EMC Basics
Interference Variables and Interference Signals Overview The disturbance variables and the interfering signals that result from them cover a wide frequency and amplitude range. They can occur in many curve forms and be put into many different classifications. When referring to time, the occurrences are classified as periodical and non-periodic interference variables. Periodic interference Periodic interference consists of sinus formed signals. External sinus formed interference sources are radio and television transmitters and radiotelephony. In industrial applications, periodic interference is caused by alternating and rotating current components, power converters, fluorescent lamps, combinational circuit components and PCs. They create continuous distortion in supply voltage, voltage fluctuation, voltage drops and dissymmetry in rotary current supplies. Periodical interference:
Non-periodic interferences - transients Non-periodic interferences are short interfering pulses (Transients). The characteristics of these transients are the rate of change voltage dU/dt and current di/dt fluctuations. In industrial networks, shut-off overvoltage can reach as high as 10 kV with rise time in the nsec. to sec. range and frequencies up to 100 MHz. The voltage increase speeds of these feared bursts lie between 2 and 5 kV/nsec with a pulse duration of 100 nsec to 1 msec. Transient pulses are noticed especially in digital systems since they can disrupt functionality by setting or clearing memory locations (flags and registers).
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