Electrical Units of Measure are used to express standard electrical units together with their pre-annexes when they are too small or too large to be expressed as a base unit.
The standard electrical measuring units used for voltage, current and resistance expression are Volt [ V ], Amper [ A ] and Ohm [ Ω ], respectively.
These electrical measuring units are based on the International (metric) System, also known as the SI System, with other widely used electrical units derived from SI base units.
Sometimes in electrical or electronic circuits and systems,it is necessary to use multiples or lower layers (fractions) of these standard electrical measuring units when the measured quantities are too large or too small.
The following table provides a list of some standard electrical units of measurement used in electrical formulas and component values.
Standard Electrical Units of Measurement
|Unit of Measurement ||Symbol||Description|
|Voltage||Volt||I or i||Electrical Potential Unit|
V = I × R
|Current||Ampere||me or me||Electric Current Unit|
I = V ÷ R
|resistance||Ohm||R or Ω||DC Resistance Unit|
R = V ÷ I
|Conductivity||Siemen||G or ℧||Resistance Against|
G = 1 ÷ R
C = Q ÷ V
|Charge||Coulomb||Q||Electric Charge Unit|
Q = C × V
|Inducing||Henry||L or H||Inducing Unit|
V L = -L(di/dt)
P = V × I or I 2 × R
|Internal resistance||Ohm||Z||AC Resistance Unit|
Z 2 = R 2 + X 2
ε = 1 ÷ T
Floors and Lower floors
There is a very large range of values encountered in electrical and electronics engineering between the maximum value and the minimum value of a standard electrical unit.For example, resistance can be lower than 0.01Ω or higher than 1,000,000Ω.Using the multiples and lower floors of the standard unit, we can avoid typing too many zeros to define the position of the dexterity point.The following table provides their names and abbreviations.
|Terra||T||1.000.000.000.000||10 of 12|
|Giga||G||1.000.000.000||10 of 9|
|Mega||M||1.000.000||10 of 6|
Therefore, we use resistance, current or voltage units or multiples as examples:
- 1kV = 1 kilo volt – which equates to 1,000 Volts.
- 1mA = 1 milli-amp – this equates to one thousandth of a Amperage (1/1000).
- 47kΩ = 47 kilo-ohm – which equates to 47 thousand Ohms.
- 100uF = 100 micro-farads – this equates to one in 100 million (100/1,000,000) of a Farad.
- 1kW = 1 kilowatt – which equates to 1,000 Watts.
- 1MHz = 1 mega-hertz – this equates to one million Hertz.
To convert from one prefix to another, it is necessary to multiply or divide by the difference between the two values.For example, convert 1MHz to kHz.
We know from above that 1MHz equals one million (1,000,000) hertz, and 1kHz equals 1,000(1,000) hertz, that is, a 1MHz is a thousand times larger than 1kHz.Then to convert Mega-hertz to Kilo-hertz we need to multiply mega-hertz by a thousand, since 1MHz equals 1000 kHz.
Likewise, if we have to convert kilo-hertz to mega-hertz, we need to divide it into a thousand.A much simpler and faster method would be to move the de-destruct point left or right, depending on whether you need to multiply or split it.
In addition to the "Standard" electrical units shown above, other units of electrical engineering are used to indicate other values and quantities, such as:
- • Wh – Watt-Hour , the amount of electrical energy consumed by a circuit over a certain period of time.For example, a light bulb consumes a hundred watts of electrical energy for an hour.It is usually used as Wh (watt-hour), kWh (Kilowatt-hour) which is 1,000 watt-hours, or MWh (Megawatt-hour), which is 1,000,000 watt-hours.
- • dB – Decibel isone tenth of the Waist (symbol B) and is used to represent gains in voltage, current or power. It is a logarithmic unit expressed in dB and is usually used to represent the ratio of input to output in amplifier,audio circuits or speaker systems. For example, an input voltage (V IN) is expressed as an output voltage (V OUT) dB ratio of 20log 10 (Vout/Vin). The value in dB can be positive (20dB) representing gain or negative (-20dB) representing loss with unity, that is, input = output is expressed as 0dB.
- • ε – Phase Angle, Phase Angle is the degree difference between the voltage waveform and the current waveform with the same periodic time.This is a time difference or time shift and may have a "leading" or "delayed" value depending on the circuit element.The phase angle of a waveform is measured in degrees or radiances.
- • ω – Angular Frequency , Another unit mostly used in AC circuits to represent the Phaser Relationship between two or more waveforms is called angular frequency, symbol ω.This is a rotational unit with an angular frequency of 2ππ in units in rad/s per second rad.The full rotation of a cycle is 360 degrees or 2π, so half a turn is given as 180 degrees or π rad.
- • τ – Time Constant , Time Constant of an impedance circuit or linear primary system, the time taken to reach 63.7% of the maximum or minimum output value of the output when subjected to a Step Response input.It is a measure of response time.
In the next lesson about DC circuit theory, we will look at Kirchhoff's Circuit Law, which, together with the Ohm Act, allows us to calculate the different voltages and currents that circulate around a complex circuit.