Why must every sensor undergo wavelength-to-physical-quantity testing before leaving the factory?
Before leaving the factory, every Fiber Bragg Grating (FBG) sensor must undergo wavelength-to-physical-quantity testing, also known as calibration, to ensure accurate and reliable measurements. Here’s why:
- Fundamental Principle of FBG Sensing: FBG sensors operate by reflecting a specific wavelength of light (Bragg wavelength), which shifts in response to changes in physical quantities such as temperature, strain, or pressure.
- Establishing the Conversion Relationship: To convert these measured wavelength shifts into actual physical values (e.g., degrees Celsius, microstrain), a precise mathematical relationship must be established. This relationship is not universal and can vary slightly between individual sensors due due to manufacturing tolerances, material properties, and sensor packaging.
- Ensuring Accuracy and Repeatability: During calibration, each sensor is subjected to known, controlled changes in the physical quantity it is designed to measure (e.g., a specific temperature range for a temperature sensor, or a controlled strain range for a strain sensor). The corresponding wavelength shifts are meticulously recorded.
- Deriving the Calibration Formula: From this data, a unique calibration formula (often a polynomial equation) is derived for that specific sensor. This formula allows the FBG interrogator to accurately translate future wavelength shifts into the correct physical quantity readings. Without this individualized calibration, the sensor’s readings would be arbitrary and lack precision.
For example, our OFSCN Alloy Tube Packaged Fiber Bragg Grating strain sensor and OFSCN® 300°C Fiber Bragg Grating Temperature Sensor both undergo rigorous calibration to provide highly accurate measurements for their respective applications.
Here is an image demonstrating a typical FBG sensor:
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