Fiber Bragg Grating Sensing Technology Encyclopedia - FBG FAQ - FBG Sensor FAQ - FBG Demodulator FAQ - FBG Common Application Problem Analysis

This article analyzes the various forces acting on the fiber Bragg grating (FBG) in traditional FBG sensors. Due to the presence of these forces, traditional FBG temperature sensors are unable to separate temperature from stress and strain, resulting in many drawbacks in temperature measurement accuracy.

It also analyzes how OFSCN® capillary seamless steel tube fiber Bragg grating temperature sensor can eliminate the inherent drawbacks of fiber Bragg gratings and achieve temperature-stress-strain separation. The article includes a physical comparison chart.

In the previous article "Basic Requirements for Fiber Bragg Grating Temperature Sensor: Accurate Measurement, High Precision," we have theoretically demonstrated that:

"The OFSCN® capillary seamless steel tube fiber Bragg grating temperature sensor (FBG thermometer) produced by DCYS is a new type of FBG temperature sensor. Its unique structural design effectively eliminates the influence of various external tensile and compressive forces on the fiber Bragg grating (FBG). Therefore, the new OFSCN® capillary seamless steel tube fiber Bragg grating temperature sensor provides accurate and high-precision temperature measurement."

 

Figure 1

In traditional FBG sensors (as shown in Figure 1), the fiber Bragg grating (FBG) is subject to various forces generated by the packaging structure (lateral forces, radial forces, local forces). These forces include, at least:

 

Ⅰ.  Forces generated by various adhesives used in the packaging structure of traditional FBG sensors.

Various adhesives used to fix the fiber Bragg grating (FBG) in traditional FBG sensors, due to their different thermal expansion coefficients from that of the glass fiber, exert different tensile forces and stress-strain effects on the fiber Bragg grating (FBG) during temperature changes.

Since the OFSCN® capillary seamless steel tube fiber Bragg grating temperature sensor (FBG thermometer) does not require adhesives to fix the fiber Bragg grating (FBG), there is no adhesive inside the sensor. It is a true adhesive-free packaging. This impact does not require experimental verification.

 

Ⅱ. Forces exerted on traditional FBG sensors during construction and use.

During the construction and use of traditional FBG temperature sensors, they are inevitably subjected to external forces such as tension and gravity. These forces act on the fiber Bragg grating (FBG) through various means (including the adhesive used to fix the fiber Bragg grating, insufficiently firm outer armor, etc.), causing the fiber Bragg grating (FBG) to experience stress and strain, thereby affecting the accuracy of temperature measurement.

The unique structural design of the OFSCN® capillary seamless steel tube fiber Bragg grating temperature sensor ensures that the fiber Bragg grating (FBG) is essentially unaffected by these forces (here, I say "essentially" because the research of DCYS includes a unique construction process that guarantees the fiber Bragg grating is not affected by these forces). This impact can be verified through experiments.

 

Ⅲ. Forces caused by various non-uniform materials and different expansion coefficients in traditional FBG sensors.

Traditional FBG temperature sensors use relatively thick seamless steel tubes to protect the fiber Bragg grating (FBG). Through the adhesive bonding process, the seamless steel tube, cured adhesive, and fiber Bragg grating form a whole. Due to the different thermal expansion coefficients of stainless steel, cured adhesive, and glass fiber, the fiber Bragg grating (FBG) is easily influenced by forces from other materials during temperature changes, leading to inaccurate temperature measurement.

The OFSCN® capillary seamless steel tube fiber Bragg grating temperature sensor, through its special structural design, keeps the FBG in a naturally relaxed state, ensuring that the fiber Bragg grating (FBG) is not affected by the tensile forces and stress-strain caused by different thermal expansion coefficients of metals. Therefore, it provides accurate temperature measurement. This impact can be verified through experiments.

 

Figure 2

 

These are the three analyses of the forces that may affect the fiber Bragg grating and cause stress and strain. Next, we will begin the experiments to prove that the new OFSCN® capillary seamless steel tube fiber Bragg grating temperature sensor is indeed unaffected by various tensile forces and stress-strain, and provides accurate and high-precision temperature measurement. The experiment will start shortly. Stay tuned!

 

Our philosophy is: "OFSCN®, make optical fiber stronger!"