Cameras with a statically pressurised enclosure

The author: Dr. Johannes Hesper, Senior Product Manager, R. Stahl

Monitoring technology can only be installed in hazardous areas if suitably explosion-protected. Until now, users who wished to install cameras for CCTV systems to protect and monitor their site or to control industrial processes had to make do with heavy, flameproof enclosures.

A fundamentally different type of protection – the pressurised enclosure (Ex-p) instead of the flameproof enclosure (Ex-d) – manages to avoid the typical drawbacks of conventional solutions. R. Stahl is introducing cameras for hazardous areas where one single nitrogen filling guarantees life-long protection from any hazardous materials intruding into the protected interior from the ambient atmosphere. Due to the much lighter, flexible and compact enclosures, such pressurised systems ensure a far greater degree of flexibility when choosing a location for cameras of all shapes and sizes. In case of unexpected damage, a pressure sensor at the enclosure will switch off the camera’s electronics before it poses an explosive risk for the ambient atmosphere. Ex-p cameras from Stahl on the basis of this SNF technology (SNF = sensor-controlled nitrogen filling) can be combined with many different additional hardware or software products, resulting in a great variety of complete, complex and powerful CCTV solutions.

As electronic equipment, cameras may produce heat or sparks which, in a sensitive environment of flammable gases or dusts, could trigger an explosion. Protection is provided by a few special models which ensure, for example, a strict energy limitation within the system (intrinsically safe cameras, protection type Ex-i). Occasionally, design measures are realised such as the encapsulation of the camera’s electronics inside the enclosure (protection type Ex-m). When a great variety of camera types that are only available as standard versions are required, the most common practice is to mount these cameras inside solid enclosures. Enclosures suitable for this purpose are designed in such a way that a possible explosion on the inside will be screened from the outside atmosphere by the strong walls. The main advantage of this approach is the relative simplicity of its construction, making it a practicable solution for almost all camera types. A flameproof enclosure (protection type Ex-d) will, however, add substantially to a camera’s weight – for example, high-end, movable zoom cameras end up weighing 30 to 40 kg in total. This makes them very inconvenient to handle. Furthermore, the bulky units are sometimes simply too big to fit into the intended space. When a camera inside an Ex-d enclosure needs to be tilted or panned, the heavy enclosure will require a strong motor with a sizeable energy requirement – frequently between 50 and 80 W. What’s more, the bulky housing and powerful motor result in an increased temperature and make heat dissipation more difficult, limiting the scope of application even further. Last but not least, condensation may accumulate inside the enclosure, steaming up the lens or even destroying the electronics.

The main focus when developing an alternative was on how to avoid the typical disadvantages of these conventional systems. This aim was achieved by using pressurised enclosures, i. e. protection type Ex-p, and filling them with nitrogen. Camera units of this type are substantially lighter, extremely temperature tolerant and also fully gas and water-proof. The Ex-p cameras in Stahl’s product range weigh between 0.6 and 15 kg. Even the heaviest version – a high-performance, stainless-steel PTZ camera – remains sufficiently manageable to be easily mounted by just one person. Due to the good heat transfer via the mechanically robust enclosures (steel grade 316L), the cameras can be installed in a wide range of temperatures from -40 to +75 °C. With their IP68 or IP69K protection, the life expec-tancy and total operating time are not impacted even by persistently rough climatic conditions, such as a desert climate with sandstorms or a maritime environment with an aggressive, strongly saline atmosphere. Nitrogen is an ideal protective gas for these explosion-protected enclosures because it is not flammable and relatively inert. Inside the camera there is permanent excess pressure that prevents the ingress of dangerous gases from the ambient atmosphere. In contrast to many other pressurised enclosures, these SNF systems do not need to be regularly refilled. The camera enclosures are manufactured by Stahl with such precise tolerances that a single nitrogen filling is sufficient for safe, life-long operation. Therefore, fixed feed lines or valves for gas refills of the kind usually required for Ex-p protection can be dispensed with for the SNF systems. Only massive mechanical damage may result in a breakdown. In this case, the pressure sensor installed inside each housing as standard ensures that the device is immediately switched off.

CCTV systems are increasingly used not only to monitor hazardous areas or to support and back up staff in these areas from the control room. More and more processes today are also monitored from remote locations where automated monitoring with different sensors would otherwise be difficult. It is particularly for these types of task that very compact, explosion-protected cameras with small dimensions and a low weight are required. For tight corners, Stahl provides the spherical EC-710 with a diameter of a mere 55 mm. A range of suitable camera models is available for classic CCTV tasks – from access control or monitoring loading and unloading processes to watching over helicopters landing on offshore rigs. The intelligent EC-750 dome camera, for example, can rotate 360°. As an option, this camera can also be directly integrated into digital networks via its own IP interface. Another camera type, the EC-740, was designed for extreme ambient conditions like heated lenses. This model is available either as a simple zoom camera or with full PTZ (pan, tilt, zoom) functionality. The EC-800 thermal imaging camera can reliably monitor objects and people across distances of more than 400 m even in difficult weather conditions or at night.

Hardware and software solutions of varying complexity are available to connect cameras and process image signals. At the client’s request, very basic systems can be conventionally connected and it is even possible to send an analogue video signal to exactly one monitor. At the other end of the performance spectrum there is the option of installing hundreds of IP-compliant cameras that feed their signals into a network, where operating stations of all kinds can then access the video data. The ISview software is eminently suitable for many small or medium-sized CCTV systems. It can display live signals from up to twelve image sources on one screen in multiple-quad views. Alternatively, users can toggle between single views displayed in window or full-screen mode. In addition to IP cameras, video servers can also be incorporated with ISview. For extremely complex safety and security systems, however – systems with many cameras and different user levels – the SeeTec video software is recommended. This software can integrate between five and over a thousand cameras, including control options for various components. If required, the system can guarantee to keep tamper-proof records for many days. Switches and terminal boxes with an explosion-proof design and a whole series of input devices from keyboards to joysticks for the PTZ cameras are offered as accessories for CCTV systems.

Hall 11.1, Booth E41

cpp-net.com/0212468