AP Sensing GmbH of Böblingen, Germany builds Raman-based distributed temperature sensing instruments that turn a single passive fibre optic cable into a continuous linear heat detector. There are no point detectors and no gaps: the cable responds to heat equally at any point along its length, and the instrument reports both the temperature and the position of the event.
SATU Innovative designs, supplies, installs, commissions and maintains AP Sensing systems in Thailand — sizing the DTS architecture and cable route, engineering the zone and alarm table, supervising fibre installation and splicing on tank roofs, in tunnels and on cable trays, and integrating the alarms into the fire and gas panel, foam release logic and SCADA.
How fibre optic linear heat detection works
- Raman backscatter. A laser pulse is launched into the fibre; the intensity ratio between the Stokes and anti-Stokes bands of the backscattered light gives an absolute temperature, with no cross-talk from strain.
- OTDR positioning. The arrival time of the returning light fixes the position of every reading, so one passive cable behaves as thousands of sensors in series.
- Software zones. The cable is divided into detection zones in software — one tank, one tunnel section, one conveyor drive — and zones are redrawn without touching the cable.
- Three alarm criteria per zone. Maximum temperature, rate of rise, and deviation from the zone average, which is what separates a sun-heated tank roof from a real fire.
- Passive sensing element. No power, no electronics and, in the metal-free cable types, no conductive path at the hazard — immune to electromagnetic interference and usable in Ex zones 0 and 20.
- Fire behaviour, not just fire. Continuous readings locate the event and track its size and spread direction in real time, independent of air currents.
LHD N45-Series controllers
| Item | Detail |
|---|---|
| Range and channels | Up to 16 km per channel, up to 4 channels per unit; measurement times down to 1 second |
| Measurement | Raman-OTDR with patented code correlation — defined pulse sequences rather than single pulses, giving roughly ten times the signal-to-noise ratio of conventional DTS |
| Zoning and I/O | 2,000 alarm zones per channel; up to 98 integrated relay contacts, each a solid-state switch |
| Configuration | Integrated web server, configurable from a browser with no client software; one-click validation of the compliance configuration |
| Approvals | EN 54-22, UL 521, FM, VdS, ULC, DNV, KFI; SIL 2; ATEX / IECEx |
| Hazardous area types | N4585A / N4586A / N4587A ATEX variants — the instrument sits outside the explosive atmosphere while the fibre radiates into it. EU-Type Examination BVS 18 ATEX F 001 X, DEKRA EXAM |
| Reliability | Specified MTBF 35 years; individual laser burn-in and a full functional test on every unit |
| DTS N45-Series | For long-asset temperature monitoring: up to 70 km range, spatial resolution below 0.5 m |
S200xA sensor cables
The cable is the entire sensing element — passive, with two multimode fibres per cable.
| Type | Construction | Key data |
|---|---|---|
| S2000A | Metal-free safety cable — FRNC sheath, GRP strength member, fibre tight-buffered in swellable aramid yarn; UV-resistant, highly flexible | 4.0 mm; 17 kg/km; crush 1,000 N/10 cm; tensile 1,000 N install |
| S2002A | Steel-armoured — AISI 316L loose tube and armour wires, gel-free fibre in metal tube, watertight, rodent-resistant; UV-resistant | 3.8 mm; 29 kg/km; crush 9,600 N/10 cm; tensile 1,500 N install |
| All types | Halogen-free flame-retardant non-corrosive sheath; two multimode sensing fibres | 2 × OM2 50/125 µm; −40 to +85 °C; functional integrity to +750 °C |
Selection guide. Use the metal-free aramid S2000A where flexibility, light weight and no metallic path matter — rim seals, cable trays, near power cables. Use the AISI 316L armoured S2002A where crush loads, rodents or water ingress are the risk. Both comply with IEC 60331-25 (2 h at 750 °C) and are approved to VdS EN 54, UL 521, CAN/ULC S530 and FM 3210.
How it compares with other linear heat detection
| Technology | Principle | Range / response / Ex |
|---|---|---|
| Fibre optic (DTS) | Temperature measured along a fibre optic cable; mounting 0.3 m to 35 m; indoor and outdoor | 100 m to 10,000 m; under 30 s per EN 54-22; ATEX compliant |
| Digital LHD | Heat-reactive polymer insulated twisted pair; requires an end-of-line unit | Under 2,000 m; under 12 s to flame; needs an additional ATEX enclosure |
| Analogue LHD | NTC polymer sheathed wires reading a resistance change; requires an end-of-line unit | Under 1,000 m per zone; response time undocumented; not ATEX |
| Pneumatic LHD | Gas volume change in a rigid tube with a pressure transducer; requires gas tightness | 20 m to 130 m per detector; per EN 54-5; usable in explosive atmospheres |
All four are immune to building vibration. Only the fibre optic and pneumatic types keep electrical energy out of the hazardous area, and only the fibre optic type locates the event.
Software, alarms and integration
- SmartVision maps the fibre onto the plant layout with colour-coded cable routing, pinpoints alarm locations, records landmarks such as joints and splices, and stores measurements for replay and export.
- SmartAlarm and machine-learning transient alarms assess historical temperature trends across the whole asset to separate normal ambient change from an abnormal thermal event, reducing nuisance alarms.
- Hard-wired outputs — up to 98 potential-free relay contacts forward alarms directly and redundantly to a fire alarm control panel.
- Bus interfaces — Modbus TCP, IEC 60870-5-104 and IEC 61850 over Ethernet to SCADA, DCS and fire and gas systems.
- Fault supervision — any failure of instrument, software, network, power or sensing fibre, including a fibre break, is annunciated separately from a fire alarm.
Where it is used
- Tank farms and terminals — floating-roof rim seal fire detection, tank shell and tension ring temperature, refineries and chemical plants
- Tunnels and transport — road and rail tunnels, metro stations, car parks, aircraft hangars
- Power and energy — cable trays and transformers, underground and subsea power cables, bus ducts, PV and battery energy storage
- Process and pipelines — pipeline leak and third-party interference monitoring, LNG terminals, conveyor belts, geothermal and CCS
- Industry and marine — production areas, warehouses and freezers, power plants, container ships and ferries
Reference installations
Floating-roof tank farm, Saudi Arabia. Five floating-roof tanks 30 m in diameter, four in a cluster and a fifth a few hundred metres away, monitored by one two-channel DTS unit and a single 3 km fibre. Each tank is a software zone; alarms trigger the automatic foam system.
Oil terminal, UAE. Twenty-four tanks from 9 m to 52 m diameter on one 8 km DTS system, with a second unit for the pump house. Cable runs around the tension ring and up the shell, so wall temperature tells responders whether the shell is nearing failure or the deluge is cooling it.
Road tunnel, Germany. A 2,230 m tunnel monitored by 3,182 m of sensor cable on the ceiling centreline. In eleven controlled fire tests a 5 MW RABT fire alarmed in 29 seconds against the 60 seconds required, and 0.5 MW fires — one tenth of the RABT fire load — were reliably detected and located.
Rim-seal installation on floating-roof tanks
- One instrument, one cable, many tanks. The DTS sits in the tank-farm substation; a single fibre runs out to the first tank, then the second, third and on to the last before returning.
- Up the shell on the existing spiral-stairway cable tray or a light protective channel, entering the tank top through a 100 mm flange or an M20 gland.
- Across the rolling ladder in a flexible cable carrier or metal conduit, fastened at about 1 m spacing along half the ladder, the remainder left free to follow the deck.
- At the rim seal, secured to fabricated L-brackets around the deck circumference at roughly 1 m spacing, then returned along the same route.
- Zones instead of extra detectors. One, two or four zones per tank, or a double-knock scheme, are programmed into the DTS. Conventional LHD would need 8 to 12 stand-alone detectors for the same result.
- Redundancy at no extra cable cost. Both fibres inside one cable can be driven by two independent DTS units, each monitoring the full length.
Approvals
EN 54-22 · EN 54-5 · UL 521 · FM 3210 · CAN/ULC S530 · VdS · ATEX / IECEx · SIL 2 · DNV · IEC 60331-25
Talk to our engineers
Tell us what you need to protect — a tank farm, a tunnel, a cable tray or a conveyor — and we will come back with a cable route, a zone table and a budget. Contact SATU Innovative.
AP Sensing product data is reproduced from the manufacturer’s published datasheets and is indicative only; specifications are subject to change and to project engineering. All trademarks are the property of their respective owners.