Many elements greatly influence image quality in a video surveillance system. In many cases, even if high quality equipment is used, the results obtained are not satisfactory.
The main causes of distortion are:
1. Quality and type of cable used for connecting video surveillance cameras
1.1. Coaxial Cable. Most coaxial cables have a characteristic impedance of 75 Ohms, the transmitted video being one balanced. The thicker the cable, the less losses for the cctv video surveillance system. The video signal is an electric current, the smallest losses we will have on a core and copper alloy shield. RG 59 is the most common coaxial cable type in CCTV video surveillance systems. With an external diameter of 6.1mm and a 0.64mm thick core, it offers increased flexibility and the main disadvantage is the signal loss especially at high frequencies. The RG 6 is a coaxially rigid video coaxial cable with an external diameter of 6.86mm, a 1mm thick core and a double screen, but it can transmit images at far greater distances without loss of signal. Another important aspect of the coaxial cable is the shield. It plays a very important role in rejecting interferences. The coaxial cable shield may be formed from a thin wire mesh or from several alternative layers of film and wire mesh. The coaxial cable is used with video surveillance systems with surveillance cameras located at relatively small distances from the DVR digital video recorder (maximum 250 meters). CCTV installers in central London by LogicalGate.
1.2. UTP. The twisted wire is a type of cable in which two conductors are twisted around each other to cancel the electromagnetic interference. Using the UTP cable for video surveillance cameras and CCTV systems can extend the maximum cabling distance to 1.2 ~ 1.5km using active video transceivers. The signal is unbalanced and the caracetristic impedance is 100-110 Ohms. It is NOT RECOMMENDED to use two pairs of UTP cable to transmit a video signal.
1.3. FTP and STP. In video surveillance systems, it is NOT RECOMMENDED to use FTP and STP cables to transmit video from video surveillance cameras using video transceivers, due to electrostatic cable and metal foil that lightens lightning faster. When using the FTP cable for video transmission, the screen foil must be connected to the ground and the distance is reduced by 5 ~ 15% compared to the UTP.
2. Video surveillance cameras – image distortions
The potential difference in video surveillance systems
The potential difference is the induction of an alternating current in the cable route between the DVR digital video recorder and the video surveillance camera. This is due to the different mass references of the equipment. It is most common when installing video surveillance cameras on metal structures. In this case, it is recommended to use a buffer zone of insulating material (wood, plastic, etc.). The effects of potential difference are various: flow effect, cross-ribbing, cross-link patterns or image noise.
Cable route for video surveillance cameras
It is NOT RECOMMENDED to make the cable route parallel to the high voltage cables. Due to the small cable spacing, the high voltage can induce an unwanted alternating current in the cable route between the DVR and the camera.
The length of the video surveillance cable
The video surveillance signal has a certain degree of attenuation proportional to the length of the cable.
The maximum installation distances for analogue video surveillance cameras are:
Coaxial – 250m
UTP – 300 ~ 400m, using passive video transceivers (we recommend using active amplifiers even near upper limits)
– 1.2 ~ 1.5km, using active video transceivers
4. Improper plugging in video surveillance cameras and digital video dvr
An imperfect contact can significantly influence the quality of video surveillance, which is the major cause of signal loss.
There are several types of dies, each with its advantages and disadvantages.
4.1 Mounting with soldering. It is the safest but does not offer a great mechanical resistance
4.2 Mechanical fitting (with infill). The easiest to use, with acceptable mechanical strength. The most susceptible to oxidation in external muffs or in high humidity environments.
4.3 Sertisation. Procedure with good electrical contact and high mechanical resistance
5. Power supply for video surveillance cameras
The distortions caused by the power supply of the video surveillance cameras are due in particular to the overloading of the source, especially at night when the consumption of video surveillance cameras with IR infrared illuminator increases significantly.
In the case of long cable routes, the source can not provide enough power to capture the image in optimal conditions.
6. Operating temperature
At low temperatures (-20 degrees C), there are negative effects on the electrical components of CCTV video surveillance equipment. At the opposite end, a very high temperature may thermally overload the equipment.
7. Sensor type of video surveillance camera
CMOS sensors are more robust, they need more light under similar illumination compared to a CCD sensor. The amount of low light influences the image quality obtained in the video surveillance camera, being the main cause of night-time noise.