Type K vs Type J
Side by side comparison: how they work, where each fits, and which to choose.
Quick answer: Type K is the general purpose choice up to about 1200 °C in oxidising atmospheres; type J gives higher output but its iron leg limits it to about 750 °C.
Type K vs Type J: Comparison Table
| Aspect | Type K | Type J |
|---|---|---|
| Materials | Nickel chromium / nickel aluminium | Iron / copper nickel |
| Upper limit (typical) | about 1200 °C | about 750 °C |
| Sensitivity | about 41 µV/°C | about 52 µV/°C |
| Atmosphere | Oxidising, inert | Reducing, vacuum, inert; iron rusts in moist air |
| IEC 60584-3 cable colour | Green | Black |
| Class 1 tolerance | ± 1.5 °C or 0.4 % | ± 1.5 °C or 0.4 % |
Choose Type K when
- Furnaces, kilns and general high temperature use
Choose Type J when
- Older equipment and plastics machinery built for J
- Reducing atmospheres below about 750 °C
Key Differences Explained
The two types have different curves, so the transmitter must be set to the correct type. A J sensor read as K, or the reverse, gives large errors.
Type N is a more stable alternative to K above about 1000 °C.
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Frequently Asked Questions
What is the difference between Type K and Type J?
Type K is the general purpose choice up to about 1200 °C in oxidising atmospheres; type J gives higher output but its iron leg limits it to about 750 °C.
How do I identify K or J wire?
By the colour code of the cable standard, or because the J positive leg (iron) is magnetic.
Why does type K drift at 250 to 550 °C?
Short range ordering in the alloy changes its output; type N reduces this.
Can J be used above 750 °C?
The iron leg oxidises quickly; use K or N.
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