Several methods of reducing noise and electromagnetic interference in PCB circuit board design

The sensitivity of electronic equipment is getting higher and higher, which requires the anti-interference ability of the equipment is also getting stronger and stronger, so PCB design has become more difficult, how to improve the anti-interference ability of PCB has become one of the key issues that many circuit board manufacturers engineers are concerned about.

The following is a summary of several ways to reduce noise and electromagnetic interference in PCB design after years of design:

(1) Use large capacity tantalum capacitors or poly cool capacitors instead of electrolytic capacitors as circuit charge and discharge energy storage capacitors. When using tubular capacitors, the housing should be grounded.

(2) As far as possible, the printed board uses 45 polylines instead of 90 polylines to reduce the external transmission and coupling of high-frequency signals.

(3) The printed board is partitioned according to the frequency and current switching characteristics, and the noise element is further away from the non-noise element.

(4) Single panel and double panel with single point power supply and single point grounding, power line, ground as thick as possible, the economy is able to withstand the use of multi-layer board to reduce the power supply, the inductance of the ground.

(5) Can use low-speed chips do not need high-speed, high-speed chips are used in key places.

(6) Can be used to string a resistor method to reduce the control circuit up and down jump rate.

(7) Weak signal circuit, low frequency circuit do not form a current loop around.

(8) Try to provide some form of damping for relays, etc.

(9) Use the lowest frequency clock that meets system requirements.

(10) The signal should not form a loop, if inevitable, let the loop area as small as possible.

(11) The clock generator is as close as possible to the device using the clock. The quartz crystal oscillator housing should be grounded.

(12) Circle the clock area with the ground line, and the clock line is as short as possible.

(13) One decoupling capacitor for each integrated circuit. A small high-frequency bypass capacitor is added to the side of each electrolytic capacitor.

(14) I/O drive circuit as close as possible to the edge of the printed board, so that it leaves the printed board as soon as possible. The signal entering the printed board should be filtered, the signal from the high noise area should also be filtered, and the method of series terminal resistance is used to reduce the signal reflection.

(15) The useless end of the MCD should be connected to the high, or grounded, or defined as the output end, and the end of the power supply on the integrated circuit should be connected, and do not hang.

(16) The idle gate circuit input end should not be suspended, the idle operation amplifier positive input end is grounded, and the negative input end is connected to the output end.

Daily maintenance of CNC cutting machine system

In the process of using the CNC cutting machine, the core part of the CNC cutting machine - the correct operation and maintenance of the CNC system is very important, if the CNC system is not carefully maintained and maintained, it often affects its work efficiency, processing accuracy and service life. Therefore, in order to make better use of the numerical control system, the following daily maintenance should be done; According to the analysis of Wuhan fire, the probability of numerical control system at home and abroad is mainly manifested in the following points:

1) Make preparations for the early maintenance:

① Spare parts preparation: Once the parts or components of the numerical control system are damaged, the system fails. In order to eliminate the fault in time, users should prepare some commonly used spare parts;

② Technical preparation: maintenance personnel should fully understand the performance of the system in peacetime;

③ Tool preparation: As an end user, the maintenance tool only needs to prepare some conventional instruments and equipment, such as AC voltmeter, DC voltmeter, which may be pointer type or digital type, and the measurement error is within the range of ±2%.

2) The numerical control system also needs to do regular maintenance when it is not used for a long time;

3) Often pay attention to the power grid voltage used in CNC devices;

4) Replace the battery for memory regularly;

5) Maintenance of spare printed circuit board. For the spare printed circuit board that has been purchased, it should be installed on the numerical control device regularly and run for a period of time to prevent damage;

6) Formulate perfect rules and regulations for daily maintenance of CNC system;

7) Regularly maintain the input/output device of the CNC system;

8) Check and replace DC motor brushes regularly;

9) As little as possible to open the CNC cabinet, especially the door of the strong current cabinet;

10) Regularly clean the heat dissipation and ventilation system of the numerical control device;