Persistent fixed negative reading deviation that measured temperature always stays lower than real hot runner actual value is common fault of mounted thermocouple on YUDO and domestic precision hot runner, standardized stepwise troubleshooting flow helps maintenance staff quickly locate fault root without blind component replacement and unnecessary mold disassembly. Step one checks probe peripheral installation environment: power off equipment and detach thermocouple outer terminal firstly, observe whether residual carbonized plastic, solidified aged thermal grease and thick oxide dirt wrap front probe outer wall completely; these attachments form heat insulation barrier to hinder heat conduction and directly cause fixed negative deviation, cleaning dirt and replacing matched standard dosage high-temperature grease can eliminate fault if dirt accumulation is root cause. Step two inspect mounting hole matching clearance: excessive oversized installation hole leads insufficient probe close contact with hole bottom metal surface, air layer filled inside clearance reduces heat transfer efficiency and generates stable negative deviation, fill proper amount thermal conductive grease to eliminate air gap for improvement.
Step three verify thermocouple precision via master reference comparative calibration: fix tested probe and certified master probe together inside same idle standard mounting hole for three-point constant-temperature testing, if measured deviation still exceeds allowable tolerance after eliminating installation environmental factor, confirm thermocouple itself has alloy aging and permanent Seebeck coefficient change which needs whole-piece replacement. Step four check cold junction terminal environment: serious terminal oxidation or cabinet local overheating leads cold junction compensation benchmark drift and full-channel fixed deviation, clean oxidized terminal and improve cabinet heat dissipation condition to solve compensation deviation problem. Workshop compiles fault troubleshooting flowchart posted beside control cabinet for maintenance staff reference, lowering blind replacement rate and reducing unnecessary spare part consumption effectively.
