Meters, Measurements, and Basic Electrical Circuits

What are the six primary classifications of the effects of current?

Chemical, physiological, photoelectric, piezoelectric, thermal, and electromagnetic.

What basic movement is employed by ammeters, voltmeters, and ohmmeters?

D'Arsonval movement.

True or False: An ohmmeter is basically a current-measuring instrument.

True.

What does the permanent magnet in a D'Arsonval meter react with?

The magnetic field set up by the moving electromagnet coil.

What are the two purposes of the springs in a D'Arsonval meter?

Improve temperature compensation and convey current in/out of the movement.

What typical materials are used to construct jewelled meter bearings?

Sapphire and hard glass.

What is "damping" in a meter movement?

A feature letting the pointer stop with minimal oscillation.

What type of meter damping utilizes eddy currents?

Electromagnetic damping.

How does a pneumatic "air damping" mechanism work?

A small vane on the shaft rotates through a wedge-shaped air chamber.

How is the range of a 0-1 mA meter extended to measure higher currents?

By using shunt resistors.

What is the typical tolerance of resistors used as meter shunts?

1% or better.

What are ammeters with multiple internal shunts called?

Multirange ammeters.

How should an ammeter always be connected in a circuit?

In series with the element being measured.

What must you never do when connecting an ammeter?

Never connect it across a source of voltage.

How is the range of a voltmeter extended?

By using multiplier resistors.

How is voltmeter sensitivity determined and expressed?

In ohms per volt, indicating circuit resistance per volt of range.

How is the accuracy of a meter typically expressed?

As a percent of the full-scale deflection value.

What does a D'Arsonval movement measure when used in an ohmmeter?

Current, when a known voltage is applied.

What are the two primary types of ohmmeters?

Series and shunt.

What safety precaution must be taken before using an ohmmeter?

Remove all circuit power.

What instrument is used to measure unusually high resistance?

A megger.

What must D'Arsonval DC meters incorporate to measure AC voltage or current?

Rectifiers.

What is the "effective value" (RMS) of AC voltage?

The amount of DC voltage that would do the same work.

How do you calculate the RMS value of AC if the peak value is known?

RMS = Peak Value × 0.707.

What three things are absolutely necessary to construct an electrical circuit?

A power source, a conductive path, and a load.

What two extra components do most practical electrical circuits contain?

Circuit protection and control.

What is the common name for a precision switch with very short plunger travel?

Microswitch.

What are two purposes of relays in electrical systems?

Controlling large current with small current, and enabling multi-use switching.

If an aircraft has 5 separate 5-Amp circuits, how many spare fuses are required?

A minimum of 3 (per the 50% rule).

What is a "trip-free" circuit breaker?

A breaker that stays open during an overload regardless of operating lever position.

What is a "non-trip-free" circuit breaker?

A breaker whose trip function can be overridden by force.

What are three types of aircraft circuit breakers classified by actuation?

Magnetic, thermal overload, and arc fault.

Which switch or relay contact is symbolized by a triangle?

Normally open contact.

What circuit configuration interrupts all current flow if one component is removed?

Series circuit.

What electrical quantity is constant throughout a series circuit?

Current.

What circuit configuration maintains a constant voltage across all branches?

Parallel circuit.

What is Kirchhoff's Voltage Law for a series circuit?

The sum of all voltage drops equals the total source voltage.

What is Kirchhoff's Current Law for a parallel circuit?

The sum of currents entering a junction equals the sum of currents leaving.

What are the three formulas used to compute electrical power (P)?

P = I²R, P = E²/R, and P = I·E.

What is a rheostat?

A variable resistor in series with a load used to control current.

What is a potentiometer?

A variable resistor in parallel with a load used to control voltage.

What is the function of a voltage divider?

To obtain multiple different voltages from a single power source.

What is an element in matter?

A substance which cannot be broken down into other substances.

What atomic feature specifically determines if a substance is a conductor, semiconductor, or insulator?

The number of electrons in the valence shell.

What is the unit of measurement for electrical charge?

Coulombs.

What four factors determine the resistance of a conductor?

Length, cross-sectional area, material, and temperature.

In which direction do electrons flow between charged terminals?

From the negative terminal to the positive terminal.

What undesirable effects does static electricity cause during aircraft operation?

Radio interference, shock hazards, and spark hazards.

Define magnetic permeability and reluctance.

Permeability is ease of flux movement; reluctance is opposition to flux passage.

What rule is used to determine the polarity of flux lines around a single current-carrying wire?

The Left Hand Conductor Rule.

What three factors determine the strength of an electromagnet?

Core permeability, amperes, and turns of wire.

How does the pull of a magnet at 1 inch compare to its pull at 2 inches?

It is four times stronger (double the distance, one-fourth the pull).

The permanent magnet contained in a D’Arsonval meter reacts with the magnetic field set up by the

Bobbin

Bobbin

Is a component that holds the wire winding in place to allow the movement of the needle based on the magnetic field.

What symbol is this?

Earth Ground

What symbol is this?

Chassis Ground

What symbol is this?

Signal Ground

What symbol is this?

Pull to trip, push to reset (trip free)

What symbol is this?

Automatic Reset

What symbol is this?

Automatic trip, push to reset

Which switch is polarized?

the one on the left

Self-Excited

Operate from a power source in the meter

Externally excited

Get power from the circuit they are connected to

Galvanometer

Device that reacts to small electro-magnetic influences caused within itself by the flow of a small amount of current

Parrallax Error

Perceived shift in an objects position as viewed from different angles

True or False: Never connect across a source voltage- cause damage

True

True or False: with an Ammeter you should connect in series with element the current flow is to be measured

True

Rs

term that determines the value of shunt resistor

Im

term for the full scale deflection current

Rm

the term for the meter movement’s internal resistance

Is

term for Shunt current

What are the three types of damping?

Electrical, Mechanical, Air