How do emissions measurement tests differ from immunity tests in EMC testing

Emissions Measurement Tests

**Purpose: Emissions tests evaluate the amount of electromagnetic interference (EMI) generated by a device during its normal operation. The goal is to ensure that these emissions do not exceed specified limits, thereby preventing interference with other electronic devices in the environment.

**Types:
- Conducted Emissions Testing: This measures EMI conducted back through power supply lines and data ports, typically focusing on lower frequency ranges (150 kHz to 30 MHz). It assesses how much electromagnetic energy is transmitted along cables connected to the device[1][3].
- Radiated Emissions Testing: This involves measuring the electromagnetic field strength of emissions that propagate through the air from the device. It is usually concerned with higher frequency emissions and utilizes antennas for detection[2][7].

**Measurement Units: Emissions are often expressed in volts and amps, but can also be represented in decibels (dB) for convenience. The tests provide assurance that the device will not emit harmful interference while operating within its intended environment[3][4].

Immunity Tests

**Purpose: Immunity tests assess a device's robustness against external electromagnetic disturbances. These tests determine how well a device can function when subjected to EMI from other sources, ensuring it operates reliably within its expected environment.

**Types:
- Conducted Immunity Testing: This evaluates how well a device can withstand RF energy entering through power supply and data ports. It measures the device's performance when exposed to specific levels of electromagnetic noise[2][3].
- Radiated Immunity Testing: This examines how a device responds when exposed to external electromagnetic fields. It assesses the device's resilience against interference from radiated sources[1][5].

**Measurement Units: Immunity levels are typically measured in volts and amps per meter, also expressed in dB. This reflects the field strength of electromagnetic waves and how well the device can tolerate them without malfunctioning[2][4].

In summary, emissions measurement tests focus on quantifying the unwanted electromagnetic energy produced by a device, while immunity tests evaluate the device's ability to operate correctly in the presence of external electromagnetic interference. Both types of testing are crucial for ensuring that electronic products meet EMC standards and function effectively in their intended environments.