How much do you know about how to correctly select distributed fiber optic sensor cables?

When using different optical cables for distributed optical fiber sensing, the following factors need to be considered in the selection:

According to measurement requirements

Strain measurement: If high-precision strain measurement is required, optical fiber with polyimide (PI) coating can be selected, such as PI optical fiber, whose coating material is harder, elastic modulus is larger, and strain tranSMission effect is better1. For complex test environments, in order to ensure the survival of the optical fiber, tight sheathed optical fiber can be selected, and the smaller the diameter, the smaller the strain transmission loss. For example, tight sheathed optical fiber with a diameter of 0.9mm is usually a better choice.

For example, the Brillouin armored micro-strain sensing optical cable BLY-SCFRGY-1B6-5.0-BL is a stress and strain sensing optical cable for professional BOTDR and BOTDA principle research. The optical cable consists of a central micro-strain sensing optical fiber + outer layer twisted steel wire reinforcement + MDPE sheath. The optical fiber is in direct contact with the steel wire reinforcement and the outer sheath, and can sense external stress changes in real time. Steel wire reinforcement is mainly used to adapt to occasions with greater stress, so that strain optical cables can be installed inside the structure, such as on the steel structure of the building, directly poured into concrete, etc. The product is particularly suitable for wiring in buried and pre-buried ways, and is widely used in monitoring the health of large buildings, geological settlement, pipeline deformation, etc.

Strain optical cable structure diagram

Vibration measurement: If the application scenario is extremely sensitive to vibration, such as in earthquake monitoring, micro-mechanical vibration detection and other fields, optical cables with high vibration sensitivity need to be selected. Usually, bare optical fiber or thin-coated optical fiber is more sensitive to vibration. Because when the coating is thin, external vibration is more easily transmitted to the optical fiber core, causing changes in the optical signal, thereby achieving effective perception of small vibrations. For general vibration measurement, such as vibration monitoring of large building structures, medium-sensitivity optical cables can be selected. This type of optical cable usually has a coating layer of appropriate thickness, which can not only ensure a certain vibration response, but also provide better protection for the optical fiber.

For such measurement needs, Wuxi Brillouin flat multi-parameter sensing cable BLY-SCJFU-5B1-2.5×6.5-B is a professional Brillouin strain DAS, which consists of tight-wrapped vibration sensing fiber + multi-core loose-tube vibration or temperature compensation fiber. The tight-wrapped fiber is in close contact with the outer sheath, and can sense external vibration changes in real time. The loose-tube fiber can be used as a reference arm for vibration or for temperature compensation, communication and other purposes. The product is soft, lightweight, flat in appearance, and naturally straight when unfolded. It is particularly suitable for surface mounting and adhesive wiring. It is widely used in large-scale building health monitoring, pipe corridors, pipelines, and railway roadbed vibration sensing monitoring.

Temperature measurement: For temperature measurement within 350℃, PI fiber can be selected; aluminum-plated fiber can be selected within 400℃; gold-plated fiber can be selected within 700℃. If only temperature measurement is required, loose-sheathed fiber can be selected, which can shield external strain and is only sensitive to temperature changes.

Wuxi Brillouin high thermal conductivity distributed temperature measurement optical cable BLY-MM03P is a high-performance temperature measurement optical cable; on the one hand, the optical cable adopts thermal insulation composite materials with a thermal conductivity of more than 1.0W; on the other hand, the optical cable manufacturing process is optimized, and ultra-micro outer diameter stainless steel hose is used for packaging. The overall outer diameter of the optical cable is less than 3MM, making its thermal conductivity far superior to that of general temperature measurement optical cables, greatly shortening the sensing optical fiber's sensing time for external temperature changes, thereby reducing the design cost and difficulty of the optical fiber distributed temperature measurement host. This optical cable is suitable for most temperature measurement occasions, especially for occasions with high response time requirements, high temperature resolution, and high spatial resolution.

BLY-MM03T optical cable structure diagram

According to environmental conditions

· Harsh environment: In humid, corrosion-risk or mechanically damaged environments, such as outdoor direct burial scenes outside subway tunnels, armored optical cables can be selected, which have good waterproof, corrosion-resistant and mechanical pressure resistance. In environments with strong electromagnetic interference, such as subway tunnel sections near large motors, substations, etc., although the optical fiber itself has anti-electromagnetic interference, special optical cables with stronger anti-electromagnetic interference capabilities can still be selected. Strong magnetic fields will have eddy current effects, and non-metallic optical cables are recommended.

· Fire risk environment: In environments with fire risks, such as near electrical equipment in subway tunnels, flame-retardant optical cables can be selected. The outer sheath is made of flame-retardant materials, which can effectively prevent the spread of fire along the optical cable.

· High temperature environment: When the optical cable needs to work in a high temperature environment (such as steel mills, thermal power plants, etc.), the temperature may exceed 200℃, and high temperature resistant optical cables should be selected. For example, quartz optical fiber with ceramic or metal sheath can withstand high temperatures of 1000℃. If the temperature is between 200-500℃, polyimide coated optical fiber can be used, which can maintain stable performance in this range.

· Low temperature environment: In cold areas or low temperature workshops, the temperature may be lower than -40℃, and low temperature resistant optical cables need to be selected. This type of optical cable usually uses special sheath materials, such as low-temperature resistant polyethylene sheath, to ensure that it is still flexible at low temperatures, to avoid brittle fracture due to low temperatures, and to affect signal transmission.

Humidity and waterproof requirements

· High humidity or underwater environment: When laying in swamps, coastal areas or underwater, optical cables are susceptible to moisture, and good waterproof performance should be selected. Common ones include oil-filled optical cables, in which waterproof grease is filled in the cable core to prevent moisture intrusion; and sealed metal sheathed optical cables, which are sealed by metal sheaths and matched with waterproof filling materials for long-term underwater or high humidity environments.

· General humid environment: In general humid environments, such as ordinary basements, optical cables with moisture-proof layers can be selected. Usually, a layer of moisture-proof aluminum foil or plastic film is added to the optical cable sheath to effectively block water vapor and protect the optical fiber from moisture damage.

Chemical corrosion environment

· Chemical corrosion environments such as strong acids and alkalis: Near chemical plants and garbage treatment plants, chemicals are prone to corroding optical cables. It is necessary to select chemical corrosion resistant optical cables, such as corrosion-resistant fluoroplastic sheaths, or add special anti-corrosion coatings on the outside of the optical cable to prevent chemicals from corroding the internal optical fiber and other structures.

· Mild chemical corrosion environment: If the environment only has mild chemical corrosion, such as near urban sewage pipes, polyethylene sheathed optical cables with certain corrosion resistance can be selected, and protective measures can be added when necessary, such as wearing protective tubes to extend the service life.

Electromagnetic interference environment

· Strong electromagnetic interference environment: In strong electromagnetic interference areas such as substations and radar stations, electromagnetic interference resistant optical cables should be selected. Optical fibers themselves are resistant to electromagnetic interference, but external electromagnetic induction may generate induced currents in metal parts. At this time, all-dielectric Self-supporting (ADSS) optical cables can be selected, without metal parts, to avoid electromagnetic interference; or optical cables with metal shielding layers and good grounding can be used to shield electromagnetic interference.

· General electromagnetic interference environment: In general electromagnetic interference environments, such as ordinary city streets, conventional optical cables can basically meet the needs. If you are not sure, you can choose optical cables with metal shielding layers to enhance anti-interference capabilities.

Mechanical stress environment

·High mechanical stress environment: In environments that are susceptible to external impact, stretching, and extrusion, such as construction sites and railway lines, high-strength, mechanical damage-resistant optical cables need to be selected. For example, armored optical cables have steel belts or steel wire armor on the outer layer, which can withstand large tension and pressure; there are also non-metallic reinforcement cables, which are reinforced with high-strength non-metallic materials to provide mechanical protection while avoiding other problems caused by metals.

·General mechanical stress environment: For general indoor wiring or light load areas, ordinary structure optical cables can meet the requirements. However, it is necessary to pay attention to selecting the appropriate outer diameter and reinforcement core to ensure that they will not be damaged by slight mechanical stress during normal installation and use.

Fire risk environment

·High fire risk environment: In places with high fire risks such as oil depots and machine rooms, flame-retardant optical cables need to be selected. The sheath of flame-retardant optical cables is made of flame-retardant materials, such as flame-retardant polyvinyl chloride (PVC) or halogen-free flame-retardant materials. They are not easy to burn when exposed to fire, and can self-extinguish, reducing the risk of fire spread while avoiding the generation of large amounts of toxic smoke.

·General fire risk environment: In general office spaces or ordinary buildings, ordinary optical cables with certain flame retardant properties can be selected. Under the premise of meeting the wiring and use requirements, try to choose products that meet the relevant flame retardant standards to improve fire safety.

According to the difficulty of construction and maintenance

·Constrained construction space: In places with narrow construction space and small bending radius, such as some corners or pipes in subway tunnels, optical fibers with good bending resistance can be selected, which have smaller bending losses at the same bending radius.

·Frequent maintenance: For areas that require frequent maintenance, optical cables that are easy to connect and repair can be selected, such as optical cables with standard optical fiber connectors, which are easy to plug and replace and reduce maintenance costs and time.