Glossary of Technical Terms

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Attenuation:: A signal (or noise) is made to decease in intensity (power). An RFI filter attenuates noise, in that the noise coming out is less than the noise going in.

ElectroMagnetic Interference (EMI): Electromagnetic Interference. This term is often used interchangeably with RFI (radio-frequency-interference). Technically, EMI refers to the type of energy (electromagnetic), while RFI refers to the frequency range of the noise frequency). Both EMI and RFI describe unwanted signals (noise) that a Corcom filter is intended to eliminate.

FILTERING: The process of removing undesired components on a signal while allowing the desired components to pass. A power line filter purifies the AC power entering the equipment by attenuating the high-frequency (typically 150kHz and up) RFI, while passing the low frequency (typically 50Hz) AC power waveform. This is called low-pass filtering.

FREQUENCY RANGE: A band of frequencies of electromagnetic energy expressed in Hz (cycles per second), kHz (thousand of cycles per second). A power line RFI filter is expected to have attenuation over a given frequency range, typically 150kHz to 30MHz (above 30 MHz noise mainly is radiated).

HIPOT RATING: A specification which confirms the potential voltage a filter can see without degration of the components. The test stresses the insulation and and capacitors at voltage ratings well above normal operations to assure the reliability and safety of the components at nominal operation conditions.

IMPEDANCE: Through opposition to flow of current put up by a circuit across which voltage has been applied. Impedance varies with frequency and is best considered in relative terms. A filter works best when its impedance in the RFI frequency range on the line and load side is greatly different from the impedance on the line and load circuits to to which it is connected. This is called impedance mismatch.

INSERTION LOSS: A statement of the filter's attenuation characteristics, exercising in decibels (dB) the ratio of noise that would get through without the filter, to that which gets through with the filter installed. Insertion loss varies widely with frequency, and with source and load impedance. It is usually presented in the form of a graph or table across the frequency range of interest using standardized source and load impedance.

LEAKAGE CURRENT: A measurement of expected current which returns to ground in a system. In the event of a faulty ground circuit this current might be passed to a body of a person, for this reason leakage current is limited within a system. Leakage current is a function of the line to ground capacitance, therefore filters are a major contributor to the leakage current of a system. The leakage current of a filter generally increases with performance.

MAXIMUM LEAKAGE CURRENT: A Limitation on the amount of current that can flow from the power conducters to the ground circuit (case) during normal operation. It is affected by line voltage and frequency.

NOISE: Literally, any undesired signal. In the case of power lines, noise means any electromagnetic energy other than the power waveform (typically 50Hz or 60Hz, but occasionally 400Hz). RFI noise refers specifically to undesired signal in the radio-frequency range, typically 150kHz to 30MHz. Power lines may transmit noise common mode (signals on both power conductors referenced to ground and differential mode (signals on one power conductor referenced to the other).

OPERATING FREQUENCY: The nominal frequency of the AC power line voltage into which the filter is designed to operate. Most Corcom filters are stamped for an operating frequency of 50/60 Hz, indicating their suitabilty for North America (60 Hz) or overseas (50 Hz) power lines. However, operation at DC or 400 Hz does not compromise the effectiveness of the filter.

OVERLOAD CURRENT: The maximum rms current that can be passed through the filter for a breif time. It is sometimes called inrush current, because it routinely occurs when equipment is first turned on. It is generally stated in terms of a constant time the rated current over a period of seconds.

PEAK CURRENT: The maximum current that can be passed through the filter without fear of saturating the inductors (and hence reducing the filter's attenuation). Generally this will be 1.4 times the rated current. However, filters designed for use in switching power supplies will be rated to handle peak currents three to four times higher than the rated current.

RATED CURRENT: The depicted face current value under normal operation (40°C ambient). Some filters are derated at 250 volts, 40 degrees to maintain VDE compliance.

RATED VOLTAGE: The depicted face voltage at which a filter operates (230V, 50Hz in Europe, 115V, 60Hz in the United States).