# What is "system latency"? **URL:** \ **Category:** OFSCN Technical Knowledge Base\ **Tags:** fbg-technology\ **Created:** [September 18, 2026, 5:02am UTC](https://forum.ofscn.net/t/what-is-system-latency/2877 "2026-09-18T05:02:47Z")\ **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:** [September 18, 2026, 5:02am UTC](https://forum.ofscn.net/t/what-is-system-latency/2877/1 "2026-09-18T05:02:47Z")
How many milliseconds does it take from the sensor being stressed to the computer displaying data? ---
**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:** [September 18, 2026, 5:03am UTC](https://forum.ofscn.net/t/what-is-system-latency/2877/2 "2026-09-18T05:03:00Z")
In a Fiber Bragg Grating (FBG) sensing system, “system latency” (End-to-End Latency) refers to the **total time from when the sensor undergoes external force causing physical deformation to when the numerical calculation is completed and the value is refreshed on the PC host interface**. This latency is composed of five physical and engineering stages, with their respective time scales as follows: * * * ### 1. Physical Deformation and Mechanical Transfer Latency ( \sim 1\ \mu\text{s} - 10\ \mu\text{s} ) - **Mechanism** : When the structure under test is subjected to force, strain waves propagate through the encapsulation matrix at the speed of sound (approximately 3000\ \text{m/s} \sim 5000\ \text{m/s} in solid media) to the fiber core, causing changes in the grating period \Lambda and effective refractive index n\_{\text{eff}}. - **Time Consumption** : For fiber strain/stress sensors on the centimeter scale, this physical process completes within microseconds and is generally negligible on a millisecond scale. ### 2. Optical Signal Transmission Latency ( \sim 5\ \mu\text{s/km} ) - **Mechanism** : The speed of light propagation in the quartz fiber core is approximately v = \frac{c}{n} \approx \frac{3 \times 10^8\ \text{m/s}}{1.468} \approx 2 \times 10^8\ \text{m/s}. - **Time Consumption** : One-way transmission latency is approximately 5\ \mu\text{s/km}. For a transmission cable length of 1\ \text{km}, the round-trip optical path latency is about 10\ \mu\text{s} (i.e., 0.01\ \text{ms}). ### 3. Demodulator Sampling and Spectral Calculation Latency (Primary determining factor, 10\ \text{ms} - 100\ \text{ms} ) The demodulator’s data update cycle is the largest source of latency in the entire link, depending on the hardware-set sampling frequency (f\_s): - **Sampling Period ( T = \frac{1}{f\_s} )**: - **100\ \text{Hz} Sampling Frequency** : Single frame data acquisition period is **10\ \text{ms}**. - **50\ \text{Hz} Sampling Frequency** : Single frame data acquisition period is **20\ \text{ms}**. - **10\ \text{Hz} Sampling Frequency** : Single frame data acquisition period is **100\ \text{ms}**. - **Hardware Processing Time** : The demodulator’s internal DSP/FPGA executes algorithms for peak finding, wavelength calibration, and filtering, typically taking about 1\ \text{ms} \sim 3\ \text{ms}. ### 4. Data Communication Transmission Latency ( \sim 1\ \text{ms} - 5\ \text{ms} ) - **Mechanism** : The demodulator pushes wavelength or strain data packets to the host computer via an industrial Ethernet interface (using protocols like TCP/IP, UDP, or Modbus). - **Time Consumption** : In conventional LAN or direct connection configurations, network stack latency is usually in the range of 1\ \text{ms} \sim 5\ \text{ms}. ### 5. PC-side Data Processing and UI Display Rendering Latency ( \sim 15\ \text{ms} - 30\ \text{ms} ) - **Mechanism** : The host software receives data packets, executes physical quantity conversion formulas (e.g., calculating stress values based on \sigma = E \cdot \varepsilon), and submits them to the operating system’s graphics engine for rendering. - **Time Consumption** : The refresh cycle of conventional displays is typically 16.7\ \text{ms} ( 60\ \text{Hz} refresh rate). Combined with software buffer queue processing, display latency is generally between 15\ \text{ms} \sim 30\ \text{ms}. * * * ### Summary: Overall End-to-End Latency Scale | Configuration Condition | Demodulator Sampling Period | Communication & Processing Latency | PC Rendering Latency | **Total System Latency** | | --- | --- | --- | --- | --- | | **Standard Dynamic Measurement (100 Hz)** | 10\ \text{ms} | 2 \sim 5\ \text{ms} | \sim 16.7\ \text{ms} | **Approximately 25\ \text{ms} \sim 35\ \text{ms}** | | **Standard Static Measurement (10 Hz)** | 100\ \text{ms} | 2 \sim 5\ \text{ms} | \sim 16.7\ \text{ms} | **Approximately 115\ \text{ms} \sim 130\ \text{ms}** | * * * ### Related Product References In practical engineering systems, sensing terminals typically employ alloy tube encapsulation structures to ensure strain transfer efficiency and are paired with multi-channel demodulators for high-speed wavelength acquisition and network communication: - Acquisition Device: [OFSCN® Fiber Bragg Grating Interrogator](https://www.ofscn.net/fbg-products/analyzer.html) (Supports 10Hz / 50Hz / 100Hz sampling frequency configuration, supports TCP/UDP/Modbus data communication) - Strain Sensor: [OFSCN® Alloy Tube Packaged Fiber Bragg Grating strain sensor](https://www.ofscn.net/fbg-products/strain-sensor.html) - Stress Sensor: [OFSCN® Fiber Bragg Grating Stress Sensor](https://www.ofscn.net/fbg-products/stress-sensor.html) ![OFSCN® Fiber Bragg Grating Interrogator](https://forum.ofscn.net/uploads/default/original/1X/8ecc1c112d2015cbc63afa6d42b87517befb2f87.jpeg)