Common Thermocouple Types: ANSI and International Codes Explained
Thermocouples are essential temperature-sensing elements widely used across industrial, commercial, and scientific applications due to their durability, cost-effectiveness, and broad temperature range capabilities. To ensure global compatibility and standardization, thermocouples are identified using ANSI (American National Standards Institute) and international codes. This blog explores the most common thermocouple types, their code designations, temperature ranges, materials, and practical applications.
What Is a Thermocouple?
A thermocouple is a temperature sensor formed by joining two dissimilar metal wires at one end (called the junction). When this junction experiences a temperature difference compared to the other ends of the wires, it generates a voltage that can be interpreted as temperature.
ANSI and International Coding System for Thermocouples
ANSI vs IEC Thermocouple Standards
- ANSI (American National Standards Institute): Used primarily in North America, designates thermocouples with letter codes like Type K, J, T, E, N, etc.
- IEC (International Electrotechnical Commission): Followed globally, especially in Europe and Asia. IEC 60584 standard defines thermocouple types, color coding, and tolerances.
Common Thermocouple Types and Their Codes
Type K (Chromel–Alumel)
ANSI Code: K
IEC Code: Type K
Color Code (ANSI): Yellow (+), Red (-)
Temperature Range: -200°C to +1260°C (-328°F to +2300°F)
Material: Nickel-Chromium / Nickel-Aluminum
Applications:
- General-purpose use
- Furnaces, kilns, gas turbines
- Chemical and petrochemical industries
Advantages:
- Wide temperature range
- Affordable and widely available
Type J (Iron–Constantan)
ANSI Code: J
IEC Code: Type J
Color Code (ANSI): White (+), Red (-)
Temperature Range: -40°C to +750°C (-40°F to +1382°F)
Material: Iron / Constantan (Copper-Nickel)
Applications:
- Older equipment
- Plastics and packaging industries
Advantages:
- High sensitivity at lower temperatures
- Good for oxidizing/reducing atmospheres
Disadvantages:
- Prone to rust (iron side)
- Not ideal for high-temperature oxidation
Type T (Copper–Constantan)
ANSI Code: T
IEC Code: Type T
Color Code (ANSI): Blue (+), Red (-)
Temperature Range: -200°C to +370°C (-328°F to +700°F)
Material: Copper / Constantan
Applications:
- Cryogenic and lab environments
- Food and beverage industry
Advantages:
- Excellent accuracy at low temperatures
- Stable performance in moist environments
Type E (Chromel–Constantan)
ANSI Code: E
IEC Code: Type E
Color Code (ANSI): Purple (+), Red (-)
Temperature Range: -200°C to +900°C (-328°F to +1652°F)
Material: Nickel-Chromium / Constantan
Applications:
- Precision temperature sensing
- Medical instruments and biotech labs
Advantages:
- Highest EMF output per °C
- Excellent sensitivity
Type N (Nicrosil–Nisil)
ANSI Code: N
IEC Code: Type N
Color Code (ANSI): Orange (+), Red (-)
Temperature Range: -200°C to +1300°C (-328°F to +2372°F)
Material: Nicrosil / Nisil (Nickel alloys)
Applications:
- Aerospace and nuclear power
- Heat treatment and metallurgy
Advantages:
- Superior stability at high temperatures
- Resistant to oxidation and drift
Type R, S, and B (Platinum-Based Thermocouples)
| Type | ANSI Code | Temp Range | Application Areas | Comments |
|---|---|---|---|---|
| R | R | 0°C to +1600°C | Glass, metals, petrochemical | High accuracy, expensive |
| S | S | 0°C to +1600°C | Pharmaceuticals, labs | Good for oxidizing atmospheres |
| B | B | +100°C to +1800°C | Furnaces, glass manufacturing | Best for high-temperature ranges |
Material Composition:
- Type R: Platinum 13% Rhodium / Platinum
- Type S: Platinum 10% Rhodium / Platinum
- Type B: Platinum 30% Rhodium / Platinum 6%
Advantages:
- Extremely accurate and stable
- Ideal for critical temperature monitoring
Disadvantages:
- High cost
- Low EMF output; sensitive instrumentation required
Color Code Comparison: ANSI vs IEC
| Thermocouple | ANSI Colors | IEC Colors |
| Type K | Yellow (+), Red (-) | Green (+), White (-) |
| Type J | White (+), Red (-) | Black (+), White (-) |
| Type T | Blue (+), Red (-) | Brown (+), White (-) |
| Type E | Purple (+), Red (-) | Purple (+), White (-) |
| Type N | Orange (+), Red (-) | Pink (+), White (-) |
Choosing the Right Thermocouple Type
Key Considerations:
- Temperature range of your process
- Environmental conditions (corrosive, oxidizing, humid)
- Accuracy and response time
- Material compatibility
- Cost and availability
Example Application Scenarios:
- Type K for industrial furnaces
- Type T for refrigeration systems
- Type R/S/B for glass and metal processing
Conclusion
Understanding the various thermocouple types and their ANSI and international codes helps engineers, technicians, and plant personnel choose the right sensor for each application. Whether you’re operating in high-temperature kilns, biomedical labs, or food-grade environments, selecting the proper thermocouple ensures precise temperature monitoring and long-term reliability.
By referencing these standardized codes and characteristics, professionals can streamline equipment specification, ensure global compatibility, and improve overall system performance in process automation and industrial control.