CCTV camera consists of:

• image sensor, which converts light into electric signal.
• lens
• a set of electronic parts, processing electric signal.

High precision of image sensor, good choice and quality of lens are the basis for good results. CCTV camera can automatically correct signal only in limited range, therefore we should treat its processing capabilities only as a useful supplement.

Pixel - the single element of sensor array.

Definition of pixel (or point).

Simple cameras have 320,000 pixels, higher class cameras reach above 1,500,000.

Image sensors of cameras are manufactured in technologies:

- CCD (Charged Coupled Device),- CMOS (Complementary Metal Oxide Semiconductor).

CCD
- image sensor based on the principle of gathering electric charge caused by light striking on each photo sensor. Manufacturing of these image sensors is expensive and not available for all companies, despite the fact they were the first devices.

CMOS
- image sensor based on technology of integrated circuits, where light controls isolated transistors being elementary sensors. Cheap technology available to many companies, which made price revolution, because image sensor had previously made 40% of the total cost of a camera.

Development of CMOS sensors follows through:

- miniaturization of micro-transistor elements,- equipping them with micro-lens elements, own signal amplifiers APS (Active Pixel Sensor) and own analog-digital converters.

In the near future we should expect so improved, advanced sensors made in this technology, that there will be no reason to treat them as a second, lower class of image sensors.

In traditional technology the whole signal was "read" from image sensor, amplified and then sent for further processing.
Technology breakthrough in operation of image sensors was started by DSP technology.

DSP (Digital Signal Processing)
in this type of image sensors means that each light-sensitive element is equipped with its own analog-digital converter. The signal is being converted to digital form at the level of light-sensitive elements - it reduces noises, makes possible to control selected light-sensitive elements. Each pixel can be read before it reaches state of saturation, which reduces the risk of overexposure. Comparing to traditional cameras, new capabilities appear, such as: motion detection, programmable backlight, remote control through RS-232 connector, name, data and time generator, and OSD menu. Generally, these cameras have better contrast, commonly have function that allows to reduce blur effect of bright points (this effect is present when we observe image with high brightness points that look as smudge). The most advanced DSP cameras can detect and compensate light changes and perform electronic zoom.

Other digitalization method at the level of light-sensitive elements is MOSAD (Multiplexed Oversample Analog to Digital Conversion).

The look of CCD image sensor

CCD and CMOS cameras in the market. In the practice of CCTV installer most used cameras are equipped with CCD sensors. CMOS cameras usually have lower sensitivity and number of TV lines (around 300 TVL). However, for the reason that CMOS technology allows to achieve small size of the camera, they find their use in, so called, hidden observation. They are commonly used by private detective agencies and other special agencies.

CMOS camera - the size of 1 grosz coin

Image sensor size. Geometric size of sensor, measured in inches. We can find cameras with image sensor size of 1", 2/3", 1/2", 1/3", 1/4" and 1/6".

Camera's sensitivity.
Proper illumination of image sensor is indispensable for generating adequate amplitude of complete (color) video signal with specified signal to noise ratio. This is the most controversial and manipulated parameter describing cameras. Most of manufacturers do not inform about conditions in which it was measured. It is important for this measurement that the camera has switched off automatic gain control function (AGC). There is also needed information on whether the light was measured on camera's sensor or the object, and in the latter case - the light reflection ratio of the object and F-number of the lens used.

Resolution
This parameter of camera is defined by the capability of showing little details on the screen. It is measured in number television lines (TVL). Resolution is defined horizontally as well as vertically. Resolution is limited by the number of sensor's pixels, however it is not a direct dependence. Like with monitors, it is estimation of the ability of transferring color or gray-scale information connected with the number of pixels of image sensor. Some of manufacturers specify only the number of pixels instead of this parameter.

According to resolution, CCTV cameras can be divided into:

- low resolution cameras - around 240 - 380 television lines (generally CMOS cameras),- standard resolution cameras - around 420 - 480 television lines,- increased resolution cameras - around 600 television lines.

Signal / noise ratio.
This parameter informs about ability of the camera to generate image of required quality. It is indirectly related to sensitivity, and expressed in dB (with AGC off).

Working temperature.
The range of temperature within which the camera can work properly, with assumed parameters. Usually from 10 to 45 deg C. To keep good environment conditions ensuring proper operation of cameras there is usually used additional equipment: heaters, fans, airtight housings and other means of conditioning.

For specific image sensor size the adequate lens must be fitted. Generally, the bigger image sensor size, the better image quality. It is related with larger quantity of light-sensitive elements reacting to the light (pixels). In the same time, many applications require miniaturization of the camera. At present, 1/4" image sensor is enough to achieve sufficient quality. It is important to remember that the size of image sensor requires to use the same size (or bigger) lens. For example, 1/2" image sensor can work with 1/2" lens, or bigger, for example 1".

Power supplying is typically realized through external DC 12V source, typical current varies between 100mA and 250mA. Sometimes we can find cameras working with 5V voltage or with built-in mains power supply. In the case of using camera equipped with Auto-IRIS lens, the camera's power consumption needs to be increased by that for lens, which isn't usually bigger than 40-80 mA. In the case of long cables with low cross sections, voltage drops appear, so it is worth to use power supplies with output voltage adjustment, e.g. M1828. There are also cameras powered with 24V AC, or 230V AC.

Besides ensuring adequate voltage value, the same important is selection of current efficiency of power supply - usually the power supplies have current capacity from 250mA to 2.5A. In special cases, for big installations, power supplies with larger load capacity are applied. Nowadays, CCTV devices are often being connected to back-up power sources - popular UPSes. It is very important subject, commonly skipped by installers. Use of UPSes is recommended for all installations in which work, broadly speaking, "PC based" devices (e.g. autonomous DVR, DVR based on DVR cards mounted in PC etc). These devices are very sensitive to any power disruptions, including voltage peaks or momentary power losses. Application of UPS can considerably increase stability, reliability and security level of the whole surveillance system.

It is recommended to use regulated power supplies e.g. M1828

It is especially important to select proper power supply for a wireless camera; inadequate power supplier is often the reason of improper work of the whole system.

Connections between cameras and monitors can be realized over distances from 100 - 600 meters with the use of 75ohm coaxial cables. The concrete maximum distance is highly depending on quality of the cable - 600m range can be achieved when using copper cable TRISET-113 E1015_500.

Depending on cable type, above 100 - 600 m it is recommended to use signal amplifiers M1840. It is important to remember that color cameras are more sensitive to, so called, "stretching cable to the limit" - the initial symptom is decrease in saturation.

Twisted-pair cables are recommended for distances from 10 - 70 meters. It is possible to transmit video signals over longer distances using these cables, up to 400 m - with the use of additional devices - video transformers M16651, M16652, M1667, or even up to 1600 m - using M1668.

Generally, good coaxial cables are more resistant to interferences. Twisted-pair cables should only be used if necessary, or they make "ready to use" infrastructure that cannot be extended with additional coaxial cables.

Video signal transformer TR-1Q M16651

Control elements in cameras.
Adjustments are available in more advanced cameras, allowing to set camera parameters to environmental conditions. Thanks to it, good quality image can be achieved even in difficult lighting conditions. Simple, compact cameras, without any adjustments, are useful for operation with relatively small changes of illumination and within limited focus depth.

AUTOMATICS IN CCTV CAMERAS

EAI or EI is, simply saying, automatic adjustment of sensitivity of the camera to illumination conditions. EAI is useful in environments with little illumination change (e.g. rooms). The advantage of electronic iris is opportunity of using simple lenses with fixed or manually set iris.

Automatic Iris (AUTO IRIS - AI) is the function of a camera allowing to control special type of lenses; it enables to match fixed proportion of light falling on image sensors, no matter the illumination conditions are. Electronic shutter is set to 1/50s, however lens with AI is being closed and opened adequately to illumination intensity. The camera and lens with AI are able to work properly even in environments with large illumination changes, where simple cameras are useless.

Cameras with AI function are equipped with special output controlling AI lens. Depending on the output signal, the lens will close or open the iris, stabilizing intensity of light coming to the sensor. It also helps to keep good contrast in whole observation area.

Control of lens with AI can be performed in two ways:

• Video - IRIS: control by the signal proportional to illumination. Camera provides signal that controls lens motor amplifier, which opens or closes the iris.
Lens with Video-AI has two potentiometers:
• Level: used to set brightness level that should be kept,
• ALC: enabling to set reaction time to illumination changes.
• Reaction mode can be changed from the option marked as PK or P (Peak) to value A or AV (Average); in first case the reaction is adequate to the brightest pixel in the screen, in second case - to average level of the whole screen. Brightness level is being changed from value marked as H (High) to L (Low).
• DC IRIS: lens controlled by direct current signal. Camera has signal output directly controlling the motor of DC-IRIS lenses, which opens and closes the Iris.
In the case of DC-AI lens, both potentiometers are inside the camera. As DC lenses are cheaper, it is worth to check in advance whether the camera has the controller enabling to use them.

AES (Automatic Electronic Shutter) - opening time is set depending on intensity of light falling on image sensor; the change occurs in the range from 1.50s to 1/100000s. Sometimes, in more technologically advanced cameras, we can find manual shutter adjustment. It should be remembered that longer exposition, although increases camera's sensitivity, decreases refresh rate of the image - time lapse effect appears (with long exposition times).

Other chosen types of automatic control are:

AGC (Automatic Gain Control) - stabilizes output signals level and improves S/N ratio; image is more clear however less natural. Switching off this function will effect in more natural image but also more noise.

BACKLIGHT - automatic adjustment of light intensity coming from behind the observed object.

BLC (Back Light Compensation) - function allowing to correct quality of overexposed image; it is enabled when over 50% of central image sensor part is overexposed.

ECLIPSE - helps to hide (cover) overexposed points; similarly to previous function it also increases image clarity.

FLON - function allowing to remove flickering.

GAIN - adjustment of Iris reaction time to illumination changes.

L.L./INT- switch (used in AC power supplied cameras) that causes synchronization with the power grid or exercises synchronization from inner camera circuit.

MES (Manual Electronic Shutter) - available adjustments are: 1/50s, 1/120s, 1/250s, 1/500s, 1/1000s, 1/2000s, 1/5000s, 1/10000s and 1/12000s.

Y/C OUT
Alternative video out (mini-DIN). Video information is provided by two signal paths: luminance (Y) and chrominance (C). Luminance means brightness, chrominance carries information on color.

WB (White Balance) this function helps to correct image due to different illumination types; in the simplest form, it is just switch IN (artificial light) - OUT (natural light). In more advanced cameras it is also possible to adjust individual parameters of this function. Then we can find switch marked as AWB/PWB. In AWB position the temperature of color is set automatically. PWB position switches off auto mode and allows to adjust white balance manually, usually with additional switch or potentiometer.

Example of practical solution

Sensitivity in infrared range. Typical B/W camera is sensitive to radiation in the range visible to human eye (400 - 770 nm) and also radiation from IR (infrared) range (770 - 850 nm). However, the sensitivity in IR scope is lower, therefore the use of cameras for IR observation is limited.

This problem is partially eliminated in special cameras with maximal sensitivity moved to infrared range i.e. 850nm - 1000nm. These cameras are called thermal (thermal vision) cameras, unfortunately their prices are very high.

Color cameras and night observation. Color cameras have no possibility of observation in IR, due to built-in IR filter eliminating influence of this radiation on color reproduction.

There are also color cameras that automatically switch to B/W mode after the dusk. Switch to monochromatic mode doesn't mean that they will properly work in IR (they still have built-in IR filter).

When we want to use color cameras for night observations, then we have to use Day/ Night type of cameras. These cameras don't have IR filter "removing" this range of light, as in standard color cameras. For example, the camera n-cam 115 M11234 can also work at night (in total darkness - no visible light) with the use of built-in IR illuminator. This construction of camera (lack of IR filter) has though some disadvantages. In normal light (visible light range) such camera has sometimes problems with white balance - it doesn't convey true colors, e.g. black color is commonly "seen" as navy blue etc. The effect is more visible with outdoor work where natural sunlight (as we know - including IR radiation) is dominant. This behavior of a camera may be treated by some installers as improper work of the device. Indoors, where other kinds of light are used (bulbs, fluorescent lamps) this effect is not so visible.

When IR illumination is not required, it is much better to use typical color cameras after all. Admittedly, they usually have lower sensitivity, but they have no problems with colors. We suggest to use u-cam 110 code M1128.

An ideal solution is provided by cameras in which IR filter is automatically removed (system based on servomechanism etc.) - there are no problems with color. However, as we can expect, this kind of cameras may be several times more expensive than these described above. They also require using high quality lenses with impoved focus for IR light.
There is yet another solution - two cameras in single housing - B/W and color. Adequate controller turns on the right camera, depending on the lighting.

Wireless or wired camera. Wireless cameras have built-in transmitters working in 900, 1200, 1500, 2400 MHz ranges, or sometimes at different frequencies. Generally the use of wireless cameras is limited only to non-professional applications. Basic disadvantage of this solution is sensitivity to environmental conditions, mainly electromagnetic noises and interferences. It should also be remembered that for the reason of limited bandwidth used by wireless cameras, there can work only limited number of such cameras in one system. In many countries this kind of operation may require adequate license or authorization.

We describe this matter in details in the chapter: Video transmission..

Synchronization problems. Comfort of observation of pictures given by channel sequencer is highly reduced, especially in short switching-over periods, by synchronization "hop" which appears on monitor. It is caused by the fact that each camera, despite that it generates synchronization signal at the same frequency, has certain phase shift. In the case when this problem has big influence on performance of the installation, it is worth to consider use of cameras with external synchronization from the AC power network, e.g. LTC0500 or LTC0600 from Philips. Additional adjustment of phase shift allows good synchronization even if the cameras are powered from different phases. Other solution is connecting the cameras with additional wire, by which synchronization signal is transmitted to each device. The most common synchronization signals are: video signal, vertical deflection pulse, horizontal deflection pulse or combination of that signals.

Additional synchronization of cameras is needed in case of quick switching

Grounding problems. Mistakes in leading the zero voltage rail may cause significant quality loss, e.g. appearance of strips coming from the hum of the power network. The zero rails should be linked together in devices like video changers. They shouldn't be connected only via the cameras. It is also very important to separate zero power rail and the zero signal leads, i.e. to avoid using single zero voltage wire.

To eliminate different types of problems connected with power supplying it is well to employ the SV-1000 M1711 separator. It is meant to be additional security device in CCTV installations - for cameras and other devices, protecting them from atmospheric discharges, however it also eliminates problems of potential difference between devices and secures them from currents running through zero signal rail.

Example of using the SV-1000 separator

Another subject is grounding of metal housings, which is obligatory if camera is powered with AC 230V. For the reason of differences in potential, it is not acceptable to connect zero signal lead with camera housing, therefore it is suggested to use housings allowing galvanic separation of zero signal conductor (including camera's own chassis) from external housing.

In the case of using heaters it should be considered, for the reason of quality and stability of the image, to power the M5415 housing (with heater) with adequate AC or DC non-stabilized voltage, and to install in the casing additional rectifier and stabilizer to power the camera (e.g. M1815). This solution allows to reduce jumps in voltage caused by switching on and off the heater.

Lens mounts. The most popular types used are C and CS. Basic difference between them is different distance from lens to sensor surface. Most of cameras and lenses are equipped with CS mount which is more universal - using additional adapter ring it is possible to mount C-type devices as well. Reverse adaptation is not possible.

Hermetic housings - norms. The IPxy signs define resistance of camera housings to outer environmental conditions. The x - is the number defining mechanical integrity, and y - resistance to humidity. Housings with good enough dust and humidity resistance have labels IP65 or IP66. Totally water-resistant housings have labels IP67 or IP68. Most of compact types of camera housings are not waterproof.

Selection of cameras. Accordingly to EN 50132-7 norm, the selection criteria should take into consideration the following factors:

• camera set should fulfill functional requirements in all demanded environmental conditions;
• it should fulfill all safety requirements ruling in the country and those specific for the application (e.g. in industrial plant)

The main points that should be considerate when selecting CCTV cameras:

- white balance for color cameras;- electronic iris - important in changeable lighting conditions;- long exposition times - in the connection with " multiplying " moving objects edges;- spectral sensitivity - in connection with illumination type;- external synchronization;- back-up powering (especially in remote sites).

Selection of optimum kind of cameras requires consideration of many factors, such as: environmental conditions during all seasons, sizes of objects in the field of view, and others, listed above. The choice of color or B/W type is connected with the use of the camera. More detailed information is provided by color image, as it allows to distinguish details that are also easier to remember; the differences are noted faster, and, in some cases, viewing the color picture is the only way to estimate preciously the situation. Disadvantages of color cameras are higher price and lower sensitivity. We should choose B/W kind when information about intrusion is enough. In low light, only B/W camera with high sensitivity can ensure right surveillance qualities.

Catalog pages of selected cameras.