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The Key Link of Electrostatic Discharge Laboratory Testing the Change of Electronic Equipment Characteristics

Electrostatic discharge will seriously affect the difference of patients in clinical application, and even damage medical machinery. Therefore, the anti-interference (ESD) test of electrostatic discharge belongs to the anti-interference test report in the electromagnetic compatibility standard. In the specific electromagnetic compatibility test, the first pass rate of electrostatic discharge test is very low, and most products need to be rectified. This paper briefly introduces the electrostatic interference. Taking the optometer of ophthalmic equipment as an example, the causes and hazards of electrostatic interference are described, and reasonable rectification measures are formulated.


1. Overview of electrostatic interference

With the rapid development of science and technology, electronic products have been widely used in all walks of life, resulting in the complex electromagnetic environment around. The magnetic field effect caused by electrostatic discharge must be considered. Electrostatic discharge experiment is used to simulate the discharge phenomenon that may occur in the daily use of electronic equipment. In this case, the instantaneous discharge current will produce a short and high intensity magnetic field, which will lead to the application of computers and other electronic products. Intelligent terminals and diagnosis and treatment electronic equipment will lead to misoperation, and even immediately lead to the destruction of the equipment circuit. Integrated circuits have been widely used in the efficient development of electronic industry. Its typical characteristics are that the central line of electronic components becomes smaller, the compression level is reduced, and the wiring area is reduced. However, this highly integrated design significantly reduces the ability of electronic equipment to resist electrostatic interference. The discharge current and magnetic field caused by electrostatic interference are directly related to the service life of high-density components. In order to solve these problems, integrated circuits use a variety of high insulation materials, but the characteristics of insulation products lead to daily assembly. Static electricity [1] is more easily generated during adjustment and use. The registration and inspection of medical devices and equipment shall be carried out according to relevant requirements. Electrostatic discharge experiment is the key link to test the characteristic changes of electronic equipment.

Electrostatic discharge standard has the following characteristics in destroying medical mechanical and electronic components: secret, except for electrostatic discharge standard, it is not easy to be directly perceived by human body. Cumulative. When electronic components are subject to electrostatic interference, the characteristics may be consistent. If the equipment is subject to electrostatic discharge for many times during use, the cumulative effect will cause major hidden dangers to the system and improve the sensitivity. Occasionally, the use of diagnostic and therapeutic electrical equipment, adjustment and use may be subject to static interference, and there are various ways to generate static electricity. Electrostatic discharge is generally caused instantaneously and cannot be maintained immediately. Possible hazards of electrostatic discharge to the diagnosis and treatment of electrical equipment: electromagnetic interference, resulting in mechanical failure and incorrect operation, reducing the accuracy of diagnosis and treatment, accelerating the aging of components, and reducing the reliability and service life of equipment; Improve the safety risk of diagnosis and treatment equipment through integrated circuits and precision electronic components.

2. Causes of electrostatic discharge

Electrostatic discharge is very common in life, and it is easy to occur in dry and manic environment. Static electricity needs to be caused by various reasons. The accumulation of electric charges causes potential differences between objects. In the process of touching or approaching, electric charge will shift rapidly, resulting in electrostatic discharge [2]. Friction and insertion: materials are composed of atoms, and the basic structure of molecules is protons, neutrons and electrons. Generally, the number of positive protons and negative electrons is the same. Positive and negative electricity balance, the object is not charged. However, the change of natural conditions will make the positive and negative charges of molecules unbalanced. The above friction is essentially a continuous contact and separation process. Induction plug-in: electrostatic discharge standard is not caused by friction, but by induction electrostatic discharge. The electric field of a charged body will cause the separation of charges near the object. As long as the object is inserted, the electric field will be generated around it, when it is close to the object.


3. Impact of electrostatic discharge on active medical devices

The charge movement will affect the electronic components of the active medical equipment, and even lead to the electrostatic failure of the active medical equipment. When electrostatic discharge occurs, electrostatic discharge will cause a large number of charge transients, which will cause high voltage current to pass through electronic components instantaneously, damage the insulation layer and immediately damage the internal circuit of electronic components. According to the serious harm to the active medical device, there are two situations: ① permanent damage, according to the immediate discharge, the electronic products in the device are damaged, such as the electrostatic discharge caused by the instantaneous pressure, indicating that the power switch is passed; ② The change of magnetic field is caused by immediate or indirect discharge, which leads to misoperation of equipment, and the detection results cannot meet the basic characteristics.

In the clinical environment, active medical devices have become sophisticated, integrated and electronic. With the development of chips, the formation of electrostatic discharge will cause serious threat to the normal startup of active medical devices, and even damage electrostatic damage. This is clinically unacceptable, which will affect the diagnosis and treatment of patients, and even threaten the personal safety of medical staff and patients. Active medical devices should take corresponding measures to avoid unpredictable damage caused by electrostatic elimination, which requires two types. Three types of active medical devices should be tested according to electromagnetic compatibility electrostatic immunity.

4. Rectification examples of electrostatic discharge test of electrical equipment

Take the difficulties encountered by a certain optometer in the electrostatic discharge experiment and the relevant solutions as an example, the details are as follows:

Problem description: Electrostatic discharge material test is conducted according to the relevant regulations and test methods of the medical device industry standard, a certain type of ophthalmic equipment optometer YY0505-2012 and the national standard GB-T17626.2-2012. During the experiment, the touch discharge ± 6kV. horizontal coupling plate ± 6kV. gas discharge ± 8kV test conducted by the optometer did not meet the requirements, and the hazard characteristics delayed the diagnosis. Specifically, the camera is disconnected The mouse fails and the display screen cannot work normally. You must restart it to restore the working state.

The main reason for the camera disconnection is that, according to the experimental phenomenon, the camera disconnection should be analyzed first. The camera is an electrostatic sensitive part. When the structure contacts and discharges, ± 6kV is easily disconnected. From the overall structure analysis, the camera USB line is connected with the internal host interface. After reinsertion, the camera can be plugged in again for maintenance. Carefully observe the USB and find the route of the line. The USB line part contacts the metal frame and the metal frame is grounded. During touch discharge, the sensitive camera is disconnected according to the touch part's crosstalk with the USB line on the construction site.

Rectification measure 1: change the release resistance value and select the resistance with larger resistance value.

The main reason for the lightning screen is that the display screen of the gas discharge system is ± 8kV. When the display is generated, the electrostatic charge is connected with the internal circuit according to the gap, and the hazard is abnormal. The reason is that the electrostatic charge cannot be successfully exported immediately according to the ground wire, which affects the working characteristics.

Rectification measure 2: expand the display grounding area, improve the display grounding effect, and successfully guide the electrostatic charge.

The result is clear: after the above rectification, the optometer will conduct electrostatic discharge inspection again, including contact discharge ± 6kV, horizontal coupling plate ± 6kV, gas discharge ± 8kV. During the experiment, the equipment will no longer disconnect the camera, mouse failure, display screen mosaic, and no other adverse test conditions. The rectification specification also proves that the rectification scheme is reasonable and effective, and the processing process can achieve continuous production.

Rectification measure 3: The camera channel USB online magnetic ring blocking interference signal damages the camera. In addition, the online magnetic ring blocking interference signal damages the camera USB to minimize the grounding metal frame.

The main reason for the mouse failure is that the device-level lotus board is indirectly discharged at ± 6kV, the mouse is easily disconnected, and the mouse interface cannot be repaired after being inserted into the outside. The internal host disconnects the USB adapter board, and can be repaired by plugging in the power supply again. It can be inferred that the electrostatic coupling USB adapter board causes the adapter board to get stuck. According to the interpretation of the circuit diagram of the adapter board, it is found that the resistance between the construction floor and the floor is too small, and it is easy to connect from the metal bottom shell to the adapter board in series, resulting in extremely high total voltage and endangering the characteristics of the adapter board.

In short, since the implementation of the electromagnetic compatibility specification, the basic rate of the electromagnetic compatibility electrostatic discharge test of active medical devices is very low. Improving the comprehensive anti-interference characteristics of electrostatic discharge is a process of combining theory with practice and applying theory to solve problems. This paper describes the influence of electrostatic discharge on medical machinery, and discusses the EMC electrostatic discharge test standard and the regulation of electrostatic rectification measures. On the premise of introducing the electrostatic discharge experiment, the EMC technical specifications were introduced and planned in the product development stage. During the production of medical devices, the impact of electrostatic discharge should be understood to prevent the risk of electromagnetic compatibility.

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