What is EMC?

EMC stands for electromagnetic compatibility. Every electronic device/machine on the market must be EMC compliant, meaning it must fulfill the EMC regulations and standards defined by the country where the product is sold.

An EMC complaint product must...

1. ... NOT interfere with other devices/machines in its environment (emission).

2. ... NOT being upset by other devices/machines in its environment (immunity).

3. ... NOT interfere with itself (signal integrity).

4. ... NOT be destroyed or malfunction when touched by a human (electrostatic discharge, ESD).

In the picture below, you see a vending machine as an EMC victim. The machine (victim) must show a certain immunity against electromagnetic emissions e.g. from mobile phones (over the air) or from high power machines (over the power lines). In addition, the user which touches the display may produce an electrostatic discharge (ESD) which must not destroy the machine.

EMC example: emissions and immunity.

There are other common abbreviations around EMC:

• EMI (Electromagnetic Interference)

• ESD (Electrostatic Discharge)

EMI and ESD are often mixed up with EMC. Therefore, I would like to explain these abbreviations to you in more detail.

EMI vs. EMC

EMI stands for electromagnetic interference. EMI means that one electronic device/machine A is causing disturbance to another electronic device/machine B, which is in the surrounding of device/machine A.

What is the difference between EMC and EMI? Now, an EMC compliant product has to be tested on EMI during its development. For an EMC compliant product, EMI should not happen any more. This is due to the fact, that EMC compliant products proved their electromagnetic immunity to be high enough and their electromagnetic emission to be low enough to work seamlessly in its predefined environment.

EMI can happen over the air (radio frequency interference, RFI) or over power and signal lines of a product.

Here some examples of EMI:

• EMI over power lines: Your TV shows starts to flicker every time you use your coffee grinder or mixer in the kitchen. This would mean that your TV got upset over its power line connection, because the grinder or mixer emits some disturbances back into the power lines. 

• EMI over the air: You are listening to some music over your audio equipment. From time to time, you can here a noise coming out of the speakers. This may be caused by your mobile phone e.g. when a short message (SMS) arrives. The radio frequency signals of the mobile phone could disturb your audio equipment.

ESD vs. EMC

ESD stands for electrostatic discharge. Every EMC compliant product has to be tested on ESD during its development. This means that EMC compliant products should withstand certain electrostatic discharges of e.g. 1kV, 15kV or more. This may sound like very high levels (e.g. compared to your power line voltage of 110V or 230V). However, it is easily possible that your body is charged to 10kV or more.

A real life example of ESD for instance is, if you get an electric shock when you are touching your cars door handle after getting off your car.

But why is that?

• Friction: While driving, your cars wheels rub on the ground and friction of non-conductive materials (e.g. your cars wheels) bring electrons from one material to the other.

• Charge: When electrons change from one material to the other, and there is an isolation in between there materials (in this case air), a charge is created (one material has less electrons (electron-deficient), whereas the other material has more electrons on its side (electron surplus)).

• Discharge: Now, when you get out of your car, your body “connects” with the ground and therefore has the same electric potential like ground (0V). However, your cars metal case has still the potential of several kV. If you now touch the handle of your car, an electrostatic discharge (ESD) happens, and this may hurt (electric shock).

I don’t know how much you know about electronics? Just in case you know a lot, here a schematic of an ESD generator (ESD test equipment) which may help you to understand the topic in more detail.

1. Charge: Close the Load Switch and bring Cs to the high voltage of e.g. +8kV.

2. Isolate: Open the Load Switch. The ESD generator is now ready to be discharged.

3. Discharge: Close the Discharge Switch and the ESD generator now discharges and an ESD pulse comes out of the ESD generator.

ESD Generator (equivalent circuit diagram). [1]

Closure

I hope this blog post helped to clarify some confusion about EMC, EMI and ESD!? If not: please let me know what you would like to have explained differently or in addition.

Please SHARE and COMMENT! Thank you.

-The Academy of EMC

References

[1] International Electrotechnical Commission, IEC 61000-4-2:2008 - Electromagnetic compatibility (EMC) - Part 4-2: Testing and measurement techniques - Electrostatic discharge immunity test, 2008.