Understanding the Johansson Mikrokator

The question asks to identify the type of comparator that the Johansson mikrokator belongs to. To answer this, let's first understand what a comparator is and how different types work.

What is a Comparator in Metrology?

In dimensional metrology, a comparator is an instrument used to compare a work piece against a known standard, such as a gauge block. Comparators don't measure the absolute dimension of the work piece; instead, they indicate the difference in size between the work piece and the standard. This difference is often amplified to make small variations easily visible on a scale or display. Comparators are crucial for inspection and quality control due to their high sensitivity and speed.

Types of Comparators

Comparators can be broadly classified based on the method they use to amplify the small variations in dimension. The main types include:

• Mechanical Comparators: These use mechanical means like levers, gears, or twisted strips to amplify the displacement of the measuring plunger. Examples include dial indicators, Reed comparators, and the Johansson mikrokator.
• Optical Comparators: These use optical principles involving light and lenses to project a magnified image of the work piece profile onto a screen for comparison or measurement. This is different from comparing dimensions with a standard gauge block using a sensitive mechanical movement.
• Electronic Comparators: These use electronic transducers (like LVDTs or capacitance probes) to convert the plunger displacement into an electrical signal, which is then amplified electronically and displayed on a meter, digital readout, or computer screen.
• Pneumatic Comparators: These use compressed air to sense dimensional variations. The air flow or pressure changes as the work piece dimension varies, and this change is indicated on a pressure gauge or flow meter.

The Johansson Mikrokator: A Detailed Look

The Johansson mikrokator is a highly sensitive comparator developed by C.E. Johansson. Its working principle relies purely on a unique mechanical amplification system. It uses a twisted metal strip, often made of phosphor bronze, with a pointer attached to the center of the strip. A measuring plunger pushes against one end of the strip. When the plunger moves vertically due to a change in work piece size, the twisted strip is caused to untwist slightly. This untwisting motion is converted into a rotational movement of the pointer attached to the strip. Because the strip is very thin and precisely twisted, a small linear movement of the plunger results in a large angular movement of the pointer, achieving significant mechanical amplification (often several thousand times).

Key features of the Johansson mikrokator:

• Purely mechanical amplification.
• Uses a twisted strip mechanism.
• High sensitivity and accuracy.
• Does not use optical projection or electronic components for amplification or indication.
• The pointer directly indicates the deviation from the standard on a calibrated scale.

Analyzing the Options

Let's evaluate the given options based on our understanding:

1. Mechanical optical comparator: This category usually refers to comparators that combine mechanical amplification with an optical system for reading the scale, or instruments that use optics to compare profiles, not necessarily direct dimensional comparison with a standard via a plunger mechanism like the mikrokator. The mikrokator's amplification is purely mechanical, and its scale is read directly, not projected optically.
2. Electronic comparator: Electronic comparators rely on transducers (like LVDT) and electronic amplification. The Johansson mikrokator uses a twisted strip and mechanical amplification, not electronics.
3. Mechanical comparator: This category includes comparators that use only mechanical means for amplification. The Johansson mikrokator's twisted strip mechanism provides purely mechanical amplification of the plunger's movement. This perfectly fits the definition of a mechanical comparator.
4. Optical comparator: This term typically refers to profile projectors which use optics to project a magnified image of a part's silhouette onto a screen. While they use optics, their purpose and working principle are different from the Johansson mikrokator which compares a specific dimension against a standard using mechanical contact and amplification.

Based on its operating principle using a twisted metal strip for purely mechanical amplification of the plunger's movement, the Johansson mikrokator is classified as a mechanical comparator.

Conclusion

The Johansson mikrokator uses a unique mechanical system involving a twisted strip to achieve high amplification. It does not rely on optics for magnification or reading, nor does it use electronic components for amplification. Therefore, it is fundamentally a mechanical comparator.

Revision Table: Johansson Mikrokator and Comparators

Additional Information on Comparators in Metrology

Comparators are widely used in manufacturing and inspection processes where accurate dimensional checks are required for large quantities of parts. They are particularly useful for checking tolerances. The choice of comparator depends on factors like the required accuracy, sensitivity, range of measurement, robustness, and cost.

• Mechanical comparators like the mikrokator are known for their reliability and lack of dependence on external power, offering high sensitivity for their type.
• Electronic comparators offer ease of use, digital display, and often data logging capabilities.
• Optical comparators are excellent for checking complex profiles and comparing them to master layouts.
• Pneumatic comparators are suitable for checking internal diameters and other dimensions without direct mechanical contact, making them ideal for soft or easily damaged parts.

Understanding the working principle of each type helps in selecting the appropriate comparator for a specific metrology task. The Johansson mikrokator, with its innovative twisted strip mechanism, stands out as a classic example of a high-precision mechanical comparator.