Instrumentation alloys—composition of Constantan used in sensors Constantan is an alloy composed of which pair and approximate proportions?

Introduction / Context:
Constantan is well known for its relatively constant electrical resistivity over a wide temperature range, making it ideal for precision electrical measurements, strain gauges, and as a leg in certain thermocouples (e.g., copper–constantan). Correctly identifying its composition helps avoid mix-ups with other copper alloys used in electrical and thermal instrumentation.

Given Data / Assumptions:

• Focus on principal alloying elements and typical nominal composition.
• Function relates to resistivity stability and thermoelectric behavior.

Concept / Approach:
Constantan belongs to the copper–nickel family. Around 55% copper and 45% nickel optimize the temperature coefficient of resistance, yielding a near-constant resistance versus temperature. This property is crucial in bridge circuits, strain gauges, and thermocouple reference legs, where predictable electrical behavior ensures measurement accuracy and compensation schemes.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer datasheets list constantan or Advance alloy as about 55% Cu and 45% Ni, confirming the nominal pairing and purpose.

Why Other Options Are Wrong:

• Cu–Sn (bronze): mechanical bearings and springs, different resistivity profile.
• Pt–Rh: thermocouple type S or R combinations, precious metals, not constantan.
• Fe–Ni (Invar-type): low expansion alloys, not constant resistivity alloys.

Common Pitfalls:
Confusing constantan with Invar or Nichrome. Nichrome is Ni–Cr for heaters; Invar is Fe–Ni for low expansion; constantan is Cu–Ni for stable resistivity.

Final Answer:
Cu (55%) & Ni (45%).