AP Sensing
AP Sensing is a German manufacturer of distributed fiber optic sensing (DFOS) technology used for infrastructure monitoring on European railways, headquartered in Böblingen and tracing its origins to Hewlett-Packard’s optical measurement business via Agilent Technologies, before becoming an independent company in 2007.
The company develops and manufactures three distributed sensing technologies at its Böblingen site: Distributed Acoustic Sensing (DAS), Distributed Temperature Sensing (DTS), and Distributed Temperature and Strain Sensing (DTSS).
All three rest on optical time domain reflectometry (OTDR), which turns a standard fiber optic cable into a continuous sensor along its full length.
For structural health monitoring, DTSS is the relevant technology. It applies Brillouin-based OTDR to track temperature and strain simultaneously along the fiber, registering mechanical stress, structural shifts, and thermal anomalies as they occur.
Application in rail infrastructure
AP Sensing positions DTSS for monitoring bridges, tunnels, and track structures, aimed at identifying landslides, track deformation, and tunnel instability at an early stage.
Its DAS systems cover a broader set of rail applications, among them track condition monitoring, track fault detection, and a “Below Ballast Scan” developed with the geophysical equipment supplier Sercel, which according to the two companies assesses ballast and subgrade conditions to depths of up to 50 meters. Some of these applications are in operational use, others remain under field validation.
Both DAS and DTS/DTSS data feed into SmartVision, the company’s asset visualization and data management software, which consolidates sensor output for network operators.
The sensing element is the fiber itself, so the trackside installation is passive: power and signal processing sit with the interrogator unit at the end of the fiber run, not along the track.
International presence and rail activity
AP Sensing operates from Böblingen with regional coverage of Europe, the Americas, Asia-Pacific, and the Middle East. Its linear heat detection systems, a DTS-based fire detection line, are rated SIL-2 (Safety Integrity Level) for functional safety under IEC 61508.
In the rail sector, the company began cable theft detection trials with Deutsche Bahn in 2018, monitoring a 36 km stretch near Berlin with a single DAS unit.
Between 2020 and 2023 AP Sensing took part in FoSSIL 4.0 (Fibre Optic Sensing for Safety Integrity Level), a research project led by DB Netz — since merged into DB InfraGO — with the Technical University of Darmstadt.
The project had a volume of around EUR 3 million, of which 67 percent came from the German transport ministry’s mFUND programme, and examined whether a fiber-based digital twin could support real-time train integrity verification as an alternative to point-based axle counters.
