Measuring the conducted emission determines which interference energies your device emits to its surroundings via the connected cables.
The main causes of unintentional emission of interference energy are, for example, AC/DC converters, dimmers, or circuits for pulse-width modulation. Depending on the area of application of your device, there are various limitations for interference energy that must be checked. For example, the conducted emissions on supply lines directly affect the grid quality via harmonic currents, voltage fluctuations/flickers. This area also includes high-frequency energies on network cables.
The standards and procedures in this area include the following:
- CISPR 16-2-1 – Interference voltage
This part of CISPR 16 is a basic standard and describes the measurement of conducted disturbances in the frequency range between 9 kHz and 30 MHz. The network simulation forms the agreed reference impedance against which the RF disturbance is measured. It simulates the impedance which is formed by actual networks (for example extensive power supply and communication lines) to the test object. In this process, the network simulation decouples the test circuit from the power supply network.
Interference voltages at connections that cannot be measured with a grid simulation can be measured with a probe (CVP). Examples of such connections are connections for antennas, control lines, signal lines and load lines. In general, the probe is used to measure the asymmetrical interference voltage. The probe provides a high RF impedance between the connection being measured and the reference ground.
- CISPR 16-2-2 – Disturbance power
For smaller test objects with only one line for connection to the power supply network or only one line of another type, the absorbing clamp measuring method offers an alternative to methods for measuring radiated emissions. The absorbing clamp measuring method is used to determine the disturbance power using an absorbing clamp. This method is based on the observation that radiated emissions of small electrical devices are primarily attributable to common-mode currents flowing for example on the devices’ power supply lines. The disturbance potential of such test objects can be seen as the power the test object is able to feed into this line, which acts as a radiating antenna.
However, there is criticism regarding the applicability of the results to the radiated emission, and as there are ever faster measuring systems for radiated emission, the method of measuring the disturbance power is used less and less frequently.
- IEC 61000-3-2 – Harmonic current emissions
During this test, the harmonic currents generated by the test object and fed back into the supply network are measured and evaluated. In this process, the total effective value of the harmonic currents of the orders between 2 and 40 (THC) is considered. Harmonic currents impair the grid quality and must therefore be limited.
- MIL-STD-461 CE101 – Audio Frequency Currents
This requirement is to limit the low-frequency magnetic fields generated by mains frequency harmonics in inductors in order to protect systems operating at very low frequencies, such as tuned receivers.
- MIL-STD-461 CE102 – Radio Frequency Potentials
This requirement limits the electric field that a device may emit. In contrast to CISPR 16-2-3, this method involves measuring at a fixed distance of 1 m (i.e. in the near field). Since the impact of reflections from the floor of the measuring chamber can be neglected, no height scan is performed. To increase the reproducibility of measurements in the near field, this requirement very precisely specifies the measurement antennas to be used. This way, the results obtained in different laboratories can be compared very well.
Carsten Möller Carsten Möller
Head of EMC Laboratory
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