The measured insertion loss (IL) and return loss (RL) values of the product are not as good as before? Is there a problem with the measuring equipment?
Obviously things have changed. If it is not a measurement device, it must be a product or a measurement setup. Over time, the production process can become a familiar but potentially boring routine. Operators can become meticulous when cleaning, use polishing films for too long, or even take shortcuts. Ultimately, this causes huge losses and reduces production.
Let's say you've eliminated that possibility by doing a thorough clean of the program and resetting it to strict production guidelines. But the problem still exists. At this stage, a "gold standard" product is useful - carefully keep a "known" example of the best product you've ever produced, and record very good IL and RL values. Re-measure this gold standard product using your current rigorous procedures. Should still look good.
Optical cable test
I've written that IL and RL testing alone cannot be done on a product. (Read more on this topic here.) Remember that we are measuring fiber optic connector loss and that the device under test (DUT) needs to be connected to a test fiber optic cable (also known as a jumper cable, reference cable, or test lead). It is important to note that the quality and condition of the test cable is directly related to the IL and RL measurements of the product under test.
Assess the quality and condition of test cables
First, make sure the test fiber optic connector is clean. Next, double-check to make sure they're in good shape. Remember that neither fiber optic connectors nor splice sleeves last forever. They degrade with use, not just scratches and dents. Sliding surfaces are worn. As the fit becomes loose, alignment can be affected.
How many matings can be done before replacing the test connector? There is an exact number that can be used. However, due to the type and quality of the connectors and the skill of the operator, it is difficult to give an exact answer.
Assume that replacing all test cables and couplers will restore your gold standard to its previous good measurements. This is useful information. Take a moment to determine approximately how many times these particular test cables were paired. What day did you arrive? Now you know how many couplings are too many!
Identify usage limitations and establish replacement schedules
I recommend that you set your usage limit to half of the above number. Weigh ongoing replacement costs against the time required to replace test cables. How does this compare to the cost if the product goes to failure?
Mechanisms for frequent monitoring of gold standard equipment may help determine test cable usage limitations. (Don't do this too often, or your gold-standard fiber optic cable will degrade.) This form of monitoring will help you develop a reasonable replacement schedule.
Here's a helpful tip: If you're using a Viavi MAP/PCT system, it can track meter patch cord usage and warn you when fiber optic cables exceed user-defined limits. If you use another test instrument, I recommend checking that it can track usage and provide such warnings.
Implement Robust Process Control
Test cables do have a limited lifespan. Lifespan will vary. For example, improper mating or cleaning can damage the end face of the test cable, making it unusable.
Implementing strong process controls will greatly extend test cable life and determine when test cables need to be replaced. As mentioned above, I recommend:
(1) Frequently check the end-to-end connection of the optical cable under test
(2) Develop good cleaning habits
(3) Troubleshooting with "well-known" optical cables
If you see reduced IL/RL results for fiber optic cable assemblies, it is recommended that you first establish tight production controls. Next, follow the guided implementation steps in this article to assess the condition of your test cables, track usage, and plan for a reasonable replacement.
