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.
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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.
Copyright Texas Education Agency, 2011. All rights reserved.
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