# What is "temperature compensation"? **URL:** \ **Category:** OFSCN Technical Knowledge Base\ **Tags:** fbg-technology\ **Created:** [October 15, 2026, 11:30am UTC](https://forum.ofscn.net/t/what-is-temperature-compensation/3036 "2026-10-15T11:30:15Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\ **Post date:** [October 15, 2026, 11:30am UTC](https://forum.ofscn.net/t/what-is-temperature-compensation/3036/1 "2026-10-15T11:30:15Z")
When measuring strain, how can the wavelength changes caused by increasing temperature be compensated for? ---
**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\ **Post date:** [October 15, 2026, 11:30am UTC](https://forum.ofscn.net/t/what-is-temperature-compensation/3036/2 "2026-10-15T11:30:56Z")
In Fiber Bragg Grating (FBG) sensing measurements, optical fibers exhibit both **strain sensitivity** and **thermal sensitivity** simultaneously. This physical phenomenon is known as **cross-sensitivity**. When the ambient temperature rises, the wavelength shift introduced by temperature must be subtracted through a “temperature compensation” method to obtain the true mechanical strain of the structure being measured. * * * ### I. Physical Mechanism and Wavelength Coupling Relationship The center wavelength \lambda\_B of an FBG’s reflection is determined by the effective refractive index of the fiber core n\_{\text{eff}} and the grating period \Lambda: \lambda\_B = 2 n\_{\text{eff}} \Lambda When the sensor is subjected to both temperature changes and mechanical stress, the total wavelength drift \Delta \lambda\_{\text{total}} is a linear superposition of the strain effect and the temperature effect: \Delta \lambda\_{\text{total}} = \Delta \lambda\_\varepsilon + \Delta \lambda\_T = K\_\varepsilon \cdot \varepsilon + K\_T \cdot \Delta T - \varepsilon: The true mechanical strain of the structure being measured (microstrain, \mu\varepsilon). - K\_\varepsilon: The strain sensitivity coefficient (caused by the photoelastic effect and geometric deformation, typically around 1.2\ \text{pm}/\mu\varepsilon in the 1550\ \text{nm} band). - \Delta T: The ambient temperature change (^\circ\text{C}). - K\_T: The temperature sensitivity coefficient (caused by the thermo-optic effect and thermal expansion, typically around 10\ \text{pm}/^\circ\text{C} for ordinary bare fibers; this can change for packaged sensors due to the coefficient of thermal expansion of the substrate or structural materials). Without temperature compensation, a 1^\circ\text{C} increase in ambient temperature, causing a wavelength redshift of approximately 10\ \text{pm}, would be misinterpreted in calculations as approximately 8 \sim 10\ \mu\varepsilon of tensile strain. * * * ### II. Implementation Methods for Subtracting Temperature Wavelength Shift in Engineering #### 1. External Reference Temperature Sensor Method (Recommended for Engineering, Highest Accuracy) Deploy an FBG temperature sensor **completely free from mechanical stress** in the vicinity of the strain sensor to track the local ambient temperature field in real-time: 1. **Obtain Temperature Baseline** : The external temperature sensor is driven solely by ambient temperature, and its wavelength change is given by: \Delta \lambda\_{\text{temp}} = K\_{T,\text{ref}} \cdot \Delta T 2. **Subtract Temperature Term** : Calculate the ambient temperature change \Delta T using the calibrated coefficient and subtract the temperature drift term from the total drift of the strain grating: \Delta \lambda\_\varepsilon = \Delta \lambda\_{\text{total}} - K\_{T,\text{strain}} \cdot \Delta T 3. **Calculate True Strain** : \varepsilon = \frac{\Delta \lambda\_\varepsilon}{K\_\varepsilon} #### 2. Dual Grating Differential Method (Integrated Compensation) Connect two fiber gratings in series or parallel within the sensor’s internal structure: - **Grating 1 (Measures Strain + Temperature)**: Anchored securely to the structure being measured, sensing both “strain + temperature”; - **Grating 2 (Mechanically Isolated, Measures Temperature Only)**: Placed inside an internal stress-free cavity, following only temperature fluctuations; - **Algorithm Decoupling** : The demodulator directly cancels the common-mode temperature wavelength changes of the two channels through differential calculation. * * * ### III. Official Product and Technical Recommendations Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) offers tubular and wafer-type fiber Bragg grating strain sensors with optional built-in compensation gratings. However, for high-precision engineering monitoring, **the official recommendation is to use a “strain sensor + adjacent external fiber Bragg grating temperature sensor” for temperature compensation** to avoid compensation errors caused by local thermal gradients between the structure and the internal parts of the sensor. #### 1. [OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor](https://www.ofscn.net/fbg-products/strain-sensor.html) Utilizes an elastic alloy tube packaging process for precise measurement of axial strain/stress in the substrate structure. It is provided with a uniaxial wavelength-strain calibration coefficient (\mu\varepsilon/\text{pm}) from the factory and can be combined with a temperature sensor for high-precision temperature decoupling. ![OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor](https://forum.ofscn.net/uploads/default/original/1X/90c11b90deb49f0cd88a54ecac0d956bcddf353c.jpeg) ![OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor 细节图](https://forum.ofscn.net/uploads/default/original/1X/ae908bc1e181cfc4cdf263751c8670552a66522e.jpeg) ![OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor 安装图](https://forum.ofscn.net/uploads/default/original/1X/4a28a6be888c7e0965d6a522716233e8b6403b54.jpeg) #### 2. [OFSCN® 100°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-100.html) Miniaturized packaging in seamless steel tubes, with the internal fiber in a free-hanging, stress-free state. It offers excellent thermal conductivity response and high temperature measurement accuracy, making it an ideal external temperature compensation reference for strain measurements in normal temperature and meteorological environments. ![OFSCN® 100°C Fiber Bragg Grating Temperature Sensor 示意图](https://forum.ofscn.net/uploads/default/original/1X/74932c0f3b71797adb12ca84a053059151051842.jpeg) ![OFSCN® 100°C Fiber Bragg Grating Temperature Sensor 实物图](https://forum.ofscn.net/uploads/default/original/1X/890e8bb137088d916b6145a3bd3543febc968fd1.jpeg)