Distributed Temperature Sensing (DTS)

Distributed Temperature Sensing (DTS) utilizes common optical fibers, typically spanning several kilometers, to serve as linear temperature sensors. This approach provides a spatially well-resolved temperature profile along the entire length of the sensor cable. DTS is based on either Raman or Brillouin scattering to obtain precise temperature data. A laser pulse is periodically launched into the fiber generating weak back-scattered light returning to the interrogator, where it is continuously analyzed. The position of the temperature reading is identified by measuring the arrival time of the returning light, analogous to radar echo analysis. This method is referred to as Optical Time Domain Reflectometry (OTDR).


Temperature Monitoring using Raman-based DTS Systems

In Raman-based DTS systems, the intensity ratio of Raman anti-Stokes and Stokes signals is used as a measure of temperature along the optical fiber. Notably, the Raman anti-Stokes signal is much more temperature-dependent than the Raman Stokes signal serving as a reference.

AP Sensing uses Raman-OTDR technology with tremendously enhanced performance by the proprietary code correlation (CC) technology. The implementation of CC-OTDR introduces several advantages: It clearly increases the signal-to-noise ratio and thus temperature resolution and distance range, and it facilitates the use of low optical power, effectively mitigating concerns related to potential laser degradation. Furthermore, a patented single-receiver design provides superior stability of relative amplitudes of both signals and thus temperature.

A noteworthy outcome of this approach is the exceptional system reliability achieved. The system proves robust against the adverse effects of strain, a factor that commonly leads to anomalous readings.

Click here to learn more about our Raman-based DTS system, the N45-Series

Video: How Does DTS/Raman Reflectometry Work?


Temperature Monitoring using Brillouin-based DTS Systems

In Brillouin-based DTS systems, the crucial variable measured is the frequency shift of the backscattered Brillouin signal. This frequency, known as the Brillouin frequency, responds to alterations induced by the temperature.

AP Sensing uses Brillouin-OTDR technology. Care has to be taken to avoid strain on fibers by proper loose tube designs because the Brillouin-frequency is cross-sensitive to strain. A major advantage of Brillouin-OTDR is the clearly stronger back-scattering signal, which enables larger distance ranges.

Find out more about our long-range DTS system, the N62-Series