Author: Thomas Nguyen – Senior Commissioning Engineer, rotating machinery instrumentation

During a commissioning session at a hydroelectric plant, we observed intermittent signal loss on a Bently Nevada 131170-01 dynamic data cable. The cable connects accelerometers and proximity probes to the 3500 vibration monitoring system, and reliability is critical.

Symptoms Observed

• Vibration readings occasionally dropped to zero for 2–5 seconds

• No alarms triggered, but trending data gaps appeared

• Issue was isolated to a single cable; all other cables functioned normally

• Occurrence increased when the probe cabinet door was opened or bumped

Initial Checks

1. Cable Continuity: Confirmed no breaks in the conductor.

2. Module Functionality: Verified 3500 module operation; no faults.

3. Environmental Inspection: No water ingress, temperature within specification.

Initial results suggested the cable itself was functional, but the intermittent nature pointed toward the connector or EMI susceptibility.

Root Cause Analysis

• Connector pins at the panel end were slightly loose due to vibration-induced torque.

• Movement caused temporary contact loss, resulting in short signal interruptions.

• Minor oxidation at the contacts worsened the effect over time.

• EMI from nearby power cables amplified the impact during transient events.

Corrective Actions

1. Connector Re-Seating: Removed and reinserted the connector to ensure full engagement.

2. Contact Cleaning: Applied contact cleaner to remove oxidation.

3. Strain Relief Installation: Added additional cable clamps to reduce movement.

4. Routing Adjustment: Separated cable from high-current AC lines.

Post-intervention, the cable operated without interruptions for the remainder of commissioning and during subsequent start-up tests.

Key Takeaways

• Even high-quality dynamic data cables like the 131170-01 can exhibit intermittent failures if connectors are not properly secured.

• Periodic inspection and cleaning of connectors are essential in vibration-prone environments.

• Cable routing and strain relief are crucial for maintaining signal integrity.

• Always isolate environmental and installation factors before replacing hardware.

The Bently 131170-01 remains reliable if installed with proper attention to connector integrity, routing, and environmental protection.

— Thomas