Contents

• Overview of ABB 07SS91 Communication Faults
• ABB 07SS91 Fault Symptoms
• Common Causes of Communication Faults
• ABB PLC Fault Diagnosis Process
• Real Field Case Example
• Repair & Recovery Solution
• Preventive Measures & Best Practices

Overview of ABB 07SS91 Communication Faults

ABB 07SS91 PLC communication faults are typically triggered by wiring errors, grounding problems, or EMI interference rather than hardware failure. This guide provides structured Fault Diagnosis and real-world recovery steps for industrial commissioning scenarios.

ABB 07SS91 PLC Communication Fault Symptoms

• Random I/O module disconnections during runtime
• Communication timeouts after 15–30 minutes
• Analog signal noise or unexpected spikes
• Intermittent loss of connection with engineering software
• System works correctly on startup but fails under operational load

Common Causes of ABB 07SS91 Communication Faults

• Cables installed parallel to high-power lines
• Poor shielding or twisted-pair quality
• Improper grounding or missing reference points
• Electromagnetic interference from inverter drives or motors
• Voltage fluctuations in power supply under load

ABB PLC Fault Diagnosis Process

• Reduce system to minimal configuration
• Disconnect all field wiring
• Test communication bus stability directly at PLC
• Reconnect cables stepwise while monitoring logs
• Observe CPU diagnostics and error counters continuously

ENTER_DIAG_MODE
DISCONNECT_IO
TEST_BUS_STABILITY
RECONNECT_STEPWISE
LOG_ERRORS

Real Field Case: ABB 07SS91

During commissioning of a drying line, the ABB 07SS91 PLC exhibited communication faults after 20 minutes. CPU remained in RUN mode, but several I/O modules dropped offline intermittently. Replacement of the module did not resolve the issue.

Diagnostics revealed communication cables running parallel to inverter power cables (~12 meters), causing EMI interference.

ABB 07SS91 PLC Communication Fault Repair & Recovery

• Re-route communication cables away from power lines
• Use high-quality shielded twisted-pair cables
• Ground shields at a single reference point
• Install ferrite cores where necessary

After implementing these corrections, the system ran 48 hours under full load with zero communication errors.

Preventive Measures & Best Practices for ABB 07SS91

• Follow proper Installation Guide during Setup & Commissioning
• Maintain cable separation from high-power lines
• Verify grounding integrity prior to startup
• Perform staged commissioning and monitor diagnostics
• Keep configuration backups updated for quick recovery

Consistently applying these practices ensures long-term reliability of ABB 07SS91 PLC Controllers and reduces future troubleshooting efforts.