Resistance alloys are specialized precision alloy materials designed specifically for manufacturing resistive components. Their performance directly determines the accuracy, stability, and reliability of resistors. It’s not merely about allowing current to pass through; rather, they must deliver stable, precise, and predictable resistance values under a wide range of environmental conditions.

Key Performance Parameters

The quality of a resistance alloy is primarily evaluated based on the following critical performance indicators:

Resistivity: Measured in μΩ·cm, it indicates how strongly a material opposes the flow of electric current. Higher resistivity allows shorter and thinner materials to achieve the same resistance value, facilitating miniaturization of components.

Temperature Coefficient of Resistance (TCR): Expressed in ppm/℃, it represents the relative change in resistance per 1°C temperature change. This is the most crucial parameter for precision resistance alloys. A lower TCR means the resistance value is less affected by temperature, resulting in better stability.

Thermal EMF vs. Copper: Measured in μV/℃, this refers to the additional thermoelectric voltage generated at the junction between the resistance alloy and copper conductors due to material differences. A smaller value is preferred, especially in DC precision measurements, as it minimizes measurement errors.

Long-Term Stability: This describes how much the resistance value drifts over extended periods of use. High-quality resistance alloys exhibit excellent stability with extremely low annual drift rates.

Main Categories and Classic Alloys

Based on their characteristics and applications, resistance alloys are broadly classified into the following categories:

1. Precision Resistance Alloys

These alloys prioritize ultra-low TCR and exceptional stability, and are primarily used in standard resistors, precision instruments, and high-accuracy measurement circuits.

Alloy Series	Typical Examples	Key Characteristics and Applications
Cu-Mn Series	Manganin, e.g., Constantan	Extremely low TCR (can reach within ±10 ppm/℃), very low thermal EMF vs. copper. The most classic and widely used precision resistance material. Commonly used for standard resistors, shunts, and high-precision current-sense resistors.
Cu-Ni Series	New Constantan, Karma Alloy	Higher resistivity than Manganin, with superior corrosion and oxidation resistance, and a wider operating temperature range. Also extensively used in precision resistors.
Modified Ni-Cr Series	Evanohm, Ni-Cr-Al-Fe	Traditional Ni-Cr alloys enhanced with Al, Fe, Cu, etc., significantly reducing TCR while maintaining high resistivity. Commonly used in precision foil and wirewound resistors.
Precious Metal Series	Gold-based, Platinum-based, Palladium-based Alloys	Exceptional oxidation and corrosion resistance, with extremely high stability, suitable for harsh environments. However, they are very costly and mainly used in standard resistors or specialized fields (e.g., aerospace).

2. Resistance Alloys for Adjustable Components

These are primarily used as winding resistors for current/voltage regulation and control in power and electronic equipment. Key requirements include high mechanical strength, corrosion resistance, oxidation resistance, and the ability to withstand elevated operating temperatures.

Ni-Cr Series: e.g., Nichrome—high resistivity and excellent heat resistance.

Fe-Cr-Al Series: e.g., Iron-Chromium-Aluminum alloys—exceptional oxidation resistance, with maximum operating temperatures up to 1400°C, and lower cost than Ni-Cr series. Widely used in heating elements such as electric furnaces and heating tubes.

3. Resistance Alloys for Sensor Elements

These alloys exhibit predictable changes in resistance in response to external stimuli (e.g., strain, temperature), making them ideal for sensor applications.

Strain-Sensitive Resistance Alloys: e.g., Strain Constantan—resistance changes with mechanical deformation (tension or compression), used in strain gauges for measuring stress, pressure, etc.

Thermistor Alloys: Utilize resistance sensitivity to temperature for manufacturing temperature sensors.

4. Heating Alloys (for Electric Heating)

Designed primarily to convert electrical energy into heat. Requirements include high operating temperatures and long service life. Main types include Ni-Cr and Fe-Cr-Al series alloys, similar to those used in adjustable components.

Summary Comparison Table

To provide a clearer overview, here is a comparison of major precision resistance alloys:

Property	Cu-Mn Series (Manganin)	Cu-Ni Series (New Constantan)	Modified Ni-Cr (Evanohm)	Precious Metal Series (e.g., Pt-Ir Alloy)
Resistivity	Medium	High	High	Medium
TCR	Extremely Low	Very Low	Extremely Low	Low
Thermal EMF vs. Copper	Very Low	Low	Moderate	Depends on composition
Stability	Exceptional	High	Exceptional	Exceptional
Cost	Moderate	Moderate	High	Extremely High
Primary Applications	Standard resistors, precision current-sense resistors	Precision wirewound resistors	Precision foil resistors, precision wirewound resistors	Standard resistors, special-environment applications