Thermocouple selection
Type J vs Type K Thermocouples: What to Compare Before Choosing
Type J uses an iron versus copper-nickel alloy pair, while Type K uses nickel-chromium versus nickel-aluminium alloys. Type K has the wider NIST reference-data range, but the complete assembly and installation still determine the usable operating limit.
Technical reference
Type J and Type K at a Glance
The values below come from the NIST Temperature Scale Database (SRD 60). They describe thermocouple reference data, not a guaranteed operating range for every probe, cable or complete assembly.
| Reference characteristic | Type J | Type K |
|---|---|---|
| Thermoelement composition | Iron versus a copper-nickel alloy | Nickel-chromium alloy versus nickel-aluminium alloy |
| NIST reference-data range | -210°C to 1200°C | -270°C to 1372°C |
| What the value means | A reference-table range for the thermocouple type. It is not the operating limit of a specific Yog Electro assembly. | |
Do not use the reference range as the product rating
The practical limit must be checked against the selected sheath, insulation, junction, diameter, cable, termination, process atmosphere, mounting and receiving instrument. Confirm the complete construction for the actual measurement point.
Selection FAQs
Type J vs Type K: Practical Answers
What does the catalogue actually show?
MI-37 and PTFE list J/K selection. Catcon lists K type only and is associated with automotive and CNG testing.
What should I compare?
Compare the receiving input, measurement point, process conditions, junction, sheath, diameter, mounting and cable against the same product record.
Can the NIST range answer suitability?
No. It is reference data for the thermocouple type, not a finished-assembly rating. Request engineering review for the actual installation.
Catalogue evidence
What the Current Product Records Show
The records below show where J and K are offered in the current catalogue. They do not establish a universal temperature range or suitability rule for either calibration.
| Catalogue record | Type J | Type K | Other documented choices |
|---|---|---|---|
| Mineral Insulated Thermocouple | Selectable | Selectable | Grounded or ungrounded junction; listed sheath, diameter and cable options. |
| Special Coated (PTFE) Thermocouple | Selectable | Selectable | Simplex or duplex; ceramic or mineral insulation; ungrounded junction; listed sheath and termination options. |
| Catcon Thermocouple | Not listed | Listed | Ungrounded junction, SS304 or SS316 sheath, and a documented cable construction for supported automotive testing applications. |
Decision boundary
Do Not Choose from the Letter Alone
Where a product offers both J and K, the catalogue confirms availability, not which calibration fits every process. The selected calibration must also match the receiving instrument and the complete measurement requirement.
Construction choices are product-specific. Do not transfer a junction, sheath, cable, diameter, insulation or termination option from one record to another unless that option is listed for the selected assembly.
Bring These Details to Engineering Review
- Process conditionsNormal and maximum temperature, process medium or atmosphere, cycling and vibration.
- Measurement pointSurface, immersion, furnace, machinery or test location and what the reading controls or protects.
- Mechanical assemblyRequired sheath material, diameter, insertion length, mounting and available space.
- Electrical interfaceJunction, simplex or duplex requirement, cable route, termination and receiving-instrument input.
A practical route
Move from Comparison to a Reviewable Enquiry
- 01
Check the instrument
Record the thermocouple input required by the existing or proposed receiving instrument.
- 02
Define the complete point
Document the process, sensing location, construction, mounting, cable route and access constraints.
- 03
Match one product record
Use only the options listed for that assembly and ask engineering to review any unresolved details.
Need a Type J or Type K Review?
Share the process conditions, measurement point, construction, mounting, cable route and instrument input.