# D

## Discrete Time System

When the time variable t takes on the discrete values t=kT, k=…,-2,-1, 0, 1, 2… the system is said to be discrete – time system.

## Dependent Sources

Voltage or current source whose value linearly depends upon the value of voltage or current of other elements in the circuit.

## Digital Multimeter

A digital multimeter (DMM) is a multifunctional meter that displays its electrical quantitative values on an LCD screen.

## Decibels

A logarithmic unit for expressing the difference between two sound, power, voltage or current levels.

## Direct Current

Current that continues to flow in the same direction is called direct current and remains constant.

## Dielectric

The material between two plates of a capacitor is non-conducting or insulating. This insulating material is called dielectric. An example of some dielectrics is air, ceramic, Formica and Teflon.

## Dielectric Strength

The dielectric strength of a material is a measure of how much voltage it can withstand, before breaking down.

## Domains

Acicular (needle-shaped), microscopic crystals containing a very large number of atoms whose spinning electrons result in a net magnetic effect in a particular direction.

## DC Machine

An electromechanical conversion device whose armature voltage and current, as well as field voltage and excitation current, are all DC.

## Developed Power

The power Converted from electrical to mechanical or from mechanical to electrical.

## Diagonal matrix

A Square matrix in which all the elements, not in the principal diagonal, are equal to zero; that is, aij=0 for all i≠ j.

## Direct-axis synchronous reactance, Xd

The ratio of the sustained fundamental component of armature voltage that is produced by the total direct-axis ﬂux due to direct-axis armature current to the fundamental component of this current, the machine running at rated speed.

## Digital Multimeter

A meter used to measure electrical quantities that can measure different electrical quantities such as voltage and amperage and displays the reading as numbers or digitally.

## Drive

A set of electronics that gives precise control over electric motors including speed and direction.

## Discrete input module

Hardware that is capable of receiving only one input consisting of either a high or low.