According to the communication method, it is divided into a one-way communication decoder and a two-way communication decoder. The one-way communication decoder only receives the communication signal from the controller and translates it into a corresponding action voltage/current signal to drive the front-end device; the two-way communication decoder transmits the communication to the controller in addition to the performance of the one-way communication decoder. Signal, so the working status of the decoder can be transmitted to the controller for analysis in real time. In addition, the front-end device signals such as alarm detectors can be directly input into the decoder to transmit the alarm detection signal of the scene by two-way communication, thereby reducing the use of the cable. .
According to the transmission mode of the communication signal, it can be divided into coaxial transmission and twisted pair transmission. The general decoder supports the communication signals transmitted by the twisted pair, and some decoders also support or support the coaxial cable transmission mode, that is, the communication signal is modulated and the video signal is transmitted together at the same frequency on the same video cable. on.
The circuit of the decoder is composed of a single-chip microcomputer, and is composed of a power supply circuit, a communication interface circuit, a self-test and an address input circuit, an output drive circuit, and an alarm input interface.
Decoders are generally not used separately and need to be used with the system host.
â— The connection line between the decoder and the pan/tilt and the lens should not be too long, because the voltage of the control lens is about 12 volts DC. If the transmission is too far, the voltage drop is too large, which may cause the lens to be out of control. In addition, since the multi-core control cable is more expensive than the shielded twisted pair, the cost will also increase.
â— The outdoor decoder should be waterproofed, and it is a good method to seal it with waterproof glue at the inlet, and it is easy to operate.
â— Shielded twisted pair cable is usually used from the host to the decoder. Multiple decoders can be connected in parallel on one line, and the total length is less than 1500 meters (depending on the site conditions). If the number of decoders is too large, you need to add some auxiliary equipment, such as adding a control code distributor or paralleling a matching resistor on the last decoder (subject to the manufacturer's instructions).
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Measuring angle: protractor, dividing head, theodolite, sextant, knife-edge angle ruler;
Weather measurement: thermometers, barometers, wind vanes, rain gauges, computers, and satellites.
More conventional: projector, hardness tester, hundred grid knife, etc.
Measuring tool: It is a tool for measuring a certain property. Including length, temperature, time, mass, force, current, voltage, resistance, sound, radio, refractive index and average dispersion.
Weight measurement: balance scale, floor scale, spring scale, etc.;
Temperature measurement: thermometer, thermometer, etc.;
Pressure measurement: pressure gauge, pressure transmitter, etc.;
Flow measurement: flow meter, differential pressure detector, etc.;
Liquid level measurement: differential pressure gauge, liquid level gauge, etc.;
Electric energy measurement: voltmeter, ammeter, field strength meter, frequency meter, etc.;
Composition measurement: analyzer, chromatograph, etc.;
Acid-base measurement: acidity meter, alkalinity meter, etc.
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