# Inquiry about measuring circumferential stress of bearings using Fiber Bragg Grating sensing technology **URL:** \ **Category:** Official Tech Inquiry & Product Q&A\ **Tags:** fbg-technology, bare-fbg, fbg-strain-sensor, fbg-custom-sensor\ **Created:** [March 17, 2026, 5:54am UTC](https://forum.ofscn.net/t/topic/1102 "2026-03-17T05:54:47Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![ZMH\_AIPPT](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/z/8baadc/32.png) [@ZMH\_AIPPT](https://forum.ofscn.net/u/ZMH_AIPPT)\ **Post date:** [March 17, 2026, 5:54am UTC](https://forum.ofscn.net/t/topic/1102/1 "2026-03-17T05:54:47Z")
We need to purchase fiber Bragg gratings for measuring circumferential stress in bearings. Currently, we estimate 13 measurement points with a 15mm spacing. The grating length is 1-2mm, with a requirement for 3dB bandwidth ≤ 0.3 and side-mode suppression ratio ≥ 15dB. We would like to know how to select the appropriate reflectivity to meet the above requirements for measuring bearing axial strain. What is your center wavelength accuracy? What is the strain sensitivity? What is the drift margin reserved for each grating? How is the pricing determined? ---
**Author:** ![OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/90ced4/32.png) [@OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/u/OFSCN_CN_PS_Engineer)\ **Post date:** [March 17, 2026, 5:54am UTC](https://forum.ofscn.net/t/topic/1102/2 "2026-03-17T05:54:56Z")
Hello, I am a pre-sales engineer from OFSCN. Regarding your application needs for bearing circumferential stress measurement (axial strain extraction), the parameters you’ve proposed are very professional and specific. Based on your working conditions, we typically recommend using **OFSCN® Polyimide Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)**, as bearing monitoring often involves high-frequency vibrations or potential temperature increases. Polyimide material offers better adhesion strength and thermal stability. Here are the answers to your specific technical questions: ### 1. Technical Parameter Responses - **Reflectivity Selection:** For a grating string with 13 measurement points on a single fiber, the choice of reflectivity primarily balances “signal-to-noise ratio” and “interrogator saturation.” - **Center Wavelength Accuracy:** The standard value for the room temperature wavelength deviation (accuracy) of OFSCN® bare fiber Bragg gratings is **±0.2nm**. - **Strain Sensitivity:** For fiber gratings in the 1550nm band, the strain sensitivity is approximately **1.2 pm/με**. (Note: In bearing stress measurement, the final stress value needs to be calculated using the formula: `σ = E × ε`, combined with the elastic modulus of the bearing material.) - **Reserved Drift Range per Grating:** This depends on the estimated maximum strain and temperature rise range of the bearing. ### 2. Recommended Product Links You can view detailed technical specifications for the following products: [OFSCN® Polyimide Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)](https://www.ofscn.com/fbg-products/polyimide-fbg.html) [OFSCN® Fiber Bragg Grating Stress Sensor (Reference for Stress Calculation)](https://www.ofscn.com/fbg-products/stress-sensor.html) ### 3. Quotation Preprocessing (Mode C) To accurately calculate the cost, we need to confirm the following customization parameters. As you have already specified the number of measurement points, spacing, and optical parameters, please provide the following additional information: 1. **Quantity:** How many of these 13-point grating strings do you plan to purchase? 2. **Geometric Dimensions (Refer to Diagram):** - Please confirm **L1 (Lead Length)**: The distance from the fiber connector to the first measurement point (typically 1 meter or more). - Please confirm **L3 (Tail Length)**: The distance from the 13th measurement point to the end. - We have noted the 15mm spacing (L2) you mentioned. - Diagram reference: [Multi-point Dimension Definition Diagram](https://www.ofscn.net/images/forum/FBGs-and-T-Sensors-Measurement-Points-Segmentation-Diagram.png) 3. **Supporting Equipment:** Do you already have a Fiber Bragg Grating Interrogator compatible with the wavelength range of 13 measurement points? If support is needed, please refer to [OFSCN® Fiber Bragg Grating Interrogator](https://www.ofscn.com/fbg-products/fbg-interrogator.html). Once the above parameters are confirmed, I will summarize your requirements and guide you to contact the relevant department for a formal quotation. ---
**Author:** ![ZMH\_AIPPT](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/z/8baadc/32.png) [@ZMH\_AIPPT](https://forum.ofscn.net/u/ZMH_AIPPT)\ **Post date:** [March 17, 2026, 5:58am UTC](https://forum.ofscn.net/t/topic/1102/3 "2026-03-17T05:58:29Z")
> [@OFSCN\_CN\_PS\_Engineer](#): > > How many of these 13-point grating strings should we procure? 1 string, the strain space is about 1000με. We don’t have a demodulator, do you? ---
**Author:** ![OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/90ced4/32.png) [@OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/u/OFSCN_CN_PS_Engineer)\ **Post date:** [March 17, 2026, 5:58am UTC](https://forum.ofscn.net/t/topic/1102/4 "2026-03-17T05:58:35Z")
Hello, thank you for your reply. Based on the additional information you provided, we are moving to the **Requirement Matching and Quotation Preparation** stage: ### 1. Recommended Equipment Since you do not currently have an interrogator and have **13 measurement points** deployed on a single fiber, there are certain requirements for the interrogator’s bandwidth utilization and performance: - **Recommended Solution:** **OFSCN® Fiber Bragg Grating Interrogator**. - **Reasoning:** With 13 measurement points, allocating 3nm of wavelength space per point (covering 1000με strain, temperature compensation, and initial installation deviation) requires a total wavelength range of approximately 40nm. Our interrogators typically have a standard bandwidth of 40nm, which perfectly accommodates your 13-point grating string. - **Product Link:** [OFSCN® Fiber Bragg Grating Interrogator](https://www.ofscn.com/fbg-products/fbg-interrogator.html) ### 2. Quotation Parameter Confirmation To finalize the parameter confirmation before providing a quote, we still need the following key geometric dimensions (used to determine fiber consumption and packaging process): 1. **Lead Fiber Length (L1)**: What is the distance from the fiber connector (connected to the interrogator) to the **1st** grating measurement point? (Usually, a length of over 1 meter is recommended for ease of routing). 2. **Tail Fiber Length (L3)**: What is the distance from the **13th** grating measurement point to the end of the fiber? (If a loop is not required, typically 10cm is sufficient). 3. **Connector Type** : We provide **FC/APC** connectors by default to match the interrogator. Do you have any special requirements? **Geometric Reference Diagram:** [Diagram Defining Dimensions for Multi-point Grating Strings](https://www.ofscn.net/images/forum/FBGs-and-T-Sensors-Measurement-Points-Segmentation-Diagram.png) ### 3. Summary of Requirements (To Be Completed) - **Product Name** : OFSCN® Polyimide Fiber Bragg Grating Strings (bare) - **Quantity** : 1 root - **Measurement Point Parameters** : 13 measurement points, 15mm spacing, 1-2mm grating length - **Optical Requirements** : 3dB bandwidth ≤ 0.3nm, Side Mode Suppression Ratio ≥ 15dB - **Geometric Dimensions** : L1 = ? / L3 = ? - **Supporting Equipment** : OFSCN® Fiber Bragg Grating Interrogator × 1 unit Please provide the specific lengths for L1 and L3, and I will compile the final requirement list for you to obtain a formal quotation. ---
**Author:** ![ZMH\_AIPPT](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/z/8baadc/32.png) [@ZMH\_AIPPT](https://forum.ofscn.net/u/ZMH_AIPPT)\ **Post date:** [March 17, 2026, 6:00am UTC](https://forum.ofscn.net/t/topic/1102/5 "2026-03-17T06:00:00Z")
L1=2m, L3=10CM, default connector ---
**Author:** ![OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/90ced4/32.png) [@OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/u/OFSCN_CN_PS_Engineer)\ **Post date:** [March 17, 2026, 6:00am UTC](https://forum.ofscn.net/t/topic/1102/6 "2026-03-17T06:00:06Z")
Hello, thank you for providing the complete technical parameters. Your required parameters are now all clear, and I have summarized them for you as follows: ### 1. Final Required Parameter Summary - **Grating Product** : **[OFSCN® Polyimide Fiber Bragg Gratings / Fiber Bragg Grating Strings (bare)](https://www.ofscn.com/fbg-products/polyimide-fbg.html)** - **Quantity** : 1 unit - **Number of measurement points** : 13 points - **Optical Specifications** : 3dB bandwidth ≤ 0.3nm, side mode suppression ratio ≥ 15dB, reflectance recommended 10%~30% (to ensure consistency of multi-point signals) - **Geometric Dimensions** : - **L1 (Lead length)**: 2.0 meters - **L2 (Point spacing)**: 15 millimeters - **L3 (Tail fiber length)**: 10 centimeters - **Connector Type** : FC/APC - **Supporting Equipment** : **[OFSCN® Fiber Bragg Grating Interrogator](https://www.ofscn.com/fbg-products/fbg-interrogator.html)** - **Quantity** : 1 unit - **Recommended Specification** : Due to the need for a wide wavelength coverage for 13 measurement points with strain margin, it is recommended to purchase the standard 40nm or above bandwidth version of the demodulator. ### 2. Next Steps Since you have provided all the necessary SKU definition parameters, you can contact us directly for a formal quotation. Please contact our sales department through the contact information (phone, email, or online form) provided on our official company website, and **attach this conversation record or parameter summary** , so that we can quickly calculate the price for you: - **Fiber Bragg Grating Sensors (Chinese Site)**: [https://www.ofscn.com](https://www.ofscn.com) - **Fiber Bragg Grating Sensors (International Site)**: [https://www.ofscn.net](https://www.ofscn.net) - **Specialty Optical Fibers and Cables (International Site)**: [https://www.ofscn.org](https://www.ofscn.org) If you have any other technical questions, feel free to discuss them in the forum at any time. ---
**Author:** ![ZMH\_AIPPT](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/z/8baadc/32.png) [@ZMH\_AIPPT](https://forum.ofscn.net/u/ZMH_AIPPT)\ **Post date:** [March 17, 2026, 6:02am UTC](https://forum.ofscn.net/t/topic/1102/7 "2026-03-17T06:02:16Z")
Reflectivity values vary between manufacturers. Is this related to their respective manufacturing processes? **Would 10% to 30% be too low?** ---
**Author:** ![OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/o/90ced4/32.png) [@OFSCN\_CN\_PS\_Engineer](https://forum.ofscn.net/u/OFSCN_CN_PS_Engineer)\ **Post date:** [March 17, 2026, 6:02am UTC](https://forum.ofscn.net/t/topic/1102/8 "2026-03-17T06:02:25Z")
Hello, this is a very professional and pertinent technical question. Regarding the selection of reflectivity, stronger is not always better, especially under your operating conditions of **single-fiber multi-measurement points (13 points)**. Addressing your inquiry with an in-depth technical principle analysis: ### 1. Why is 10% ~ 30% a reasonable choice? While reflectivity is indeed related to manufacturing processes (such as UV masking lithography intensity, hydrogen loading, etc.), it is more dependent on **system-level optical balance**. For multiple Fiber Bragg Gratings (FBGs) in series on a single fiber (FBG Strings), excessively high reflectivity can lead to two main problems: - **Shadowing Effect and Insertion Loss** : Each grating reflects the signal while also causing loss in the transmitted spectrum. If preceding gratings have very high reflectivity (e.g., 90% for each point), the light intensity reaching the 13th grating will be extremely weak, causing a severe drop in the signal-to-noise ratio (SNR) for the end sensors, potentially making them unrecognizable by the demodulator. - **Multipath Interference (MPI)**: When light repeatedly reflects between multiple high-reflectivity gratings, it can generate