# Johansson Mikrokator Comparator: Construction And Working Principle.

Like sigma comparator, Johansson Mikrokator is also a measuring instrument and it was developed and introduced by C.F. Johansson.Ltd. Johansson Mikrokator is a type of mechanical comparator.

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## What is Johansson Mikrokator?

Johansson Mikrokator is a type of mechanical comparator invented by a Swedish engineer named H.Abramson, which was later introduced and manufactured by a Sweden company called  C.H. Johansson.Ltd. This comparator is used as measuring and comparing device. It is one of the most important mechanical comparators due to its simple working principle and its construction.

## Construction (or) parts of Johansson Mikrokator

This comparator is constructed by the following components or parts,

• Plunger
• Slit washer
• Elbow
• Bellcrank lever (or) spring elbow
• Twisted strip
• Cantilever strip
• Scale
• Pointer

Let’s discuss them in detail.

### Plunger

Plunger act as a detecting component in the comparator. It is arranged in a vertical setup.

### Slit washer

This circular slit washer helps in mounting the plunger to give a frictionless motion. It is made up of polymer material. The slit washer is held by the elbow. It is a flexible diaphragm. It prevents axial rotation of the plunger.

### Elbow

Elbow holds the slit washer at the bottom where the measuring plunger is mounted. Both sides of the elbow hold the bell crank lever and the cantilever strip.

### Bellcrank lever

The base of the bell crank lever is fixed with the plunger and one arm of the spring elbow. It acts as a kinematic link.

### Twisted strip

The twisted strip is fastened between the bell crank lever and the cantilever strip. It is flexible in nature. It is made up of phosphor bronze.

### Cantilever strip

The cantilever strip is fastened with the twisted strip and the base is fixed with the arm. This cantilever strip is an adjustable type.

### Pointer

The pointer is lightweight in nature and it is made up of glass materials. It is attached to the twisted strip.

The reading scale is placed parallel to the glass pointer to estimate the readings.

## Working principle of Johansson Mikrokator

Johansson Mikrokator works on the simple principle of button spinning on a loop of string. Since H. Abramson developed this instrument, this simple basic principle was also known as the Abramson movement.

When there is vertical movement either upward or downward in the plunger is transmitted through the elbow to the bell crank lever.

The bell crank lever moves either left or right side respective to the vertical movement of the plunger.

The displacement of the bell crank lever makes the strip to twist or untwist (stretching) which is fastened to the cantilever strip at the opposite end. Stretching subjects it into the tensile force.

Perforated stripes are used in this comparator to prevent excessive stress.

The glass pointer placed in the center of the twisted strip start rotates either in the clockwise or anti-clockwise direction. This rotation is directly proportional to change in length of strip due to stretching caused by the plunger movement.

The deflection of the glass pointer is recorded by the calibrated scale parallel to the pointer.

## Magnification of Johansson Mikrokator

The magnification of the Johansson MikroKator is expressed in the ratio shown in the below equation.$$\displaystyle \text{Magnification = }\frac{{d\theta }}{{dl}}$$ $$\displaystyle \frac{{d\theta }}{{dl}}\propto \frac{l}{{n{{w}^{2}}}}$$where,

• l = Length of the metal strip
• n = Number of turns on the metal strip
• w = Width of the metal strip.

Magnification of this instrument depends upon the length of the strip and the number of twists in the twisted strip.

To obtain better magnification the twisted strip must be smaller in dimension(width). The average dimension of the twisted stip may up to 0.06 mm to 0.0025 mm.

By adjusting the length of the cantilever strip by the screws fitted on it can result in the variation of magnification.

Johansson Mikrokator has an accuracy of  $\displaystyle \pm 1\%$.

• It is small and compact in size.
• It is easy to handle and operate.
• It has a simple basic working principle compared to other comparators.
• Since it is a portable device, it can be easily carried from one place to another place.
• It is cheaper in cost.
• It is robust and magnification up to 5000 times can be obtained.
• Higher sensitivity can be obtained under certain controlled laboratory environmental conditions.
• No external power source is required to perform the operation.