electricaltestequipments.ppt

7/27/2019 ElectricalTestEquipments.ppt

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Electrical Test Equipment

Copyright Texas Education Agency, 2011. All rights reserved.


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LEARNING OBJECTIVES

Voltmeter use

How to measure voltage

Ammeter use

How to measure current

Ohmmeter use

How to measure resistance

Use of Ohm's Law



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Voltage Testing DevicesVoltage testers are used to measure or check the presents of voltage in an

electrical circuit

Wiggy Voltmeter

Neon Light



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Types of Voltage Testers

VT201, Non-Contact Voltage Detector

Quickly check for the presence of ac

voltages, with no electrical contact

Safe non-contact detection of voltages from

70 V to 440 V ac

Both visible and audible indicators

Detector emits loud audible chirping that

changes pitch based on probes proximity to

the ac voltage source

Bright flashing LED also indicates presence

of ac voltage

VT102, Voltage Tester 4 Bright neon lights indicate ac voltage

4 Ranges indicated from 110 V to 460 V ac

No battery needed

Tests 2 wire and 3 wire ac outlets



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Types of Voltage Testers

ST102, GFCI Socket Tester and

the ST101, Socket TesterTest GFCI breakers for proper wiring and operation

Easy to read light indicators show common wiring

problems

Confirm GFCI socket is wired for protection

GFCI circuit trips to confirm tester is working

Fast, easy socket test for use on 110-125 V ac

Confirm proper wiring and operation of ac socket

Wiggy Solenoid Voltage Tester120V to 600V AC (50/60 Hz), or 120V to 600V DC

current.

Locates blown fuses, grounds and system leaks

quickly.

Has large, easy-to-read voltage indicator scale andDC polarity indicator.

Operates without the use of batteries.

http://www.mytoolstore.com/klein/kln04.html


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Using a Voltage Tester

The simplest and least expensive tester is the

neon 2-wire 0-500 volt tester. Put one of the

leads on a ground reference (box screws, neutral

side of a plug, neutral or white wire, etc.) and the

other lead on the hot wire (hot side of a plug, black

or red wire, etc.) (see figures #1 and #2).

Figure 1: Neon 2-Wire 0-500 Volt Tester

Figure 2.

If the neon light glows, then you have

voltage at the outlet, as is the case

here.



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Using a Voltage Tester

Another handy device to have around is the "plug

tester". Just plug this device into a receptacle,

and it will not only tell you if there is voltage present,

but also if it is wired correctly. Just follow the codes

on the tester to determine the situation.

Figure 3: Plug Tester

Figure 4.



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Using a Voltage TesterThe type of meter that most electricians will use

is the digital multi-meter. These come in variousbrand names, price ranges and quality, and the

old adage, "you get what you pay for" is the best

advice to follow here.

Figure 5: Digital Multi-Meter(Testing

from hot wire to box ground)

Figure 6: (Testing from neutral to box

ground. Notice the accuracy of only .077

volts AC)

*Note: The multi-meter will be discuss in detail later on in

the presentation



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The Ammeter

It is essential that electricians be able to use

clamp-on ammeters, or multi-meters, for in-place

troubleshooting of motors and controllers as well

as other circuits. Many clamp-on ammeters can

be used to measure voltage and resistance as

well as current. They come in various sizes with

selections of scales that make them extremelyversatile tools.



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Using the Ammeter

The amps flowing through the cable registers on the

LCD display. Because an amp clamp does not plug

in to the line, there is no current loss and the reading

is more accurate.

Clamp-on transformer jaws. Take current readings

without interrupting service. Clamp around conductors

up to 1" (2-54cm) in diameter or 500MCM. 2" (5.08cm)

Or 2000MCM for 1000 ampere models.

It allows current draw to be measured quickly and

accurately. The jaws of the clamp are clamped around

one of the cables and the motor is started.



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Using the Ammeter

An amp clamp is a non-invasive method of

checking current draw with any electrical set up.

The jaws of the clamp are spring loaded so that

they can be clamped around a cable; usually

the positive lead in a DC electrical set-up. It

works by measuring the impedance of the

current flowing through the cable.

This method has many benefits. It is easy to set

up; you only have to be able to access one cable

to be able to take a reading. It is non-invasive

because you do not have to plug anything in to

the line between battery and speed controller, or

between controller and motor. Plug in methodsare cumbersome (shunted meters or wattmeters),

especially in the field, and always have some

associated power losses which make the reading a

little inaccurate.

A sample test-bed for a brushless motor.

Note that the amp-clamp jaws are clamped around

the positive lead between the battery pack and

speed controller. This is and older type of amp clamp

that requires a separate multi-meter to take a reading;

modern types have an LCD read-out built in to the unit



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Testing Electrical Circuits with the Multi-

meter

A multimeteris an electrical instrument capable of measuringvoltage, current, and resistance. Digitalmultimeters have

numerical displays, like digital clocks, for indicating the quantity

of voltage, current, or resistance.Analogmultimeters indicate

these quantities by means of a moving pointer over a printed

scale.

Analog multimeters tend to be less expensive than digital

multimeters, and more beneficial as learning tools for the firsttime student of electricity.

Connect the black lead to the common (-) hole. This may well

already be done, depending on the type of meter you use.

Connect the red lead to the volts (+) hole. Be careful, if this lead

Is placed in the wrong hole (ohm or amp) it can cause

permanent damage to the meter. This may well already be

done, depending on the type of meter you use.

Turn the selector switch to AC volts (usually red). If there are

Multiple selections, use the highest setting possible (if power

unknown) or go one level higher than the estimated power.

Some digital meters have "Auto-range" and don't require any

selection apart from AC volts.



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Measuring Current in a Circuit

Current is the measure of the rate of electron "flow" in acircuit. It is measured in the unit of the Ampere, simply

called "Amp," (A).

The most common way to measure current in a circuit is to break

the circuit open and insert an "ammeter" in series (in-line) with the

circuit so that all electrons flowing through the circuit also have to

go through the meter. Because measuring current in this manner

requires the meter be made part of the circuit, it is a more difficult

type of measurement to make than either voltage or resistance.

Some digital meters, like the unit shown in the illustration, have a

separate jack to insert the red test lead plug when measuring

current. Other meters, like most inexpensive analog meters, use

the same jacks for measuring voltage, resistance, and current.

Consult your owner's manual on the particular model of meter you

own for details on measuring current.

When an ammeter is placed in series with a circuit, it ideally dropsno voltage as current goes through it. In other words, it acts very

much like a piece of wire, with very little resistance from one test

probe to the other. Consequently, an ammeter will act as a short

circuit if placed in parallel (across the terminals of) a substantial

source of voltage. If this is done, a surge in current will result,

potentially damaging the meter:



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Measuring Resistance in a Circuit

Resistance is the measure of electrical "friction" as electrons move

through a conductor. It is measured in the unit of the "Ohm," that unit

symbolized by the capital Greek letter omega ().

Set your multimeter to the highest resistance range available. The resistancefunction is usually denoted by the unit symbol for resistance: the Greek letteromega (), or sometimes by the word "ohms."

Touch the two test probes of your meter together. When you do, the metershould register 0 ohms of resistance. If you are using an analog meter, youwill notice the needle deflect full-scale when the probes are touched

together, and return to its resting position when the probes are pulled apart.

The resistance scale on an analog multimeter is reverse-printed from theother scales: zero resistance in indicated at the far right-hand side of thescale, and infinite resistance is indicated at the far left-hand side. Thereshould also be a small adjustment knob or "wheel" on the analog multimeterto calibrate it for "zero" ohms of resistance. Touch the test probes togetherand move this adjustment until the needle exactly points to zero at the right-hand end of the scale.

Digital multimeters set to the "resistance" mode indicate non-continuity bydisplaying some non-numerical indication on the display. Some models say"OL" (Open-Loop), while others display dashed lines. If you are using adigital multimeter, you should see a numerical figure close to 10 shown onthe display, with a small "k" symbol on the right-hand side denoting themetric prefix for "kilo" (thousand). Some digital meters are manually-ranged,and require appropriate range selection just as the analog meter. If yours islike this, experiment with different range switch positions and see which onegives you the best indication



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Measuring Resistance in a Circuit

Connect the meter's test probes across the resistor as such, and note its

indication on the resistance scale:If the needle points very close to zero,you need to select a lower resistance range on the meter, just as you

needed to select an appropriate voltage range when reading the voltage of a

battery.

Resistance is the measure of friction to electron flow through an object. The

less resistance there is between two points, the harder it is for electrons to

move (flow) between those two points. Given that electric shock is causedby a large flow of electrons through a person's body, and increased body

resistance acts as a safeguard by making it more difficult for electrons to flow

through us, what can we ascertain about electrical safety from the resistance

readings obtained with wet fingers? Does water increase or decrease shock

hazard to people?

Be sure to nevermeasure the resistance of any electrically "live object or

circuit. In other words, do not attempt to measure the resistance of a battery or

any other source of substantial voltage using a multimeter set to the resistance

("ohms") function. Failing to heed this warning will likely result in meter

damage and even personal injury.



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Using Ohms Law

Take and the measure the voltage and resistance ofa

circuit, use the Ohm's Law equation to calculate circuit

current. Compare this calculated figure with the

measured figure for circuit current:

Taking the measured figures for voltage and current, use

the Ohm's Law equation to calculate circuit resistance.

Compare this calculated figure with the measured figure

for circuit resistance:

Taking the measured figures for resistance and current,

use the Ohm's Law equation to calculate circuit voltage.

Compare this calculated figure with the measured figure

for circuit voltage:



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Summary

Working with live electrical current can be very hazardous. Testing voltage outputrequires working with electrical current. Do not attempt this measurement withoutthe proper tools and safeguards.

It is essential that electricians be able to use clamp-on ammeters, or multi-meters, for in-place troubleshooting of motors and controllers as well as othercircuits.

Always test your test equipment for proper operation before use.

A multimeteris an electrical instrument capable of measuring voltage, current,and resistance. There are two types of multimeters, the digital and the analogmeters.

Digitalmultimeters have numerical displays, like digital clocks, for indicating thequantity of voltage, current, or resistance.Analogmultimeters indicate thesequantities by means of a moving pointer

over a printed scale.

Ammeters are use to check current in a circuit. An amp clamp is a non-invasivemethod of checking current draw with any electrical set up.


electricaltestequipments.ppt

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