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Transmission Devices: The indispensible link

Transmission Devices: The indispensible link

The choice of transmission technology largely depends on the environment and system requirements. For example, new installations are most likely to use PoE technology, but distances are limited to within 100 meters. If there are no legacy systems in place, PoE would be the most cost-effective option. Installations are not limited to outdoors or indoors, but they are limited by distance, unless fiber optics is part of the budget consideration.

Installations where they are pre-existing cables would consider the option of EoC. “Some project sites will already have an extensive coaxial infrastructure in place, which were costly to install in the first place. It would be costly to remove, but a waste to leave idle as well. In such circumstances, the system integrator can use them as a tool and integrate the existing coaxial cables into the security system via EoC transmission. Of course it is still possible to overhaul the existing system and use PoE completely, but that would inevitably affect the budget and schedule of the project,” explained Ben Chiang, Business Development Manager at EtherWAN. The transmission distance is, therefore, limited by the length of the pre-existing cables.

Finally, standalone buildings are most likely to opt for PLC, with transmission distance and infrastructure dependent on the power lines. However, as power lines are generally connected to the national power grid and may complicate matters, PLC is mostly applied in standalone buildings, such as houses or single office buildings where ownership is simple and clear.

The winning formula is the careful calculation of system requirements at the planning stage, prior to installations or refurbishments.

Devices Glue Transmission Infrastructure Together
Regardless of the transmission technology chosen, there are key devices, each with its own unique role in the transmission infrastructure.

According to Calvin Wong, Sales Director of OT Systems, media converters, Ethernet switches, and EoC converters are the main transmission devices for CCTV and surveillance applications that support PoE. These devices may or may not have PoE functions.

Most media converters and network switches in the market supporting PoE follow these specifications, said Wong. There are three power standards in PoE devices: IEEE 802.3af, IEEE 802.3at (medium power), and IEEE 802.3at (high power). For IEEE 802.3af, the power output of power supply equipment (PSE) is 15.4W and the power input of powered device (PD) is 12.95W. Next, the IEEE 802.3at (medium power) allows PSE to have 30W output and PD to have 25.5W input, while the IEEE 802.3at (high power) sees PSE with 60W output and PD with 51W input.

In Ethernet transmission through optical link, the data rate is 10/100/1000Mbps, while it is 100/1000Mpbs for optical. In EoC transmission, the data rate can be up to 300Mbps, depending on the coaxial cables and technologies used, explained Wong.

Repeaters help strengthen signals during transmission by regenerating signals to be sent to other segments. However, it influences the signal in analog transmission, as noise is introduced into the system every time the signal is boasted. Hence, transmission distance is largely limited to signal-to-noise ratio.

Selecting Proper Ethernet Switches
The choice of switches can affect system performance and maintenance costs.

Mainstream PoE devices today are designed to be intelligent. “For example, a PoE switch would be able to calculate power demands, distribute power, and even schedule that distribution amongst its ports to accommodate the varying needs of different PDs. Of course, it is possible for all ports to supply a high power consistently, but the cost for such a product would be considerably higher. Hence, it invariably depends on end-user budgets and realistic requirements,” noted Chiang.

First up is determining whether the system requires the more rugged industrial grade products or will suffice with robust commercial grade products. “It's extremely important to consider the installation environment when selecting IP equipment. Outdoor environments including environmentally designed enclosures, parking garages, and factory floors are all much harsher than standard commercial building or residential applications,” noted Richard Malstrom, IFS Product Marketing Manager for Lenel & Interlogix at UTC Climate, Controls & Security, on the operating environment. Hence, “it is important to use environmentally hardened products designed to operate under wide temperature ranges to ensure reliable performance.”

These considerations play a large part in deciding the choice of devices. For example, EtherWAN's PoE switches varied on specifications depending on whether they are commercial or industrial grade, in terms of power budget, power input, EMC protection level, and operating temperature. “While the transmission speed is the same in commercial grade and industrial grade products, the design and concept values are different. For example, the difference begins with the component selection; industrial grade products contain components with twice or thrice the reliability levels of their commercial counterparts,” said Chiang.

Power budgets for commercial grade range from 123W to 370W, while they range from 62W to 420W on some industrial grade models. Power input for commercial grade switches are 50/60Hz, 100-240AVC, but 18-57VDC, 47-55VDC, or 47-57VDC for industrial grade ones. Operating temperature range also varies, with zero to 45 degrees Celsius for commercial applications, and -40 to 75 degree Celsius to within harsher environment conditions in industrial applications.

“Even if the outdoors temperature is 37 degrees Celsius, the actual environment temperature of an industrial switch would be much higher than that due to it being in an enclosed environment,” added Chiang.

Temperature can raise another issue. “High temperatures can also impact the ability of a power supply to provide sufficient power to a device. Make sure to review the de-rating curve when using industrial-rated power supplies to make sure the chosen power supply will provide the required power at the highest ambient temperature the power supply may have to operate under,” highlighted Malstrom.

Finally, there are vertical-specific standards that must be kept in mind when selecting Ethernet products. “Just because something is rated as industrial grade, it doesn't mean that it will meet the industrial standards of every vertical. For example, in the oil and gas vertical, products must pass an explosion test, due to the unique nature of the operating environment. Products have to be certified by a third party and the standards may vary from country to country and vertical to vertical," said Chiang.

Factors to consider During Selection
Depending on the transmission medium chosen, different factors need to be considered. “In PoE transmission, the power supplied by PSE must be sufficient to power up PD; the distance between PSE and PD must be within 100 meters; the total data rate of front-end devices (eg. IP cameras) should not exceed what the transmission devices are capable of handling; the data rate throughput or the actual payload must be factored in,” explained Wong.

In some cases, the end user may prefer to utilize existing coaxial cables due to cost considerations. It is possible to combine digital and analog infrastructure, but system integrators and installers must be aware of certain issues. “Utilizing existing coaxial cables for data/power transmission simplifies installation and reduces costs. [However], installers would need to confirm that the coaxial cable can be adapted for network infrastructure,” said Ronnie Pennington, National Accounts Manager at Altronix. Moreover, “power requirements for every network device must be taken into consideration,” added Pennington.

Distance is another factor to be considered. The longer the distance, the more risk there is for weaker signals, said Wong. In addition, if your EoC transmission also carries power, power drops against transmission distance along the coaxial cables. However, the actual maximum distance of a transmission depends on the data rate, cable quality, and connectors. Overall, the total input data rate into the EoC devices must not exceed the data rate of the coaxial link (20~300Mbps), according to Wong.

Technology is improving
As with other technology, transmission technology continues to evolve and improve. For example, extenders can be added to transmission infrastructure to achieve up to 500 meters of quality Ethernet transmission.

At the same time, end users can expect quality and reliable transmission with current technology. The key is to understand the specifications of each transmission device, and planning out the entire transmission infrastructure carefully. Central to any transmission infrastructure, however, is careful calculations, making the experienced manufacturer/system integrator/installer the defining factor of any infrastructure.

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