What Is EMI Testing? A Plain-English Guide

EMI testing is how a product demonstrates it can operate without interfering with other equipment. It splits into two halves — emissions and immunity (susceptibility) — and further into whether energy travels through cables (conducted) or through the air (radiated).

The Four Categories of EMI Testing

• Conducted emissions (CE) — interference the device puts back onto its cables.
• Radiated emissions (RE) — energy the device and cables radiate into the air.
• Conducted susceptibility (CS) — how well it tolerates interference injected on cables.
• Radiated susceptibility (RS) — how well it tolerates external electromagnetic fields.

Key Standards by Market

Standard	What it covers
FCC Part 15 (US commercial)	emission limits; Class A industrial, Class B residential; conducted 150 kHz–30 MHz, radiated 30 MHz+.
CISPR 32 / IEC 61000 (EU/international)	emissions (CISPR 32) plus immunity (IEC 61000).
MIL-STD-461G (US defense/aerospace)	full CE, RE, CS, RS.
IEEE 299	measures enclosure shielding effectiveness, performed by an accredited lab.

Where Shielding Fits — and Deep Coat’s Role

When a product fails emissions or immunity testing, the fix is usually filtering, grounding, and shielding. Shielding is the containment layer — a conductive barrier that keeps radiated energy in or out. Deep Coat does not run the test lab; we engineer and apply the vacuum-metallized shielding that helps a housing pass, working alongside your accredited lab — since 1981, under ISO 9001:2015.

Frequently Asked Questions

What is the difference between EMI and EMC testing?

EMC (electromagnetic compatibility) is the goal — a device coexisting with its environment. EMI testing is how that goal is verified, by measuring emissions and immunity. The terms are often used interchangeably.

What is the difference between emissions and immunity testing?

Emissions testing measures the interference a device sends out; immunity (susceptibility) testing measures how well it keeps operating when interference is directed at it. Commercial standards emphasize emissions; defense standards add immunity.

What standards apply to EMI testing?

US commercial products follow FCC Part 15; EU/international products follow CISPR 32 and the IEC 61000 family; US defense and aerospace follow MIL-STD-461. Enclosure shielding effectiveness is measured per IEEE 299 by an accredited lab.

Does Deep Coat perform EMI testing?

No — Deep Coat engineers and applies the EMI/RFI shielding that helps a product pass, and works alongside your accredited test lab. The formal scan and report are performed by the lab.