Unit 35 , Electrical Measuring and Test instruments

Always read and follow all ____ provided by the meters manufacturer

Read and follow all safety and operating instructions

Analog meters periodically need to be ?

Recalibrated

Why aren't solenoid based testers used anymore

Safety issues , most aren't fused , sensitivity issues - low voltage control circuits won't register.

A higher cat number is used for higher ?

Voltages and energy transients .

live circuit precautions?

Asses location find a place for your meter to hang or rest determine if leads will reach in cabinet without extenders minimum amount of exposed metal at probe tips , .12 " or 4 mm

Connect the ____ test lead first and then the _____ test lead last . Reverse this procedure for ______

Connect the ground test lead first, and then the hot test lead. Reverse this procedure for removal .

Always try to work on ______ circuits whenever possible

de energized circuits

Before testing a high voltage capacitor always begin by

discharging the capcacitor first

Digital meters display _________ number values while Analog meters provide a _________ reading

display descrete number values while analog meters provide a releative reading.

Higher megger readings mean

good insulation .

megohmeters are used to test the resistance of

insulation , particularly in electric motors.

Capacitance meters measure

microfarads

define Range

min and max reading on a meter

try to keep your hands free when using a meter by

resting or hanging it whenever possible , also use alligator clip test leads

Multimeter drawbacks?

room for operator error by turning dial to wrong function.

A momentary surge or spike of voltage c an be several times higher than

the circuit voltage

closed contacts or a short will read as ( using an ohmmeter)

0 ohms

Procedure to follow when testing a de energized circuit

1. Know the unit electrically / know your meters functions 2. Able to read wiring diagrams and have them available 3. be able to use proper electrical test instrument / read instructions .

The term low voltage is deceiving, because test meters for this category is considered to be ?

1000 vols or less .

Testing procedure ( 4 steps )

1.Make sure circuit are off and properly locked out and tagged out. 2. test the meter on a known voltage source. 3. Test the circuit that should be de energized 4. Test the meter again on a known source to ensure you didn't damage your meter or blow a fuse to get a 0 volt reading accidently in step 3.

The difference between an ohmmeter an an ammeter or voltmeter is that it uses what for a power supply? and why?

A battery which furnishes the current needed for resistance measurements.

When connecting test leads , try to keep one hand in your pocket to lessen the chance of?

A closed circuit across your chest and through your heart.

Analog display readings by ?

A mechanical needle that swings across the dial to point over a scale , the reading is taken by looking directly at the face of the meter dial and comparing the needle location to the appropriate scale.

Define RMS , what is it ?

Abbreviation for root - mean square, a math formula for calculating electrical power through an AC circuit .

test instrument and test meter are used in the HVACR field to describe devices that are used to detect some aspect of_____

An electrical systems operation. Usually to determine how a system is operating or why a system isn't operating.

Category numbers range from ?

CAT I to CAT IV

Multimeters made for HVACR use include what measurements?

Capacitance , temperature, frequency and power

There are also voltages ratings within categories, give an example

Cat III 1,000 volt and cat III 600 Volt

Which has superior transient protection? Cat III meter at 600 V or a cat II at 1000V ?

Cat III meter

The test leads for the meter should be

Certified to a category and voltage the same or higher than the meter.

The meter measures capacitance by ?

Charging the capacitor with a known current and measuring the time of the charging period.

two types of amp meters include

Clamp on and inline

Clamp on ammeters work by

Clamping the jaws of the instrument around a single wire . Functions like a transformer .

Amp meters are used to measure

Current flow through a circuit

Cat 111 is required for?

Distribution circuits such as three phase bus and feeder circuits , load centers and distribution panels. Used for permanently installed loads such as 3 phase , large commercial lighting systems and heavy appliance outlets with short connections to the service entrance

Ohmmeters are used to measure and check

Electrical resistance and can check electrical continuity .

Transient voltages can be caused by ?

Electrical storms several miles away , when a major load is added or dropped from the system . Ex : auto accident where a utility pole was damaged or a large piece of equipment starting or stopping

Failing to follow operating and safety instructions can result in

Equipment damage and injuring yourself

Many inexpensive test meters are not approrpriate for

HVACR use

When using a test meter that is not auto ranging always start to measure voltage using the ____ range on the meter , reduce to proper range after for greater reading _____

Highest range on the meter , reduce to proper range after for greater reading accuracy

define : Accuracy

How close to the actual value the meter is going to read , usually as a + or - percentage . can be anywhere from .5 to 3 percent depending on the function and scale

if an ohmmeter measures the resistance of an open circuit , it should read?

Infinity , because the resistance is too large to be measured. means lack of continuity or no current flow

Cat I is required for use on

Low energy equipment . such as protected electronic circuits and on high/low energy sources from a high winding resistance transformer . typical example would include a photo coper machine

A higher category meter can be used for any _____ category applications

Lower

Digital meters are

Mainly used in the field today and have replaced all but analog meters

The only test meters that can be considered to meet CAT requirements are ?

Ones stamped with a symbol from a recognizable independent testing laboratory or approval agency can be considered to meet CAT requirements .

Any time you are working with electricity , there is a possibility of an ________ situation occuring

Overvoltage

Voltmeters are connected in _____ with the ____ to read the ______ drop or ______ difference

Parallel with the load to read the voltage drop or potential difference .

A low voltage or non contact voltage tester should be followed by a direct contact why?

Proximity readings vary by distance and strength of voltage field, they are unreliable in accuracy.

Cat IV

Required for outside and service entrance from the pole to the meter and the meter to the service panel . Also used for outside overhead and underground cable runs that may be affected by lightning strikes.

2 types of Electrical testers what kind of contact

Solenoid based and electronic both have test leads that come in direct contact

It is never safe to work on high energy circuits without

Someone else present

Motors ,c apacitors and power conversion equipment such as variable speed drives can be prime generators of

Spikes

Analog meters may be made completely inoperable if

Subjected to excessive current

Megohmeters / meggers are used to read resistances of

Tens of millions of ohms ( megohms)

Low voltage proximity or noncontact voltage tester does not have ____ but still needs to be placed close to the _______

Test leads, but still needs to be placed close to the conductor.

An analog meter's most accurate reading is at

The midpoint of the scale

Testing for proper supply voltage is usually

The first thing when troubleshooting a circuit.

Always choose a test meter rated for

The highest category you should be working in .

Test meters should be selected based upon?

The standards required for their application.

What do RMS meters do ?

They apply a correction factor to sensed voltage or amperage, may be more accurate than standard meters. They average true voltages and amperages

Advantages of digital meters ( 4 points)

They are direct reading, no need for a scale Give accurate readings to three decimal places They have no moving parts and are less likely to fail or get out of calibration. They often have automatic scaling

Why is true RMS Needed?

They can measure momentary change in incoming line voltage and to Accurately measure voltage and amperage in nonlinear power applications

Surges are also known as

Transient Voltages

Advantages of electronic testers?

Used for transient protection , more accurate , higher imput impedance , work with lower voltages . Act like solenoid but better, works on wider range of equipment.

Inline meters are more accurate than clamp because

all system current flows through the meter

power that is measured by simply multiplying the current by the voltage is called ?

apparent power

Inline ammeters are connected in ___ with the circuit

in series with the circuit.

Advantage of the clamp on meter

no need to disconnect or make contact with wires for a reading.

3 types of test instruments that may be used when testing a de energized circuit?

noncontact proximity tester, electrical tester and a multimeter.

one microfarad is equal to ?

one millionth of a farad

To mathematically calculate power in watts using the measured volts and amps , it is necessary to know the ?

power factor

A test meter fuses are designed to

protect the meter from being destroyed when test meter operation is wrong.

Surge protectors on computers

protect them from overvoltage

Properly designed test meters shouldn't cause ( name 4 )

shock, fire, arcing or explosion.

Cat II is required for ?

single phase receptacle connected loads , such as appliances , portable tools and other household type loads. Outlet should be located at least 30 feet from a cat III source.

Wattmeters can be used to measure watts on ?

single phase, split phase and three phase power sources.

define Resolution

tells you what units of measure are used for each function , may be expressed as the number of digits or decimal points. can range from 3 to four digits and 1 to 3 decimal laces

Multimeteres measure

voltage , current and resistance all with one instrument

The power formula is ?

watts = volts x amps x power factor