JOHANSSON MIKROKATOR or Abramson's Movement | Working and construction of mechanical comparator.

Summary

This video explains the Johnson micro crater, a mechanical comparator developed by Johnson Ltd. It operates on the Abramson moment principle, providing high mechanical magnification of length differences. The device uses a twisted metal strip to transfer moment without friction, eliminating backlash. The construction includes a spring elbow that adjusts magnification and a split washer to prevent rotational movement. The instrument is calibrated to a standard, and differences in specimen measurements cause plunger movement, resulting in pointer readings on a scale. Subscribe for more informative videos.

Takeaways

• 🔧 The Johnson micro crater is a mechanical comparator developed by Johnson Ltd, USA.
• 📏 It operates on the Abramson moment principle, named after H. Abramson, for high mechanical magnification.
• 🔄 A twisted thin metal strip holds a pointer, which indicates readings on a scale, ensuring no friction or backlash.
• 🛠️ The construction includes a twisted metal strip fixed between two ends, with one end attached to an adjustable cantilever and the other to a spring elbow.
• 🔗 The spring elbow, consisting of a flexible strip and a stiff diagonal, has a bell crank lever that changes the strip's length when a moment is applied to the plunger.
• ⚙️ The magnification can be adjusted by changing the length of the spring elbow.
• 🔩 Perforations in the metal strip prevent excessive stress under tensile force.
• 🛑 The rotational moment of the plunger is stopped by a split washer, allowing only vertical movement.
• 📈 The instrument is calibrated to a standard, with two pointers for upper and lower limits.
• 🔍 When a test specimen is measured, differences in dimensions cause the plunger to move, which in turn twists or untwists the metal strip, moving the pointer to show the reading.

Q & A

What is a Johnson micro crater?

The Johnson micro crater is a type of mechanical comparator developed by Johnson Ltd company of USA.

What principle does the Johnson micro crater use?

It uses the principle referred to as Abramson moment, named after H Abramson, to achieve high mechanical magnification.

How does the Johnson micro crater achieve its readings?

It uses a twisted thin metal strip that holds a pointer, which shows readings on a suitable scale.

What is the advantage of the Johnson micro crater in terms of friction and backlash?

The Johnson micro crater is free from backlash because there is no friction involved in the transfer of moment from the strip to the pointer.

What is the role of the spring elbow in the Johnson micro crater?

The spring elbow, consisting of a flexible strip and a stiff diagonal act, has a bell crank lever that causes the twister strip to change its length when there is a moment in the plunger.

How can the magnification of the Johnson micro crater be adjusted?

The magnification can be varied by changing the length of the spring elbow.

What is the purpose of the perforations made in the metal strip?

Perforations are made in the strip to prevent excessive stress on the central portion of the metal strip when a pull subjects it to tensile force.

How does the Johnson micro crater respond to a difference in the measured dimension of a specimen?

Any difference in the measured dimension of the specimen will result in either lowering or rising of the plunger, which in turn moves the bell crank lever and changes the twist of the metallic strip.

What is the function of the split washer in the Johnson micro crater?

The split washer arrests the rotational moment of the plunger, only allowing vertical movement of the plunger.

How is the Johnson micro crater calibrated?

The instrument is initially calibrated to a standard, and the zero is set to this value.

What are the two pointers on the Johnson micro crater used for?

The two pointers on the Johnson micro crater can be set as upper and lower limits for measurement.