Power over Ethernet (POE) allows you to very simply install network cameras (or other network devices such as VOIP phones) with just a single network cable.

We get a lot of queries about POE, so we’ll try to give you a quickand simple explanation:

An ethernet network is the standard format of network cabling that you use to connect your networked and other devices.

The cables used are commonly known as Cat5 cable (other variants such as Cat5e and Cat6 are available).

The plugs on the ends of the network cables are terminated in RJ45 connectors.

Each Cat5 network cable contains four pairs of cable cores, all of these cores are terminated in the RJ45 plugs, but only two of the pairs are actually used for the transmit and receive signals used by the network for data transmission.

This means that there are two pairs of spare cable cores available within every network cable.

Quite simply these can be used to carry power, electricity, volts & amps to devices on the network.

There’s an IEEE standard governing the proper format and use of Power over ethernet, and the basic version of this is the 802.3af standard. This standard governs things such as the configuration and use of the spare cores and the voltage used being common in all 802.3af compliant devices (nominally 48 volts DC). This relatively high voltage is used to enable the power feed to be useful over relatively long distances – up to 100m. If a lower voltage was used, the voltage drop caused by the cable length might render the even lower voltage arriving at the far end useless for powering the camera.

So, you can take a device known as a poe power injector and place this at the source end (PC, control room …) and route your network cable through the power injector on its route to the camera.

At the camera end, if the camera is a POE enabled device (has 802.3af compliant POE built-in) you can plug the far end of the network cable directly into the rear of the camera and the internal camera circuitry will split-out from the network cable the power that it needs to operate. In this way just a single network cable is all that is required to both feed power to the camera and to take the IP video signal away from the camera and back to the PC or other recording device.

This Power Over ethernet solution makes for really simple low-voltage installations without the need for a specialist electrical installation contractor, or the requirement for mains or other power cables. Hence, you save not only labour costs but also the cost of a second copper cable.

If the camera or network device does not have built-in POE compatibility, it is still possible to use Power over Ethernet by deploying a device called an Active Splitter at the camera end of the network cabel. An active splitter (as the name implies) is simly an electronic gadget which splits the power and data signals from the one combined network cable to the two cables that a non-POE device requires; one cat5 for data, one power for the camera supply. NB if you are using a splitter be sure to select a device which is able to transform from the 48V carrier signal used in POE down to the correct voltage for the camera you are using (likely to be 3.3V, 5V, 9V, 12V or similar) and is able to present the power in the correct physical format to plug into the rear of the camera e.g. 4.5mm barrel connector.

So, as you can see from the above, the basics of power over ethernet are simple, but there are a few potential pitfalls to catch out the unwary. If you need any help with selecting the correct POE devices for your application please just give us a call.

use-IP Ltd supply a range of POE devices.

Further explanation of Power Over Ethernet

Wikipedia

Axis cameras are expected to go up in price from 1st December – by more than the drop in VAT!

We wish we could have given you more notice but have only just heard ourselves.

Contact us now for best pre price rise offers on all Axis network cameras, servers and software …

Axis have just announced the launch of a new range of VGA H.264 compact cube network cameras.

Axis Communications introduces AXIS M10 Network Cameras, a series of small and smart cameras, ideal for securing locations such as small businesses, boutiques, restaurants, hotels and residences. These affordable, intuitive and reliable cameras from the market leader in network video offer best-in-class image quality and professional monitoring capabilities.

There are three new models coming:

Axis M1011 Network Camera

Axis M1011-W Wireless Network Camera

Axis M1031-W Wireless Network Camera

These new models are due for launch in January 2009.

The Axis 1031 has some really novel features such as a built-in passive infra-red (PIR) movement detector AND a white LED that can be used to illuminate the scene. It also has built-in two-way audio capability.

Axis have produced a great little M1031 demo video to showcase this state-of-the-art network video camera in a security application.

Official Axis Press Release

Keep an eye on our Axis Camera Shop for availability.

As always, we look forward to your comments and feedback:

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Megapixel resolution – what do we mean by megapixel?

Before network IP CCTV cameras came along the resolution of traditional analogue CCTV cameras (connected by co-ax) was measured in TeleVision Lines (TVL).

This TVL parameter indicated that if you ran your finger horizontally across a CCTV image this would be the number of vertical lines that you would be able to resolve. Obviously, the higher the number the greater the level of detail indicated.

The highest specification analogue colour CCTV cameras currently available can resolve to 540-560 TVL. Monochrome (black & white) analogue CCTV cameras perform slightly better and the best will claim somewhere around 620TVL.

Just to put these analogue TVL figures in perspective with the current IP camera performance – 540TVL is equivalent to 0.4 Megapixels.

Pixels is a term of resolution used commonly in the IT world. Computer monitors will have their resolution specified by means of a horizontal and a vertical pixel resolution e.g. 1440 x 900 pixels.

Digital still cameras also express their resolution capability in terms of pixels, of course nowadays these too all deliver megapixel images.

A typical megapixel IP CCTV camera might have a resolution specification of 1920 x 1080 pixels.

If you multiply the horizontal (1920) by the vertical (1080) pixels you get a total pixel count of 2,073,600 pixels.

This value may also be expressed as 2.073 Megapixels (Mega equals millions).

It is interesting to note that the co-ax connected analogue CCTV camera has been stuck at or below the current glass ceiling of 560TVL for about the past five years.

In an era when you can readily purchase a mobile phone with a built-in 8 megapixel camera, why would anybody install a security imaging solution based upon co-ax which is unlikely to ever exceed 1/20th of the performance of a mobile phone?

Gigabytes is a term that we have all become familiar with, as the Hard Disc Drives (HDDs) in most Personal Computers (PCs) are now typically sized in the Gigabyte range.

A reasonably modern PC is likely to be supplied with a 250 or 500GB hard drive. A disc of such capacity is likely to be more than adequate for most standard PC usage.

Back in the days when Digital Video Recorders (DVRs) were a new technology the first units were typically supplied with a 40GB hard disc, that being the largest single drive capacity available at the time.

As with all things technological HDD sizes have developed greatly, and it is now quite simple to purchase a single HDD with a capacity of 1.5 Terabytes!

What’s a Terabyte? One Terabyte is equivalent to one thousand Gigabytes.

Therefore 1.5 TB = 1,500GB!

That’s a heck of a lot of storage capacity on a single drive.

Why do we need all of this capacity for IP CCTV recording solutions? If you are familiar with taking and manipulating digital still photographs you’ll be aware that a single high quality image file may be 1MB (MegaByte) in size. Bear in mind that with a network camera CCTV solution we will effectively be capturing many such images every second, from every camera, and you’ll begin to understand that we can very soon accumulate GigaBytes of storage.

The amount of storage available directly dictates how much video we can store. We can regulate this by either adjusting the file size of the images (using some form of video compression) or by adjusting the number of images per secnd that we capture (the frame rate or fps – frames per second).

The really big IP CCTV camera solutions (see our IP CCTV Facts page) are now using PetaBytes of storage.

• 1 GigaByte = 1,000 MegaBytes (10⁶)
• 1 TeraByte = 1,000 GigaBytes (10⁹)
• 1 PetaByte (10¹⁵) = 1,000 TeraBytes (10¹²)
• 1PB = 1,000,000,000,000,000 Bytes – that’s a lot of image storage!!!!