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Selecting the right power supply for the job

System reliability also depends on knowing exactly what is going on related to a system's various power supplies. Sometimes power system status is communicated locally or remotely. Alerting security personnel of system status in real time enables personnel to react quickly and efficiently, and helps reduce costly system downtime and maintenance.

Centralizing Power Supply Systems

Systems can gain design efficiencies by centralizing the management of power supplies. Supplying power to multiple systems using a single power supply can minimize cost and make the system easier to monitor, use and manage.

One way to centralize a power supply system is by leveraging the unshielded twisted pair (UTP) cable that is sometimes used to transmit video and data signals back and forth from video cameras to a central location. Video surveillance systems using UTP employ video baluns (transceivers) at each camera to convert the video signal from the coaxial output of the camera to enable it to travel along with data (RS-422/RS485 to direct pan/tilt/zoom, camera controls, etc.) to a centralized transceiver hub. The hub takes the signals from various cameras and transitions them back to coax to be used by a DVR or video multiplexer.

Transceiver hubs can also provide power to the cameras across the UTP cable by way of a centralized power source, thus eliminating the need for an individualized power source at each camera. Using transceiver hubs with integral camera power - such as the HubWay Series from Altronix - also provide system operators with video signal and power status for each camera in the form of LED indicators.

Another way to centralize power supplies is by using Power-over-Ethernet (PoE) with IP-based networked systems. As technologies for the security industry transition to a networked environment, the market demand for integrated systems on a network platform has gained significant traction as users become aware of the enhanced functionality and lower total cost of ownership they offer. Equipment to power those networked technologies is also evolving.

PoE offers many benefits to the security industry. It eliminates the need to have a power outlet and low-voltage power supply at every camera location. A single network CAT5 cable can supply both the power to operate the cameras and transmit back the images. The power, in effect, enjoys a "free ride" on the CAT5 cable that is fundamentally required for network connectivity. PoE can reduce the need for multiple power supplies to one common and centralized unit and share a common power backup scheme.

The power sourcing equipment can either be a PoE switch (a network switch that has the PoE feature), or a "mid-span" power source that is located between a regular (non-PoE) Ethernet switch and a PoE network device. This configuration enables networks to accommodate PoE devices without the replacement of an existing Ethernet switch.

The PoE power sourcing equipment will inject power onto the CAT5 cable after interrogating a PoE-powered device - such as a camera - to determine if it is compliant with the standard. Non-compliant devices will be denied power, thus safely restricting operation to intended PoE devices. Altronix offers the NetWay Mid-Span PoE products to provide power over standard network infrastructure, and can accommodate PoE and conventional IP video cameras, as well as edge devices.

Currently, the PoE standard (IEEE 802.2af) accommodates only PoE-powered devices that require less than 13 watts of power. This means that a PoE power source must be capable of sourcing 15 watts to allow for line loss. This power restriction excludes use of numerous camera products that have features including pan-tilt-zoom and infrared illumination. A future standard (IEEE 802.3at) is slated to accommodate up to 25 watt devices, meaning the PoE power sourcing equipment must be capable of supplying 30 watts to allow for line loss.

A non-compliant PoE device that requires less than 13 watts for operation can also be connected to a network by use of a PoE splitter. A splitter is an adapter that presents a PoE authenticating signature from the power supply to the IP device and then splits out the power to a separate 12VDC connection while supplying the non-powered data signal via an RJ45 connector. This configuration, in effect, converts the network device into a virtual PoE-powered device.