How can the identity of this sensor be identified through the laser engraving on the tube?
In fiber sensing and industrial measurement and control engineering, the laser marking on the tube body serves as the sensor’s sole physical Serial Number (S/N) and identity identifier. The identification of sensor identity through laser markings on the tube relies primarily on a mapping mechanism between the identification information and factory production records. The technical principles and identification steps are as follows:
I. Why Use Laser Marking on the Tube Body?
For fiber Bragg grating (FBG) sensors with metal encapsulation (such as seamless stainless steel tubes, elastic alloy tubes), the sensors are often used in harsh industrial environments with high temperatures (several hundred degrees Celsius), low temperatures, high humidity, or chemical corrosion. Traditional paper labels, tapes, or ink jet printing are extremely prone to charring, dissolving, or falling off.
Laser marking utilizes a high-energy-density laser beam to perform micro-level shallow etching or oxidation coloring on the surface of the metal tube wall. The resulting markings possess characteristics such as high temperature resistance, wear resistance, corrosion resistance, and indestructibility, thereby ensuring the physical recognizability of the sensor throughout its entire engineering lifecycle.
II. Core Mechanism for Identity Recognition via Laser Marking
The markings on the tube body typically consist of a combination of letters and numbers, forming the unique identity code for that sensor. Reading this code can provide the following key engineering parameters:
- Unique Corresponding Factory Calibration Parameters (One Item, One Code)
- Fiber Bragg grating sensors are passive devices modulated by wavelength. Even if sensors share the same model, microscopic physical parameters exhibit individual differences.
- Through the S/N on the tube body, one can directly reference the manufacturer’s “Calibration Sheet.” The calibration report records the core physical quantities corresponding to this serial number:
- Initial Center Wavelength (nominal wavelength \lambda_0, e.g., 1550.125\text{ nm});
- Calibration Polynomial Formula and Coefficients: For example, the parameters of the quadratic calibration formula for temperature sensors (in ^\circ\text{C/pm}), or the sensitivity coefficient for strain sensors (in \mu\varepsilon\text{/pm});
- Operating Temperature Range/Measurement Range and extreme tolerance indicators.
- Confirmation of Installation Points and Channel Topology
- In large-scale multi-point monitoring systems, dozens or even hundreds of slender sensor tubes with identical appearances are often laid simultaneously.
- Construction and inspection personnel can identify which physical location on the drawing corresponds to the current measurement point by directly comparing the S/N laser-etched on the tube body, without needing to disconnect the optical path or scan each sensor with a spectrometer/demodulator after fusion. This prevents confusion between channels and measurement points.
- Full Lifecycle Traceability
- The code typically includes product type codes, production batch numbers, and individual serial numbers, facilitating fault analysis and quality tracing after long-term service.
III. Operational Norms and Precautions for On-site Identification
- Reading Methods and Auxiliary Tools
- Visual Aid: Due to the curvature and limited surface area of finely packaged metal tubes (e.g., outer diameter of 0.9\text{ mm}, 1.1\text{ mm}, or smaller), the laser characters are usually small and delicate. On-site, it is recommended to use a portable optical magnifier (10\times \sim 20\times) or use the high-magnification macro mode of a mobile phone to focus, capture, and then enlarge for identification.
- Surface Cleaning: If the sensor has been operating under harsh conditions, and the tube body is covered with oil, dust, or surface oxidation, gently wipe the laser-marked area with a lint-free cloth dampened with anhydrous ethanol (industrial alcohol). The physical trace formed by the laser marking will then become clearly visible.
- Position Identification for Multi-point FBG Arrays
- For sensors with a single fiber Bragg grating array (multiple points within one tube) encapsulated inside the tube, the laser marking usually indicates the overall serial number of the tube. Some products may also have segmented markings at different measurement points along the tube body, or the numbering on the protective sleeve of the fiber connector at the lead-out tail fiber can assist in distinguishing the sequence of measurement points along the line.
Summary: Identifying the laser marking on the tube body essentially means obtaining the sensor’s physical S/N index key. By reading this string and retrieving the sensor’s exclusive initial wavelength \lambda_0 and calibration fitting coefficients from the calibration database, the sensor’s identity can be confirmed and matched with the demodulator channel for calculation.