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This article explains the concept of temperature resolution (temperature accuracy) of FBG sensors from a sensitivity perspective. It refers to the minimum temperature change that FBG sensors can measure when used with demodulation equipment. This data determines the minimum accuracy of FBG temperature sensors (which is related to the packaging of the sensors and the demodulation accuracy of the FBG demodulator).

Additionally, it introduces the minimum resolvable temperature values of two types of OFSCN® Capillary Seamless Steel Tube Fiber Bragg Grating Sensors under conventional FBG demodulator conditions.

1. Concept of Temperature Sensitivity of Fiber Bragg Grating Temperature Sensors

The temperature sensitivity of FBG temperature sensors is sometimes referred to as the resolution, accuracy, or temperature sensitivity of the sensors.

Specifically, under the same FBG demodulator conditions, the temperature sensitivity (resolution, accuracy) of each FBG temperature sensor is different. This data is mainly determined by the reflection wavelength of FBG and the inherent characteristics of fiber‘s glass. Sometimes, it is also related to the sensor's packaging method, as different packaging methods can enhance or reduce the sensitivity of the FBGs.

Figure 1

Figure 2

2. Temperature Sensitivity (Testing Accuracy) of OFSCN® Capillary Seamless Steel Tube Fiber Bragg Grating Temperature Sensors

For the commonly used single-ended OFSCN® Capillary Seamless Steel Tube FBG Temperature Sensors by DCYS (refer to Figure 1 and Figure 2), around the 1550nm wavelength, the sensitivity (resolution) of the FBG temperature sensors is approximately 11 picometers per Celsius degree (refer to Figure 3).

In other words, when the temperature of the measured object or the environment changes by 0.1 degrees Celsius, the reflection wavelength of the FBG temperature sensor changes by 1 picometer. Therefore, we can say that the sensitivity (temperature resolution) of the FBG temperature sensor is 0.1 degrees Celsius.

Figure 3

3. Temperature Sensitivity (Testing Accuracy) of Enhanced Fiber Bragg Grating Temperature Sensors

For the OFSCN® Capillary Seamless Steel Tube FBG Sensors (which can function as temperature sensors, stress sensors, or strain sensors), with the double-ended fixation of the FBG, the sensors reflect the material characteristics of the stainless steel seamless tube. Due to the higher thermal expansion coefficient of stainless steel compared to glass fibers, this packaging structure enhances the sensitivity of the FBG temperature sensors.

Figre 4

Similarly, around the 1550nm C-band, the sensitivity (temperature resolution) of the FBG temperature sensors is approximately 28 picometers per Celsius degree (refer to Image 5). In other words, when the temperature of the measured object or the environment changes by 0.035 degrees Celsius, the reflection wavelength of the FBG temperature sensor changes by 1 picometer. Therefore, we can say that the sensitivity (temperature resolution) of the FBG temperature sensor is 0.035 degrees Celsius.

Figure 5

It should be further emphasized that the mentioned OFSCN® Capillary Seamless Steel Tube FBG Temperature Sensors (single-ended or double-ended) have temperature sensitivities (resolution, accuracy) of 0.1 degrees Celsius and 0.035 degrees Celsius. This statement is more related to, or limited by, the FBG demodulator rather than the sensors themselves.

If a demodulator with a higher resolution is used, capable of detecting wavelength changes below picometers, the sensitivity or resolution of the FBG temperature sensors defined here would correspondingly increase. For example, if your FBG demodulator can detect a wavelength change of 0.1 picometers, the temperature sensitivity (resolution, accuracy) of the two mentioned FBG sensors would become 0.01 degrees Celsius and 0.0035 degrees Celsius.

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