Rail industry experts would tell you that one of the the most challenging places to deploy video surveillance cameras is on the exterior of trains. With regular traveling speeds of up to 125 mph (200 kph), cameras that are installed on the exterior of the train need to be specially designed to withstand the extreme forces that will be encountered, including extreme weather, corrosion and scratches.
For a rail customer, there are two main advantages to installing cameras on the exterior of trains – they can assist train operators to ensure that doorways are clear, which is particularly important as this is the most likely place for accidents to occur; and they also help monitor the pantograph, the apparatus mounted on the roof of an electric train or tram that collects power through contact with an overhead line. Clear footage of a problem that occurred with a pantograph, makes it easy for train operators to determine when and why it malfunctioned.
For security integrators, deployment and installation is not a simple task; in fact, there are three major challenges to deal with, including weather and temperature resistance, corrosion and scratching problems, and, of course, the physical installation itself.
Challenge: The Weather
Surveillance cameras installed on the exterior of trains must be able to withstand any type of weather throughout the year. When the train is moving at high speeds and the weather is extreme, the challenge becomes even more convoluted. Integrators must ensure cameras will work reliably in these challenging conditions. Here are several factors to consider:
1. High temperatures: In some parts of the world, summer temperatures can regularly reach and exceed 100 degrees. Cameras on the exterior of a train can reach much higher temperature because of the many heat-generating electrical components and cables contained within.
A camera designed to withstand the weather will be contained within a tightly sealed metal housing, making it difficult for heat to dissipate – further increasing its temperature. For this application, integrators should choose cameras where each component has been tested to withstand high temperatures for prolonged periods of time. The lens, ICR, optical filter and image sensor should all be subjected to temperature tests over a period of at least 48 hours with high humidity. The testing should also include high and low temperature cycles to ensure that image quality is not impacted.
In addition to the cameras, all cables must be UL-certified to withstand the outside temperature as well as the additional heat generated within the camera housing. Choose components with a slightly wider temperature range than is expected to be encountered as this will protect against unexpectedly high temperatures. Products and components that can withstand high temperatures receive appropriate thermal and reliability certifications – indicating the camera should last for at least five years with little risk of malfunction due to high temperatures.
2. Low temperatures: Obviously, trains can run during extremely cold conditions as well, and cameras in environments where temperatures can dip into the double-digit negatives are subject to challenges that can impact the mechanical operation of cameras as well as its usability for the customer. Further compounding the cold weather challenge is that trains moving at high speeds disperse heat away from the camera.
While manufacturer specifications should address the mechanical function of the device in cold weather, the challenge of keeping snow or frost from covering the front of the camera – making recording impossible – is a major headache for end-users and integrators. Some of these problems can be averted by choosing a weatherproof casing, and the front lens/window of the casing should be completely flat to make it difficult for snow to build up.
Even with good design and specifications, frost and snow is sometimes unavoidable when operating in extremely low temperatures at high speeds. One solution is to add a heater for the front lens/window of the casing. Quick and even heating is normally achieved by ensuring the heater goes all the way around the screen, as opposed to placing a heater at the bottom. In addition, a highly reliable heating method is required, which is usually achieved by using a printed circuit board (PCB) which allows the heater to be activated using a digital power switch as opposed to a less-reliable mechanical switch.
Tempered glass has many advantages over plastic and normal glass as it will withstand weather extremes much better, and will not become discolored over long deployment periods – thus making it is essential for exterior train surveillance.
3. Water resistance: Technology has evolved over the years to help protect cameras reliably in outdoor environments; however, in order to guarantee a camera remains waterproof on the exterior of a train, several additional factors must be considered.
IP66 and IP67-rated cameras are both designed to withstand heavy rain; however, IP67 cameras are also designed to withstand pressure. Thus, choosing IP67 cameras is advantageous when deploying on trains that travel at high speeds and encounter heavy rain. It should also be noted that tests for IP66 and IP67-rated cameras simulate different scenarios that can be experienced on the outside of trains. For train customers demanding extra reliability, integrators can choose cameras with both IP66 and IP67 ratings.
4. Condensation: The environmental conditions on the exterior of a train can lead to condensation inside a camera – often because of the heat generated by its processor. When the temperature outside is cold, the difference in internal temperature of the camera causes condensation to form on the inside of the camera. Even cameras with an IP68 rating are only dustproof and waterproof and cannot protect against humid air traveling from one side of the glass to the other.
Since high ingress protection alone is not sufficient to prevent condensation forming on the inside of the camera, the best way to overcome this problem is to use a protective coating on the inside of the front of the camera that prevents condensation.
Challenge: Prevention of Corrosion and Scratches
A scratch-resistant casing should be deployed on any cameras mounted on the exterior of the train to protect against getting damaged or broken. Avoiding corrosion is particularly important, because the cameras are constantly subjected to conditions such as pollution, acid rain or salt water, and it is critical that they do not develop weak points because of corrosion.
Smart manufacturer design is the first step to corrosion prevention. The shape of the camera should not have any sharp angles, which can produce weak points in the protective coating and cause it to peel away – leaving the camera exposed to the elements. The casing of the camera should be coated with powder paint because it offers the hardest finish; however, if too little coating or treatment is applied, the camera will not be sufficiently protected against corrosion, whereas too much coating will destroy its smooth finish – thus making it less resistant to water.
Screws and fasteners are another key area of consideration when it comes to corrosion. A standard screw that uses SAE 304 (EN 10088-2 1.4301) stainless steel will not withstand extreme weather – especially in coastal areas. For higher levels of reliability, SAE 316 (EN 10088-2 1.4401) stainless steel screws should be used.
Scratch resistance: A scratch-resistant screen is essential for surveillance cameras deployed on the exterior of trains, because the train’s slipstream often causes small stones and grit to get sucked in and collide with the front of the camera.
Integrators have two options: 5H tempered glass, which is very hard and provides good scratch resistance but does not effectively protect against deliberate acts of vandalism; or, plastic, which is less likely to break when vandalized, but is more susceptible to being scratched.
Since the chance of abrasion from small stones and other debris poses more of a risk than vandalism, most train customers will opt to deploy a front casing made from tempered glass as opposed to plastic in order to fulfill project requirements.
Challenge: Installation and Maintenance
In order to increase the chances of a camera being suitable for a particular deployment, integrators should offer train operators a selection of different lenses, as well as an adjustable pan and tilt function to increase the likelihood of meeting the varied requirements for each project deployment. In addition, it is essential that the camera components fit into a very compact unit to comply with the EN 50155 standard.
EN50155 is an international standard covering electronic equipment used on rolling stock for railway applications, including the equipment’s temperature, humidity, shock, vibration and related parameters.
This applies to video surveillance in that the components of a camera must not move when a train is in motion. The strong vibrations when trains travel at high speeds means any moving parts are weaknesses that are liable to malfunction. This includes features such as pan, tilt and zoom. When a camera is attached to a train, an adjustable pan and tilt function allows the integrator to set the angle the train customer wants, but it must be locked before the train becomes operational. When train operators have this increased flexibility, it significantly increases the chances that the installation will meet the project requirements.
In some situations, an adjustable pan and tilt function may be insufficient, such as when a train operator needs the camera to record the platform and the train door at the same time. Alternatively, they may request multiple cameras on the train that all require different viewing angles. The best way to overcome this problem is to provide the train operator with a variety of different lens options to ensure that their cameras can always fulfill the project requirements.
Integrators must ensure that all of the different lenses can still fit within the compact housing and that the viewing angle is not impacted by the housing design.
Kevin Shen is product manager for Moxa. Request more info about the company at www.securityinfowatch.com/10816805.
