ATEX-ready plug & play solution for process analytical technology (PAT)
Process analysis with ready-to-lay special optical cable for industrial spectroscopy in harsh industrial environments and potentially explosive atmospheres (ATEX)
In many areas of modern manufacturing, process parameters have to be kept to extremely demanding requirements – and this can only be achieved by using a real-time analysis system. Examples of this include the logging of relevant parameters such as the purity of substances and concentrations in the chemicals industry, the food industry, and pharmaceuticals. Earlier practice was to take individual samples from the process that were then analyzed in the lab; today, readings are taken from the production process continuously and in near-real time.
Optical spectroscopy in particular is now a key part of this process analysis, since it offers a quick, exact, and contact-free way to record a wide range of relevant parameters. Optical spectroscopy involves shining a light through (for liquids) or onto (for solids like powders) the sample: the spectrum of the light transmitted or backscattered is then analyzed in a spectrometer, providing information about constituent substances and their concentrations. Real-time measurement enables rapid intervention in the manufacturing process.
While the use of process analysis originated in the chemicals industry, it has since expanded to include applications in pharmaceuticals, the food industry, and agriculture.
For many analysis systems, the delicate spectrometer is sited in a protected area and the optical signal is routed to the measuring points, often located in a harsh environment, using fiber optic cables. A spectrometer may have multiple optical cables connected to it, each monitoring separate processes. The lengths of fiber are correspondingly connected to the spectrometer signal input with optical switches.
Very harsh environments are often found in large-scale chemical or pharmaceutical plants. For these industries, Leoni developed an especially rugged cable that has since been deployed in a number of projects and has even now become the standard cable for some of our major customers. One reason for this is the fact that the cable was developed in cooperation with our end users.
The ruggedness of the cable during the laying process was an especially important point here. This step is complex, and often requires the whole production process to be shut down for as small a time frame as possible. In the past, the use of conventional solutions often resulted in a situation where the delicate fiber connectors on optical cables became damaged during laying. Fiber breakage was also caused by pulling-in the cables, which can be up to 100 m long. Both of these events meant that the cable had to be replaced and the schedule for the plant retrofit could no longer be kept to.
Our optical cable for industrial spectroscopy is equipped with an Easy Pull system: this protects the connectors during the laying process while also including a pull loop to which the cable can be attached during the laying process. The sensitive fiber connectors are mechanically protected continuously during the installation process. After pull-in, the installation aid can be easily removed and the connectors can be connected to the couplings as usual at the target location. Our customers have now tested the product extensively in the field and are very satisfied with the fact that no damage has been recorded to date during the pull-in procedure.
Another key advantage of our optical cable for industrial spectroscopy is the fact that the cable can be laid directly and needs no further protection – even when laid in an outdoor facility. Unlike previous solutions, the cable does not need to first be pulled into a corrugated protective tube. This lets our customers save up to a third of their overall costs, thanks to the reduced costs involved in installation. All of this is enabled by the exceptionally robust, electrically conductive polyurethane (PUR) outer jacket that offers good crush protection and UV resistance as well as stability versus oils and aggressive fluids.
The chemicals industry often has to meet high standards relating to the use of cables in potentially explosive atmospheres (ATEX). Cables also have to be barrier sealed, to avoid the risk of “zone entrainment”. Zone entrainment refers to a situation where a leak allows explosive mixtures of gases to escape into areas where operators are unprepared to deal with them, for example.
Even in areas where no ATEX qualification is currently necessary, our optical cables for industrial spectroscopy give you planning reliability for a later ATEX qualification for your plant. For this reason, a good approach is to replace existing cable harnesses with our solution as part of plant maintenance, to ensure your plant is well-equipped for the future.
LEONI Fiber Optics has developed an optical waveguide cable featuring a 600 µm fused silica fiber especially for use in process analysis that can be deployed in harsh industrial environments and potentially explosive atmospheres. This usage information is designed to offer an overview of the relevant provisions from the ATEX Directive 2014/34/EU that were used as the basis for developing the cable.
In Germany, this Directive was transposed into the German Explosion Protection Ordinance (11th ProdSV).
The Directive classifies cables as “components”. Since only active parts – “devices”, as defined by the Directive – need to be certified, this is not required for cables. Accordingly, CE or ATEX markings are not (and must not be) used on the cable sheath or in accompanying documents.
Technical standards that must be met to comply with the Directive and national laws are described in IEC 60079-0 ff. and IEC 80079-36 ff. Essentially, a distinction is made between cables that carry live current and fiber optical cables, which are a different type of cable. Fiber optical cables are covered by IEC 60079-28, which states that cables of this type are always safe according to the ignition protection type “op pr” for the EPLs (equipment protection levels) Gc, and Dc, but may need to pass certain specialized tests to meet requirements for some EPLs. On the other hand, fiber optical cables that do not form part of devices with optical fibers are exempted from the standard if they meet relevant industrial standards.
Our new cable design also offers protection from the buildup of electrostatic charge in accordance with IEC 60079-32: this is achieved with a specialized polyurethane compound that makes the cable conductive as defined by the standard. The limit values for conductive materials lie between 104 Ω and 109 Ω at 50% ±5% rel. humidity or 1011 Ω for 30% ±5% rel. humidity.
The dangers of zone entrainment have also been accounted for. One example of zone entrainment is a situation where explosive mixtures can escape from the pump to the outside due to the presence of leaks. As a result, the inner explosive zone is entrained (trapped) and moved outside, where the plant operator does not expect to need to handle explosive mixtures. This therefore increases potential hazards. To avoid zone entrainment via the cable, steps have been taken in its design to ensure that the cable is barrier sealed and has passed the corresponding test according to IEC 60079-14, annex E1. This involves the cable being installed under a constant ambient temperature in a sealed housing of 5 l ±0.2 l (one cable end is located inside, the other end is located outside). The cable passes the test if the time required to reduce an internal overpressure of at least 0.3 kPa (30 mm of water column) to 0.15 kPa (15 mm of water column) is not less than 5 s. The cable is therefore suitable for use in zones 0–2 and 20–22.
While, as mentioned above, the standard is not directly relevant for a fiber optic cable, this changes when the system is considered as a whole. For LEONI as a cable specialist, working with our customers is the first and most important step towards fulfilling the system requirements for successful qualification according to the ATEX Directive.
Our expertise in light transmission for the field of optical metrology has been clearly demonstrated in a number of real-world projects featuring high-end metrology applications, including the Cold Atom Lab on the International Space Station (ISS), NASA’s New Horizons mission to Jupiter and Pluto, and the detection of gravitational waves with LIGO. Your sophisticated measuring environment can also benefit from the insights gained from these projects.