Unqualified counterfeit and inferior thermocouple spare parts occupy a certain share of the aftermarket; directly storing them in the workshop inventory will lead to sudden production failures after installation. Establishing a complete incoming inspection standard before warehousing can screen out defective probes in advance, reducing mold downtime losses caused by inferior sensors. The inspection process relies on visual observation, multimeter testing and simple temperature comparison without large professional calibration equipment.
First item: Visual appearance inspection covering sheath, wire, connector and welding points. Check the probe sheath surface for scratches, pits, perforations and uneven polishing; inferior products use unpolished rough steel with many tiny corrosion points that drift rapidly after short use. Observe the cable outer braid: qualified high-temperature shielding wires have dense uniform weaving without broken wires, while cheap inferior cables have sparse braids with many gaps unable to block electromagnetic interference. Check the hot junction sensing tip weld: formal qualified probes have smooth full welding without tiny cracks or gaps; inferior probes have incomplete welding with hidden disconnection risks. Distinguish K/J wire color codes according to international IEC standards; mixed color wires indicate irregular production without unified calibration, and such batches are rejected directly.
Second item: Multimeter continuity and resistance testing to screen open and short-circuit hidden defects. Adjust the multimeter to resistance gear, connect two test leads to the positive and negative terminals of the thermocouple plug. Normal intact probes show stable resistance values corresponding to wire length; if the resistance value is infinite, internal wires are broken and unqualified. If resistance is close to zero, internal positive and negative wires short-circuit, also rejected. Shake the cable back and forth while measuring resistance; if the resistance value fluctuates drastically, there are hidden broken strands inside the wire, which will fail after heating expansion and cannot be put into storage as spare parts.
Third item: Simple temperature comparison test to screen severe drift uncalibrated products. Take a verified standard calibrated thermocouple as a benchmark, bind its sensing tip tightly with the test probe's tip, then heat the joint with a hot air gun to 300–400°C. Connect both probes to two independent channels of the same temperature controller, observe the reading difference. If the temperature gap exceeds ±4°C, the test probe has serious uncalibrated drift and is judged unqualified, as it cannot meet normal production temperature control accuracy requirements.
Fourth item: Bending fatigue spot check for customized bent and miniature probes. Randomly select 10% of the batch miniature thermocouples, bend the cable at the specified minimum bending radius back and forth 100 times, then measure resistance again with a multimeter. If open circuit or fluctuating resistance appears after bending, the multi-strand wire core has poor production quality and the whole batch is returned to the supplier. This inspection item targets micro probes and flexible transition section thermocouples prone to bending fracture.
Fifth item: Material identification screening for special-grade spare parts. For food-grade, medical and anti-corrosion thermocouple batches, check attached material test reports to confirm sheath alloy composition, oil-free insulation and PTFE coating standards. If supporting certification documents are missing, suspend warehousing and return goods until complete qualification materials are provided.
After passing all five inspection items, affix qualified warehousing labels on each thermocouple, mark type, sheath diameter, wire length and calibration date, and classify storage by application scenario to avoid mixed picking during mold maintenance. Strict incoming inspection of thermocouple spare parts eliminates over 80% of inferior sensor hidden risks from the source, stabilizing daily production operation of hot runner molds.
