How to Identify Thermocouple Type

Knowing your thermocouple type is essential before wiring it to your logger or configuring software. This guide explains how to identify it reliably.

1. Check the Cable Label or Documentation

Most high-quality thermocouples will include identifying information on:

  • A printed label near the probe or cable

  • A heat-shrink sleeve with type markings (e.g., “Type K”)

  • The product packaging or specification sheet

This is the most reliable method. If you have access to documentation from the supplier, consult it first.

2. Look at Wire Insulation Colors

Many thermocouple wires follow regional color coding standards. These can help you make an educated guess—though they should not be relied upon as the sole method of identification.

Common Color Codes

Type ANSI (USA) Colors IEC (Europe) Colors
K Yellow (+), Red (–) Green (+), White (–)
J White (+), Red (–) Black (+), White (–)
T Blue (+), Red (–) Brown (+), White (–)
E Purple (+), Red (–) Purple (+), White (–)
N Orange (+), Red (–) Pink (+), White (–)

Warning: Inexpensive or imported thermocouples (especially from unverified sources) may not follow color standards. Always confirm with testing.

3. Check Connector Color (If Present)

Thermocouples with standard miniature connectors often use color-coded plastic housings.

  • Yellow = Type K

  • Blue = Type T

  • Black = Type J

  • Green = Type E

This is useful if the connector is original and hasn't been replaced.

4. Can You Identify the Type by Looking at the Probe Tip?

No. The physical appearance of the thermocouple junction (tip) is not sufficient to identify the type. All thermocouple types use metal alloys that look nearly identical.

5. Still Not Sure? Try These Steps

If you're unable to identify the thermocouple type based on labeling, color codes, or supplier documentation, you can try a controlled process of elimination using the most common thermocouple types. This approach works best when you’re in a stable environment like a lab or office where you can estimate the expected room temperature.

Start with Type K

  • Type K is the most widely used thermocouple type in industrial and lab settings.

  • In the software, select Type K and observe the temperature reading.

  • If your sensor is at room temperature, the displayed value should be roughly 20–25 °C.

  • If the reading is significantly off (e.g., 60 °C or –80 °C), the type is likely incorrect.

Next, Try Type J

  • If Type K readings are clearly wrong, switch to Type J in the logger setup.

  • Again, compare the temperature reading to room temperature.

  • Type J has a different voltage-to-temperature curve and may give a more plausible result.

Finally, Try Type T

  • Type T is often used in lab environments or applications involving lower temperatures.

  • If K and J are off, select Type T and check again.

Note: This process only works if:

  • The thermocouple polarity is correct.

  • The thermocouple is functioning properly.

  • The probe is at ambient temperature during testing (or held at a known, stable temperature).