What does the CJC specification cover?
NI explains that connecting a thermocouple to the measurement system introduces additional metal junctions. Cold-junction compensation accounts for their temperature effect. Its CJC sensor accuracy specification describes that sensor, while a product-specific total thermocouple accuracy specification can already account for CJC.
Commissioning Docs is independent and is not affiliated with NI. This is a documentation distinction, not a calibration method or a universal uncertainty formula. Check the selected module, connectors and sensor documentation rather than adding or subtracting generic accuracy numbers.
Sources: NI: NI: Specifications Explained, C Series Modules, checked 21 October 2026
Which evidence belongs in the temperature record?
Use the approved test channel and equipment identities, not a nearby ambient sensor merely because it also reports temperature. Preserve the original unit, configuration and test interval with the accepted accuracy assessment.
| Evidence | Record | Why it matters |
|---|---|---|
| Sensor | Actual thermocouple type and identity | Different sensor basis |
| Acquisition | Module and channel reference | Applicable specification |
| Connection | Actual terminal or connector arrangement | CJC basis can differ |
| CJC | Source and relevant specification | One contribution only |
| Complete accuracy | Approved specification or uncertainty assessment | Avoid omission or double counting |
| Acceptance | Criterion and responsible reviewer | No automatic pass from a label |
How can a correct number support the wrong claim?
Illustrative example. A fictional commissioning folder contains a CJC sensor specification and a temperature trend. A summary relabels the CJC number as total system accuracy without identifying the thermocouple or applicable complete specification. The copied number may be accurate as a sensor specification, but its new description is unsupported.
The reviewer keeps the trend and original specification, records the missing sensor and acquisition references, and asks the commissioning lead for the approved complete basis. No numerical tolerance is invented, and a calibration certificate is not treated as proof that every connection or configuration was correct during the test.
What closes the documentation gap?
Link the accepted accuracy basis to the exact channel and test configuration. Confirm whether its stated total already includes the CJC contribution before another allowance is added. Record assumptions and unresolved conditions for the technical reviewer.
Do not change wiring, reference temperatures or software compensation settings from this worksheet. Test work needs the approved procedure and competent personnel. Engineering sign-off is performed only by the registered engineer on the job.
Common questions
What else should the bid team know?
Is CJC accuracy the entire measurement accuracy?
No. Identify the applicable complete system basis.
Should every CJC term be added again?
No. First check whether the stated total already includes it.
Does this worksheet calibrate a thermocouple?
No. It organizes evidence for the designated technical reviewer.