Pulse, Electric

a change of short duration in voltage or in current intensity. Short duration is defined as a time interval comparable to the duration of transient processes in electric circuits. Electric pulses may be classified as high-voltage pulses, pulses of high current intensity, video pulses, and radio pulses. High-voltage pulses are usually observed during the discharge of a capacitor into an active load; they have an aperiodic shape. Lightning discharges are usually of the same shape. Single pulses of similar shape are used to test high-voltage electrical equipment and installations; they have an amplitude of several kilo-volts to several mega volts, a wave front of 0.5–2 microsec, and a duration of 10 to 10 ⁻² microsec. Current surges of large magnitude can have a shape analogous to that of high-voltage pulses.

Electric current or voltage pulses (predominantly of the same polarity) are called video pulses if they have a nonzero direct component. Video pulses may be square, sawtooth, trapezoidal, exponential, or bell-shaped (Figure 1, a-d). Characteristic elements that determine the shape and quantitative parameters of a video pulse (Figure 2) are the amplitude A, front τ_f, duration τ_p, fall-off τ_fo, and the slope of the pulse top (Δ A), usually expressed in percent of A. A periodic sequence of video pulses is characterized by the repetition frequency and the off-on time ratio (the ratio of the repetition period to the duration of the electric pulse). The duration of video pulses ranges from fractions of a second to tenths of a nanosecond (10⁻⁹ sec). Video pulses are used in television, computer technology, radar, experimental physics, and automation.

Radio pulses are intermittent, high-frequency or ultrahigh-frequency oscillations of electric current or voltage (Figure 1, e). The duration and amplitude of such pulses depend on the parameters of the modulating oscillations. The duration and amplitude of radio pulses correspond to the parameters of modulating video pulses; the carrier frequency is an additional parameter. Radio pulses are used mainly in radio engineering and communications technology. The duration of radio pulses ranges from fractions of a second to a nanosecond.

Figure 2. Video pulse: (A)amplitude, (τ_f,) forward front, (a) top, (τ_fo) fall-off, (b) tail, (τ_p) pulse duration, (ΔA)slope of pulse top