Checking method for lighting out of control If the lighting is out of control, first of all, it is necessary to check whether there is any problem with the program of the controller, whether there is any problem with the address code of the lamp, whether the connection of the control line is correct, and whether the shielding of the control line is subject to bad interference. , Whether the limit adjustment of the lamps and lanterns is appropriate, etc. Bulb damage inspection of computer lights is the most likely to occur in stage audio lighting because the bulb is easily broken, so if there is a problem, it is necessary to check whether the installed bulb is reliable, whether it is contaminated with dust and water vapor, and check whether the heat dissipation of the bulb is correct. In the normal range, the best thing to check is whether the voltage is in the normal range, and whether the power switch is used too frequently. Checking method for interference noise If there is noise in professional audio equipment, first check for dimming interference, whether the audio and lighting power supplies are disconnected, and then check whether the lighting power supply and control lines are too close to the audio signal line. Is there any situation where the silicon box is too close to the audio equipment.
Normally, the speaker system has noise, which is usually caused by unreasonable signal transmission. Therefore, when there is a problem with the shielding of the signal line or the grounding of the signal is not correct, noise interference is likely to occur. (Yellow River Lighting culture is rigorous and professional as its slogan, with a serious and responsible attitude, as long as you can think of it, we can do it.) The order of inspection of the live phenomenon of the stage lighting equipment shell The order of the live inspection of the equipment shell is to check the power supply first Whether the line is damaged, followed by whether the line phase is correct, and whether the equipment grounding and voltage are correct Stage lighting DMX512 control signal transmission line Since the stage lighting control entered the digital age, the DMX512 protocol has long occupied the dominant position of the stage lighting control protocol , has become a technology that every stage lighting worker knows.
But in practical application, people seem to be very confused about the selection and use of DMX512 transmission lines, and the phenomenon of using signal transmission lines that do not meet the requirements is common. Not only in temporary mobile performances, but also in theater construction. The transmission line is the nervous system in DMX512 control, and its quality directly affects the transmission quality of the control signal.
Inferior transmission lines will threaten the reliability and stability of lighting control, and will bring fatal damage to the performance. For theaters, system cabling is the basic construction of the "hundred-year plan", and people should pay more attention to it. In recent years, there has been an upsurge in the construction of theaters in China. The author has participated in the evaluation of lighting design schemes of many theaters and the evaluation of lighting engineering and equipment. During the evaluation, I found that this issue has generally not received due attention.
Even in some national key projects, problems also exist. What kind of communication cable should the DMX512 control system use to make the system work reliably? Why must a dedicated cable be used? Why is using non-standard transmission lines a problem? To answer these questions, we must first understand the DMX512 protocol. DMX512 is a protocol standard developed by the United States Institute of Theater Technology (USITT) for data communication between stage lighting consoles and dimmers, and later expanded to the control field of various stage equipment such as moving lights and color changers.
The main content of DMX512 is to stipulate the communication data protocol, and the main content directly related to the signal transmission cable is as follows: 1. The communication interface adopts the general EIA-485 standard in computer communication, and its electrical characteristics completely refer to the regulations of EIA-485. 2. DMX512 protocol signal transmission rate is 250kbps. The following is an analysis of the reliable transmission of DMX512 signals and the wires that should be used.
Long line problem In the basis of radio theory, there is a long line theory. The so-called "long line" refers to the line when the length of the transmission line can be compared with the wavelength of the current propagating along the transmission line. It is generally considered that the length of a transmission line is greater than one-tenth of a wavelength (l> ——l), it can be considered as a long line (some people think that l> ——l is the long line). So a long line is not necessarily a very long line.
For example, the main frequency of the CPU of an ordinary personal computer has reached the order of gigahertz (G, 109), and the external frequency of the motherboard has reached one or two hundred megabytes accordingly. Therefore, the design of small printed circuit boards should also consider long line problem. In the case of long lines, some common circuit principles are no longer applicable, and special transmission line theories need to be used for analysis. The transmission rate of the DMX512 control signal is 250kbps, that is, 250,000 binary codes are sent per second, in other words, 250,000 rectangular pulses are sent per second.
According to the spectrum analysis theory of the signal, it can be seen that the rectangular pulse contains a large number of high-order harmonics, even if only the fundamental wave with the lowest frequency and l> ——L conditions to calculate, when the frequency is 250kHz, the wavelength is 1200m, then the transmission line greater than 120m should be regarded as a long line. In fact, its harmonics cannot be ignored, so this distance is even shorter. Therefore, the transmission of DMX signals must be handled as a long line.
In ordinary lines, the capacitance of the circuit is concentrated in the capacitor, the inductance is concentrated in the coil, and the resistance is concentrated in the resistor. Although the resistance of the wire is a distributed parameter, it is often regarded as an equivalent of an ordinary resistor. It is the so-called lumped parameter circuit. In the lumped parameter circuit, the voltage and current of each point along the transmission line are the same at each specified moment, and the phenomenon on the transmission line can be judged from the process of any point on the transmission line, that is, the voltage and current are just A function of time, independent of position in the circuit. But in the case of long lines, its distribution parameters must be considered, and each small section of the line has resistance, capacitance, inductance and conductance.
Therefore, the long line should be regarded as being connected by many line units of the four-terminal network, and each four-terminal network has the resistance R, inductance L, capacitance C and conductance G of the line unit (as shown in Figure 1). The properties of a long line are determined by its distribution parameters R, L, C and G.