How to Judge If Thermocouple Spare Parts Are Qualified Before Warehouse Storage?

The unqualified counterfeit and inferior thermocouple spare parts occupy a certain market share in the aftermarket, and their direct storage in the workshop inventory will lead to rapid production failure after installation. Establishing a thorough incoming inspection standard before warehousing can pre-screen the defective probes and reduce the mold downtime loss caused by inferior sensors. The inspection method is done by visual observation, testing with multimeter and basic temperature comparison not using large professional calibration instruments.

Visual checking of sheath, wire, connector and welding locations. Check the surface of the probe sheath for scratches, pits, perforations and uneven polishing. Inferior products are made of unpolished rough steel with many microscopic corrosion points that rapidly drift after brief use. Look at the outer braid of the cable: the high temperature shielding wires of qualified products are densely and uniformly woven, without broken wires, and the cheap inferior cables are sparsely woven with numerous gaps. This is to prevent electromagnetic interference. Check the hot junction sensing tip weld: qualified probes are formally made with full smooth welding, no tiny cracks or gaps; inferior probes have incomplete welding, with hidden disconnection dangers. The K/J wire color codes are distinguished according to worldwide IEC standards. The wires with mixed colors indicate abnormal manufacture without unified calibration, and the batch is directly discarded.

Second item: Multimeter continuity and resistance test for screen open and short circuit concealed flaws Set the multimeter to resistance. Connect the two test leads to the positive and negative terminals of the thermocouple plug. Normal undamaged probes have steady resistance value according to wire length. If the resistance value is unlimited, the internal wires are broken and unqualified. If the resistance is almost zero, the positive and negative internal wires are shorted, also rejected. Shake the cable back and forth and measure the resistance. If the resistance value swings considerably, there are concealed broken strands inside the wire, which will fail following heating expansion and cannot be used as spare parts.

3. Easy temperature comparison test to rule out severe drift uncalibrated items. Tie the sensing tip of the thermocouple snugly to the tip of the test probe and heat the connection with a hot air pistol to 300-400 °C using a calibrated standard thermocouple as reference. Connect both probes to two separate channels of the same temperature controller and observe the difference in the reading. When the temperature gap is larger than ±4°C, it is deemed that the test probe has substantial uncalibrated drift and is unqualified, because it cannot match the standards of typical production temperature control precision.

4. Check of bending fatigue for bespoke bent and tiny probes. Randomly select 10% of batch micro thermocouples and bend cable at given minimum bending radius back and forth 100 times, then measure resistance again with multimeter. If open circuit or fluctuating resistance takes place after bending, the multi-strand wire core has poor quality of manufacture and the entire batch is returned to the supplier. This inspection item is for micro probes and flexible transition section thermocouples that tend to bend fracture.

Item 5: Identification of special-grade spare parts and material screening. Review attached material test results for food-grade, medical and anti-corrosion thermocouple batches for sheath alloy composition, oil-free insulation and PTFE coating criteria. Hold warehousing and return items until the whole qualified materials are submitted if certification documents are not provided.

For all five inspection items, stick certified warehousing labels on each thermocouple, type, sheath diameter, wire length and calibration date, and classify storage by application scenario to avoid mixed picking during mold maintenance. Strict incoming examination of thermocouple spare parts to eliminate over 80% of substandard sensor hidden risks from the source, stabilize hot runner molds daily manufacturing operation.