Type T Thermocouples
Type T Thermocouple at a Glance
| Spec | Type T |
|---|---|
| Conductors | Copper (+) / Constantan (-) |
| Temperature range | -200 to 370 °C (-328 to 700 °F) |
| Special limits of error | ±0.5 °C or ±0.4%, whichever is greater |
| Standard limits of error | ±1.0 °C or ±0.75%, whichever is greater |
| Output | About 43 µV/°C (0 to 100 °C average) |
| ANSI color code | Blue (+), red (-), blue connectors |
| IEC color code | Brown (+), white (-), brown connectors |
How Accurate Is Type T?
Type T has the tightest tolerance of any standard base metal thermocouple. Its advantage is biggest at and below room temperature, and it fades near the top of its range:
| Temperature | Type T special limits | Type K special limits |
|---|---|---|
| -100 °C (-148 °F) | ±0.8 °C (suggested by ASTM) | Not established |
| 25 °C (77 °F) | ±0.5 °C | ±1.1 °C |
| 100 °C (212 °F) | ±0.5 °C | ±1.1 °C |
| 350 °C (662 °F) | ±1.4 °C | ±1.4 °C |
Tolerances are from ASTM E230 for new wire. Above about 370 °C the copper leg oxidizes and the sensor drifts, so if your process runs hotter, choose Type K.
Why the Range Is Narrow
Type T's copper leg oxidizes quickly in air above about 370 °C, so the sensor drifts and fails if it runs hotter. Thinner wire and the insulation lower the practical limit further: ASTM suggests 200 °C (400 °F) for 24 AWG wire, and PFA insulation is typically rated to 260 °C (500 °F). Below 0 °C the opposite is true. Copper and constantan stay stable in the cold, which is why Type T is so good there.
Where Type T Fits Best
- Ultra-low freezers, vaccine storage and cryogenics, down to -200 °C
- Cold rooms, coolers and cold chain monitoring
- Pharmaceutical stability chambers and temperature mapping
- Laboratory and research measurements
- Food processing and HACCP, from freezing to cooking
- HVAC, data centers and environmental chambers
- Battery and electronics testing near room temperature
Choose the Right Style
- Air and gas: PFA insulated 24 AWG beaded wire thermocouples with stripped leads or a miniature connector. For longer runs, custom length Type T thermocouples go up to 30 ft.
- Fast response and small parts: 36 AWG fine gauge thermocouples with a miniature connector or stripped leads.
- Surfaces: the iSur flat junction sensor or an adhesive backed surface thermocouple.
- Liquids and immersion: the TSTP tube style probe or the rugged transition joint probe.
Keep the whole circuit Type T with Type T wire, miniature and standard connectors. Mixing alloys adds error.
Common Mistakes to Avoid
- Shallow probes. Copper conducts heat along the wire and pulls the reading toward ambient. Insert probes at least 10 to 20 times the sheath diameter.
- Mixed alloys. A Type K connector or plain copper hookup wire anywhere in the circuit adds error.
- Reversed leads. In the ANSI code the red lead is always negative. Swapped leads make the reading move the wrong way.
- An instrument that can't keep up. Cold junction compensation in many readers is only ±0.5 to ±1.0 °C. Check your instrument's Type T accuracy.
- Moisture in cold spaces. Condensation causes erratic readings. Use PFA insulation or a sealed probe in freezers and cold rooms.
Calibration Available
Most of our Type T thermocouples can be calibrated at three points before they ship, with a NIST-traceable or ISO 17025 accredited certificate. Calibration is available on new orders only. See calibrated thermocouples or calibration details.
Type T Thermocouple FAQ
Is Type T the most accurate thermocouple?
It is the most accurate standard base metal thermocouple. Special limits Type T is ±0.5 °C near room temperature, versus ±1.1 °C for Types K and J.
Type T or Type K?
Use Type T below about 200 °C when accuracy matters, especially below freezing. Use Type K if your process ever goes above 370 °C.
Type T thermocouple or RTD?
A platinum RTD is more accurate and stable. Type T is cheaper, smaller, faster to respond and needs no excitation current.
What is the Type T temperature range?
About -200 to 370 °C (-328 to 700 °F). Wire gauge and insulation often set a lower practical limit, so check each product's rating.
Can a Type T thermocouple measure liquid nitrogen?
Yes. Liquid nitrogen boils at -196 °C, inside Type T's range. For the best accuracy that cold, order wire selected for sub-zero use or calibrate the sensor.
What color is a Type T thermocouple?
In the US, the positive lead is blue, the negative lead is red and connectors are blue. Under IEC, Type T is brown and white with brown connectors.
Why is my Type T reading wrong?
Check that the instrument is set to Type T, the leads are not reversed, all connectors and extension wire are Type T, and the sensor has good thermal contact.
Want the full details? Read our complete guide to Type T thermocouples, or talk to a real engineer about your application.