Mitsubishi Warns of Aging Fiber Optic Cables in MELSECNET Systems

Industrial communication networks relying on fiber optic cables may face unexpected reliability issues as these critical components have a limited lifespan. Mitsubishi Electric System & Service Co., Ltd. has issued an important technical notice highlighting aging risks in fiber optic cables used for its MELSECNET networks, particularly in long-running systems.

Fiber Optic Cable Aging: A Hidden Operational Risk

The company's "Sales & Technical News No.14-004" bulletin warns that fiber optic cables gradually degrade over time, especially when exposed to harsh environments. This aging process can increase signal transmission loss and potentially lead to cable fractures, resulting in communication failures. For facilities depending on MELSECNET networks for data transmission and equipment control, such deterioration poses significant operational risks.

Identifying Vulnerable Cable Models

The notice specifies two categories of MELSECNET fiber optic cables susceptible to aging:

• SI Cable Series: Includes Type A (orange, CA9003, launched 1985), Type AN (orange, CA7003, 1993), Type AQ (green, 1993), Type AS (yellow, DL-72ME, current product, 1995), Type QH (light blue, 2001), and Type QL (purple, CA7003, current product, 2005). Types A, AN and AQ have been discontinued.
• GI Cable Series: Includes Type A (orange, CA9103, 1985), Type AG (light blue/black, 1993), and Type SG (black, DL6-CP, current product, 1998). Types A and AG are no longer in production.

Facilities using these cables, particularly older models, are advised to conduct immediate inventory checks to assess potential vulnerabilities.

Environmental Factors Accelerate Degradation

While fiber optic cables typically have a 20-year design life, Mitsubishi identifies several environmental conditions that can significantly shorten operational lifespan:

• Water immersion causing internal corrosion
• Mechanical stress from impact, compression, bending or vibration
• Extreme temperature exposure
• Chemical contact with oils or corrosive substances
• Prolonged UV, ozone or salt exposure

Regular visual inspections for surface cracks, discoloration or hardening are recommended, along with protective measures like conduit installation or environmental controls.

Proactive Maintenance Recommendations

Mitsubishi emphasizes periodic transmission loss measurements as the most reliable method for detecting cable degradation. Significant increases in signal loss should trigger replacement considerations.

For cables exceeding their 20-year service life or operating in harsh conditions, preemptive replacement is advised regardless of current performance. This preventive approach helps avoid unplanned downtime that could disrupt production operations.

When replacing cables, compatibility with existing network specifications must be maintained, and installations should be performed by qualified technicians to ensure proper system integration.