How to avoid static electricity damage to laboratory equipment

Winter is coming! The damage caused by static electricity to electronic components and equipment cannot be ignored in winter. Why do production lines invest so much in anti-static measures? It is because they are afraid of being hit by static electricity! So how can we avoid the damage of static electricity to equipment in the laboratory?

1. How is static electricity generated?

• Friction: Static electricity can be generated when two objects of different materials come into contact, rub against each other, and then separate.

• Induction: For conductive materials, since electrons can flow freely on the surface of conductive materials, if they are placed in an electric field, positive and negative charges will be transferred due to the repulsion of like charges and attraction of opposite charges, thus generating static electricity.

• Conduction: For conductive materials, since electrons can flow freely on its surface, if it comes into contact with a charged object, charge transfer occurs, thereby generating static electricity.

Figure 1 is a schematic diagram of the human body electrostatic model. When the switch in the circuit is connected to A, the voltage source charges the capacitor, simulating the process of human body accumulating static electricity; when the switch is connected to B, the charge stored on the capacitor is discharged to the device through the resistor (equivalent human body resistance), which is equivalent to the moment when the human body touches the device. The discharge process will generate a certain amount of instantaneous discharge current in just a few hundred microseconds, which may damage the internal components of the device.

Figure 1 Human body static electricity model

2. Why are instruments so easily broken down by static electricity?

Instrument products usually need to meet the electromagnetic compatibility requirements of the IEC61326-1 standard, which includes electrostatic immunity tests and requires that instrument products meet the test levels of 4KV for contact discharge and 8KV for air discharge according to IEC61000-4-2.

1. The higher the frequency of the instrument, the weaker the electrostatic protection ability

The oscilloscope is a high-resistance device, which is very susceptible to external static electricity induction and generates static electricity. However, the charge is difficult to discharge in the presence of strong static electricity, which easily leads to static electricity breakdown. Since the parasitic parameters of the electrostatic protection device will affect the measurement of high-frequency signals, it is impossible to integrate too many electrostatic protection devices in high-frequency instruments, resulting in a decrease in electrostatic protection capabilities.

Therefore, the higher the frequency of the instrument, the more attention should be paid to electrostatic protection.

2. Improper operation can also cause the instrument to be damaged by static electricity

For oscilloscopes, be sure to connect the ground first and then the signal. For example, the following two operations are very dangerous and must be avoided as much as possible.

Wrong operation 1: When using an oscilloscope to measure a circuit board, the probe is connected to the signal line first, and the probe ground line is connected to the ground later;

Wrong operation 2: Touch the probe needle directly with your hand, as shown in Figure 2.

Figure 2 Incorrect operation

3. What measures can we take to protect against static electricity?

Although the instrument has a certain anti-static ability, if the environmental static electricity is higher than the standard requirement, the instrument may still be damaged by static electricity, so it is necessary to understand some basic static protection measures when using the instrument.

Electrostatic protection mainly follows the principle of release before operation.

1. Keep the instrument well grounded

The purpose is to discharge static electricity to the ground. If floating ground measurement is necessary, be sure to ground before specific operations to release static electricity.

2. Perform electrostatic treatment on the environment before measurement

If conditions permit, the production line needs to be paved with anti-static flooring, and people need to wear anti-static clothing and shoes. For the use of high-frequency instruments, people also need to wear anti-static wristbands to discharge static electricity directly to the ground, as shown in Figure 3.

Figure 3 Common anti-static measures for instruments

If conditions do not permit, we have a more convenient way. Before touching the instrument, you can touch something that is well grounded with your hand. It is best to do this once in a while.

3. Be sure to connect the ground first and then the signal.

The device under test will also have static electricity (the contact resistance is small, and the release current may be higher). Therefore, when using an oscilloscope to measure a circuit board, you must first connect the probe ground wire and then connect the probe to the signal line. If you connect the probe to the test point first and then connect the probe ground, the static electricity will be released directly through the oscilloscope signal circuit and may break down the internal components of the oscilloscope. This is a very important operating step.

There are similar applications in the design of many boards and cards. For example, in the PCIE board and card shown in Figure 4, the gold finger of the clock signal is significantly shorter than other pins. This is to allow the ground wire to contact first for discharge when the card is inserted, and then the signal wire can contact safely.

Figure 4 Common anti-static measures for boards

4. Try not to touch exposed interfaces

Never touch the exposed interfaces of electronic equipment, including the probe tip of an oscilloscope.

IV. Conclusion

When using the instrument, the operator must be aware of electrostatic protection, especially in the dry winter, so as to minimize the damage of electrostatic discharge to the instrument. I emphasize again: especially in the north, especially in winter.