1. What is Comparator ?
A comparator is a precision instrument used to compare the dimensions of a workpiece with a standard reference. Unlike direct measuring instruments (like vernier calipers or micrometers), comparators do not give the actual dimension but indicate the deviation from the standard size.
They are widely used in mass production and quality control where high accuracy and repeatability are required.
2. Principle of Operation
Comparators work on the principle of:
- Magnification of small displacement
When a workpiece is placed under the measuring probe:
- Any small deviation from the standard size
- Is amplified mechanically, optically, or electronically
- And displayed on a scale or digital display
3. Characteristics of a Good Comparator
- High magnification
- High sensitivity
- Quick response
- Stability and repeatability
- Low friction and backlash
- Easy to read scale
4. Types of Comparators
4.1 Mechanical Comparators
Description
- Use mechanical linkages (gears, levers) for magnification
Example: Dial Indicator
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Features
- Plunger movement is amplified by gears
- Reading shown on circular dial
Advantages
- Simple and robust
- No external power required
Disadvantages
- Friction and wear affect accuracy
4.2 Mechanical-Optical Comparators
Description
- Combine mechanical movement with optical magnification
Example: Sigma Comparator
4
Working
- Small movement of probe tilts a mirror
- Light beam is reflected and magnified on a scale
Advantages
- High magnification
- Less mechanical wear
4.3 Optical Comparators (Profile Projector)
Description
- Use optical projection to enlarge the image of a component
Working
- Workpiece is placed on stage
- Magnified image projected onto screen
4
Applications
- Checking profiles, threads, gears
Advantages
- No contact measurement
- High accuracy
4.4 Electrical Comparators
Description
- Use electrical transducers (e.g., LVDT)
Working
- Probe displacement converted into electrical signal
- Amplified and displayed
Advantages
- Very high sensitivity
- Fast response
Disadvantages
- Requires power supply
4.5 Electronic Comparators
Description
- Advanced version of electrical comparators
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Features
- Digital display
- High accuracy and reliability
Advantages
- No parallax error
- Easy data recording
4.6 Pneumatic Comparators
Description
- Use air pressure variation for measurement
Working
- Air is passed through a nozzle
- Gap between nozzle and workpiece affects pressure
4
Advantages
- No mechanical contact
- Suitable for delicate parts
Disadvantages
- Sensitive to air pressure variations
5. Advantages of Comparators
- High accuracy and precision
- Suitable for mass production
- Reduces human error
- Quick inspection
- Detects small deviations
6. Disadvantages of Comparators
- Do not give absolute measurement
- Require standard reference
- Calibration needed
- Some types are costly
7. Applications of Comparators
- Inspection of manufactured parts
- Quality control in industries
- Checking tolerances
- Gauge calibration
- Mass production inspection
8. Difference: Comparator vs Measuring Instrument
| Feature | Comparator | Measuring Instrument |
|---|---|---|
| Output | Deviation only | Actual dimension |
| Accuracy | Very high | Moderate |
| Use | Comparison | Direct measurement |
| Example | Dial indicator | Vernier caliper |