VFL (visual fault locator) are indispensable tools in fiber optic network maintenance. They provide a quick and cost-effective way to detect faults, bends, breaks, or poor connections in optical fibers. However, how to use a visual fault locator is simple; many technicians—especially those new to fiber optics—often make critical errors during testing that can lead to misdiagnosis, network inefficiencies, or even safety hazards.
In this blog, we’ll explore the most common mistakes to avoid when using a VFL to test fiber optic cables, and how to ensure accurate and safe testing every time.
Preparation of Fiber testing
1. Using a VFL on Active Fiber Links
Mistake: Applying a VFL to a live fiber that is presently transmitting data signals
Why It’s a Problem: VFLs typically use red laser light at 650nm, which does not combine well with the wavelengths used for data transmission (typically 1310nm, 1490nm, or 1550nm). Applying a VFL to a live system can not only interfere with data transmission but may also damage active optical equipment.
Solution: Always disconnect the fiber from live equipment before connecting the VFL. Verify that the link is inactive and safe for testing.
2. Improper Connector Cleaning
Mistake: Connecting a VFL to a dirty fiber optic connector.
Why It’s a Problem: Dirt or debris on the connector can scatter or block the laser light, resulting in misleading results. In some cases, it may even damage the VFL’s output port.
Solution: Clean all fiber connectors with approved cleaning tools and solutions before testing.
3. Exceeding Recommended Length Limits
Mistake: Using a VFL on long-distance links beyond its effective range.
Why It’s a Problem: VFLs are designed for short-range fault location (typically up to 5 km). Beyond this range, the laser light attenuates and may not be visible even if a break exists, leading to false assumptions that the link is fault-free.
Solution: Use VFLs only for short-distance troubleshooting. For longer links, rely on an OTDR (Optical Time Domain Reflectometer) for precise fault localization.
Fiber testing
1. Ignoring Safety Precautions
Mistake: Looking directly into the fiber end or VFL output.
Why It’s a Problem: VFLs use visible red lasers that can cause eye injury if viewed directly. Even low-power lasers can cause long-term damage to the retina.
Solution: Never look directly into the fiber or the VFL port. Always assume that a fiber may be live, and wear appropriate laser safety glasses when necessary.
2. Using the Wrong Adapter or Interface
Mistake: Using an incompatible or loose connector interface.
Why It’s a Problem: Poor connector fit can result in laser leakage or false negatives, affecting test accuracy.
Solution: Ensure the VFL is equipped with the correct adapter sleeve (e.g., 2.5mm for SC/FC/ST or 1.25mm for LC connectors), and make sure the connection is firm and clean.
3. Applying Excessive Bending Force
Mistake: Use the VFL to detect microbends by bending the fiber firmly.
Why It’s a Problem: While microbends can cause light leakage, bending a fiber too tightly may cause permanent damage or breakage.
Solution: Handle fibers with care, and never exceed the minimum bend radius specified by the manufacturer.
Fiber testing report
Misinterpreting Results
Mistake: Mistaking a connector’s red light leak for a fiber malfunction.
Why It’s a Problem: Connectors, bends, or even tight splices may leak light visibly, but this doesn’t always indicate a fault. This can lead to unnecessary maintenance or cable replacement.
Solution: Recognize that light leakage isn’t always a bad thing. Combine VFL testing with inspection microscopes or power meters for a more accurate assessment.
Conclusion
VFL testing remains one of the most straightforward and effective methods for identifying visible faults in fiber optic cables. However, improper use can lead to incorrect diagnoses, safety hazards, and unnecessary downtime. By avoiding these common mistakes, technicians can ensure safer, more reliable, and more efficient troubleshooting operations.
If you’re looking for a high-quality, rugged, and user-friendly VFL visual fault locator, Baudcom offers a full range of fiber optic testing tools designed for field use and laboratory environments. Feel free to contact us to learn how to use a visual fault locator or get a quote.
