[Guide]In many tests, we can make the equipment pass the test smoothly by changing the installation method of the filter. The following are some examples of the impact of common filter installation methods on filter performance.
In the process of experimental testing, we often encounter such a situation: Although the design engineer has connected the power supply filter to the equipment power line, the equipment still cannot pass the “conducted disturbance voltage emission” test. The engineer suspects that the filter effect of the filter is not good. Well, if you keep changing the filter, you still can’t get the desired effect.
Analyzing the reasons for equipment exceeding the standard is nothing more than the following two aspects:
1. The harassment generated by the device is too strong
2. Insufficient filtering of equipment
For the first case, we can take measures at the source of the disturbance to reduce the intensity of the disturbance, or increase the order of the power filter to improve the filter’s ability to suppress the disturbance. For the second case, in addition to the poor performance of the filter itself, the installation method of the filter also has a great impact on its performance. This is often overlooked by design engineers.
In many tests, we can make the equipment pass the test smoothly by changing the installation method of the filter. The following are some examples of the impact of common filter installation methods on filter performance.
Input line is too long
After the power cords of many devices enter the chassis, they go through a long wire before connecting to the input end of the filter. For example, the power cord is input from the rear panel of the chassis, travels to the power switch on the front panel, and then returns to the rear panel to connect to the filter. Or the installation position of the filter is far away from the entrance of the power cord, causing the lead wire to be too long (as shown in Figure 1).
Because the lead wire from the power inlet to the filter input is too long, the electromagnetic disturbance generated by the device is re-coupled to the power line through capacitive or inductive coupling, and the higher the frequency of the disturbance signal, the stronger the coupling, causing the experiment to fail.
figure 1
Flat walking line
In order to make the wiring inside the chassis beautiful, some engineers often bundle the cables together, which is not allowed for power cables. If the input and output lines of the power filter are wired in parallel or bundled together, due to the distributed capacitance between the parallel transmission lines, this wiring method is equivalent to connecting a capacitor in parallel between the input and output lines of the filter, which is a disturbance signal. Provides a path to bypass the filter, resulting in a significant drop in the performance of the filter, and even failure at high frequencies (as shown in Figure 2).
The size of the equivalent capacitance is inversely proportional to the wire distance and directly proportional to the length of the parallel traces. The larger the equivalent capacitance, the greater the impact on the filter performance.
figure 2
Grounding and housing
This situation is also relatively common. When many engineers install the filter, the connection between the filter housing and the chassis is poor (there is insulating paint); at the same time, the grounding wire used is long, which will cause the filter’s high-frequency characteristics to deteriorate and reduce the filtering performance.
Due to the long grounding wire, the distributed inductance of the wire at high frequencies cannot be ignored. If the filter is well connected, the interference signal can be directly grounded through the housing. If the connection between the filter shell and the chassis is poor, it is equivalent to a distributed capacitance between the filter shell (ground) and the chassis, which will cause the filter to have a large ground impedance at high frequencies, especially in distributed inductance. Near the frequency where the distributed capacitance resonates, the ground impedance tends to be infinite.
image 3
The influence of poor grounding of the filter on the performance of the filter: Due to the poor grounding of the filter, the ground impedance is large, and a part of the disturbance signal can pass through the filter (as shown in Figure 3). In order to solve the poor overlap, the insulating paint on the case should be scraped off to ensure that the filter case and the case have a good electrical connection.
In this installation mode, the filter shell and the case are in good contact, which can block the opening of the power cord on the case, and improve the shielding performance of the case; in addition, the input and output lines of the filter are separated by case shielding , Eliminate the disturbance coupling between the input and output lines, and ensure the filtering performance of the filter.
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[Guide]In many tests, we can make the equipment pass the test smoothly by changing the installation method of the filter. The following are some examples of the impact of common filter installation methods on filter performance.
In the process of experimental testing, we often encounter such a situation: Although the design engineer connects the power supply filter to the equipment power line, the equipment still cannot pass the “conducted disturbance voltage emission” test. The engineer suspects that the filtering effect of the filter is not good. Well, if you keep changing the filter, you still can’t get the desired effect.
Analyzing the reasons for equipment exceeding the standard is nothing more than the following two aspects:
1. The harassment generated by the equipment is too strong
2. Insufficient filtering of equipment
For the first case, we can take measures at the source of the disturbance to reduce the intensity of the disturbance, or increase the order of the power supply filter to improve the filter’s ability to suppress the disturbance. For the second case, in addition to the poor performance of the filter itself, the installation method of the filter also has a great impact on its performance. This is often overlooked by design engineers.
In many tests, we can make the equipment pass the test smoothly by changing the installation method of the filter. The following are some examples of the impact of common filter installation methods on filter performance.
Input line is too long
After the power cords of many devices enter the chassis, they go through a long wire before connecting to the input end of the filter. For example, the power cord is input from the rear panel of the chassis, travels to the power switch on the front panel, and then returns to the rear panel to connect to the filter. Or the installation position of the filter is far away from the entrance of the power cord, causing the lead wire to be too long (as shown in Figure 1).
Because the lead wire from the power inlet to the filter input is too long, the electromagnetic disturbance generated by the device is re-coupled to the power line through capacitive or inductive coupling, and the higher the frequency of the disturbance signal, the stronger the coupling, causing the experiment to fail.
figure 1
Flat walking line
In order to make the wiring inside the chassis beautiful, some engineers often bundle the cables together, which is not allowed for power cables. If the input and output lines of the power filter are wired in parallel or bundled together, due to the distributed capacitance between the parallel transmission lines, this wiring method is equivalent to connecting a capacitor in parallel between the input and output lines of the filter, which is a disturbance signal. Provides a path to bypass the filter, resulting in a significant drop in the performance of the filter, and even failure at high frequencies (as shown in Figure 2).
The size of the equivalent capacitance is inversely proportional to the wire distance and directly proportional to the length of the parallel traces. The larger the equivalent capacitance, the greater the impact on the filter performance.
figure 2
Grounding and housing
This situation is also relatively common. When many engineers install the filter, the connection between the filter housing and the chassis is poor (there is insulating paint); at the same time, the grounding wire used is long, which will cause the filter’s high-frequency characteristics to deteriorate and reduce the filtering performance.
Due to the long grounding wire, the distributed inductance of the wire at high frequencies cannot be ignored. If the filter is well connected, the interference signal can be directly grounded through the housing. If the connection between the filter case and the case is poor, it is equivalent to a distributed capacitance between the filter case (ground) and the case, which will cause the filter to have a large ground impedance at high frequencies, especially in distributed inductance. Near the frequency where the distributed capacitance resonates, the ground impedance tends to be infinite.
image 3
The influence of poor grounding of the filter on the performance of the filter: Due to the poor grounding of the filter, the ground impedance is large, and a part of the disturbance signal can pass through the filter (as shown in Figure 3). In order to solve the poor overlap, the insulating paint on the case should be scraped off to ensure that the filter case and the case have a good electrical connection.
In this installation mode, the filter shell and the case are in good contact, which can block the opening of the power cord on the case and improve the shielding performance of the case; in addition, the input and output lines of the filter are separated by case shielding , Eliminate the disturbance coupling between the input and output lines, and ensure the filtering performance of the filter.
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