This is a metaphor for EMI/EMS/EMC that can be understood at a glance.

The problem of electromagnetic radiation of electronic products is attracting more and more attention. I believe that most of them are familiar with term EMC (electromagnetic compatibility), because in order to obtain our country's 3C certification, it is necessary to pass EMC test of a professional organization.

However, similar professional terms such as EMI and EMS often appear in front of everyone in various media reports and promotional materials. They seem to be related to radiation shielding (electromagnetic radiation) which makes people confused. So what are similarities and differences between them?

EMP Attack

EMI (Electro Magnetic Interference) literally translates to "electromagnetic interference", which refers to phenomenon where electronic equipment (interference source) interferes with other electronic equipment through electromagnetic waves.

For example, when we are watching TV, someone next to us is using a hair dryer, electric razor, or other home appliance, and there will be noise of snowflakes on TV screen; Starting... It's normal electromagnetic interference.

What's more, electromagnetic interference can be disastrous if it interferes with medical electronics that monitor health or an aircraft in flight. Judging by these examples, it appears that electronic equipment has an invisible "attack force" causing disruption and damage to normal operation of other electronic equipment.

The primary and secondary EMI filter circuits of power supply are designed to reduce EMI generated by power supply.

From an "attack" point of view, there are two main types of electromagnetic interference: conducted interference and radiated interference. Conducted electromagnetic interference refers to an interference source connecting (interference) a signal in one's own electrical network to another electrical network via a conductive medium (eg wire).

The most common example is that our computer's power supply affects electrical network at home. When computer is turned on, lights in house may dim. This is more evident on computers with low-quality power supplies from other brands.

In internal structure of a modern power supply, primary and secondary EMI filtering circuits are essential. "EMF" here is aimed at electromagnetic conduction interference to prevent power supply from affecting outside world too much.

The EMI contacts on case are designed to reduce EMI inside shielded case.

Electromagnetic interference is often referred to as electromagnetic radiation for short. This means that interference source couples (interfering) a signal in its own electrical network to another electrical network through space, just like "hitting objects in air". in martial arts novels.

Because human life activities include a number of bioelectrical processes, these bioelectrics are very sensitive to electromagnetic waves of environment, so excessive electromagnetic radiation can affect human body and damage it.

"Radiation" that people often worry about refers to this part of electromagnetic interference. Apply various anti-radiation designs on chassis, such as EMI shrapnel, EMI contacts, where "EMI" is directed to electromagnetic interference, to reduce amount of electromagnetic waves in chassis that propagate outward.

EMC protection

Where there is a spear, there is a shield, and where there is electromagnetic interference, there is also anti-electromagnetic interference. Please name our second EMS protagonist below.

EMS (Electro Magnetic Susceptibility) literally translates to "Electromagnetic Susceptibility", which refers to ease with which electronic equipment is degraded by external electromagnetic energy.

For example, same interference from a hair dryer or an electric shaver on some TVs causes noise of snowflakes on screen, but some TVs are safe.

This shows that in event of an "attack" of electromagnetic interference, former have a higher electromagnetic sensitivity and are more vulnerable to injury, i.e. a lower "strength of protection", while latter have a lower electromagnetic sensitivity and are less vulnerable to injury, i.e. "Protection" above.

Snowflakes on a TV screen are serious, and interference from other electronic devices is a major factor.

Comprehensive EMC Offensive and Defensive Capabilities

With a spear and a shield, we finally use them to arm our third protagonist, EMC.

▲ Electromagnetic Compatibility Laboratory

An EMC laboratory is used for EMC testing, which can conduct EMC interference tests.

EMC (Electro Magnetic Compatibility) literally translates as "electromagnetic compatibility", which means ability of electromagnetic energy generated by electronic equipment not to interfere with or interfere with other electronic equipment.

Therefore, EMC includes two requirements of EMI and EMC: on one hand, it is required that electromagnetic interference generated by electronic equipment in environment during normal operation does not exceed a certain limit, that is, EMI; interference in environment has a certain degree of anti-interference ability, that is, EMC.

In particular, when conducting EMC tests on electronic equipment, relevant standards stipulate a maximum EMI value and a minimum EMC value, which is equivalent to limiting "attack power" at a lower level and requiring "protective power" at a lower level. highest level.

That's easy to understand too, just like we raise a watchdog, you don't want him to run out door to bite people, but you require him to be able to tolerate when enemy comes.

▲ 3C certification includes EMC standards

Now everyone knows that good electronic equipment should play role of "low attack and high defense", which not only creates little interference with outside world, but can also resist interference from outside world well.

So how do you choose such a product? In fact, national regulations have already prepared for us. Since 1996, European Community has adopted rules in its single market: any electrical and electronic equipment without "CE" certification mark must not be placed on European Community market.

The Chinese government has also decided that as of August 1, 2003, any electrical and electronic equipment without "CCC" (ie 3C) certification mark must not enter Chinese market. Both CE certification and 3C certification include EMC requirements.

So when you buy an electronic product, you can know whether it has low interference (including low radiation), high anti-interference performance.