PoE (Power over Ethernet)

Power over Ethernet (PoE) is a mechanism for supplying power to network devices over the same cabling used to carry network traffic. In this technology no infrastructure upgrade is necessary.
A digital security camera normally requires two connections to be made when it is installed:

A network connection, in order to be able to communicate with video recording and display equipment and a power connection, to deliver the electrical power the camera needs to operate. However, if the camera is PoE-enabled, only the network connection needs to be made, as it will receive its electrical power from this cable as well and this enables the elimination of a separate cable solely for power use.

Cisco was one of those manufacturers that began including PoE capability within its switches in 2000.

Advantage of the Ethernet cable
• The challenge during installation is to calculate the total power consumption required so it is less than the power budget of the switch. The total power consumption requirement of all equipment that will be connected to a specific switch on a network needs to be calculated to ensure sufficient power is available per switch.

 • Without being tethered to an electrical outlet, devices such as IP cameras and wireless access points can be located wherever they are needed most and repositioned easily if required.

 • POE power comes from a central and universally compatible source, rather than a collection of distributed wall adapters.

 • Having power available on the network means that installation and distribution of network connections is simple and effective.

 • Wifi and Bluetooth APs and RFID readers are commonly PoE-compatible, to allow remote location away from AC outlets, and relocation following site surveys.

 • Unlike standards such as Universal Serial Bus which also power devices over the data cables, PoE allows long cable lengths.

 • Simply connect other network devices to the switch as normal and the switch will detect whether they are PoE-compatible and enable power automatically.

There are several standardized or ad-hoc systems which pass electrical power along with data on Ethernet cabling. Two of them have been standardized by IEEE 802.3: standard IEEE 802.3af and new prepared standard IEEE 802.3at.

In addition to standardizing existing practice for spare-pair and common-mode data pair power transmission, the IEEE PoE standards provide for signaling between the power source equipment (PSE) and powered device (PD). Up to a theoretical 51 watts is available for a device, depending on the version of the standard in use and the vendor of the hardware.

A midspan (or PoE injector) is used to add PoE capability to regular non-PoE network links. Upgrading each network connection to PoE is as simple as patching it through the midspan, and as with POE switches, power injection is controlled and automatic. It is also possible to upgrade powered devices, such as IP cameras, to PoE by using a PoE splitter.

The following chart shows the power consumption at both the PSE and the PD.

Class Usage Power Level Output at the Power Sourcing Equipment (PSE) Maximum Power Levels at the Powered Device (PD)

PoE Applications

IP Cameras Cabling

However small it might appear, a problem with network cabling can have a catastrophic effect on the network’s operation. Even a small kink in a cable can cause a camera to respond alternatively, and a poorly crimped connector may arrest Power over Ethernet (PoE).

Wiring standards

When wiring up an IP camera, you must use a CAT5 data cable containing 4 pairs of wires. We have two wiring standards for network cabling: T568a and T568b. T568a and T568b should not be combined on the same cable.

These two wiring standards are used to create a cross-over cable (T-568A on one end, and T-568B on the other end), or a straight-through cable (T-568B or T-568A on both ends).

Use high-quality CAT5e or CAT6

Cables are categorized based on the data rates that they can transmit effectively. The specifications also describe the material, the connectors and the number of times each pair is twisted per meter. Cat5 and Cat6 are twisted pair cable.  Basically they both have 4 pairs of wires that are twisted around each other for the cable’s length. The most widely-installed category is CAT5e.

There are physical differences between Cat5 and Cat6, but the most important difference is that Cat5 is rated for 100Mbps, Cat5e is rated for 350Mbps, and Cat6 is rated at 1000Mbps.

Video files are commonly very large data files, and to be moved around the network as quickly as possible. It is recommended to utilize Cat5e or Cat6 cabling for gigabit connectivity, even if existing network switches and routers support 100 Mbps.

Have good cable runs

Ensure that cabling meets the requirements of your equipment. The distance between a transmitter and a receiver cannot be greater than 100m (325 ft.) in total. A good rule of thumb is 90 meters for horizontal runs, and 10 meters for the patch cabling. It is also important to be aware of the whole length of cable and connectors are the same type, such as STP.

Cabling should not run next to electrical mains cabling (because of interference). It is especially important to use of STP cables to maintain a high degree of immunity to RF (Radio Frequency), electrical and magnetic disturbances as well as provide the lowest possible degree of radiated and conducted Radio Frequency emission.

It is also mandatory to use an STP cable where the camera is set outdoors, or where the network cable is routed outdoors. STP cables also lower the effects of close situated power relays, motor inverters and electrical cables that are run in parallel close to network cables. This is normally accomplished since the switch or POE adapter is connected to an earthed mains socket.

The tradeoff in using UTP cables is a higher level of emitted Radio Frequency emission and higher susceptibility to radio frequency immunity.

Since network cabling typically uses solid wire, cabling should not be twisted or bent into a tight radius (not less than 4 times the diameter of the cable). Metal staples should not be used to secure cable runs. Avoid a daisy chain network topology.

Correct connectors

Network connections use RJ45 connectors designed for either stranded or solid cable, but usually not both. It is important to certify that the type of RJ45 connectors is coordinated with the type of cable, STP or UTP, used.

Keep the pairs together and wire correctly

A network cable has four pairs of twisted wires, and these are color coded (orange, green, blue and brown). The cable specification has been designed for high-speed data transfer and so little cross-talk. It is very important that no more than about 6 mm of the cable is untwisted at either end; otherwise, problems such as ‘near end cross-talk’ can arise. It is essential that wire the plug correctly and not just from pins 1 through 8 at both ends.

Environmental conditions

Environmental considerations, for example whether the camera will be installed indoors or outdoors, determine the cabling and connectors. Depending on the environment, the camera must be installed with the adequate housing to provide the correct level of protection. If the camera is exposed to acids, severe weather conditions, or extreme heat or cold, the camera needs a housing that tolerates this kind of environment.

Wide Dynamic Range (WDR)

The challenge that often arises with video security systems is the inability of standard network cameras to capture clear video in situations where there is a significant variance in lighting levels within a single scene.

In surveillance, Wide Dynamic Range (WDR) is intended to provide clear and useful images/video even under backlighting, where the intensity of illumination varies a lot—namely when there are very bright and very dark areas simultaneously in the camera’s field of view. Hence WDR allows system to correct for the intense back light surrounding a subject and thus elevates the ability to distinguish features and shapes on the subject.

There are many areas and conditions, both inside and outside, where video surveillance cameras with WDR should be installed:

• A store or an office that has a lot of windows.

• Inside parking garages, tunnels, train stations and another transportation centers where people and vehicles enter or exit.

• Environments with intense light reflection, like office buildings, shopping malls, locations with water features or areas that are prone to water puddles.

There are two basic techniques that are generally used to provide WDR: multi-frame imaging and non-linear sensors.

Multi-frame imaging – In this technique the camera captures multiple frames of the field-of-view; each frame having a different dynamic range. The camera then combines the frames to produce one improved WDR frame.

Non-linear sensors – These are typically logarithmic sensors, where the sensitivity of the sensor at different illumination levels varies, enabling the capture of a wide dynamic range image in a single frame.

So the performance of a WDR camera is very dependent on the sensitivity of its sensor and the processing ability of its DSP, in combination with its iris type and shutter speed.

WDR cameras are becoming increasingly popular as being able to tell colors apart at night is important for identifying suspects and culprits.  The professional WDR security camera can be used to provide surveillance of areas that have a wide range of lighting conditions. This technology is used in famous security camera brand like Sony, Axis, RedLeaf and JVC.

Camera Sensors

Over the years, the security cameras are improved. Housings have gone from the behemoths of the 1970s and ’80s to the compact versions we see today. Images have gotten more obvious and have changed from black and white to color. However what has driven these remarkable changes? The cameras can’t get smaller unless the components inside the camera get smaller and use less power. Video can’t improve unless the image sensors and processors work better. An image sensor is the piece of camera that captures the light hitting the camera lens and turns it into electrical signals.

As light passes through your camera lens, it hits the image sensor. The sensor is made up for many little photosites (each photosite becomes a pixel in the video resolution), and the amount of light on each individual photosite determines how much light will be in each pixel of video. The light/dark sections of each pixel make up a cohesive image in the final video.

Image sensors for IP cameras are typically categorized into two main technologies: charge-coupled devices (CCD), complementary metal oxide semiconductor (CMOS). Both CCD sensor and CMOS sensor are actually using same kind of sensor called Photo diode. Even though analog CCD sensors are an old technology (around for over 30 years), requiring complex implementation systems and costly manufacturing processes, they are still the most common image sensor used in the security industry.

In CCD sensors, signal readout is an analog voltage, which is then converted to digital signals using additional, high-speed electronic components. Image quality is affected because signals are converted of analog to digital far away from the capture’s original point. CMOS image sensors utilize newer technology to record better HD resolution and fast-moving activity, and are found in the majority of IP new cameras.

CCD

CCD sensors generally record more resolution than CMOS sensors. Even though a CCD sensor has to spend more time and energy converting each pixel than an equivalent CMOS sensor, it can hold more across its surface. The noise level on a CCD sensor is inherently less than that on a CMOS sensor of the same size. In CCD sensor, colors tend to be more saturated and vibrant in contrast to those that are taken through a CMOS sensor.

CMOS

Each CMOS pixel is packaged with the circuitry to convert it to digital signal, thus each sensor takes up more space. CMOS sensor is become idle under 10 lux. The clutter on CMOS sensors reduces the light sensitivity of the chip. CMOS sensors have 10 times more fix pattern noise then CCD sensors.

CMOS sensor very useful for fast frame camera, the speed of frame can be as high as 400 ~2000 frame/sec. Early CMOS sensors were based on standard technology already extensively applied in memory chips inside PCs, for example modern CMOS sensors use a more specialized technology and the quality of the sensors is rapidly increasing. CMOS sensors also have a faster readout (which is advantageous when high-resolution images are need), lower power dissipation at the chip level.

Depth of Field

The depth of field (DOF) is the distance in front of and beyond the point of focus that appears acceptably sharp in an image.

A large depth of field means that a large percentage of the field of view is in focus, from objects close to the lens often to infinity. You can control the depth of field by focal length, iris diameter and distance of the camera to the subject.

The smaller focal length and iris opening or a long distance between the camera and the subject, the greater the depth of field. In other words, the larger the f-number the greater is the depth of field.

The small depth of field is most apparent at night when the lens is fully open and the depth of field is at its minimum so objects that were in focus during the day may now be out of focus.

Depth of field may be important, for instance, in monitoring a parking lot, where there may be a need to identify license plates of cars at 20, 30 and 50 meters (60, 90 and 150 feet) away.

F-number and Exposure

In optics, the f-number (sometimes called focal ratio, f-ratio, f-stop, or relative aperture) is the ratio of the lens’s focal length to the diameter of the aperture or iris diameter. It is a dimensionless number that is a quantitative measure of lens speed. The f-number N is given by where  is the focal length, and  is the diameter of the aperture or iris diameter. For example, if a lens’s focal length is 10 mm and aperture diameter is 5 mm, the f-number is 2 and the aperture diameter is f/2.

Ignoring differences in light transmission performance, a lens with a greater f-number, the smaller the lens opening (f16 – narrow aperture), projects darker images. The brightness of the projected image (illuminance) relative to the brightness of the scene in the lens’s field of view (luminance) reduces with the square of the f-number. Doubling the f-number reduces the relative brightness by a factor of four. To maintain the same exposure when doubling the f-number, the exposure time would need to be four times as long.

Some lenses change the size of the aperture stop and thus the aperture or iris diameter. While lenses with automatically adjustable iris (DC-iris) have a range of f-numbers, often only the maximum light gathering end of the range (smallest f-number) is specified. There is also another precise iris control called P-Iris. It is an automatic system that involves a P-Iris lens and specialized software that optimize image quality. The system is designed to address the shortcomings of an auto-iris lens. A lens with a lower f-number is normally more expensive than a lens with a higher f-number. Most popular video security systems like Axis, Sony, RedLeaf, etc. apply these technologies in their cameras.

Exposure is the light’s amount that reaches to the sensor of camera. The longer the exposure time, the more light an image sensor takes. Bright environments require shorter exposure time, while low-light situation require longer exposure time. Note that when the exposure time is increased, motion blur is also increased, and increasing the iris opening has the downside of decreasing the depth of field.

Exposure Value (EV) is a number that represents a combination of two fundamental camera settings, speed of camera shutter and f-number, such that whole combinations that yield the same exposure have the same EV value (for any fixed scene luminance).

Although all camera settings with the same EV nominally give the same exposure, do not necessarily have the same picture. The f-number (relative aperture) determines the depth of field, and the shutter speed ( exposure time) determines the value of motion blur.

Exposure value is:where

• N is the relative aperture (f-number)
• t is the exposure time in seconds

When deciding on the exposure, a shorter exposure time is recommended when fast movement or when a high frame rate is required. Image quality in poor lighting conditions will be improved by longer exposure time, but it may increase motion blur and lower the total frame rate since a longer time is required to expose each frame. In some network cameras, an automatic exposure setting means the frame rate will increase or decrease with the available light amount. It is only as the light level decreases that artificial light or prioritized frame rate or image quality is important.

Note that if more light than necessary can reach to device, the image will be over-exposed, and as a result, a white-out image is recorded. On the other hand, if insufficient light could reach the image capturing device, the image will not form properly, and will be dark (i.e., under-exposed). An over- or under- exposed image contains less details. Therefore, the right amount of light that can reach the image capturing device must be controlled a camera lens.

EV=0 corresponds to the exposure time of 1s and a relative aperture of f/1.0. If the EV is known, it can be used to select combinations of exposure time and f-number.

Field of View Calculation

As mentioned in the previous post, Field of view (FOV) relates to the size of the area that a camera will see at a specific distance from the camera. The field of view is dependent on lens focal length and the camera sensor’s size.

The FOV width and height are calculated using the following formulas:

Manipulating the FOV formula allows the distance calculating in feet from the camera for a required FOV width.

Before camera’s FOV is selected, the minimum desired resolution for a viewed intruder or target must be determined (i.e., whether to identify a person or to just determine if a person is within the scene). This will limit the maximum FOV width and is referred to as the resolution-limited FOV. The resolution-limited FOV width is determined with using camera resolution in horizontal lines per foot and the number of lines of resolution per foot. The following formula is used to calculate the resolution-limited FOV width:

A resolution of 16 lines per foot is considered passable for identifying most people. If a camera with 350 horizontal lines of resolution is utilized, the resolution-limited FOV width for a resolution of 16 lines per foot is calculated as follows:

Another method of calculating the field of view is to use a lens selection wheel. Mechanical computing wheels are accessible from many lens manufacturers and CCTV manufacturers. They will give a good approximation of FOV parameters.

A viewfinder also is used to determine the field of view of a lens. This is a specially designed lens through which one can view the scene of interest. The scene is masked through the lens in such a way as to represent the picture that will be seen on the monitor. The desired scene is dialed up on the viewfinder and the focal length of the lens required for the particular sensor size of the camera read from the side of the viewfinder. A viewfinder only determines a lens focal length value; other parameters must still be calculated.

Most of lens manufacturers have developed tables for determining the field of view. The sensor’s size and focal length is cross-referenced to the column of the desired distance, and the width/height of the field of view is read from that column.

Lens Size	Viewing Angle		Field of View (in feet)
			5 feet away		10 feet away		15 feet away		25 feet away		50 feet away		100 feet away
(mm)	Width	Height	W	H	W	H	W	H	W	H	W	H	W	H
3.6	74	55	7.5	5.2	15.1	10.4	22.6	15.6	37.7	26.1	75.4	52.1	151	104
4.0	69	49	6.0	4.5	12	9.0	18	13.5	30	22.5	60	45	120	90
4.3	65	45	5.6	4.2	11.2	8.4	16.7	12.6	27.9	20.9	55.8	41.9	111	84
6.0	42	32	3.8	2.9	7.7	5.7	11.5	8.6	19.2	14.4	38.4	28.7	77	57
8.0	32	24	2.9	2.1	5.7	4.3	8.6	6.4	14.4	10.7	28.7	21.3	57	43
12.0	22	17	1.9	1.5	3.9	3.0	5.8	4.5	9.7	7.5	19.4	14.9	39	30
16.0	19	15	1.5	1.2	3.0	2.5	4.5	3.6	7.2	6.1	14.4	12.2	28	24

In summary, whether a camera scene is useful depends on whether targets are distinguished. Camera resolution, camera sensor’s size, lens focal length, as well as lighting, shadowing, camera aiming, and camera sensitivity all have a role in target distinguishing ability. Resolution and performance of other components such as TV monitors, recorders, and signal transmission equipment must be considered also. Most security cameras present today range from 300 to 700 horizontal lines of resolution. Black-and-white security cameras commonly have a horizontal resolution of 500 to 600 lines, while color cameras for security applications have 300 upto 400 lines.

Field of View

In surveillance, the field of view (FOV) is visible part of the scene through the camera at a particular position and orientation in space. The field of view is determined by the focal length of the lens (FL) and the image sensor’s size; both are specified in a network camera’s datasheet.
A Len’s focal length is defined as the distance between the entrance lens (or a particular point in a complicated lens assembly) and the converge point of all light rays (normally the camera’s image sensor). The longer the focal length, the narrower the field of view.

The fastest way to find out what focal length lens is required for a desired field of view is to use a rotating lens calculator or an online lens calculator.

A Varifocal lens allows the user to manually adjust the camera lens, generally using adjustment screws or knobs.

The size of a network camera’s image sensor, typically 1/4”, 1/3”, 1/2” and 2/3”, must also be used in the calculation. Using simple geometry the scene size seen by the sensor is inversely proportional to the lens focal length. The field of view is useful if you want to monitor a specific target, such as cash register or doorway.

The field of view is classified into three types:
Normal view: offering the same field of view as the human eye.

Telephoto: a narrower field of view, providing, in general, finer details than a human eye could deliver. A telephoto lens is used when the surveillance object is either small or located far away from the camera. A telephoto lens generally could gather less light than a normal lens.

Wide angle: a larger field of view and less detail than in normal view. A wide-angle lens generally provides good depth of field and fair, low-light performance. Wide-angle lenses sometimes produce geometrical distortions such as the “fish-eye” effect.

Smart IR Camera

As mentioned in “Day and night network cameras” post, in order to see at night or in other situations in which there are low levels of visible light, IR security cameras capture clear images. Such cameras use infrared LED arrays to augment the available ambient lighting.

Sometimes, customers can make the mistake of purchasing an IR camera that does not fit their application because they do not know the size of their coverage area and overexposure is happened. For instance, a person’s face will be “whited out” so that no features can be recognized, making the images captured unusable for identification purposes. This can easily happen for an infrared camera with a 65 foot IR range, but the camera is monitoring an area where people can approach the camera at a much closer distance (5 to 10 feet for example).

Smart IR is a technology was invented to adjusts the intensity of the camera’s infrared LEDs to compensate for overexpose problem. These cameras automatically (combination of hardware and software) adjust the intensity of their built in infrared LEDs to compensate for objects within close distances to the camera lens.

Applications which would greatly benefit from Smart IR include high traffic areas where subjects move towards and away from the camera such as:

• Store fronts
• Gated access points
• Home entry and exit points

Many infrared cameras like VIVOTEK, RedLeaf and Hikvision that are available today include this technology, but not all do, so check your camera’s specification.

Day and Night Network Cameras

Regular, color network cameras are available which delivers color images during the day. But when daylight fades, cameras sense the lower light levels. There are a variety of techniques to improve image quality in condition of poor light.

Camera with IR filter

In this camera, the end user can see picture in total darkness at the distance of infrared emission produced by LEDs. A day and night camera can have infrared LEDs mounted surrounding the lens. These LEDs can emit their own light anywhere from 20 meters all the way up to 70 meters and beyond.

During day time, when the filter is put in place, it filters the wavelengths, improving the quality of the image by showing only the “visible” light, removing the “infrared” light from the spectrum.

When the camera is in night mode (light diminishes below a certain level), the IR-cut filter is removed by a small motor, allowing the camera’s light sensitivity to reach down to 0.001 lux or lower. In this mode, the camera starts recording in black and white.

Remember that a camera’s infrared capabilities are, for the great majority of applications, be used for less than half the day.

Digital day/night cameras

Digital day/night cameras (or electronic day/night cameras) are also available, which electronically adjust colors during the day, instead of using an infrared filter. Once it becomes dark, the camera digitally switches to black and white. Checking the LUX rating is the best way to see how digital day/night cameras are performed.  Without the need for a physical filter, digital day/night technology can also be leveraged for smaller form factors. Day/Night recording is available on dome, fixed dome, bullet, box, and PTZ security cameras.

Almost every IP camera on the market now has some form of day/night feature, from basic image optimization technologies such as the Panasonic BL-C101 and the Sony SNC-CH110, to advanced, day/night functionality in models like the Axis P1347, the RedLeaf RLC-DF2035 and the RedLeaf RLC-BF2422.