# Fiber Bragg Grating Sensor for Underwater Use at 500m **URL:** \ **Category:** Official Tech Inquiry & Product Q&A\ **Created:** [September 18, 2026, 6:55am UTC](https://forum.ofscn.net/t/500m/2880 "2026-09-18T06:55:59Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![zhy3323](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/z/13edae/32.png) [@zhy3323](https://forum.ofscn.net/u/zhy3323)\ **Post date:** [September 18, 2026, 6:56am UTC](https://forum.ofscn.net/t/500m/2880/1 "2026-09-18T06:56:00Z")
Fiber Bragg Grating sensor suitable for use underwater at depths of up to 500m ---
**Author:** ![OFSCN\_PS\_Eng](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/839c29/32.png) [@OFSCN\_PS\_Eng](https://forum.ofscn.net/u/OFSCN_PS_Eng)\ **Post date:** [September 18, 2026, 6:56am UTC](https://forum.ofscn.net/t/500m/2880/2 "2026-09-18T06:56:15Z")
Hello! Thank you for your message on the Dacheng Yongsheng technical consultation section. Operating at a depth of 500 m underwater (corresponding to a hydrostatic pressure of approximately 5 MPa) is typical of deep-sea conditions, which impose specific requirements on the sensor’s encapsulation, sealing, and pressure-resistant structure. OFSCN® offers several fiber Bragg grating products that can be customized for this purpose. However, to recommend the most suitable solution for you, I need to confirm a few key pieces of information. Please help me confirm points 1 and 2 below first: 1. **Measurement Target** : What physical quantity are you primarily looking to measure? 2. **Installation and Object to be Measured** : Will the sensor be directly and permanently submerged in seawater, or installed within a sealed cavity or on the surface of an underwater structure? What are the general material and structural characteristics of the object being measured? Once you provide me with these two details, I can determine the necessary encapsulation process (e.g., alloy tube encapsulation / seamless steel tube encapsulation / polymer encapsulation with waterproof steel conduit, etc.) and suggest corresponding recommended models. I look forward to your further information so we can continue our discussion. ---
**Author:** ![zhy3323](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/z/13edae/32.png) [@zhy3323](https://forum.ofscn.net/u/zhy3323)\ **Post date:** [September 18, 2026, 6:58am UTC](https://forum.ofscn.net/t/500m/2880/3 "2026-09-18T06:58:32Z")
Water temperature 5°C Water depth 500m Underwater pipeline strain The sensor is immersed in seawater for a long time, installed on the surface of a tubular structure, and made of steel ---
**Author:** ![OFSCN\_PS\_Eng](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/839c29/32.png) [@OFSCN\_PS\_Eng](https://forum.ofscn.net/u/OFSCN_PS_Eng)\ **Post date:** [September 18, 2026, 6:59am UTC](https://forum.ofscn.net/t/500m/2880/4 "2026-09-18T06:59:32Z")
With the additional working conditions you’ve provided, the information is now very clear. Let’s start by summarizing the requirements, and then we’ll present our recommended solution. ## I. Requirements Summary - **Water Temperature Measurement** : Approximately 5℃ (low-temperature condition, the sensor needs to cover the low-temperature range) - **Water Depth** : 500 m, corresponding to a hydrostatic pressure of about 5 MPa - **Object Under Test** : **Strain/Stress** on the surface of underwater steel pipelines - **Operating Environment** : The sensor will be **permanently immersed in seawater** , surface-mounted on a tubular structure ## II. Recommended Solution ### 1. Primary Measurement: Underwater Pipeline Strain We recommend the **[OFSCN® Alloy Tube Packaged Fiber Bragg Grating Strain Sensor](https://www.ofscn.net/fbg-products/strain-sensor.html)** ![OFSCN Alloy Tube Strain Sensor](https://forum.ofscn.net/uploads/default/original/1X/90c11b90deb49f0cd88a54ecac0d956bcddf353c.jpeg) ![OFSCN Alloy Tube Strain Sensor 2.0mm](https://forum.ofscn.net/uploads/default/original/1X/ae908bc1e181cfc4cdf263751c8670552a66522e.jpeg) ![OFSCN Alloy Tube Strain Sensor Fixation](https://forum.ofscn.net/uploads/default/original/1X/4a28a6be888c7e0965d6a522716233e8b6403b54.jpeg) **Technical Rationale** : - Utilizes **elastic alloy tube** encapsulation, providing excellent **waterproof, pressure-resistant, and mechanical strength** properties suitable for long-term seawater immersion; - Default strain range ≥ 6000 με, with customizable measurement segment lengths (default 10 cm to 2 m) for easy conformity to pipeline surfaces; - Default outer diameter ≤ 1.1 mm, minimizing impact on the pipeline structure when surface-mounted; - Standard operating temperature range (-20℃ to 55℃) fully covers your 5℃ water temperature requirement. ### 2. Temperature Compensation: Underwater Temperature Measurement We recommend the **[OFSCN® 100°C Fiber Bragg Grating Temperature Sensor](https://www.ofscn.net/fbg-products/temperature-sensor-100.html)** ![OFSCN 100C FBG Temperature Sensor](https://forum.ofscn.net/uploads/default/original/1X/74932c0f3b71797adb12ca84a053059151051842.jpeg) ![OFSCN 100C FBG Temperature Sensor FC](https://forum.ofscn.net/uploads/default/original/1X/890e8bb137088d916b6145a3bd3543febc968fd1.jpeg) **Technical Rationale** : - Features **single-layer seamless steel tube encapsulation** , offering waterproof and pressure-resistant capabilities for long-term immersion; - Temperature range of -40℃ to 100℃ covers the 5℃ water temperature; - Default outer diameter of 0.9 mm allows for co-cabling with the strain sensor, enabling **temperature compensation** for the strain measurement point (Fiber Bragg Grating strain measurements are sensitive to temperature; using an external temperature sensor for compensation is recommended for higher accuracy). ### 3. Installation and Fixation For surface mounting, the **[OFSCN Installation Fixture](https://www.ofscn.net/fbg-products/fixtures-01.html)** can be used, supporting methods such as adhesive bonding or spot welding for secure fixation onto the steel pipeline surface. ## III. A Technical Note Factory calibration for strain sensors is typically a single-term formula (unit: με/pm). Since the final stress = Young’s Modulus of the material × strain, the **Young’s Modulus of the steel** parameter must be input into the OFSCN® Fiber Optic Grating demodulator to output the final stress data. You can click the links above to view detailed technical specifications. Please feel free to discuss any specific technical questions you may have (such as the number of measurement points, installation details, etc.).