Question

The material most preferred for control spring is ________.

• A. german silver
• B. platinum silver
• C. silicon bronze
• D. phosphor bronze

Hint:

Control springs need resilience and stability → phosphor bronze is best for that!

Answer 1

The Correct Option is D

Step 1: What is a Control Spring?
In measuring instruments (e.g., PMMC, moving iron), a control spring provides a controlling torque and also acts as a conductor in some cases. Step 2: Properties Required in Control Spring Material
The ideal material must have:
- High fatigue strength
- High elasticity
- Non-corrosive nature
- Stable mechanical properties over time
Step 3: Why Phosphor Bronze?
Phosphor bronze is a copper alloy with tin and phosphorus. It offers:
- High resilience and fatigue resistance
- Corrosion resistance
- Good conductivity and dimensional stability
Step 4: Other Options
- German silver → used for resistors.
- Platinum silver → costly, rarely used.
- Silicon bronze → more structural, not ideal for springs.
Conclusion:
Option (4) is correct — phosphor bronze is the most preferred material for control springs.