ECG (electrocardiography, ECG or EKG) is a kind of electrophysiology that records the heart in time through the chest Electrodes are placed in different parts of the human body and connected with the positive and negative electrodes of the electrocardiograph through the lead wire. This circuit connection method of recording ECG is called ECG lead. Phenomenon description: the internal mechanism of the electrocardiograph is shown in the figure below. When ESD test was carried out, it was found that ± 4KV contact discharge occurred to the shell of USB port or other communication port, resulting in machine crash or restart.

Cause analysis: ESD interference is a kind of common mode interference. The common mode current flows through the internal PCB to the earth through the exposed port shell. During this period, the common mode current will produce unexpected common mode voltage in the PCB, which will interfere with the main control IC in the PCB, resulting in machine crash or reset. Treatment measures: since the cause of interference is determined, we only need to make the common mode current flow path flow directly to the earth instead of through the internal PCB. (1) To extend the floor area, the new material bottom plate under the original PCB board is paved with aluminum foil and connected with the large area metal plate. The ground of the motherboard port is connected with the newly laid aluminum foil plate by screws. As shown in the figure:

(2) The port ground is isolated from the PCB ground by two inductors. As shown in the figure

Thinking summary: external interference is easy to enter the internal PCB through the port, but as long as a low impedance path is provided, the external interference will bypass the interference current that originally flows into the PCB to the large metal ground with low impedance. In this case, on the one hand, it “creates” a path to bypass the interference current, on the other hand, it “blocks” the interference current through the inductor, so that the interference current cannot flow through the internal PCB.

Editor in charge: CC

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