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Grades and composition
Which alloy each calibration type uses, what we melt it from, and what the positive and negative legs are called on the certificate.
Base-metal types
| Type | Positive leg | Negative leg | Designation | Standard |
|---|---|---|---|---|
| K | NiCr 90/10 (Chromel) | NiAl 95/5 + Mn, Si (Alumel) | KPX / KNX | IEC 60584-1 |
| N | NiCr 14/1.5 Si (Nicrosil) | NiSi 4.5 (Nisil) | NPX / NNX | IEC 60584-1 |
| J | Iron | CuNi 45/55 (Constantan) | JPX / JNX | ASTM E230 |
| T | Copper | CuNi 45/55 (Constantan) | TPX / TNX | ASTM E230 |
| E | NiCr 90/10 (Chromel) | CuNi 45/55 (Constantan) | EPX / ENX | IEC 60584-1 |
Compositions are the nominal values in the standard each grade is ordered against. The certificate quotes the result measured on the lot, not the nominal.
Which grade is bought for what
- K — the volume grade. Ordered when the application is a clean oxidising furnace and the buyer wants one alloy that covers a wide temperature band.
- N — ordered where the same furnace runs hot for long periods and the buyer has been losing readings to drift. Costs more per metre than K; the reason to choose it is repeatability, not price.
- J — reducing or vacuum atmospheres, and where the user needs the higher EMF output per degree.
- T — cryogenic and moist service, typically low temperature and not corrosive.
- E — the highest output per degree of the base-metal types; chosen when the instrument is at the edge of its resolution.
What the buyer receives with the grade
| Composition | Result for the lot, by element, on the material certificate. |
| EMF | Per-lot calibration against the reference table on request. |
| Diameter | Measured in-line, 0.001 mm resolution, recorded on the spool label. |
| Resistivity | Measured per lot; the value the cable maker sizes the circuit from. |