The mid-span temperature cycling test is designed to evaluate how environmental changes impact unopened buffer tubes in loose tube cables. This is particularly important for cables used in mid-span entries that are stored in pedestals, closures, or similar devices.
Purpose
The test measures the change in attenuation caused by thermal contraction and expansion of unopened buffer tubes. This is crucial for ensuring the reliability and performance of fibre optic cables in various environmental conditions.
Applicability
Cable Types: This test applies to loose tube outdoor cables with buffer tubes of 2.0 mm outer diameter (OD) or larger. It can also be adapted for other outdoor cables based on agreements between the manufacturer and the customer.
Installation Scenarios: The method is suitable for evaluating cables in generic simulation assemblies or actual installations like pedestals and closures.
Sample Preparation
Length: The cable sample must be long enough to enter and exit the climatic test chamber, cover the exposed buffer tube section, and provide a coupling length of cable. At least 6 meters of cable at each end of the exposed section is required to prevent movement during the test.
Fibre Selection: At least one fibre of each type per loose tube should be selected for testing.
Apparatus
Generic Assembly: A generic apparatus is used to represent the cable installation. This ensures that the test results are independent of specific closure designs.
Storage Configuration: The exposed buffer tubes should be stored in loops within a basket or area with dimensions between 75 mm to 300 mm in width and 200 mm to 600 mm in length. The minimum bend radii of the cable and buffer tubes must not be violated.
Climatic Chamber: The chamber should meet specified standards to ensure accurate temperature cycling.
Testing Procedure
Cable Preparation: Follow the manufacturer's instructions for preparing the cable, if available.
Exposing Buffer Tubes: Open the cable to expose the buffer tubes, removing sheaths and cutting strength members if present.
Installation: Install the cable with exposed buffer tubes on the generic assembly or specified closure, then place the assembly in the climatic chamber. Ensure buffer tubes are loosely coiled and straightened during coiling.
Attenuation Measurement: Measure the initial attenuation of the specified fibres.
Temperature Cycling:
Use the specified temperature range (default: -40°C to +70°C).
Soak times: 14 hours for the first hot soak and 3 hours for subsequent cycles.
Perform at least 2 cycles.
Final Measurements: Measure the attenuation at low and high temperatures of the final cycle and at the final ambient temperature. Calculate the change in attenuation from the initial value.
Requirements and Specifications
Attenuation Change: The maximum change in attenuation for single-mode fibres at 1550 nm is specified in the detailed specification. Criteria for multimode fibres are currently under study.
Details to Specify: The detailed specification should include cable type, number of tubes, sample length, stored loop size deviation, cycling temperature range, number of cycles, and soak times. If testing actual closures or similar devices, complete details of the apparatus and test criteria must be specified.
This test is critical for ensuring the durability and performance of fibre optic cables in varying environmental conditions, providing a reliable measure of how these cables will perform in real-world scenarios.