Special Limits of Error (SLE) and Class 1 accuracy are similar in that they both refer to higher accuracy thermocouples, but they are not exactly the same because they are defined by different standards with slightly different tolerances.
| Feature | Class 1 (IEC 60584-2) | Special Limits of Error (ASTM E230) |
|---|---|---|
| Standard | IEC 60584-2 | ASTM E230 |
| Primary Usage | International (Europe, etc.) | USA & North America |
| Accuracy Level | High | High |
| Tolerance Differences | Slight variations exist by thermocouple type | Slightly different tolerances by type |
For many thermocouple types (e.g., Type K), Class 1 and SLE tolerances are very close, but they may not always be identical. If exact compliance with a specific standard is needed, it’s best to compare the tolerances in the respective standards for the given thermocouple type.
| Standard | Class 1 (IEC 60584-2) | Special Limits of Error (ASTM E230) |
|---|---|---|
| Class 1 (IEC 60584-2) | -40°C to 1000°C | ±1.5°C or ±0.004×T (whichever is greater) |
| Primary Usage | 0°C to 1250°C | ±1.1°C or ±0.002×T (whichever is greater) |
Key Differences
Special Limits of Error (SLE) has a tighter tolerance than Class 1 at most temperatures.
SLE uses a factor of 0.002×T, while Class 1 uses 0.004×T, meaning SLE allows half the percentage error in some cases.
Class 1 covers a lower temperature range (-40°C and up), whereas SLE starts at 0°C.
Summary
SLE is more precise than Class 1 at many temperatures.
Class 1 allows a slightly larger error margin compared to SLE in most cases.
If your application requires the highest accuracy, SLE (ASTM E230) is the better option.
If your application requires compliance with IEC standards, Class 1 is the correct classification.