ABOUT DTS: Examples of Specification Issues

Among the variety of issues related to DTS Specification, two important topics to understand are the following:

Distance Measurement (Range) versus Optical Loss

To date, the industry has seen DTS suppliers specifying performance against range, i.e. the length of the fiber. However, this metric is misleading, because DTS performance is actually affected by its ability to cope with optical losses in the system. System optical losses vary by virtue of the fiber loss (which varies by fiber type and supplier), as well as splices, connectors, and optical switches. Basically, it is insufficient to use measurement distance (range) to specify DTS performance.

Please consider the following example which illustrates the differences in optical loss across different fiber configurations within a DTS deployment.

It is especially eye-opening to see that, once optical loss is factored into the equation, measurement distance then varies greatly based on the selected fiber and the switches, splices, and connectors that are built into the system itself.

Temperature Resolution versus Measurement Time

Temperature resolution and measurement time must be considered carefully, as the two metrics are directly related, influencing each other. These two metrics are affected by the optical loss at a specified distance along the fiber. DTS suppliers frequently quote temperature resolution and measurement time for ambient temperature conditions even though the actual measurement temperature affects these metrics. Temperature resolution should be stated with measurement time against optical loss for a specific measurement temperature.

The key issue is that no standard exists for defining the test and calculation methods that define temperature resolution.