Mechanical Comparator : Working, Types & Its Applications

Generally, comparators are used for linear measurements & currently various comparators are available but they vary in their techniques of amplifying & also recording the variations measured. At present, engineers desire to categorize comparators as high & low amplification comparators, which also reproduce the complexity of the technology that is behind these devices. Comparators are classified into different types based on the principle utilized for amplifying as well as recording measurements like mechanical, mechanical-optical, electronic & electrical, pneumatic and other types like multi-check & projection comparators. These types of comparators have numerous variants which provide flexibility to the user to make a proper & cost-effective selection for a specific metrological application. This article discusses an overview of a mechanical comparator – working with applications.

What is Mechanical Comparator?

A mechanical comparator is a measuring instrument that is made up of mechanical means like gears, levers, pinions & racks to get the magnification. These kinds of means are mainly used for magnifying the means’ movement to enhance the precision of the instrument. The mechanical comparator diagram is shown below.

Mechanical Comparator
Mechanical Comparator

Working Principle

The working principle of a mechanical comparator is to use mechanical means for magnifying small deviations. The magnifying method of the indicator’s small movement in all mechanical comparators is affected through gear train levers. These comparators have magnifications that range from 300 to 1000. The mechanical comparator is also known as “microcator” which is used for linear measurements through the relative contact technique.

Mechanical Comparator Types

Mechanical comparators are classified into different types like the following.

  • Dial Indicators.
  • Read type Comparators.
  • Johanson Mikro kator.
  • Sigma Comparators.

Dial Indicators

A dial indicator is one type of simple mechanical comparator and it is a sensitive & versatile instrument. It uses a gear system jointly with a pinion & rack. This kind of comparator works on the Rack & pinion system principle that is, the spindle’s linear movement is magnified through the arrangement of rack & pinion.

Dial Indicator
Dial Indicator

The dial indicator mechanical comparator is used to determine the error in geometrical form like roundness, taper, ovality, etc. Determining the errors is say alignment, surfaces, squareness, parallelism, etc.

  • This comparator is used to compare two heights or distances in small limits.
  • It is used for testing material’s compression & tension.
  • It is used to verify the reality of milling machine arbors.
  • It is used to verify the arrangement of lathe machine centers with a bar between centers.

Read type Comparator

A reed-type mechanical comparator is used to compare the dimension of the workpiece by typical dimensions. So, in this kind of comparator, the outside of the comparator looks like same as other mechanical comparators. But, its internal construction and working principle are very simple as compared to other mechanical comparators.

Reed Type Comparator
Reed Type Comparator

In this type of mechanical comparator, the plunger’s linear movement is simply specified through the read mechanism. At first, this comparator is set with a known dimension. After that, the reading of the indicator is adjusted merely to zero. Once the measured part is kept below the pointer, then this comparator displays the difference in this dimension.

Johanson Mikro kator

Johansson Mikrokator is one type of mechanical comparator and it was invented by a Swedish engineer namely “H.Abramson”, which was introduced & manufactured later by a Sweden company like C.H. Johansson. Ltd. This mechanical comparator is mainly used as a comparing and measuring device. This is one of the most significant mechanical comparators because of its simple construction & working principle.

Johanson Mikro kator
Johanson Mikro kator

Johanson Mikro kator is the simplest mechanical comparator used to obtain mechanical magnification. This comparator simply works on a button-spinning principle on a string loop. Once the measuring plunger turns up or down using a bell crank lever, the strip modifies its length because the elbow works like a bell crank lever. When the strip is expanded, the glass pointer turns to an amount equivalent to the change within the strip length or movement of the plunger.

Sigma Comparator

Sigma comparator is one kind of mechanical comparator and it is introduced by a manufacturing company of instruments in the USA. These comparators are mainly used for measuring the roughness of the surface by measuring the dimensional difference between the standard value & measured value of the surface material. The magnification range of this comparator ranges from 300 to 500. A compression spring limits the measuring pressure. The magnification achieved depends upon the length of the lever on both sides of the pivot.

Sigma Comparator
Sigma Comparator

Mechanical Comparator Vs Electrical Comparator

The difference between the mechanical comparator and electrical comparator includes the following.

Mechanical Comparator

Electrical Comparator

A mechanical comparator is a type of measuring instrument that is made up of mechanical means to get magnification An electrical comparator is an electro-mechanical measuring system that is made up of electrical means to get the magnification.
This comparator includes a number of moving parts.


This comparator includes less number of moving parts.


There is a high rate of wear & friction because of more moving parts available in this system. There is a low rate of wear & friction because of fewer moving parts available in this system.
This comparator is not highly accurate. This comparator is highly accurate.
This comparator reading does not affect variations within the power supply. This comparator reading will affect by variations within the power supply.
Its maintenance is easy. Its maintenance is not easy.
It is not expensive. It is expensive.
This does not depend on the external current supply. This comparator needs an external current supply.
This comparator is very sensitive to vibrations. This comparator is not sensitive to vibrations due to less number of movable parts
The range of Magnification is fairly low compared to the electrical type. The range of Magnification is higher.


The advantages of mechanical comparators include the following.

  • Mechanical comparators are not expensive as compared to other types of amplifying devices.
  • These types of comparators don’t need any external electricity supply.
  • It has extremely high magnification.
  • Its optical lever is lightweight.
  • These are easily understood due to a linear scale.
  • These are compact, strong & very easy to operate.
  • They are apt for normal workshop conditions & they are handy.


The disadvantages of mechanical comparators include the following.

  • The mechanical comparators include more moving parts, so eventually, the accuracy is low & the friction is high.
  • The comparator accuracy will be decreased if any negligence within moving parts.
  • This comparator has more inertia so it causes the device to be responsive to vibrations.
  • This measuring instrument range is limited once the pointer moves above a fixed scale.
  • It has a high Parallax error because the pointer moves on a fixed scale.
  • It is extremely hard to integrate arrangements to adjust the magnification.


The uses of mechanical comparators include the following.

  • The reed-type mechanical comparator is mainly used for measuring the dimensional deviation of the workpiece by the standard dimensions.
  • This comparator is used in mass production & laboratory testing for analysis purposes.
  • This comparator is mostly used in different manufacturing companies like an outer rings, bearing inner, bearing cages race, and automobile cylindrical components.
  • The mechanical comparator mechanism is utilized in micators/ small spring measuring heads, ; minicators/ spring-lever indicators & opticators/ spring-optical measuring heads.
  • A mechanical optical comparator uses mechanical & optical components to increase the plunger’s movement.
  • These comparators are useful in measuring the surface roughness by measuring the dimensional variation between the standard & measured value of the surface material.

Thus, this is an overview of mechanical comparator – types and their applications. These components are one type of linear measurement device which are more suitable for verifying a large number of identical dimensions. Generally, comparators will not show the actual workpiece dimensions but they will show simply the variation in size. A comparator is capable of providing the variation of the dimension from the set dimension throughout the measurement. It cannot be utilized as a complete measuring device however it can compare only two dimensions. Mechanical comparators are normally designed in numerous types to meet various conditions. So these comparators mainly comprise a type of magnifying device which magnifies how many dimensions move away from the standard size. Here is a question for you, what is a comparator?