EMC, or Electromagnetic Compatibility

denotes the capability of a device to operate without causing interference in its electromagnetic (EM) environment. It ensures that the device does not emit excessive levels of EM energy that could lead to Electromagnetic Interference (EMI) in nearby devices.

Electromagnetic Interference (EMI) occurs when one electronic device disrupts the operation of another through the electromagnetic fields it generates during its functioning.

For instance, a common observation is the flickering of a tube light when certain devices like a water pump or motor are in operation. This phenomenon is attributed to the increased current drawn by the motor, resulting in a voltage drop. This alteration in electrical current and voltage gives rise to Electromagnetic Interference (EMI), which needs to be controlled within specified limits to prevent disruption to other devices in the vicinity.

An EMC test serves to identify and assess the electromagnetic interference produced by a device. Furthermore, these tests evaluate how well a device can withstand and function in the presence of electromagnetic interference generated by other devices.

Types of EMC

Every device possesses the capacity to produce electromagnetic fields. Everyday items like televisions, mobile phones, washing machines, ATMs, RFID tags, and more, can either generate electromagnetic interference or be susceptible to damage caused by interference from other devices. To guarantee the reliable performance of these devices, an EMC test conducts various sub-tests on the Equipment Under Test (EUT) to assess the immunity of the affected device, ensuring its ability to endure in an environment with electromagnetic emissions. Additionally, the electromagnetic interference (EMI) produced by the EUT must adhere to the interference limits stipulated by the respective country’s regulations.

Types of EMC tests

The fundamental block diagram of EMC tests is presented below. It’s important to note that not all of these tests are applicable to every product, and additional tests may be included based on the specific application of the product.

EMC tests encompass two primary assessments: one focusing on Electromagnetic Interference (EMI) and the other on Electromagnetic Susceptibility (EMS).

Block diagram of types of EMC tests

Electromagnetic Interference, often abbreviated as EMI

Current and voltage fluctuations produced by electronic devices result in the generation of electromagnetic interference (EMI). Consequently, it is crucial to employ effective electronic design and shielding measures to restrict the EMI emitted by a device, preventing its impact on neighboring devices.

For instance, the operation of a drill machine in one household may lead to TV flickering in a nearby house if they share the same supply line.

EMI effect on other devices

Types of Electromagnetic Interference (EMI) 

Conducted Emission

When a device releases an electromagnetic field through the conductor of a wire, it is termed conducted emission. This has the potential to create issues across the entire power distribution network, impacting other devices.

Conducted emission

Radiated Emission

When a device emits electromagnetic energy, it disperses as electromagnetic fields that travel through the air and may disrupt other nearby devices.

Radiated emission

Voltage Flicker Emission
Voltage flicker arises from fluctuations in load current, causing variations in both frequency and amplitude. This phenomenon is evident in changes in the brightness of a light bulb or adjustments in the speed of a motor or fan.

Voltage flickering in DC (Image: Science Direct)

Harmonic Current Emission

When a device releases harmonics, causing distortion in the main supply, it is referred to as harmonic current emission. This phenomenon is commonly associated with switch-mode power converters and other non-linear loads, including motors, transformers, and lamp dimmers.

Harmonics from the device(Image: Science Direct)

Electromagnetic Susceptibility (EMS)

Electromagnetic Susceptibility (EMS) refers to a device’s ability to either withstand or operate as intended in an environment where other devices generate electromagnetic interference. Since every device tends to emit electromagnetic interference, it is crucial that the affected device functions appropriately in such environments. These requirements are outlined in the electromagnetic susceptibility (EMS) test standards established by the country.

To illustrate the necessity of EMS testing, consider a real-life scenario where a user hears noise on their mobile phone while another mobile device or household appliance is in use. This occurrence is indicative of the device’s low immunity to external electromagnetic interference.

Effect of other devices on the user device

Types of Electromagnetic Susceptibility (EMS)

• Conducted immunity

During the conducted immunity test, an RF amplifier induces disturbance in the cable or power supply, and the device’s performance should remain unaffected by the resulting distortion or interference in the power supply.

Radiated and conducted emission (Image: Academy of EMC)

Radiated Immunity

During a radiated immunity test, the device generates an electric field disturbance, noise, or magnetic field interference through the air. In this context, the device is expected to maintain its normal performance.

Radiated emission

Electrostatic Discharge (ESD)

Electrostatic Discharge (ESD) is the release of static electricity from the human body into the metallic components of a device. When a person touches the device, they may experience a shock. This can potentially cause permanent damage to the device, so the purpose of this test is to assess the device’s protection and immunity against ESD.

ESD symbol (image: Incompliance Magazine)

Electrical Fast Transient (EFT)

The EFT immunity test replicates the real-world scenario of switching inductive loads. The switching of inductive loads results in small sparks, manifesting as bursts of pulses. The device needs to demonstrate its capability to withstand and manage these pulses.

Bursting by EFT (Image: EMCfastpass)

Surge

ESD and EFT share similarities in terms of rise times, pulse width, and energy levels. In the case of a surge, the pulse has a rise time of only 1.2 microseconds, with a longer duration. The pulse width extends to 50 microseconds, necessitating circuit protection to effectively manage the surge.

Magnetic Field

Magnetic fields are omnipresent; whenever a current flows through a wire, it produces a magnetic field around the wire. In this test, a magnetic field is intentionally generated to assess the device’s response, with the expectation that the device’s functionality remains unaffected.

The magnetic field generated in wire (Image: source)

Voltage Dip and Short Interruption

In this test, fluctuations in power supply are induced, either in AC or DC, and the device is then examined under these conditions.

Voltage dip and short interruption (Image: EMC FastPass)

Global rules and regulations

The EMC standards vary from one country to another. In the United States, the Federal Communications Commission (FCC) establishes regulations and standards for EMC certification. In Canada, Industry Canada serves as the equivalent to the FCC. In Europe, the CE mark is analogous to the FCC.

Here are some of the marks issued by these regulatory authorities: