Different ground potential difference between hot runner mold metal frame and control cabinet grounding bar forms closed ground loop after thermocouple outer shielding double-side grounding, producing low-frequency alternating induced current inside shielding layer and leading to periodic cyclic measuring drift on domestic and Synventive multi-channel hot runner matched double-shield thermocouple. Factory building ground grid exists inherent tiny potential difference due to long-distance cable layout and multi-equipment concentrated grounding, when thermocouple outer shielding connects ground both at mold terminal and cabinet terminal, potential difference drives alternating loop current flowing along shielding sleeve, induced current generates new stray alternating magnetic field which continuously cuts internal signal core wire and superimposes periodic fluctuation noise on original measuring signal. Such ground loop interference features regular cyclic temperature floating following power grid frequency change, difficult to eliminate through controller parameter adjustment and frequently puzzles on-site maintenance technicians. Many maintenance operators habitually implement two-end grounding for convenient wiring fixation during rush repair, unconsciously creating ground loop hidden trouble and triggering long-term unstable temperature control problem.
Core improvement measure strictly follows international double-shield wiring standard: cancel mold side shielding grounding connection completely, only realize single-point reliable grounding of outer shielding layer at control cabinet terminal strip, cut off closed ground loop forming condition fundamentally. For old hot runner wiring unable to re-route large scale temporarily, add isolated signal converter between thermocouple wire and controller input terminal to isolate ground potential difference transmission path and restrain loop current generation. Monthly fixed equipment inspection checks grounding mode of all double-shield thermocouple channel by channel, rectifies wrong double-side grounding fault timely and records rectification data into equipment ledger. After grounding rectification, maintain continuous 72-hour running monitoring to confirm periodic drift disappears thoroughly, optimizing grounding construction standard for subsequent new mold wiring project.
