Power over Ethernet for IP Surveillance Systems

You've probably seen advertisements for POE switches and POE-compatible IP cameras. Here's what this all means, at least as far as IP cameras and other devices that are installed over an Ethernet network.

POE is an established technology that provides low-voltage direct current (DC) power delivery to network devices over the same wires that currently carry data. This means you can now run only one cable and still be able to both power the device and transfer data. The specifications come from the IEEE standard 802.af. This allows the powering device to use a voltage from 36-57 VCD. The most common voltage found is 48 volts.

Here are the different classes of POE devices.
Class Usage Maximum Power Levels at Input of Powered Device [Watt]
0 Default 0.44 - 12.94
1 Optional 0.44 - 3.84
2 Optional 3.84 - 6.49
3 Optional 6.49 - 12.95
4 Reserved (PSEs classify as Class 0)

One of the problems with CCTV IP cameras is that sometimes a heater, blower and a PTZ device are needed in some applications. The current standard only provides a maximum of 15.4 watts. Most PTZ devices and heaters and blower exceed this maximum.

There is good news on the horizon. A future standard, commonly referred to as POE+, is being developed by the IEEE 802.3at task force. There is still debate on the maximum wattage, but it is typically between 24 and 30 watts. This will allow many manufacturers to design their PTZ cameras with heaters and blowers around this new standard and still only run one cable to the camera location from the network switch.

Understanding IP Megapixel Resolution

Many end users will specify a mega pixel resolution camera but not consider what they will actually see with the cameras themselves. Many manufacturers have their own numbers for the ability to identify people and license plates. This number is called the pixel density (how many pixels are available in a given space) and is stated as pixels per foot. We will use one manufacturer’s number of 45 pixels per foot to be able to read a license plate.

Let’s say we have a three megapixel camera and we want to know if we will be able to have license plate recognition (LPR). The formula for determining this is as follows:
Pixel Density (PD) = Pixels (camera resolution)/ Field of View.
For our example, our field of view is 30 feet.
The horizontal pixel count for a 3 mega pixel camera is 2048 pixels.

PD = 2048 / 30
PD = 68.2 pixels per foot

The answer is yes, we will be able to read the license plate with a field of view of 30 feet, using a 3 megapixel camera.

We can look at this from another perspective. What would my field of view be if I have a 5 megapixel camera and I still want to have the ability to view license plates?
The horizontal pixel count for a 5 mega pixel camera is 2592 pixels.
Field of View (FOV) = Pixels / Pixel Density

FOV = 2592 / 45
FOV = 57.6 feet

Before the camera system is installed, examine what exactly you want to view and don't just blindly install cameras in all locations.

Success in Flushing Community School District

Between top education priorities and the Fourth of July weekend, we didn't have time to put together a new tip for you. Fortunately, our friends at Exacq have a success story to share.

The Flushing Community School District covers 65 square miles, with a population of approximately 25,000. K-12 enrollment is approximately 4,277 students, with 8 school buildings serving the educational needs of the students.

exacqVision video management software (VMS) was installed to help Flushing administration "monitor student behavior after the fact." exacqVision is installed on two industry standard servers with video recording to a 30TB iSCSI disk array. ExacqVision manages 149 IP cameras and encoders located throughout 8 school buildings to provide a safe and orderly environment in which all student have an opportunity to realize their potential.

Each school has the exacqVision client software installed on the principals' and secretaries' PCs, giving them access to only those cameras located in their buildings. When an incident is reported, staff will search digital video recorded on the servers to investigate and support their findings. Video can be easily exported to a DVD or USB flash drive and may be shown to students, parents or police as per board policy. Video evidence helps Flushing reduce repeat offenses.

The complete success story can be found at http://www.exacq.com/downloads/exacqvision-education-fcs.pdf.