The fuse in decoder basically has 2 major roles:
1. Prevent 220V power from short-circuiting or causing harm to the personnel during the construction process, when 220V power short-circuits or personnel electrocution, the fuse will automatically cut off the 220V power, to ensure the safety of personnel and equipment. Usually 220V fuse will be designed with a transparent plastic housing to prevent electric shock caused by the metal connector of the fuse.
2. To prevent the camera short-circuit caused by the power transformer burned out, this usually do not use the fuse holder shell.
In some of the more well-designed decoder, there are three fuses, adding a 24-volt output protection for the external output AC, to prevent short-circuiting caused by the head of the decoder internal devices and power transformer burned. The action of the decoder is controlled by the CPU to realize the suction and closure of the relay, but the CPU's driving ability is generally not strong, the need to use the driver chip to achieve the control of the relay, such as the first Keriker Shenyang first Keriker company's first Keriker decoder on the use of 2 pieces of the NLU2003 model driver chip, when the CPU sends out the action command by the NLU2003 chip to drive the relay suction and closure of the two pieces of The NLU2003 controls the PTZ control relay and the lens control relay respectively.
First of all, observe the glossiness of the decoder board, whether it is full, whether the font printing is clear, whether the components are neatly arranged. Whether the Chinese wiring instructions, decoder board thickness is thick enough, the standard should be more than 1.5 mm, thick enough decoder board tension is strong, can adapt to more complex environments, circuit board deformation chances are smaller, the edge of the circuit board with a hand touch will not be scratching feeling, if there is an illustration of the production of the board cutter is not advanced enough.
The decoder usually has two parameters that need to be set manually, namely the communication baud rate and the address code. Baud rate refers to the decoder and DVR or matrix through the 485 bus communication rate, different communication protocols communication rate is not the same, but can be roughly divided into 1200, 2400, 4800, 9600 kinds. They are usually set with a binary dipswitch, the specific setup method for each brand is different. To the first Ke decoder as an example, *** count 8 bits of dip switches, of which 1, 2 bits for the communication baud rate setting switch, 3-8 bits for the address setting switch.
Address code setting, due to the 485 communication bus are generally linked to multiple decoders in order to distinguish them from each other, respectively, each decoder to set an address. The address code is also expressed in binary. The protocol is the information storage format for data communication. There are more than 100 kinds of communication protocols for decoders, among which there are several versions of the more common ones, and there are about 7 versions of the most commonly used protocol, which is the Pellco D. Take the Pellco D as an example, it can be analyzed and analyzed by the analyzer. The most commonly used protocol, Pelco D, has about seven versions. Take Pelco D as an example and analyze the data structure of the protocol.
Communication data is 7 bytes, respectively: 1-2-3-4-5-6-7
1. Flag bits: determine the type of protocol
2. Address bits: the type of protocol
3. p>2. Address bit: the address of the decoder corresponding to the action issued;
3. 4. Action bit: the specific working instruction
5. 6. Speed and preset bit: defines the speed of the action and the coordinates to which the action is preset;
7. Check bit: verifies whether the data is correct.
Often the decoder will identify the type of protocol according to the format of the protocol, which is commonly referred to as the self-recognition protocol decoder, also known as the 10,000-code decoder. After the DVR sends out the control command, the serial interface RS-232 of the DVR will send out the control protocol code with the baud rate and data format of the protocol set by the software, and the RS-232 to RS-485 code converter will convert the RS-232 signal into RS-485 signal and then transmit it. -485 signal, and then transmitted (theoretically can be transmitted 1200 meters), the system passes through the 485 bus on each decoder will receive the control protocol code, and then compared to their own address, the control protocol code and the address of the same decoder will perform the action. The use of 232 to 485 code converter is mainly RS232 signal transmission distance is relatively close to about 15 meters, while the 485 signal can be transmitted 12,000 meters, so that the control distance is greatly lengthened. Embedded DVR itself has a 485 communication interface, no need to add RS-232 to RS-485 pass-through protocol converter.
The communication between the DVR and the decoder is a one-way communication, the data DVR sent to the decoder to receive until the decoder, the decoder does not send any data to the DVR. Therefore, in order to reduce the cost of monitoring systems use a significant proportion of the code converter is a single-power code conversion, that is, from 232 signals into RS485 signals. Therefore, the use of surveillance system code converters in two-way communication systems such as access control may result in poor communication problems. Decoder power supply generally use multi-voltage output linear transformer, linear transformer can be roughly divided into three kinds:
1. EI-type transformer
2. R-type transformer
3. toroidal transformer. EI type iron core transformer manufacturing process is simple, relatively low cost. Because the iron chip and its matching coil skeleton have formed a series and mass production, so it is widely used.
EI-type core transformer used in the core material is very complex, there are hot rolled silicon steel plate (commonly known as low selenium), cold rolled non-oriented silicon steel strip, cold rolled oriented silicon steel strip (commonly known as high selenium). Today's use of cold-rolled non-oriented silicon steel strip is mainly 0.5 mm thick (commonly known as medium selenium), 0.35 mm (commonly known as domestic high selenium) has been eliminated. These materials in the cold-rolled oriented silicon steel strip material is best, its thickness is below 0.35 mm, cold-rolled non-oriented silicon steel strip followed by hot-rolled silicon steel plate material quality is the worst. Thus the same size transformer, different core materials, transformer output power difference is large. R-type transformer than the EI transformer 30% smaller, 40% thinner, 40% lighter.
R-type transformers have the smallest magnetic leakage, 10 times smaller than EI-type transformers.
The heat generated by R-type core transformers is at least 50 percent less than that of EI-type transformers.
The R-type transformer does not generate noise, a feature that is far superior to the EI-type transformer or the core gap cut core transformer.
The R-type transformer has a stronger working performance, higher reliability, stronger insulation and easier installation than the toroidal transformer.
The construction of R-type transformer is simpler than EI and C-type transformer but the reliability and quality are higher than them. The core of the toroidal transformer is made of high-quality cold-rolled silicon steel sheet (sheet thickness is generally 0.35mm or less), seamlessly rolled, which makes its core performance superior to that of the traditional stacked-sheet core. The coil of the toroidal transformer is evenly wound on the core, and the direction of the magnetic line of force generated by the coil is almost completely coincident with the magnetic circuit of the core, so the excitation energy and core loss will be reduced by 25% compared with the stacked piece type. Toroidal transformer has the following characteristics:
(1) high electric efficiency heart without air gap, stacking coefficient can be as high as 95% or more, core permeability can be taken 1.5 ~ 1.8T (stacked piece of core can only be taken 1.2 ~ 1.4T), the electric efficiency of up to 95% or more, no-load current is only 10% of the stacked piece of type.
(2) small dimensions, light weight toroidal transformer than stacked transformer weight can be reduced by half, as long as the core cross-sectional area is equal to keep the toroidal transformer is easy to change the core length, width, height ratio, can be designed to meet the requirements of the dimensions.
(3) less magnetic interference toroidal transformer core has no air gap, the windings are uniformly wound in the ring on the core, this structure leads to a small leakage, electromagnetic radiation is also small, without the need to add another shielding can be used to high sensitivity electronic equipment, such as applications in low-level amplifiers and medical equipment.
(4) less vibration noise, the core has no air gap can reduce noise. Chain connection diagram is the standard wiring, all decoders are hooked up to the RS485 bus, communication distance, stable transmission data, the last decoder needs to be jumpered through the 120Ω resistor to improve the quality of communication, it is recommended that the construction of such wiring.
Star connection diagram in the decoder are alone through a RS485 bus and sending device connected to the 485 communication data through the node to more than two directions, the transmission distance will be greatly reduced. It is recommended to avoid utilizing this wiring method during construction. If this wiring method is used, it is recommended to use RS485HUB to solve the problem. The external structure of the decoder can be divided into two kinds, the first kind of iron box painting, this kind is more common, accounting for about 85% of the decoder market share. The second type of cast aluminum shell, market share of 10%, with good waterproof, generous appearance and other characteristics. Due to the high cost of cast aluminum shell, the use of less, usually brand decoders will be selected.
In the indoor environment, the two shells of the decoder function has no difference. In the outdoor environment, there is no difference between the function of iron box decoder and cast aluminum decoder, but the cast aluminum shell decoder sealing is better can be placed directly on the ground, will not occur in water and other situations, while the iron box decoder due to sealing is not as good as the cast aluminum structure, is usually mounted on the wall or monitor pole, configure waterproof junction head, you can prevent the rain from entering, due to the cast aluminum structure of the decoder is usually more than the price of the iron shell structure is higher than 1 times! Because the price of cast aluminum decoder is usually 1 times higher than the price of iron housing, so in the middle and low-end market, the cast aluminum housing is not common anymore.
There are many kinds of outer structure of the iron shell, in which there is a kind of pull-out structure design is more successful, and now the application is also the most, the pull-out structure consists of two parts, one part of the lower face of the iron box cube for the empty, the other part of the drawer like a L-type iron plate, the decoder board, power supply, etc., is installed in the iron plate, in the iron plate inserted into the iron box, galvanized (rust) screws to fix the outlet at the mouth. Configure 2 waterproof heads. The L-type iron plate can be inserted under the direction of construction to prevent rainwater from pouring in and protect the internal electrical components. When debugging, you can remove the two screws on the L-type iron plate, the iron plate can be pulled down, when all the decoder board is exposed, the hook on the L-type iron plate automatically hangs the decoder shell, which is more convenient for installation.