Ten Daily Electronic Common Sense-Section 110

What can the antenna be divided into according to the band?

Long-wave antennas, medium-wave antennas, short-wave antennas, ultra-short-wave antennas and microwave antennas.

How is the noise generated by the transformer itself generated?

Because the iron core is used in the transformer, the inductance and resistance of the winding become nonlinear, so it cannot be analyzed by a method similar to the previous one.
Generally, only qualitative analysis can be made. If quantitative analysis is required, it must be carried out by means of measurement. The resistance of the primary and secondary windings of the transformer. Both hysteresis and eddy current losses in the core can generate thermal and excess noise, and eddy current losses also increase with frequency.
The inductance of the primary winding will affect the low frequency end of the passband, increasing the equivalent input noise at the low frequency end. The distributed capacitance of the windings and the stray capacitance of the wiring affect the high frequency end of the passband. The inductance of the winding is nonlinear, and it is affected by the magnetic permeability of the iron core. The permeability is related to the winding current, whether the iron core has residual magnetism, and the filling factor of the core lamination.
In addition, the alternating magnetic field or mechanical vibration can cause the core to vibrate or the relative displacement between the core and the winding. These can induce additional electromotive force in the winding, which is a noise called chattering effect. In order to reduce this effect, when making the transformer, the iron core should be properly compressed and fasteners should be added, and vacuum dipping should be carried out.
In addition, the core and its fasteners should also be demagnetized. When using a transformer, make sure that the current in the winding does not contain a DC component. Even measuring the resistance of the windings should avoid the DC method, the transformer should be fixed on a shock mount, etc.
In addition, in order to meet the needs of common mode rejection, the bypass capacitance between the two terminals of the center tap is required to be equal.

What are the assembly language programming steps?

1. Analyze the problem: determine the algorithm, which is the most important step in program design
2. Draw a flowchart
3. Allocate storage units
4. Debug and test the program

What are the advantages of photon counting technology compared to analog detection technology?

1. The measurement result is less affected by the drift of the photodetector, the change of the system gain and other unstable factors.
2. The influence of most of the thermal noise of the detector is eliminated, and the signal-to-noise ratio of the measurement result is greatly improved.
3. There is a relatively wide linear dynamic region.
4. It can output digital signal, suitable for digital data processing by connecting with computer interface.

What methods does the signal generator classify by source?

There are many ways to classify signal generators by signal source:
One of the methods can be divided into two kinds of mixed signal source and logic signal source.
Among them, the mixed signal source mainly outputs the analog waveform, and the logic signal source outputs the digital code shape.

What are the functions of each component of the PLC system?

The basic unit (ie the main unit) is the core of PLC control;
The expansion unit is a device that expands the number of I/O points, and there is a power supply inside;
The expansion module is used to increase the number of I/O points and change the ratio of the number of I/O points, and there is no internal power supply. Powered by the base unit or expansion unit, both expansion units and expansion modules have no CPU and must be used together with the base unit;
Special function modules are devices with special purpose.

What is the operating frequency of the MIFARE system?

l3.56MHz.

What do the three elements of the line sensor network mean?

The three elements of a wireless sensor network are sensors, sensing objects and observers.

What is a sensor?

A sensor is a device that can convert physical or chemical quantities into electrical signals that are easy to use.

What is the working principle of photodiode?

Photodiodes are semiconductor devices that convert optical signals into electrical signals. Its core part is also a PN junction, which is different in structure compared with ordinary diodes. In order to facilitate receiving incident light, the PN junction area should be as large as possible, and the electrode area should be as small as possible. And the junction depth of the PN junction is very shallow, generally less than 1 micron.
Photodiodes work under reverse voltage. When there is no light, the reverse current is very small (generally less than 0.1 microamps), which is called dark current. When there is light, the energy-carrying photons enter the PN junction and transfer the energy to the bound electrons on the covalent bond. Some electrons break free from covalent bonds, thereby generating electron-hole pairs, which are called photogenerated carriers.
They participate in the drift motion under the action of the reverse voltage, so that the reverse current becomes significantly larger. The greater the intensity of the light, the greater the reverse current. This property is called “photoconductivity”.
The current generated by the photodiode under the light of general illumination is called photocurrent. If a load is connected to the external circuit, an electrical signal is obtained on the load, and this electrical signal changes accordingly with the change of light.
Photodiodes and phototransistors are photosensitive devices widely used in electronic circuits. The photodiode has the same PN junction as the ordinary diode, the difference is that there is a transparent window on the outer shell of the photodiode to receive the light and realize the photoelectric conversion.
The text symbol in the circuit diagram is generally VD. In addition to the function of photoelectric conversion, the phototransistor also has the function of amplification. The text symbol in the circuit diagram is generally VT. Because the input signal of the phototransistor is an optical signal, there are usually only two pin lines of the collector and the emitter. Like the photodiode, the phototransistor housing also has a transparent window to receive light.
The shape of the photodiode and phototransistor is basically the same, and the judgment method is as follows:
Cover the window, select the R1K block of the multimeter, and measure the forward and reverse resistances between the two pin leads. Both are infinite for the phototransistor. The forward and reverse resistance values ​​are larger and smaller for the photodiode. Photodiode detection: first judge its pole according to the mark on the shell, the pin marked with colored dots on the shell or the pin close to the key is the positive pole, and the other pin is the load. If there is no mark, use a black cloth to cover the window that receives the light signal, and set the multimeter to R1K to measure the positive and negative electrodes. At the same time, it is measured that its forward resistance should be between 10K~20K, its reverse resistance should be infinite, and the needle does not move. Then remove the shading black cloth, and the photodiode receiving window faces the light source. At this time, the multimeter needle should be deflected to the right, and the deflection angle indicates its sensitivity. The larger the deflection angle, the higher the sensitivity.