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    What is RS422,RS485,comparison with RS232?

    RS 232 is well-known due to popularity of today's PC's: unlike the RS422 and RS 485. These are used in industry for control systems and data transfers (small volumes, less than hundreds of Mb/s).

    So, what is the main difference between RS 232 and RS 422 & 485? The RS 232 signals are represented by voltage levels with respect to ground. There is a wire for each signal, together with the ground signal(reference for voltage levels). This interface is useful for point-to-point communication at slow speeds. For example, port COM1 in a PC can be used for a mouse , port COM2 for a modem, etc. This is an example of point-to-point communication: one port, one device. Due to the way the signals are connected, a common ground is required. This implies limited cable length? About 30 to 60 meters maximum. (Main problems are interference and resistance of the cable.) Shortly, RS 232 was designed for communication of local devices, and supports one transmitter and one receiver.

    RS 422 & 485 uses a different principle: Each signal uses one twisted pair(TP) line-two wires twisted around themselves. We're talking 'Balanced data transmission', or 'Differential voltage transmission'. Simply, let's label one of the IT wires 'A' and the other one 'B'. Then, the signal is inactive when the voltage at A is negative and the voltage at B is positive.
    Otherwise, the signal is active, A is positive and B is negative. Of course, the difference between the wires A an d B matters. For RS 422 & 485 the cable can be up to 1200 meters (4000 feet) long, and commonly available circuits work at 2.5 MB/s transfer rate.

    What is the difference between RS 422 and RS 485? Electrical principle is the same : both use differential trans miners with alternating voltages 0 and 5V. However, RS is intended for point-to-point communications, like RS 232. RS 422 is intended uses two separate IT wires, data can be transferred in both directions simultaneously. R S 422 is often used to extend a RS 232 line, or in industrial environments.

    RS 485 is used for multipoint communications: more devices may be connected to a single cable- similar to e.g ETHERNET networks, which use coaxial cable. Most RS 485 systems use Master/Slave architecture, where eac h slave unit has its unique address and responds only to packets addressed to this unit. These packets are generat ed by Master (e.g PC), which periodically polls all connected salve units

    Video Security Basics

    Coaxial Cable - Overview

    The most common means of conducting video signals from one piece of equipment to another is coaxial cable. Coaxial cable is often referred to as simply "coax". Not only is coax the most commonly used cable, but also the least expensive, most reliable, most convenient, and easily maintained way of transferring electronic images in a CCTV system.

    Coax is available from many manufacturers and comes in a variety of sizes, shapes, colors, specifications and ca pabilities. The most commonly recommended "coax" type is RG59/U, but this designation actually represents a family of cables with widely varying electrical characteristics. Other varieties like RG59/U are RG6/U and RG I 1/U; these are used predominately in CCTV and video work.

    Though similar in many ways, each cable group has its own various physical and electrical characteristics, whic h must be taken into consideration.

    All three "coax" cable groups are included in the same general family classification for coaxial cables. The RG r eference is the cable specification for use as a "radio guide ", while the numerical value helps differentiate the sp ecifications of each individual cable. Although each cable has its own number, characteristics, and size, there is no difference in the way these different numbered cables work.

    Coax Construction

    Common "coax" cable RG59//U,RG6/U, and RG11/U is circular. Eachhas a center conductor surrounded by diel ectric insulating material, which in turn is covered by a braid to shield against electromagnetic interference (EM I). The outer covering is the "jacket".

    The coaxial cable's two conductors are separated by a nonconductive or dielectric material. The outer conductor (braid) acts as a shield and helps isolate the center conductor from spurious electromagnetic interference. The outer covering helps physically protect the conductors.


    Center Conductor

    The center conductor is the primary means of carrying a video signal. The center conductor comes in varying di ameters, usually ranging from 14 gauge to 22 gauge. The structure of the center conductor generally is solid cop per or copper- clad steel, designated as bare copper weld, or BCW. For CCTV applications, solid copper conduc tors are required. Copper clad, copper weld, or BCW cables have much greater loop resistance at baseband vide o frequencies and should never be used for CCTV. To determine the type, look at the cut end of the center condu ctor. Copper clad cable will be silver in the center instead of copper all the way through. Variation in the size of t he center conductor has an overall effect on the amount of DC resistance offered by cable. Cables which contain large diameter center conductors have lower resistances than cables with smaller diameters.This decreased resis tance of large diameter cable enhances the ability of a cable to carry a video signal over a longer distance with b etter clarity, but, it is also more expensive and harder to work with.

    For applications where the cable may move up/down or side-to-side, select cable that has a center conductor con sisting of many small strands of wire. As the cable moves, these strands flex and resist wear due to fatigue better than a cable with a solid center conductor.

    Dielectric Insulating Material Surrounding the center conductor is an evenly made dielectric insulating material which is available in some for m of either polyurethane or polyethylene. This dielectric insulator helps determine the operating characteristics of coax cable by maintaining uniform spacing between the center conductor and its outer elements over the entir e length of the cable. Dielectrics made of cellular polyurethane or foam are less likely to weaken a video signal t han those made with solid polyethylene. This lower attenuation is desirable when calculating the loss/length fact or of any cable. Foam also gives a cable greater flexibility, which may make an installer's job easier. Although f oam dielectric material offers the best performance, it can absorb moisture, which will change its electrical beha vior.

    Because of its rigid properties,solid polyethylene maintains its shape better than foam and withstands the pressures of accidental pinching or crimping,but this characteristic also makes it slightly more difficult to handle during installation.In addition,its loss/length attentuation factor is not quite good as foam,which should be considered in long cable runs.

    Braid or Shield

    Wrapped around the outside of the dielectric material is a woven copper braid(shield),which acts as a second conductor or ground connection between camera and the monitor.It also acts as a shield against unwanted external signals commonly called electromagnetic interference or EMI,which may adversely affect a video signal.
    The amount of copper or wire strands in the braid deter- mine how much EMI it keeps out. Commercial grade c oax cables containing loosely woven copper braid have shielding coverages of approximately 80 percent. These cables are suitable for general purpose use in applications where electrical interference is known to be low. They also work well when the cable is to be installed in metal conduit or pipe, which also aids in shielding.

    If you are not sure of the conditions and are not running pipe to screen out more EMI, use a cable with a "maxim um shield" or heavy braid--type cable containing more copper than those of commercial grade coax. This extra c opper obtains the higher shielding coverage by having more braid material made in a tighter weave. For CCTV applications, copper conductors are needed.

    Cables using aluminum foil shielding or foil wrap material are not suitable for CCTV work. Instead, they usuall y are intended to transmit radio frequency signals such as those employed in transmitter systems or in master ant enna distribution systems.

    Aluminum or foil cable may distort a video signal to such a point that signal quality may be far below the level r equired for proper system operation, especially over long cable runs, and therefore not recommended for CCTV use.

    Outer Jacket

    The last component comprising a coax cable is the outer jacket. Although other materials are used, polyvinyl chl oride, or PVC, is commonly used in its construction. Available in many colors such as black, white, tan, and gra y, the jacket lends itself to both indoor and outdoor applications.

    What is super smear rejection?

    The left photo shows an image of a back illuminated rectangular aperture with an exposure time of 1ms in a stret ched scaling (48-100 counts correspond to 0-255 gray levels). The white line indicates the position of the readou t pixel row shown in the next graph. The right photo shows an image of the same aperture with the same scaling at 100ms exposure time and reduced back illumination. The resulting right image in general has the same intensi ty values like the left image.
    If an interline-transfer-CCD-image sensor is read out, the generated charge carriers are transferred from the light sensitive part (photodiode) of a pixel to the shift register, which is next to the photodiodes and acts like a potent ial bucket. Because of the weak light sensitivity of these shift registers, they are shaded to prevent the additional generation of charge carriers. When the charge transfer to the shift registers is complete, they are shifted vertica lly row by row to the horizontal readout line, which is read out in a serial way. This vertical shift of row by row can be best compared with an endless conveyor belt process. With every shift step all registers are shifted by one register location including register rows that were already drained from the image.
    If an intense light source is imaged to the CCD-image sensor, this can generate unwanted charge carriers in the s hadowed shift registers (mainly due to scattering of light on the CCD ship) in every line or row, which is shifted below the spot. This results in unwanted additional light signals, called "smear", which can be recognized as bri ght vertical bands above and below the bright image spot. This phenomenon is more often seen at very short exp osure times (because the light signal has to be intense to achieve a good image with a sufficient signal-to-noise r ation) and is a characteristic of the corresponding CCD-image sensor.

    What is CMOS camera.Why is it different from CCD camera?

    CMOS sensor is a kind of sensor that is normally 10 times less sensitivity than CCD sensor.As human eye can see object under 1 lux illumination (full moon night ). CCD sensor normally will see better or as good as human eye in the range of 0.1 —3 lux and are 3 to 10 times more sensitive then CMOS sensor.



    What is EX-View CCD camera?and What is good or bad about it?

    "EX-View" is a sensitivity-enhancement technology developed by SONY to improve lighting sensitivity to its CCD by a factor of two for visible light and a factor of four for near-infrared wavelengths.

    EXView is a proprietary SONY technology in which the P/N junction of each photodiode in the CCD matrix is s pecially fabricated to have much better photon-to-electron conversion efficiency. In addition, each photodiode (r epresenting one pixel in an image) has a microscopic lens fabricated over it to better capture and focus light ont o the active semiconductor junction. This results in an improvement in light sensitivity of 2 times for visible ligh t and 4 times for near-infrared (800 — 900 nm) compared to the conventional CCD versions offered by SONY. The lux rating of the EX-View CCD is two times better than the premium SONY "Super HAD" CCD for both vis ible and near-infrared wavelengths.

    What is Super HAD CCD camera?

    Super HAD CCD is a trademark of Sony Corporation. The Super HAD CCD is a version of Sony's high performance CCD HAD (Hole-Accumulation Diode) sensor with sharply improved sensitivity by the incorporation of a new semiconductor technology developed by Sony Corporation.Our various KT&C cameras come with SONY SUPER HAD CCD!
    Efforts for more pixels and smaller size for CCD have resulted in a smaller aperture area of sensor, presenting th e problem of lower sensitivity. To improve this, a lens has been provided on the top of the sensor for focusing, w hich increases the virtual aperture area of the sensor for higher sensitivity. That is what is called the on-chip mic ro-lens. Sony, the first to adopt it for the CCD image sensor, has thus successfully achieved higher sensitivity. This "Super HAD CCD" optimizes the shape of on-chip micro-lenses in order to minimize the invalid area betw een micro-lenses on each pixel, which thereby minimizes the lost incident light. By doing so our product has bee n improved the sensitivity per unit of area, despite reducing the unit pixels. Comparison of Conventional CCD and Super HAD CCD Sensor Structure



    What is WDR?

    Wide Dynamic Range(WDR) Technology uses two shutter speeds in alternative video fields, high and normal, a nd combines these two fields into one frame. It allows every detail to be captured accurately even if one portion is bright while other portions are dark. As a result, combined fields yield a frame of high quality images. Below is a comparison of camera technologies with its video images of Regular, Backlight Compensation (BLC), and Wide Dynamic Range.

    Why IR Filter in Color Cameras necessary?

    An IR filter ? or ER. cut filter - is a color filter blocking the infrared light. There are several good reasons for usin g an IR-cut filter. Using a color camera to achieve realistic colors in white light requires an IR-cut filter. The col or spectrum seen by the human eye is quite limited compared to the spectrum seen by a CCD camera. Especially , in the near infrared region of the spectrum the difference in sensitivity is significant. This is important to know since many light sources, including the sun, emit infrared light. A CCD color camera in daylight without an IR-c ut filter will therefore see a significant amount of infrared light resulting in strange colors. Another reason for us ing an IR-cut filter is the limited color correction for many lenses. It is difficult to design imaging optics coverin g both the visible spectrum and the near infrared spectrum at the same time. Therefore, many lenses have differe nt depth of focus for the visible and the infrared spectrum. Anyway, the IR-cut filter cuts away a significant amo unt of the overallcollected light and thereby affects the sensitivity in a negative way. In general, color cameras ar e one factor less sensitive compared to monochrome (depending on the CCD chip). This is primarily due to the I R-cut filter.

    How mechanical day and night cameras work?

    These cameras incorporate IR cut filters which automatically move over the CCD sensor for day time (color) us age, to prevent IR light to the CCD. At night time, the filter will be removed automatically to bring in IR right to the CCD, and maximize the low light sensitivity with black and white image.

    What is optical low-pass filters (OLPF)?

    In high-quality digital imaging systems, optical low-pass filters (OLPF) are used to eliminate color more fringes . An OLPF cuts off the lens MTF above the sampling frequency of the imager resulting in an overall MTF curve that approximates a step function in spatial domain. IR cut-off function is often incorporated into OLPF as well.

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