Abstract：The problem of stray current corrosion in subways is becoming increasingly prominent, posing a threat to the safe operation of rail transit facilities.This paper proposes an intelligent monitoring solution based on signal isolator modules，Effectively suppress interference through electrical isolation technology, enhance data acquisition accuracy, and provide a reliable basis for stray current protection.This paper primarily discusses the hazards of stray currents in subways and the necessity of establishing monitoring systems for such currents，For subway stray current monitoring systems, the use of Shun Yuan Technology's ISOEC U/A-P-O and ISOEM U/A-P-O series signal isolation modules is recommended.

一、Introduction

Subway systems primarily rely on DC traction power supply. During operation of the DC traction power supply system, some current leaks into the ground, forming stray currents that cause electrochemical corrosion of underground metal structures. Traditional monitoring methods suffer from issues such as weak interference resistance and data distortion. Signal isolator modules, however, utilize electrical isolation technology to significantly enhance the stability and reliability of monitoring systems.

二、Protection and Monitoring of Stray Currents

From a systematic perspective, current stray current protection design methods can be categorized into three types: prevention, discharge, and detection.

一、control the source of stray current generation to reduce its quantity and enhance the insulation resistance between the track and ground by using wooden sleepers.；Reduce voltage drop in rail circuits by adopting seamless rail structures；Measures such as insulating sleeves are employed on the outer layer of buried metal pipelines along the route to prevent stray currents.

二、adopt drainage or other methods to mitigate the corrosive effects of stray currents that have already been generated.Artificially divert stray currents from metal pipelines to flow directly back to the negative terminals of rails or substations.

三、 stray currents are monitored in real time, and if excessively high stray currents are detected, countermeasures are implemented to mitigate their harmful effects. Monitor stray currents at specific leakage points to gain real-time insights into traction return leakage conditions in subway systems and the extent of corrosion on underground metal structures caused by stray currents. Subsequently, implement current drainage measures to return stray currents or directly replace equipment to ensure safe subway operations. According to the （Technical Specifications for Protection Against Stray Current Corrosion in Subways CJJ49-92,） it is necessary to measure and monitor parameters such as track voltage, polarization potential of underground metal structures, track transition resistance, and track longitudinal resistance.

三、Design Proposal for a Monitoring System Based on Signal Isolators

Due to the inherent potential difference between the diverter, smart sensor, and data acquisition unit, a “ground” loop current will exist between them without electrical isolation, which will affect the accuracy of stray current measurements.；This “ground” loop can even cause an increase in common-mode voltage, leading to damage to electrical ports or interface chips. To address this issue, the ISOEC U/A-P-O and ISOEM U/A-P-O series signal isolation modules are specifically recommended to resolve signal port matching issues and ground loop problems.

1. System Architecture

The system adopts an integrated “prevention-discharge-detection” design principle, with core components including:

‌    Sensor Layer: Deploy shunt resistors and rail voltage/current sensors to collect raw signals.

‌    Isolation Processing Layer: The signal isolator module isolates and conditions the sensor output to eliminate interference.

‌    Data Acquisition Layer: Embedded controllers (such as microprocessor-based units) process isolated signals to enable real-time monitoring.

‌    Communication Layer: Transmits data to the central monitoring platform via RS-232 or Ethernet interfaces.

2.The Key Role of Signal Isolators

‌    Front-end isolation: Insert an isolator between the sensor and the acquisition device to block ground loop interference.

‌    Power Isolation: Provides an independent power supply for the monitoring circuit to prevent power supply noise coupling.

‌    Multi-channel adaptation: Supports parallel processing of signals from multiple monitoring points, enhancing system scalability.

四、 Application Case Analysis

1.Scene Description

Taking a subway depot as an example, stray current issues are particularly prominent in this area due to its complex track layout and weak insulation performance.Traditional monitoring solutions without signal isolators exhibit significant data fluctuations in this environment, compromising protective decision-making.

2.Deployment Effect of Isolator Modules

‌    Precision Enhancement: Signal noise reduced by over 90% after isolation, with significantly improved data consistency.

‌    System Stability: Reduced equipment failure rates, lowering maintenance costs.

‌    Protection Optimization: Provides reliable data support for drainage screens and intelligent flow-through devices, effectively suppressing corrosion.

五、Features of the Active Series ISOEC U/A-P-O and ISOEM U/A-P-O Signal Isolation Modules

1.  Resist EMC interference, safeguard data integrity

SunYuan Technology's ISOEC U/A-P-O and ISOEM U/A-P-O series signal isolation modules are active isolation modules featuring front-end current/voltage signal input and rear-end current/voltage signal output. The product incorporates a highly efficient low-power power supply capable of providing power to the internal input and output signal processing circuits. Thanks to the use of capacitive isolation and electromagnetic isolation technology internally, the product exhibits superior temperature drift characteristics and linearity compared to solutions employing optocoupler isolation. Featuring a compact SIP12Pin flame-retardant package (UL94V-0 standard), it delivers triple isolation protection rated at 3000VDC while effectively blocking high-frequency noise and ground loop interference within the server. 3000VDC triple isolation design ensures complete electrical separation between input, output, and auxiliary power sources, preventing damage to sensitive circuits from high-voltage spikes (such as power module surges) and significantly enhancing operational reliability. When using multiple modules, only a single or multiple power supplies are required, enhancing system redundancy.

2.  Calibration-free design reduces operational and maintenance costsBuilt-in isolated DC/DC converter supports single-power-supply operation at 5V/12V/15V/24V, eliminating the need for negative power sources on-site and boosting deployment efficiency by 60%.

Fixed unit gain configuration eliminates the need for zero and gain adjustments, removing external potentiometers and repetitive calibration steps to reduce field maintenance costs. Full-range linearity reaches ±0.01% FSR, with accuracy grades spanning 0.01 to 0.2, meeting stringent signal precision requirements for data acquisition.

3.  Multi-functional signal conversion, adaptable to complex scenariosSupports bidirectional isolated signal transmission between signals such as 0-75mV/0-2.5V/0-5V/0-10V/0-±100mV/0-±5V/0-±10 and 0-±20mA/4-20mA, enabling mutual isolation, amplification, and conversion. Achieves seamless conversion between single-ended and differential signals, compatible with various sensor interfaces in servers.

4.   Multi-Channel Smart Sensor Integration

Supports 1-in&1-out, 1-in&2-out, 2-in&2-out, and 4in&4-out signal isolation amplification, enabling parallel processing of multiple sensor signals to enhance data acquisition efficiency.

六、Summary

Stray currents in subway systems can cause corrosion to steel structures and metal pipelines along the tracks, significantly impacting the operational lifespan of the subway. Strengthening monitoring of stray currents and promptly implementing current diversion measures can prevent their corrosive effects on metal components.The signal isolator module employs electrical isolation technology to resolve interference challenges in subway stray current monitoring, thereby enhancing data quality and system reliability. In the future, with advancements in intelligent isolation technology, monitoring systems will evolve toward higher integration and adaptive protection, providing long-term safeguards for the security of rail transit facilities.