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  • Ten Daily Electronic Common Sense-Section 117

    What are the characteristics of Rongchao network that are significantly different from traditional Internet networks such as Internet?

    1. Intermittent connections
    2. Extremely high latency
    3. Limited resources
    4. Topology structure changes randomly and dynamically
    5. Heterogeneous interconnection
    6. Low signal-to-noise ratio and high bit error rate
    7. Poor security

    What are the advantages of electric double layer capacitors compared with batteries?

    Compared with batteries, electric double layer capacitors have the advantages of high power and long life. But it also has the disadvantage of low energy density.
    At present, the research direction of electric double layer capacitors is to improve existing electrode materials and develop new materials.

    Why is the amount of calculation often related to image quality and compression efficiency?

    Generally speaking, better image quality and higher compression ratio require higher computational burden. Moreover, once the encoding process J-°C and encoding parameters are selected, the computational complexity of the encoding is basically determined.
    However, in actual encoding, with changes in video content, channel bandwidth and quality, and changes in decoder requirements, the fixed-complexity encoding method often has two situations: idle computation and insufficient computation.
    For example, if the video content is still for a long time, the computing power may be excessive. The channel bandwidth is suddenly narrowed, which requires high-intensity compression, which may make the computing power insufficient. This will make the encoder not work at its best. In order to overcome the shortcomings of certain complexity algorithms, video encoders with variable complexity algorithms are also required.

    What is the core of the agreement level?

    Transport layer.

    What is a field device?

    Basic equipment for realizing presence sensing or performing functions.

    What are the main applications of 3D helmet displays?

    1. Military application
    2. CAD/CAM operation
    3. Simulation and training
    4. Medical

    What are the external trigger signal input sections?

    The external trigger signal input is used to access the external trigger source.
    In most cases, the oscilloscope uses the internal trigger mode, that is, the signal under test is used as a synchronous trigger source. However, when the measured signal waveform cannot be used as a synchronous trigger source, it is necessary to select an external trigger synchronous signal. the
    The external trigger signal needs to have sufficient amplitude. If the signal amplitude is low, it may fail to trigger the action of the horizontal scanning unit because its amplitude does not reach the trigger level. In short, if the external trigger signal is too small, it will not work as a trigger signal. But the amplitude should not be too large, otherwise it will damage the external trigger signal channel.
    When you need to use an external trigger signal, you need to check the oscilloscope manual to confirm the voltage amplitude of the external trigger signal channel.

    What forms of data objects do VHDL share?

    There are three types of data objects in VHDL: constants, variables, and signals.

    What is the working principle of the remote login service?

    The remote login service is implemented through the remote terminal protocol, which uses TCP at the transport layer for transmission.
    The working mode is client computer/server mode, which consists of two parts: client computer and TELNET server.
    The TELNET server process runs on the TELNET server. This process is a daemon process and runs on port 23 all the time, waiting for the user’s TELNET request. When a user wants to request TELNET service, he will start a TELNET client process on the client computer, and send a request to the TELNET server through port 23. After receiving the request, the TELNET server process will start a sub-process to respond to the TELNET request and provide specific services for the user. Then return to the TELNET server process and continue to wait for other users’ TELNET requests. the
    The client and the TELNET server in the remote login service may be heterogeneous, and the Internet uses a Network Virtual Terminal (NVT) to adapt to the differences between different systems. That is, the NVT format is used between the client process and the TELNET server process.
    Therefore, the server process running on the TELNET server should include a TELNET server process, a child process and a network virtual terminal driver process for converting to the NVT format. The client process running on the client computer should include the TELNET client process and the network virtual terminal driver process for converting to the NVT format.

    How to choose super capacitor?

    There are two main applications for supercapacitors: high power pulse applications and instantaneous power retention.
    Features of high-power pulse applications: instantaneous flow of large current to the load;
    The characteristics of instantaneous power maintenance applications: it is required to provide power to the load continuously, and the duration is generally several seconds or several minutes.
    A typical application of instantaneous power retention: resetting of disk drive heads when power is lost.
    Different applications have different requirements on the parameters of ultracapacitors. High-power pulse applications use the small internal resistance (R) of the supercapacitor, while instantaneous power retention uses the large electrostatic capacity (C) of the supercapacitor.
    Two calculation formulas and application examples are provided below: C(F): nominal capacity of supercapacitor; R(Ohms): nominal internal resistance of supercapacitor; ESR(Ohms): equivalent series resistance at 1KZ; Uwork( V): the normal working voltage in the circuit; Umin(V): the minimum voltage required for the device to work; t(s): the hold time required in the circuit or the pulse duration in pulse applications; Udrop(V): in At the end of discharge or high current pulse, the total voltage drop; I(A): load current; the approximate calculation formula of supercapacitor capacity is used for instantaneous power maintenance. The energy required during the hold period = 1/2I(Uwork Umin)t; the energy reduced by the supercapacitor = 1/2C(Uwork2-Umin2). Therefore, its capacity can be obtained (ignoring the voltage drop caused by IR) C=(Uwork Umin)t/(Uwork2-Umin2) Example: Assume that the working voltage of the tape drive is 5V, and the safe working voltage is 3V. If the DC motor requires 0.5A for 2 seconds (can work safely). Then, according to the above formula, its capacity can be at least 0.5F. Because the voltage of 5V exceeds the nominal operating voltage of the single capacitor. Thus, two capacitors can be connected in series. If two identical capacitors are connected in series, the voltage of each capacitor is its nominal voltage of 2.5V. If we choose a capacitor with a nominal capacity of 1F, the two strings are 0.5F. Considering the capacity deviation of the capacitor – 20%, this choice does not provide enough margin. You can choose a capacitor with a nominal capacity of 1.5F, which can provide 1.5F/2=0.75F. Considering the capacity deviation of -20%, the minimum value is 1.2F/2=0.6F. This supercapacitor provides ample safety margin. After the high-current pulse, the tape drive switches to a low-current operating mode to use the remaining energy of the supercapacitor.
    In this instance, the equalizing circuit ensures that each cell does not exceed its rated voltage. Pulse power application The characteristics of pulse power application: relatively small continuous current compared with instantaneous large current. The duration of the pulsed power application ranges from 1 ms to several seconds. The design analysis assumes that the supercapacitor is the only energy provider during the pulse.
    The total voltage drop in this example consists of two parts: the instantaneous voltage drop caused by the internal resistance of the capacitor and the voltage drop across the capacitor at the end of the pulse. The relationship is as follows: Udrop=I(R t/C) The above formula shows that the capacitor must have lower R and higher C voltage drop Udrop to be small. For most pulse power applications, the value of R is more important than C. Take 2.5V1.5F as an example. Its internal resistance R can be estimated by DC ESR, nominally 0.075Ohms (DCESR=ACESR1.5=0.060Ohms1.5=0.090Ohms). The rated capacity is 1.5F. For a 0.001s pulse, t/C is less than 0.001Ohms. Even the pulse t/C of 0.010 is less than 0.0067Ohms, obviously R (0.090Ohms) determines the Udrop output of the above formula.
    Example: A GSM/GPRS wireless modem requires a current of 2A every 4.6ms for 0.6ms. This modem is now used on PCMCIA cards in laptop computers. Notebook and PCMCIA connection limit output voltage 3.3V / -0.3V notebook provides 1A current. Many power amplifiers (PAs) require a minimum voltage of 3.0V. It is possible to output a voltage of 3.0V for a notebook computer. The voltage to the power amplifier must first be raised to 3.6V. Under the operating voltage of 3.6V (minimum 3.0V), the allowable voltage drop is 0.6V. Choose a supercapacitor (C: 0.15F, ACESR: 0.200Ohms, DCESR: 0.250Ohms). For a 2A pulse, the battery provides about 1A and the ultracap provides the remaining 1A. According to the above formula, the voltage drop caused by internal resistance: 1A×0.25Ohms=0.25V. I(t/C)=0.04V which is small compared with the voltage drop caused by the internal resistance.
    Conclusion Whether it is power maintenance or power pulse application, the above formula can be used to calculate. When the working voltage of the circuit exceeds the working voltage of the supercapacitor, the same capacitor can be connected in series. In general, series connections should be balanced to ensure even voltage distribution. The voltage drop caused by the internal resistance of the supercapacitor is usually a minor factor in pulsed power applications. The ultra-low internal resistance of the capacitor provides a new solution to overcome the high impedance of the traditional battery system.


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