What Is Distributed Temperature Sensing?

Distributed sensor is a multi-sensor data processing method based on distributed computer. In a distributed sensor network, each sensor can independently process its own information, provide a large amount of data, further obtain the classification characteristics of the target, and avoid the severe performance degradation caused by electronic countermeasures to a single sensor system.

With the development of modern technology, the first-generation systems based on independent sensors can no longer meet many requirements in reality, such as system persistence, low observability, target classification and recognition, and so on. Multi-sensor network, which can provide a large amount of data, can further obtain the classification characteristics of the target, and avoid the serious performance degradation caused by electronic countermeasures to a single sensor system. So distributed multi-sensor networks have aroused great interest.

The distributed sensor network mainly involves the following:

1. Structural design of multiple sensors

2. Local processing capacity and data communication method required for a single sensor

3. Data fusion process

4. Performance estimation for multi-sensor layouts

5. Online management / control of multi-sensor networks

6. The guarantee of software and hardware must take into account the ability to grow, restructure, and relocate ^[1]

   along with

   Assume that the external input signal is z and the sensor output signal y is input to the local detector. The local detector uses the corresponding decision criterion to make a local decision u based on the result of y. The data fusion center uses the received decision u of each local detector as its observation value. Because the observations of each sensor are statistically independent, and assuming that there is no data interaction between the local detectors, the local decision-making is also statistically independent. According to the classical reasoning theory, the fusion center can obtain a joint probability density function based on multi-sensor decision, and then make a final decision u according to certain criteria. That is, a distributed multi-sensor system includes a series of sensor nodes and corresponding processing units, and a communication network connecting different processing units. Each processing unit is connected to one or more sensors, and each processing unit and the sensors connected to it are called clusters. The data is transmitted from the sensor to the processing unit connected to it, and the data is integrated at the processing unit. Finally, the processing units are fused with each other to obtain the best assessment of the environment.

   Distributed sensor networks are roughly divided into three categories according to different structures. The first category is centralized, as shown in Figure 1.

   Optical fiber distributed sensing technology refers to the technology that uses the relevant physical characteristics of optical fibers to monitor the space and time behavior of the measured field in real time. This technology has important application value for the effective monitoring of the stress field distribution and temperature field distribution of large structures such as dams, bridges, and aircraft.

   Basic principles of distributed sensors

   Optical fiber distributed sensors are generally based on the backscattering mechanism or the forward scatter mechanism, of which the backscattering type has a wide range of practical significance. The figure shows a simple physical model of a fiber-optic distributed sensor. When light passes through the dotted box area of the diagram, energy is distributed in three ways:

   A part of the energy continues to propagate along the transmission channel;

   A part of the energy is absorbed or lost or scattered outside the optical fiber during transmission;

   A part of the energy is coupled to the receiving channel and returns to the end face at the speed of light. This part of the energy can be detected by the photodetector. This part of the energy returned by the receiving channel reflects the average value of the measured field M (L) from L to L + dL.

   Distributed sensor typical system

   1.Intrinsic fiber-optic distributed sensor

   The intrinsic optical fiber distributed sensor generally works based on the basic loss or scattering mechanism of a single optical fiber distributed along the length. The figure shows the basic system model of this type of distributed sensor.

   System Block Diagram

   OTDR, FWCM, OFDR and other technologies are the core technology of intrinsic optical fiber distributed industrial sensors. Such distributed sensors can effectively monitor the stress and temperature distribution of the entire fiber, and can also detect the location of the fault point of the fiber.

   2. Quasi-distributed fiber optic sensors

   The basic physical model of a quasi-distributed fiber optic sensor is shown in the figure. Compared with the intrinsic optical fiber distributed sensor, the quasi-distributed optical fiber sensor adds a discrete sensing unit distributed along the length of the optical fiber, and mainly monitors the field parameter value at the position of the sensing unit. The resolution of the points is greatly improved, but the loss is more obvious. Time division multiplexing (TDM), frequency division multiplexing (FDM), and wavelength division multiplexing (WDM) are technologies commonly used in quasi-distributed sensors. ^[2]