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Component type fiber optic temperature sensor

Fluorescent fiber optic temperature sensors are currently the most advanced instrument based temperature measurement systems.

Fiber optic temperature sensors can be divided into two types: element type and transmission type.

The former uses optical fibers as sensitive components, while the latter uses optical fibers as transmission lines.

The working principle of component type fiber optic temperature sensor

The fiber optic temperature sensor diagram is a sensor that utilizes the variation of optical vibration amplitude with temperature.

The diameter and refractive index of the fiber core vary with temperature, and the light propagated in the fiber is dispersed due to uneven routing, resulting in changes in the amplitude of the light.

It is a sensor that utilizes optical polarization plane rotation.

The polarization plane of a single-mode fiber rotates with temperature, and the amplitude change is obtained through a polarizer.

It is a sensor that uses optical phase change. The length, refractive index, and core diameter of a single-mode fiber vary with temperature, and the phase change of light propagation in the fiber can be obtained using an interferometer. The basic system used for detecting phase changes is the Mahzard interferometer. The basic system for measuring phase change is that in this instrument, the light from the signal fiber is mixed with a stable reference beam. Due to the influence of measurement parameters on the signal fiber, the phase of the optical signal propagated by the signal fiber changes, resulting in interference between two light columns. In principle, a suitable phase detector can be used to detect small changes, while a stripe counter can be used to detect large changes.

The reference beam can be shifted through or without frequency depending on the application state, and the frequency shift of light is usually completed by the Bulger box. The layout of the interferometer is very strict. One of the main difficulties is that the polarization plane of light will be scattered after passing through the fiber. In this way, sometimes interference fringes cannot be observed due to the orthogonal polarization of the reference beam and the signal beam. Fiber optic thermometer is a very sensitive instrument. If the reference optical path is stable, a small portion of the temperature can be measured. The above-mentioned fiber optic temperature sensors have their own advantages and disadvantages, but the subsequent fiber optic temperature sensors are in a leading position in practical applications. The working principle of a transmissive fiber optic temperature sensor. The transmission fiber optic temperature sensor is a type of fiber optic temperature sensor composed of a thermal sensor, LED, and optical fiber.

A fiber optic temperature sensor that converts temperature into optical transmittance and reflectivity. Usually, transmission sensors can obtain a large amount of optical flux in optical fibers, so multi-mode optical fibers are used. The application prospects of fiber optic temperature sensors in various temperature sensors are not yet clear, but they have broad application prospects in medical, environmental protection, industrial automatic control and other fields. At present, there are two main types of fiber optic temperature sensors: radiation (infrared) fiber optic temperature sensors and semiconductor absorption fiber optic temperature sensors. The radiation (infrared) fiber optic temperature sensor consists of a fiber optic coupler, a transmission fiber optic, and a photoelectric converter. The principle and structure of the radiation fiber optic temperature sensor, as shown in the following figure, utilize the coupling and transmission characteristics of the fiber optic to mainly transmit the radiation energy on the surface of the measured object (related to the surface temperature of the measured object) to the photoelectric detector, and convert it into electrical energy output.

1. Optocouplers are the main components that determine the sensitivity of sensors, so the efficiency of optocoupling is a very important issue. The coupling efficiency of optical fibers is directly related to their numerical aperture. In order to improve the sensitivity of sensors, large numerical aperture optical fibers must be used. However, the numerical aperture of optical fibers directly affects the performance indicators of sensor distance coefficients, so comprehensive consideration is needed. Transmittance is the main parameter of transmitting fibers.

In order to improve the transmittance, the main method for fixing materials is to increase the diameter of the optical fiber and shorten its length. Experiments have shown that when the material, structure, and coupling method of optical fibers are fixed, transmittance is a stable parameter. However, when optical fibers use different materials, diameters, and lengths, their transmittance varies.

The main function of this section of the photoelectric converter is to convert optical information into electrical output and display. Photoelectric conversion elements typically use silicon photocells, PBS, or other detectors. Due to the large area of the photosensitive element in infrared detectors, direct coupling with optical fibers can achieve the efficiency of the photosensitive element. The efficiency of a typical direct outlet coupling can reach over 85%.

In addition to direct coupling between the output end of the fiber optic and the detector, modulation disk coupling can also be used. The semiconductor fiber optic temperature sensor is shown in the following figure. The cutting fiber of the fiber optic temperature sensor is installed in a thin steel pipe. There is a semiconductor thermosensitive film between the two sides of the fiber (such as GaAs or InP), and the transmitted light intensity of the semiconductor thermosensitive film varies with the measurement temperature. Therefore, when a constant light intensity is input at one end of the optical fiber, the transmission capacity of the semiconductor temperature sensor varies with temperature, and the light intensity received by the receiving element at the other end of the optical fiber also changes with the measured temperature. Therefore, the sensor position can be measured by measuring the output voltage of the receiving element

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