- Practice · 6 marks
Classification and merits of comparators
Short answer
A comparator indicates the difference between a workpiece and a standard on a magnified scale. Types: mechanical (cheap, robust, limited magnification), optical (high magnification, dark room, bulky), electrical (very high magnification, remote recording, needs stabilised power), pneumatic (non-contact, self-cleaning, slow, requires clean dry air).
What is a comparator? Classify comparators and compare the advantages and disadvantages of mechanical, optical, electrical and pneumatic types.
A comparator is a precision instrument that compares the size of a workpiece with a known standard (master or slip gauge) and indicates the difference on a magnified scale. It does not give the absolute size. Principle: set the instrument to zero on a master of the basic size; the pointer reading when the work replaces the master gives the deviation.
Classification
- Mechanical (dial indicator, reed-type, sigma comparator): amplification by levers, gears, reeds.
- Optical (Zeiss Ultra-optimeter, optical projector): amplification by a light beam and mirrors.
- Electrical / electronic (LVDT, capacitance, inductive): displacement converted to an electrical signal.
- Pneumatic (Solex type): the change of air gap is measured through back pressure or flow.
- Combinations: mechanical-optical, electro-pneumatic.
Comparison
| Type | Advantages | Disadvantages |
|---|---|---|
| Mechanical | Cheap, robust, no power needed, portable | Friction, backlash and wear; moving parts; limited magnification (up to about 1000) |
| Optical | Very high magnification (up to 1000-2000), no inertia, few moving parts | Needs power and a darkened room, costly, bulky, eye strain |
| Electrical | High magnification (up to 10 000), remote reading, easy to record and automate | Needs power supply and stabilisation, heat from supply affects result, costly |
| Pneumatic | Non-contact, high magnification, self-cleaning, can measure many dimensions at once | Needs clean, dry air at constant pressure, slow response, scale not linear over a wide range |
Comparators are used for the inspection of large batches where the tolerance is small.
✓ Answer checked by Claude Opus 5.5 (high effort)
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