Electrical Units, Measurement Instruments and Prefixes

Electrical Quantities and Measuring Instruments

• Tensão Elétrica (U ou E): Volt (V); Voltmeter
• Corrente Elétrica (I): Ampere (A); Ammeter
• Electrical Resistance (R): Ohm (Ω); Ohmmeter
• Resistividade Elétrica (ρ): Ohm-meter (Ω·m); Resistivity Meter
• Potência Elétrica Ativa (P): Watt (W); Wattmeter
• Potência Elétrica Reativa (Q): Volt-Ampere Reativo (Var); Varmeter
• Potência Elétrica Aparente (S): Volt-Ampere (VA); Apparent Power Meter
• Capacitância (C): Farad (F); Capacitance Meter
• Indutância (L): Henry (H); Inductance Meter
• Frequência Elétrica (f): Hertz (Hz); Frequencímetro

Measurement Instrument Components

A Measurement Instrument is responsible for energy transformation, converting electrical energy into mechanical energy. It consists of a fixed part and a moving part. The moving part is connected to a scale or Indicator, housed within a Case that protects the device.

Moving Coil Instrument

The Moving Coil Instrument operates with one fixed magnet and one moving coil. It is a DC meter that measures current flow in one direction. The current to be measured passes through the coil, creating a magnetic field. The interaction between this field and the fixed magnet causes the pointer to displace.

Metric Prefixes

Exa (E): 10¹⁸ = 1,000,000,000,000,000,000
Tera (T): 10¹² = 1,000,000,000,000
Giga (G): 10⁹ = 1,000,000,000
Mega (M): 10⁶ = 1,000,000
Kilo (k): 10³ = 1,000
Hecto (h): 10² = 100
Deca (da): 10¹ = 10
Deci (d): 10^-1 = 0.1
Centi (c): 10^-2 = 0.01
Milli (m): 10^-3 = 0.001
Micro (µ): 10^-6 = 0.000001
Nano (n): 10^-9 = 0.000000001
Atto (a): 10^-15 = 0.000000000000001

Electrodynamic Instrument

The Electrodynamic Instrument works with two coils: one fixed and one moving. Current circulates through both coils, and as it flows through the moving coil, it displaces relative to the other due to opposing magnetic fields. These are rarely used for DC systems because they are less precise and economical than moving coil types. The scale is wider in the center and compressed at the ends. They are among the most precise instruments for AC measurement but are sensitive to external magnetic fields when built without a magnetic core.