Failed Type J Thermocouple Analysis

The Customer’s Problem

The customer submitted a failed Type J Thermocouple reported to have developed an open circuit after extended time at temperature.  Initial evaluation confirmed the open circuit.

The Findings / Analysis

Sectioning of the thermocouple probe confirmed that the thermocouple wires remained intact. Further examination revealed the breaks to be in the extension wire portion of the probe.

Further sectioning of the extension wire isolated the open circuit to be adjacent to the transition section shown in Figure 1. Removal of the armoring and insulation reveled the break within one inch of the transition.

Figure 2 shows comparison between the un-corroded negative leg and the heavily corroded positive leg.

At higher magnification (Figure 3) shows the degree of corrosion in the positive leg.

The Solution

In conclusion, it was determined the leg corroded because of oxidation. Recommended to client to swap wire for non-oxidizing material(s).

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14006 Macro 300

Figure 1 | Section of Failed Probe



Figure 2 | Negative Top – Positive Bottom


14006 JPX photo 3 300

Figure 3 | Close-Up of Corroded Negative Leg

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