A 400-ton hydraulic press keeps triggering E-Stop during the clamp phase, but the operator panel shows no button pressed and all guards are closed. Diagnose the fault from PLC diagnostics and wiring data.
200 XP
📋 Scenario
Production has stopped 4 times in 2 hours — always during clamp descent between 60% and 80% of stroke. The E-Stop circuit is dual-channel (IEC 62061 SIL 2). Channel A reads open intermittently. Channel B stays healthy. The press is 7 years old. The E-Stop circuit was rewired 3 months ago after a panel upgrade.
🚨 Active Alarms
SA001 — Safety Relay CH-A Open (Category 4)
SA002 — E-Stop Loop Fault — Clamp Zone
P_FAULT_003 — Press cycle aborted at 67% stroke
📡 Sensor / I/O Status
FALSE
TRUE
TRUE
TRUE
38
310
TRUE
67%
TRUE
FALSE
FALSE
🔌 Wiring NotesE-Stop rewired 3 months ago. Cable route runs along press frame — 2.4m unsupported span from terminal block to safety relay.
✓ Solution & Explanation
Root cause: loose_crimp_ch_a
Steps
Root cause: loose or faulty crimp terminal on Channel A, introduced during panel rewire 3 months ago
Why 60-80% stroke: maximum hydraulic force and frame vibration occurs at this point — enough to momentarily open a marginal crimp
Immediate fix: check crimp terminal on CH-A at both ends (panel-side and safety relay), torque all terminals, re-crimp if deformed
Verify: run press in slow jog mode through 60-80% range while monitoring CH-A continuity with handheld meter
Long-term: re-route cable away from frame vibration path, add cable support at 600mm intervals, document in maintenance log
Validate: safety relay test per IEC 62061 after repair, full stroke test x10 without fault
Dual-channel E-Stop is designed so a single fault (one channel opening) triggers the safe state. The fact that only CH-A faults, always under mechanical load, and only since the rewire 3 months ago points conclusively to a wiring fault introduced during that rewire. A crimp that passes a static pull test can still open under vibration — this is a common post-maintenance fault mode.