Banner Sensors – An introduction to the application of fiber optic sensors

1. Detection of temperature

The optical fiber temperature sensor adopts a polymer temperature-sensitive material that matches the refractive index of the optical fiber and coats it on the outside of two optical fibers that are fused together, so that the light energy is input from one optical fiber to the reflective surface and output from the other optical fiber. Its physical essence is to use the characteristic parameters of the light waves transmitted in the optical fiber, such as amplitude, phase, polarization state, wavelength and mode, etc., which are sensitive to external environmental factors, such as temperature, pressure, radiation, etc. It is a non-contact temperature measurement.

The working principle of the system is as follows: In the low temperature region (below 400°C), the radiation signal is weak, and the system turns on the light-emitting diode (LED) to make the fluorescence temperature measurement system work. The light-emitting diode emits modulated excitation light, which is coupled to the branch end of the Y-shaped fiber through a condenser, and the Y-shaped fiber is coupled to the fiber temperature sensing head through an optical fiber coupler. The fluorescence signal is emitted by the optical fiber and emitted by the excitation light, and the fluorescence signal is exported by the optical fiber and emitted from the other branch end of the Y-shaped fiber through the fiber coupler, and is received by the photodetector. The optical signal output by the photodetector is amplified and processed by the fluorescence signal processing system to calculate the fluorescence lifetime and obtain the measured temperature value. In the high temperature area (above 400°C), the radiation signal is strong enough, the radiation temperature measurement system works, and the light-emitting diode is turned off. The radiated signal is output through the sapphire optical fiber and through the Y-shaped optical fiber, which is converted into an electrical signal by the detector, and the system calculates the measured temperature by detecting the strength of the radiated signal. The end of the optical fiber sensing head is doped with Cr3+ ions to achieve fluorescence emission during light excitation.

Second, the detection of pressure

There are three main types of fiber optic pressure sensors: intensity modulation, phase modulation and polarization modulation.

An intensity-modulated fiber optic sensor is a high-precision sensor that can be used to measure a variety of physical quantities such as displacement, temperature, pressure, and gas concentration. Most of them are based on the mechanical deformation of the elastic element under compression, and the pressure signal is converted into a displacement signal for detection.

3. Detection of liquid level, flow rate and flow rate

In the fields of chemical industry, machinery, water conservancy, petroleum, medical treatment, pollution detection, etc., it is often encountered that it is necessary to measure physical quantities such as liquid level, flow rate, and flow rate in harsh environments. Fiber optic sensors have a unique role to play in these inspections.

The optical fiber is softened by a high-temperature flame and folded in half, and the ends are sintered into a spherical shape. The light is introduced from one end, and at the spherical folded end, a part of the light is transmitted out, and the other part of the light is reflected back and directed to the detector by the other end of the fiber. This makes up a spherical fiber optic level detector. Fiber optic flow meters allow for non-contact measurements, so they do not affect the flow state of the object to be measured. The fluid to be measured can be either a liquid or a gas.

Banner Sensors – An introduction to the application of fiber optic sensors

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