If the temperature profiles of your processes and assets are key indicators, then you’ve most likely been using a variety of measurement methods in the past, such as spatially distributed sensors or thermal cameras.
Yokogawa’s optical fibre temperature sensing systems – in which the data acquisition station (DTSX series) is the central component – are an attractive alternative. They allow you to capture the temperature profiles of your processes and assets directly and continuously, and integrate the measurement technology into your existing automation environment with just one Ethernet interface. This opens up new opportunities and hence new applications like liquid level measurements via vessel surfaces, temperature monitoring in reactors or monitoring for mechanical component failure.
What Is Distributed Temperature Sensing?
Distributed temperature sensing (DTS) measures temperature distribution over the length of an optical fibre cable using the fibre itself as the sensing element. Unlike traditional electrical temperature measurement (thermocouples & RTD), the length of the fibre optic cable is the temperature sensor. Distributed temperature sensing can provide thousands of accurate and precise temperature measurements over a long distance. Compared to traditional electrical temperature measurements, distributed temperature sensing represent a cost effective method for obtaining accurate and high resolution temperature measurement.
How Does It Work?
Yokogawa DTSX3000 measures temperature and distance over the length of an optical fibre using the Raman scatter principle. A pulse of light (laser pulse) launched into an optical fibre is scattered by fibre glass molecules as it propagates down the fibre and exchanges energy with lattice vibrations. As the light pulse scatters down the fibre optic cable, it produces stokes signal (longer wavelength) and anti-stokes (shorter wavelength) signal, of which both signals shifted from the launch of the light source. The intensity ratio of the two signals components depends on the temperature at the position where the Raman scatter is produced. This temperature can thus be determined by measuring the respective intensities of the stokes and anti-stokes signals. Furthermore, part of the scattered light, known as the backscatter, is guided back towards the light source. The position of the temperature reading can thus be determined by measuring the time taken for the backscatter to return to the source.