparator is a type of mechanical comparator developed by the Sigma Instrument Company, USA.

Sigma Comparator is which type of comparator?

Sigma Comparator is Mechanical Comparator.

More Resources:

Johansson Mikrokator Overview: In-Depth

References:

Media Credit:

Comparator image: Engineering Metrology by R. K Jain- Khanna Publishers
Feature image: Designed by Author

Sigma Comparator: Construction, Working Principle, Applications, Advantages, and Disadvantages [PDF]