Electrical Instruments 251

AC

Alternating current. Electricity that reverses direction at regularly recurring intervals of time. AC switches direction 60 times a second, or 60 hertz, in the U.S.

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. AC switches direction 60 times a second, or 60 hertz, in the U.S.

ammeter

A device that measures amperes in an electrical circuit. Some ammeters are located inside machines.

amperage

A measurement that indicates the amount of current flowing in a circuit. Amperage is measured in amperes, also known as amps.

amperes

A unit of electrical measurement that describes an amount of electricity and the time it takes to travel a certain distance. Also known as amps, amperes are multiplied by volts to determine electrical power.

amps

A small unit of current flow within an electrical circuit. Amps, also known as amperes, are a commonly used unit of measurement to evaluate current levels.

analog

A continuously variable signal. Analog signals differ from digital signals in that small fluctuations in the analog signal are meaningful.

analog

A mode of display using a scale and pointer. Analog meters give a sense of quantity relative to other possible values.

arc flash

An electrical explosion that generates an extreme amount of heat. When a worker is near an exposed, energized circuit component, Arc flashes are dangerous to workers near exposed, energized circuit components due to the risk of burns and other injuries.

circuit

A completely enclosed path, consisting of various devices, that contains an electrical current. Circuits normally include a source, path, load, and control.

circuits

A completely enclosed path of electrical current consisting of various devices. An electrical circuit usually includes a source, path, load, and control.

clamp

A device on a meter that measures current. The clamp on an ammeter must become part of a circuit to measure the current in it.

coil

A bundle of wire that is wrapped continuously around a magnetic core. Coils are used to create magnetic fields when current passes through them.

coils

A bundle of wire that is wrapped continuously around a magnetic core. Coils create a magnetic field when current passes through them.

compass

A tool for determining geographic direction. Compasses use magnetic needles as pointers to indicate that direction.

constant

A variable or number that does not change. A voltage reading should be constant when a power supply is known.

continuity

The state of having a complete path to accommodate the uninterrupted flow of electricity. Continuity in a circuit can be checked by an ohmmeter.

current

The flow of electricity through a circuit. Current is measured in amperes or amps.

D'Arsonval movement

Movement using a permanent magnet and a wire coil. The D'Arsonval movement is the basic movement seen in most meters.

DC

Direct current. Electricity that travels in only one direction. Direct current never reverses the direction of current flow.

decibel meters

Devices used to measure the intensity of sound. The decibel meter function is often found on a digital multimeter.

decibels

dB. The unit used to convey the intensity of sound. Decibels can be measured by standard multimeters.

deflection

The amount of movement away from true north by a needle or pointer in a meter. Deflection shows the amount of current able to pass through the component being tested.

digital

A display system that shows numbers or values. Digital multimeters are the most versatile and commonly used meters used today.

digital multimeters

DMM. A device that can measure voltage, current, or resistance. Digital multimeters are the most versatile and commonly used meters used today for electrical maintenance.

diode

A device that allows electricity to flow in a single direction only. Diodes are the most common type of rectifiers.

direct current

DC. Electricity that travels in only one direction. Direct current never reverses the direction of current flow.

directly proportional

A constant ratio between two values in which one value changes in the same way as the other. For example, if values are directly proportional, it means that when value A increases, value B increases, and if value A decreases, value B decreases.

dynamometer movement

An action using one stationary and one moving coil to measure power output. Dynamometer movement occurs when one coil is energized by voltage, the other by amperage, producing deflection.

electric shock

The flow of electricity through the body. Severe electric shock can be fatal.

electromagnet

A magnet formed from electric current. An electromagnet is typically constructed by wrapping several windings of wire around an iron core.

electromagnetic deflection

The ability of an electrical current to displace a magnetic field. Electromagnetic deflection reacts to and is able to measure the magnitude or intensity of a field.

energy

The ability to do work. Energy is measured in kWh and expressed as the product of power and time.

frequency

A measurement of the number of complete AC cycles in one second. Frequency is measured in hertz (Hz).

full-scale deflection

Moving the indicator all the way up without hitting the stop pin in an electrical instrument. The more sensitive the instrument, the less input it takes to reach full scale deflection.

galvanism

The effect that takes place when electrical current causes mechanical motion. Galvanism reacts to polarity and accurately measures magnetic flux.

galvanometers

A basic device for measuring small electric current. Galvanometers measure current using a mechanical motion derived from electromagnetic forces produced by the current.

in series

A circuit configuration in which current passes through all components one after another because there is only one path for current to flow. An ammeter is connected in series with a circuit.

induced

The state in which magnets cause voltage in a conductor. Any time a conductor passes through magnetic lines of flux, induction occurs.

International Electrotechnical Commission

IEC. An organization that prepares and publishes electrical, electronic, and related technology standards. The IEC regulates these standards in Europe and other countries.

kilowatt-hour

kWh. A unit that measures the use of electrical energy over time. Kilowatt-hours measure the power consumption of 1000 watts per hour.

kilowatt-hour meter

A device that measures the electricity in a circuit. Also known as watt-hour meters, kilowatt-hour meters track power output over time.

kilowatt-hour meters

A device that measures the electricity in a circuit. Also known as watt-hour meters, kilowatt-hour meters track power output over time.

kilowatts

kw. A unit of measurement for the power being used in a circuit. A kilowatt is a larger unit of watts, with 1,000 watts equaling one kilowatt.

leads

Conductors that provide an easy path for electricity to flow. The shape and number of leads varies for different electronic components.

magnetic field

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

meters

A device that measures electricity. Meters may measure many different values, including voltage, amperage, and wattage.

milliammeter

A device used to measure small electrical currents. Milliammeters express measurements in milliamperes.

multimeter

A device that combines the functions of an ammeter, voltmeter, and ohmmeter. Multimeters are the most versatile and common meters used today.

multimeter

A device that combines the functions of an ammeter, voltmeter, and ohmmeter. Multimeters can be digital or analog.

multirange

A meter able to measure wide ranges using fixed internal series resistances. A meter is made multirange by the use of a dial on the meter to switch to the different ranges.

National Electrical Code

NEC. The minimum standard for safe electrical installations. The National Electrical Code is written and produced every three years by the National Fire Protection Association.

National Electrical Manufacturers Association

NEMA. An advocacy group for legislative issues that may affect the electrical manufacturing industry. NEMA provides a forum for electrical equipment standards.

National Fire Protection Association

NFPA. A non-profit organization that maintains standards of public safety and fire prevention. The National Fire Protection Association produces the standard for minimum safe electrical installations as well as arc flash prevention and safety procedures.

National Institute of Standards and Technology

NIST. An organization that defines the standard units of current, voltage, and resistance. NIST works to establish reliability and accuracy in the measurements vital to electrical maintenance.

needle

A pointer in a compass that is magnetized to align with a magnetic field. Needles can be displaced by DC.

ohmmeter

A device used to measure resistance. Ohmmeters attach to resistors that are removed from circuits.

ohms

A unit of measurement for electrical resistance. Ohms indicate the amount of resistance in a circuit.

Ohm's law

The law describing the relationship between voltage, amperage, and resistance. Ohm's law states that volts equals amperes multiplied by ohms.

oscilloscopes

A device that produces a visual trace of a voltage or current wave shape. Oscilloscopes display AC waves.

overload

A level of current that exceeds the recommended level for a device or circuit but is less than the level of a short circuit. Overload is not always detected by wattmeters.

perfect conductor

A material that allows a completely free flow of electrons. Perfect conductors have zero resistance.

perfect insulator

A material that does not allow any flow of electrons. Perfect insulators have infinite resistance.

personal protective equipment

PPE. Any of the various articles of clothing or safeguarding devices that assemblers or operators are required to wear to ensure their safety. PPE for electrical work may include gloves and rubber-soled footwear.

polarity

Having a positive or negative charge. Polarity determines the direction in which current tends to flow.

power

P. The rate at which a device converts electrical energy into another form, such as heat or light. Power is an electrical variable.

power

The amount of work accomplished within a given period of time. With electricity, power is the product of current and voltage and is measured in watts.

power

The rate at which a device converts electrical energy into another form, such as heat or light. Power is measured in watts.

rectifier

A device used in an electrical circuit that converts AC to DC. Rectifiers allow meters to measure both AC and DC.

resistance

R. The opposition to current flow. Resistance is an electrical variable.

resistance

The opposition to current flow. Electricity flows in the path of least resistance.

resistor

A device that controls electric current. Resistors restrict current flow and produce work such as heat or light.

resistors

Devices that restrict current flow. Resistors produce work, such as heat or light.

sensitivity

The degree of response of an instrument to an incoming signal. A more sensitive meter can make more exact measurements.

sensitivity

The minimum input required to produce a noticeable output on a measuring device. Increasing an instrument's sensitivity increases its accuracy.

short circuits

An interruption in the intended flow of electricity, especially when current flows short of reaching a device. Short circuits cause excess current flow.

shunt

A low-resistance connection between two points in an electric circuit that forms an alternative path for a portion of the current. Shunts allow meters to produce accurate readings in a much wider range.

solenoid

A coil of wire that generates a force when an electrical current is applied. Wiggies use solenoids to detect voltage.

variables

Factors in electricity that change according to their situation. Variables in electrical work include amperage, voltage, current, and resistance.

voltage

A measure of electrical pressure or potential known as electromotive force. Voltage is measured in volts.

voltmeter

A device that measures the voltage in an electrical circuit. Digital voltmeters are sometimes built into machines.

voltmeter

A device used to measure voltage. Voltmeters measure voltage between separate points in circuits.

volt-ohm-milliammeters

VOM. The most common setup of a multimeter. VOMs combine the functions of voltmeters, ohmmeters, and milliameters.

W

Watts. A unit of measurement for the power being used in a circuit. In order to exist, watts require a change in energy.

watt-hour meter

A device that measures the electricity in a circuit. Watt-hour meters, also known as kilowatt-hour meters, track power output over time.

wattmeter

A device that accounts for both current and voltage when used to measure electrical power. Wattmeters rely on a dynamometer movement to complete measurements.

watts

W. A unit of measurement for the power being used in a circuit. In order to exist, watts require a change in energy.

Watt's law

A law that describes the relationship between watts, amperage, and voltage. Watt's law states that one watt equals one amp times one volt.

waveforms

The type or shape of a wave produced by alternating current. Waveforms can be measured by oscilloscopes.

Wiggins solenoid meter

A testing device that vibrates when a current is detected. Wiggins solenoid meters, also called wiggies, are small and durable but can be replaced by more versatile and safer digital multimeters.

zero resistance

A state in which electrons are able to move freely without encountering any obstacles. Zero resistance indicates the presence of a perfect conductor.