AC: (Alternating Current) A signal or power source that varies with time, switching polarities. Typically, sinusoidal and constant frequency.

AC Power Supply: Power supply that delivers an AC voltage.

A/D Conversion: Analog-To-Digital Conversion. The process of changing an analog signal into a digital value.

Alternating Current: Electric current that rises to a maximum in one direction, falls back to zero, and then rises to a maximum in the opposite direction and then repeats.

Ammeter: Instrument for measuring the current in amps, milliamps or microamps.

Ampere or Amp: Ampere(s), the unit of electrical current. Current is defined as the amount of charge that flows past a give point, per unit of time. The symbol I is used for current in equations and A is the abbreviation for Ampere.


  • I
  • current
  • A

 Amplitude: The highest value reached by voltage, current or power during a complete cycle.


Analog: System in which data is represented as a continuously varying voltage. Also spelled Analogue.

ANSI: American National Standards Institute.

 Apparent Power: Power attained in an AC circuit as a product of effective voltage and current (which reach their peak at different times).

 ASCII: American Standard Code for Information Interchange. Standardized method of encoding alphanumeric characters into 7 or 8 binary bits.

AWG: American Wire Gauge. A system that assigns a number value to the diameter of a wire.

 Battery: DC voltage source containing two or more cells that convert chemical energy to electrical energy.

Baud: Unit of signaling speed equal to the number of signal events per second.

Binary: System based on the number 2. (The binary digits are 0 and 1.)

Bit: Binary Digit. Smallest unit of binary data.

Bus: In Electricity. A bus bar.

Byte: A sequence of adjacent bits operated on as a unit by a computer.

Cascade: Method of connecting circuits in series so that the output of one is the input of the next.

Capacitance: A capacitor is a passive electronic component that consists of two conductive plates separated by an insulating dielectric. A Voltage applied to the plates develops an electric field across the dielectric and causes the plates to accumulate a charge. When the Voltage source is removed, the field and the charge remain until discharged, storing energy. Capacitance (or C, measured in farads), dictates the amount of charge that can be stored at a given Voltage (a One-Farad capacitor charged to one Volt will hold one Coulomb of charge).


  • Capacitor

Charge: Quantity of electrical energy.

Chassis: Metal box or frame into which components are mounted.

Chassis Ground: Connection to a chassis.

Choke: Inductor designed to present a high impedance to alternating current.

Circuit: Interconnection of components to provide an electrical path between two or more components

Circuit Breaker: Protective device used to open a circuit when current is greater than a maximum value. A circuit breaker acts as a reusable fuse.

Circuit Diagram: Structural or procedural diagram of an electrical system. Also see Schematic.

Closed Circuit: Circuit having a complete path for current flow.

Coil: Conductor wound in a series of turns.

Collector: One of three terminals of a transistor.

Continuity: The state that occurs when a complete path for current is present.

Current: Passage of electrons measured in amps (milliamps and microamps).

Controller Area Network: The CAN protocol is an international standard defined by ISO 11898. It is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It is a message-based protocol, designed originally for multiplex electrical wiring within automobiles, but is also used in many other contexts.


  • CAN

D/A Conversion: Digital-To-Analog Conversion. Translating discrete data into continuously varying signals.

DC: Direct current is the unidirectional flow of electric charge or current that flows in one direction. Direct current is produced by sources such as batteries, power supplies, thermocouples, solar cells, or dynamos. Direct current may flow in a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams.

Direct Current (DC) VS. Alternating Current(AC)

Direct current and alternating current are the two ways of transferring power from one point to another with the use of conductors. The main difference between the two is in how the current flows. Direct current, commonly abbreviated as DC, flows uniformly in one direction while alternating current, also commonly abbreviated as AC, changes direction at a given rate or frequency. The main consequence of this is the polarity of the voltage. With the DC, the polarity remains constant while with AC, it constantly switches between positive and negative. With AC, the voltage is expected to constantly reverse and polarity is not really important. That’s why you can plug-in your appliances to a wall socket in either orientation and not have any problem. Because DC keeps a constant polarity, it is important that you pay attention to how you connect your device as reversing the polarity can damage your device.


  1. DC has a constant polarity while AC has a changing polarity
  2. DC is particular about polarity while AC is not
  3. You only get DC from batteries and not AC
  4. AC is easier and more efficient to step up or down than DC
  5. DC has a much wider variety of standard Voltages than AC

DC Power Supply: Any source of DC power for electrical equipment.

Digital Electronics: Branch of electronics dealing with information in binary form.

Distortion: Amount by which a circuit or component fails to accurately reproduce the characteristics of the input.

DMM: Digital Multimeter Measuring instrument (e.g. Voltage, Resistance, Current) with a digital display.

Duplex Transmission: Ability to both send and receive data at the same time over the same communications line.

DVM: Digital Voltmeter: Measuring instrument for voltage with a digital display.

Earth: Ground. Connection to the earth itself or the negative lead to a chassis or to any point to zero voltage.

Electron Flow: Direction in which electrons flow (from negative to positive since electrons are negatively charged).

EMF: Electromotive Force. Force that causes the motion of electrons due to potential difference between two points (voltage).

Emitter: One of three terminals of a transistor.

Farad: Unit of capacitance.


  • F

Feedback: Portion of the output signal of an amplifier that is connected back to the input of the same amplifier.

Firmware: Computer software usually permanently stored in a computer.

Fuse: Protective device in the current path that melts or breaks when current is over a predetermined maximum value.

Gain: Ratio of the output level of a circuit to the input.

GFCI: Ground Fault Circuit Interrupt. Used for AC convenience outlets to provide maximum personal protection from electrical shock. A GFCI is not suitable for use with certain portable test equipment.

GPIB: (General Purpose Interface Bus) A standard bus for controlling electronic instruments with a computer. Also called IEEE-488 bus because it is defined by ANSI/IEEE Standards 488-1978, and 488.2-1987. Also called HP-IB, a trademarked term of Hewlett-Packard, which invented the protocol.


  • General Purpose Interface Bus
  • IEEE-488
  • HP-IB
  • 488

Ground: A large conducting body, such as the earth or an electric circuit connected to the earth, used as an arbitrary zero of potential. A ground is often used as the common wiring point or reference in a circuit.

Ground Plane: Earth or negative rail of a circuit and a considerable mass that presents the effect of earth (ground) to a signal.

Hertz: Unit of Frequency measurement

Henry Basic unit of inductance.

High Frequency: High Frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 MHz

I/O: Input/output

I²C: I²C (pronounced “I-Squared-C” and typeset as I²C but often typed as I2C) is short for “inter-IC bus.” I²C is a two-wire, low-speed, serial data connection IC bus used to run signals between integrated circuits, generally on the same board.


  • IIC
  • inter-IC bus

Impedance: Impedance is similar to resistance but applies to alternating current circuits and is measured in ohms (represented by the symbol “Z” ).

Input: The part of a circuit that accepts a signal for processing.

In-Rush Current: A momentary input current surge, measured during the initial turn-on of the power supply. This current reduces to a lower steady-state current once the input capacitors charge. Hot swap controllers or other forms of protection are often used to limit inrush current, because uncontrolled inrush can damage components, lower the available supply voltage to other circuits, and cause system errors.


  • Inrush Current
  • Inrush
  • In-Rush

Insulator: Material that resists the flow of current.

Interface: Usually the hardware that provides communication between various items of equipment using common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals.

Inverter: A device used to convert direct current into alternating current.

KVA: A Volt-Ampere (VA) is the Voltage times the Current feeding an electrical load. A Kilovolt-Ampere (kVA) is 1000 Volt-Amperes. Electrical power is measured in Watts (W): The Voltage times the Current measured each instant. In a direct current system or for resistive loads, the Wattage and VA measurements will be identical. But for reactive loads, the voltage and current are out of phase and the volt-ampere spec will be greater than the wattage. For determining power, watts are appropriate. For determining capacity for the driving circuits (circuit breakers, wiring, and uninterruptible power supplies, for instance), VA is appropriate.

KW: Kilowatt (or Kilowatts): 1000 Watts.

KWh: Kilowatt hour(s)

Leakage: Passage of small electric current through an insulator or dielectric that is unintended and undesirable.

LED: Light-emitting diode, a semi-conductor that emits light, used in displays such as meters, clocks and calculators.

Limiter: Circuit or device that prevents some portion of its input from reaching the output.

Line Regulation: Ability of a voltage regulator to maintain a constant voltage when the regulator input voltage varies. The change in output voltage when the AC input voltage is changed from minimum to maximum specified. It is usually a small value, and may be near zero with current mode control.

Load: Component or piece of equipment connected to a source and draws current from a source is a load on that source.

Load Current: Current drawn from a source by a load.

Load Impedance: Sum of reactance and resistance in a load.

Load Regulation: Ability of a voltage regulator to maintain a constant output voltage under varying load currents. The change in output voltage when the load on the output is changed.

Load Resistance: The resistance of a load.

Logic: The principle and applications of gates, relays and switches.

mA: milliAmpere, or milliamp: 1/1000 of an Ampere. Ampere is the basic unit for measuring electrical current.


  • milliamp
  • milliAmpere

mAh: A measure of charge (or current flow over time).

  • One Ampere-hour (or Amp-hour or Ah) is a current of one Ampere flowing for one hour. The amount of charge transferred in that hour is 3,600 Coulombs (Ampere-seconds).
  • A milliampere-hour (mAh or milliamp-hour) is a thousandth of an Amp-hour.
  • An Ampere-second (A-s or Amp-second) is an Amp supplied for one second.

A common use of the term is rating energy storage device capacity, especially rechargeable batteries.

Matched Impedance: Condition that exists when the output impedance of a source is equal to the input impedance of a load.

Megahertz (MHz): Measurement of frequency — million cycles per second.

Megohm: One million ohms (represented by the symbol “M” ).

Mnemonic: Relating to, assisting, or intended to assist the memory. A device, such as a formula used as an aid in remembering.

MOS-FET: Metal Oxide Field Effect Transistor. Field effect transistor with a metal oxide insulating layer between the gate electrode and the channel. Also referred to as an insulated gate field effect transistor.

Multimeter: Electronic test equipment that can perform multiple tasks (such as measuring AC and DC voltage, current and resistance. A digital multimeter is often referred to as a DVM.

Multiplexer: Device that sends messages or signals simultaneously using a multiplex system.

Mutual Inductance: The ability of one inductor’ s lines of force to link with another inductor.

MUX: see Multiplexer.

Noise: Unwanted electromagnetic radiation within an electrical system.

Normally Closed: When the contacts of a switch or relay are closed or connected when at rest. When activated, the contacts open or separate.

Normally Open: When the contacts of a switch or relay are normally open or not connected. When activated the contacts close or are connected.

Ohm: Unit of resistance (represented by the Greek capital letter omega “W_” and the symbol “R” ). Impedance, represented by the symbol Z, is a measure of the opposition to electrical flow. It is measured in Ohms. For DC systems, impedance and resistance are the same, defined as the Voltage across an element divided by the current (). In AC systems, the “reactance” enters the equation due to the frequency-dependent contributions of capacitance and inductance. Impedance in an AC system is still measured in ohms and represented by the equation  but V and I are frequency-dependent.


  • Impedance
  • Z

Ohm’s Law: I=V/R where I is the current flowing, V is the voltage and R is the resistance.

Open Circuit: Circuit having an incomplete path for current flow.

Oscilloscope: Electronic instrument that produces an instantaneous trace on the screen of a cathode ray tube corresponding to oscillations of voltage and current.

Output: Part of a circuit where the processed signal is available.

Output Impedance: Impedance measured at the output terminals of a device, without a load connected.

Output Power Amount of power that a component, circuit or system can deliver to a load.

Overload Condition that occurs when the load is greater than a system can handle.

Overload Protection: Protective device such as a circuit breaker that automatically disconnects a load when current exceeds a predetermined value.

Parallel Circuit: Circuit having two or more paths for current flow.

Passive Component: Component that does not amplify a signal (such as resistors and capacitors).

PCB: Printed Circuit Board. See also PWB.

pF: Pico Farad. A Farad is the unit of capacitance. A pF is 10-12 of a Farad. (1000pF = 1nF, 1000nF = 1 microFarad).

Phase: The angular relationship between two waves.

Polarity: Terminology used to describe positive and negative charges.

Polarized: Component that must be connected in correct polarity to function and/or prevent destruction.

Power: The amount of energy converted by a circuit or component in a specific unit of time, normally seconds. Measured in watts.

Power Factor: The ratio of actual power to apparent power.

Power Loss: The ratio of power absorbed to power delivered.

Power Supply: Electrical equipment used to deliver either voltage (either AC or DC).

PWB: Printed Wiring Board. See also PCB.

Real Time: Data that is immediately acted upon rather than being accumulated and processed at a later time.

Rectifier: AC-to-DC converter with output typically connected in parallel with battery backup.

Regulation: The ability of a power supply to maintain an output voltage within a specified tolerance as referenced to changing conditions of input voltage and/or load.

Regulated Power Supply: A power supply that maintains a constant output voltage under changing load conditions.

Relay: An electromechanical device that opens or closes contacts when current is passed through a coil. A relay is an electromagnetic switching device consisting of an armature which is moved by an electromagnet to operate one or more switch contacts.

Some advantages of relays are that they provide amplification and isolation and are straightforward. They can switch difficult voltages (e.g. RF or high-powered AC) with complete isolation and no worries about level translation. Relay disadvantages, compared to solid-state switching, include power efficiency, noise (both mechanical and electrical, including “contact bounce”), size, speed, and reliability. Analog switches are commonly used instead of relays in signal switching applications. Driving a relay can be tricky because it’s an inductive load. Special relay drivers are often used.


  • Switch
  • Relay
  • analog switch
  • contactor

Resistance: Opposition of a body or substance to current passing through it (resulting in a change of electrical energy into heat or another form of energy).

Resistor: Passive component with a known resistance.

Regulator: A circuit which is connected between the power source and a load, which provides a constant voltage despite variations in input voltage or output load.


  • Voltage Regulator

Rheostat: Variable resistor used to control current.

 Ripple and Noise: The amplitude of the AC component on the DC output of a power supply usually expressed in millivolts peak-to-peak or RMS. For a linear power supply it is usually the frequency of the AC mains. For a switching power supply, it is usually the switching frequency of the converter stage

The output “Ripple” frequency is primarily determined by the switching frequency of the power supply. The higher frequency “Noise” spikes are generated by the fast rise and fall times of the pulses associated with the switching and rectification components of the power supply. Typical ripple and noise specs are defined as peak-to-peak measurements in mV units. There is a graphic here on the website.

RS-232: A serial interface published by the EIA for asynchronous data communication over distances up to a few hundred feet. Characterized by a single-ended (not differential) physical layer, it uses one signal wire for transmission, another for reception, and a common wire (ground), plus some timing and control signals. It is still very common interface but largely replaced by USB in recent years.

The term “serial” interface is often used for an RS-232 interface.


  • RS-232C
  • EIA232
  • RS232

RS-422/RS-485: RS-485 and RS-422 are serial interface standards in which data is sent in a differential pair (two wires, or twisted pair cable), which allows greater distances and higher data rates than non-differential serial schemes such as RS-232. RS-485 and RS-422 can be configured for full-duplex or half-duplex bus systems.


  • EIA-485
  • RS-485
  • RS-422/RS-485
  • RS422
  • RS485
  • EIA-422

 Schematic: Structural or procedural diagram of an electrical or electronic circuit with the components represented by symbols. Also see Circuit Diagram.

Semiconductor: Any of various solid crystalline substances, such as silicon, having electrical conductivity greater than insulators but less than good conductors. Semiconductors’ properties can be altered by a control voltage.

Series Circuit: Circuit in which the components are connected end to end so that current has only one path to follow.

Series Parallel Circuit: Circuit that contains components connected in both series and parallel.

Short-Circuit: Unintended path that conducts electricity that typically causes excessive current.

Signal: Impulse or a fluctuating electric quantity, such as voltage, current, or electric field strength, whose variations represent coded information.

Signal Generator: Circuit that produces a variable and controllable signal.

Source: A device that provides signal power or energy to a load.

SPDT: Single-pole/double-throw switch: A switch with three leads, one of which is common. The common lead can connect to one or the other leads exclusively.

Spike: A brief and sudden change (usually an increase) in the voltage on a power line. A surge is similar to a spike, but is of longer duration.

SPST: Single-pole/single-throw switch

Step-Down Transformer: A transformer in which the output AC voltage is less than the input AC voltage.

Step-Up Transformer: A transformer in which the output AC voltage is greater than the input AC voltage.

Supply Voltage: The voltage that is provided by a power source.

Surge: A sudden change (usually an increase) in the voltage on a power line. A surge is similar to a spike, but is of longer duration.

Surge Current: The high charging current that flows into a power supply filter capacitor when power is first turned on.

Switch: Device for connecting and disconnecting power to a circuit.

Terminal: A point at which electrical connections are made.

Test: A methodical sequence of operations or steps intended to verify the correct operation or malfunctioning of a piece of a system or piece of equipment.

Thermistor: Resistor that varies according to temperature.

Thermal Switch: A circuit that opens and closes a conductive path based on temperature.

Three Phase Supply: AC power supply that has three AC voltages, 120° out of phase with each other.

Threshold: Minimum point at which an effect is produced or detected.

Transducer: Device that receives energy in one form and supplies an output in another form.

Transformer: An inductor with two or more windings. An inductive electrical device for changing the voltage of alternating current.

A transformer consists of two magnetically coupled coils. Alternating current in one (called the “primary”) creates a changing magnetic field which induces a current in the second coil (the “secondary”). A core made of iron or ferrite generally connects the two coils, but higher frequency devices can work without a ferrous core.

Transformers have two primary functions: Voltage transformation and isolation:

  • The Voltage of the secondary can be higher or lower than the Voltage that drives the primary and is determined by the ratio of turns of wire in the two coils.
  • Isolation refers to the fact that the coils are connected only by a magnetic field, so they can be independent of a common ground.

Primary applications are for power and for signal isolation / impedance transformation.

An autotransformer is a transformer with a single coil with intermediate “taps” to effect the changed outgoing voltages. They do not provide isolation.

Transformer capacity is rated in Kilovolt-Amps (KVA).


  • Xfmr

Transformer Coupling: The coupling of two circuits using mutual inductance provided by a transformer.

Transistor: Three-leaded device (Collector, Base, Emitter) used for amplifying or switching.

Transient: Transients – whether current or voltage — occur momentarily and fleetingly in response to a stimulus or change in the equilibrium of a circuit. Transients frequently occur when power is applied to or removed from a circuit, because of expanding or collapsing magnetic fields in inductors or the charging or discharging of capacitors.

  • Overshoot
  • Settling Window
  • Settling time
  • Signal DC Level

Trigger: A pulse used to start a circuit action.

Trimmer: Small value variable resistor, capacitor, or inductor used to finely adjust a larger value.

Troubleshooting A methodical or systematic series of steps for locating the cause of a fault or problem in an electronic circuit or system.

Tuned Circuit: Circuit in resonance at a particular frequency.

UPS: Uninterruptible Power Supply.

Universal Serial Bus (USB): A standard port that enables you to connect external devices (such as digital cameras, scanners, keyboards, and mice) to computers. The USB standard supports data transfer at three rates: low speed (1.5Mbps), full speed (12Mbps) and high speed (480 Mbps).

Mbps=Million bits per Second.


  • Universal Serial Bus

VA: Volt Ampere

VFC: Voltage-To-Frequency Converter. Device that converts an analog input

voltage into a sequence of digital pulses.

Volt (or Volts): Unit of voltage. Unit of measure for electromotive force (EMF), the electrical potential between two points. An electrical potential of 1 Volt will push 1 Ampere of current through a 1-Ohm resistive load.


  • Voltage
  • Electromotive Force
  • V
  • EMF
  • E


Volt-ampere: A unit of electric power equal to the product of one volt and one ampere, equivalent to one watt. A Volt-Ampere (VA) is the Voltage times the Current feeding an electrical load. A Kilovolt-Ampere (kVA) is 1000 Volt-Amperes. Electrical power is measured in Watts (W): The Voltage times the Current measured each instant. In a direct current system or for resistive loads, the Wattage and VA measurements will be identical. But for reactive loads, the Voltage and Current are out of phase and the Volt-Ampere spec will be greater than the Wattage. For determining power, watts are appropriate. For determining capacity for the driving circuits (circuit breakers, wiring, and uninterruptible power supplies, for instance), VA is appropriate.


  • KVA

Voltage: Electromotive force or potential difference, usually expressed in volts.

Voltage Drop: Due to current flow, the voltage or difference in potential developed across a component.

Voltage Feedback: Voltage feedback where a portion of the output voltage is fed back to the input of an amplifier.

Voltage Rating: The maximum voltage a component can withstand without breaking down.

Voltage Regulator: A circuit or device that maintains a constant output voltage even when there is changing line voltage and/or load current.

Voltage Source: Circuit or device that supplies voltage to a load.

Voltage: Volt (or Volts): Unit of measure for electromotive force (EMF), the electrical potential between two points. An electrical potential of 1 Volt will push 1 Ampere of current through a 1-Ohm resistive load. Using a common plumbing analogy, Voltage is similar to water pressure and current is analogous to flow (e.g. Liters per minute). In equations, the symbol E is often used (as in: ). V is the symbol for the unit of measure, Volt.


  • Volt
  • Electromotive Force
  • V
  • EMF
  • E

Watt: Unit of power. One watt is the product of one volt and one amp (represented by the symbol “W” ).

Wattage: An amount of power, especially electric power, expressed in watts or kilowatts. Also, the electric power required by an appliance or a device.

Wattage Rating: The maximum amount of power a device can continuously safely handle.