ch -8 equipment maintenance

8/14/2019 Ch -8 Equipment Maintenance

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8. EquipmentMaintenance

SpecificationCalibration

Operating

Prevention Maintenance
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Terminology

Ketepatan Kecapaian bacaan dengannilai sebenar kuantiti yang diukur.

Kejituan Darjah perbezaan ukuran yg

didapati antara satu kumpulan datadengan yg lain.

Kepekaan Gerakbalas jangka kpd

perubahan masukan & pembolehubahyang diukur.


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Multimeter

A multimeter is an electronic measuring

instrument that combines several functions inone unit. The most basic instruments includean ammeter, voltmeter, and ohmmeter. Analogmultimeters are sometimes referred to as

"volt-ohm-meters.Useful for basic fault finding and field servicework or a bench instrument which can measureto seven or eight and a half digits of accuracy.

Can be used to characterise resistance andvoltage standards or adjust and verify the

performance of multi-function calibrators.


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Current, voltage, and resistancemeasurements are considered standard

features for multimeter. AVO multimeters, amanufacturer of early multimeters, derivedtheir name from amperes, volts, and ohms,the units used for the measurement ofcurrent, voltage, and resistance.

Implemented with an analog meterdeflected by an electromagnet, as a classicgalvanometer.

Using suitable switching arrangement forfunction & range selection.


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Safety Rules for Multimeter

1. Before making measurement, check if thefunction & range is set at proper position.

2. Always start with this instrument from thehighest range of the function to measured. Paycareful attention to the max. rated voltage of

each range & i/p terminal.3. Never ground yourself when taking electrical

measurements. Keep your body isolated fromground by using dry clothing, rubber shoes,

rubber mats, or any suitable & approvedinsulating material.

4. Disconnect line power @ i/p signal beforeaccessing fuse.


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Note :

1. Indication of zero correction. Before measuring, placethe pointer on zero position of the scale left byadjusting the screw of zero corrector.

2. Range selection. When measuring unknown value ofvoltage @ current, start from the highest range, thenadjust to a proper lower range. Measurement is moreaccurate as near to the full scale, for resistancemeasurement, near to the middle scale.

3. Converting the range selector.4. As range change is desired, remove test leads from

source to be tested, then convert selector. This willextend the life of selector contact.

5. OFF Range. After measurement, place range selector

to OFF range. This is to prevent pointer from swaying& to protect multitester.


7/45Specification of multimeter


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How to use multimeter in a correct way?

Select correct range mode

For better sensitivity, select the nearer value range modeto the measured value. i.e 1.5V battery should use range

mode of 2.5V DC. Error is bigger at the right scale. Forresistance mode the most reliable value is at the center scale.

Unknown value measurement

Start with the highest value. After the first reading value,set the range mode to lower for more reliable reading value.

Safe keeping meter

Vibration or shock situation should be avoided because thisequipment is very sensitive.

Failure because of wrong operating method

Internal resistance broken when high AC voltage measuredat current & resistance mode.

High voltage cct (


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Method of measurement [DCV & ACV]

1. Place range selector to a proper range on DCVposition.

2. Plug short end of red test lead to + connector,& shortend black test lead to - connector.

3. Connect the other long ends of test leads to thetested load or current in parallel.

4. Read the value indicated on DCV scale.

1. Place range selector to a proper range on ACV

position.

2. Plug short ends of test leads each to + & -connectors & connect the long ends of testleads to the tested circuit in parallel.

3. Read the value indicated on ACV scale.


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Method of DCV measurement [DCmA & Resistance]

1. Place range selector to a proper range on DCmA position.

2. Plug short end of red test lead to + connector, & short end blacktest lead to - connector.

3. Connect the long ends of test leads to the tested current in series.4. Read the value indicated on DCV scale.

1. Place range selector to a proper range on position.

2. Plug short ends of test leads each to + & -. 0 adj.

3. Separate long end of 2 test leads,then connect to the tested point

4. Read the value indicated on scale.

* As for 0 adjustment, it is unable to place the pointer to 0 line,check battery. If battery power is not sufficient, replace immediately.As measuring a resistor in circuit, turn off the source first.


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Used as an ammeter, an analogue multimeter has avery low resistance and is very sensitive, withscales down to 50 A. More expensive digital

multimeters can equal or better this performance.Most modern multimeters are digital andtraditional analogue types are destined to becomeobsolete.

Meter DArsonval system movement are based on 3force ( daya) :-

1. Daya kilas pesongan akibat kesan magnet,elektrostatik & elektromagnet.

2. Daya kilas kawalan disebabkan sistembergerak kembali i.e. spring.

3. Daya kilas redaman Pergerakan sistem meterpenunjuk.


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Digital Multimeter

Basic DM is consist of Analog to digital converterand Also known as multi function meter @ VOM

(volt-ohm-miliampere) meter.Newer equipment can measure many otherquantities. Some common additional measuredquantities and the units in which they aremeasured:

Inductance in henrys.

Capacitance in farads.

Conductance in siemens.

Temperature in degrees

Frequency in hertz.

Duty cycle as a percentage.

Implemented with a digital display such as an LCD


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Digital multimeter

AutorangingSwitch range


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Operating Method

The central knob has lots of positions.Choose the most appropriate position. Ifthe meter is switched to 20 V DC, then20 V is the max voltage which can bemeasured, This is sometimes called 20 V

fsd (full scale deflection).For circuits with supplies up to 20 V, the20 V DC voltage range is the mostuseful. DC ranges are indicated by on

the meter. To measure smaller voltages,the 2 V or 200 mV ranges are used.

Cli k t dit M t t t t l


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Click to edit Master text stylesSecond level

Third level Fourth level

Fifth level

M th d f t [DCV & ACV]


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Method of measurement [DCV & ACV]

1. Select the V function.

2. Set the range switch to the desire range.

3. If measuring DCV, select AC/DC switch to DC. Ifmeasuring ACV, select AC/DC switch to AC.

4. Connect black test lead to COM& red to V- i/p.

5. Connect test lead to the measuring point & read the

displayed value.Method of measurement [DCA & ACA]

1. Select the mA function.

2. Set the range to the desire range.

3. If measuring DC, select AC/DC switch to DC. Ifmeasuring AC, select AC/DC switch to AC.

4. Connect black test lead to COM i/p terminal & red testlead to A or 20A i/p.


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Operating Method

DC means direct current. In any circuitwhich operates from a steady voltagesource, such as a battery, current flow isalways in the same direction.

AC means alternating current. In an electriclamp connected to the domestic mainselectricity, current flows first one way, thenthe other. That is, the current reverses, or

alternates, in direction. With UK mains, thecurrent reverses 50 times per second.


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Megger / Megaohmmeter

A megger is a circuit tester which puts a very highvoltage at a very low current across two conductors tomake sure that they are properly insulated. The nameis short for megohm-meter

The Meter are used to :-

1. Measure very high resistance.

2. Measure insulated conductor i.e. cable

Type of megger :-

1. Hand driven generator (penguja terengkoltangan)

2. Battery power

- Digital meter

- Analog meter


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4 types of basic testing wiring that are usingMegaohm meter

Cable Continuity Test (Gelang) - To determinewhether a circuit is open or closed.

Cable Continuity Test ( Pengalir pelindung)

Insulation Resistance Test To determine the

strength of conductor insulator between thephase line conductor. (2 or more) Whethershort cct occur at the cct.

Pole Test To makesure all one pole control

device like fuse, suis satu hala satu kutub is atthe life point.


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4 types of earthing efficiency testingthat are using Megaohm meter

Ujian bagi pengalir pelindung &pengikat

Ujian galangan gelung bumi

Ujian pemutus litar bocor ke bumi

Ujian rintangan elektrod bumi


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Operating Method

The moving element of the ohm meter consistsof two coils, A and B, which are rigidly mountedto a pivoted central shaft and are free to rotate

over a C-shaped core (C on Figure 17). Thesecoils are connected by means of flexible leads.The moving element may point in any meterposition when the generator is not in operation.

As current provided by the hand-driven

generator flows through Coil B, the coil will tendto set itself at right angles to the field of thepermanent magnet. With the test terminalsopen, giving an infinite resistance, no currentflows in Coil A. Thereby, Coil B will govern themotion of the rotating element, causing it to

move to the extreme counter-clockwiseposition, which is marked as infinite resistance.


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Coil A is wound in a manner to produce aclockwise torque on the moving element. Withthe terminals marked "line" and "earth"shorted, giving a zero resistance, the currentflow through the Coil A is sufficient to produceenough torque to overcome the torque of CoilB. The pointer then moves to the extremeclockwise position, which is marked as zeroresistance. Resistance (Rl) will protect Coil A

from excessive current flow in this condition.When an unknown resistance is connectedacross the test terminals, line and earth, theopposing torques of Coils A and B balance eachother so that the instrument pointer comes to

rest at some point on the scale. The scale iscalibrated such that the pointer directlyindicates the value of resistance beingmeasured.


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AB

C

Megohmmeter


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An original "Megger" from World War II


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Comparison between Ohm Meter & Megger

Voltan Kenaan until 24V 500, 1000, 2500, 5000 VJulat Pengukuran Kohm Megaohm

Meter ohm Megger

How to use megger?n Connect line probe to the measureddevice & the gnd probe to the earth.

n Voltage supply generate by the hand

driven generatorn Insulation failure will be shown on the

scale.


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Measured data should be analyze by the experience person.

Measured data usually 500V @ 1000V DC taken in 1 minute.

Example of measure data & the analyze data :-

- Reading > 50 Mohm cable in good condition- Reading 2-50 Mohm maybe long cct, slightly

damp or cantamination

- the analyze data might

not be true

- Reading < 2Mohm maybe the insulation not

in good condition


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Wattmeter / Power meter

The wattmeter is an electrodynamicinstrument for measuring or record the

electric power @ the supply rate ofelectrical energy of any given cct/ used bythe customer.

The device consists of a pair of fixed coils,known as current coils, and a movable coilknown as thepotential coil.

The current coils are connected in serieswith the cct, while the potential coil isconnected across the line.


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Also, the potential coil carries a needle thatmoves over a scale to indicate themeasurement.

A current flowing through the current coilgenerates an electromagnetic field around thecoil.

The strength of this field is proportional to theline current & in phase with it.

The potential coil has a high-value resistorconnected in series with it to reduce the

current that flows through it

h d fl i f h dl i


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On a DC cct, the deflection of the needle isproportional to both the current & thevoltage, thus conforming to the equation

W=VA or P=EI.

On an AC cct the deflection is proportional tothe average instantaneous product of voltage

& current, thus measuring true power, andpossibly (depending on load characteristics)showing a different reading to that obtainedby simply multiplying the readings showing

on a stand-alone voltmeter and a stand-aloneammeter in the same circuit.


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The two circuits of a wattmeter are likely to bedamaged by excessive current. The ammeter andvoltmeter are both vulnerable to overheating - incase of an overload, their pointers will be driven off

scale - but in the wattmeter, either or even both thecurrent and potential circuits can overheat withoutthe pointer approaching the end of the scale! This isbecause the position of the pointer depends on thepower factor, voltage and current.

Thus, a circuit with a low power factor will give a lowreading on the wattmeter, even when both of itscircuits are loaded to the maximum safety limit.Therefore, a wattmeter is rated not only in watts,

but also in volts and amperes.


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How is it operates?

1. Bila voltan diguna, cakera aluminium

berputar.2. Dan dgn itu menggerakkan susunan gear

kepada gear utk menghitung.

3.

Kelajuan cakera aluminium berkadar dgnhasil darab voltan yang dibekal dgn arussefasa.

4. Hasil darab islah no watt yg digunakan

oleh setiap putaran cakera.5. Tenaga yg digunakandirakam dgn

menggunakan nombor putaran.


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Wattmeter


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A V

To loadLN

W

Connection between Watt meter with load

H t tt t ?


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How to use watt meter?

1. Before connect the meter to the cct :-

- Adjust the position of zero.

- Choose the range mode same or above the

supply voltage.

- Start with the higest range mode, then select

the mode that gave the highest scale movement.

2. Current cct connected series with the load.

3. Voltage cct connect parallel with the load.

4. If the needle meter move to the left side of zeroposition, current @ voltage terminal should be

change the position.


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There is 3 type of watt meter / powermeter adjustment :-

1. Pelaras kelajuan utama

2. Pelaras kelajuan induktif Bilafaktor kuasa meter tenaga kurang drnilai yg ditetapkan.

3. Pelaras geseran Apabila dayakilas penimbal utk atasi geseran padabearing

O ill


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Oscilloscope

Electronic test equipment that allowssignal voltages to be viewed, usually as a

two-dimensional graph of one or moreelectrical potential differences (verticalaxis) plotted as a function of time or ofsome other voltage (horizontal axis).

Amplitude measurements Volt p-p Xvolt/div

Time period measurements 1 cycle X

time/div

Frequency - 1 / Time period


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Method of oscilloscope measurement

1. For the first time use, the oscilloscope must

be calibrated to ensure all the result frommeasurement will be accurate.

2. Select the probe setting to 1X.

3. Place the probe to 0.5 cal pin. Make sure theclip on the probe clipped on the ground.

4. Turn on the oscilloscope and see on the CRTdisplays if any waveform displayed. A square

waveform should appear.5. Calculate the peak-to-peak amplitude (Vpp)

and the measured value should same withthe 0.5 cal pin.


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Prevention Maintenance & Troubleshooting

Meter

1. Multimeter is a precision instrument, so

storage at high temp. on in moisture should beavoided. The suitable operating temp. is from 0 C 40 C & humidity is below 80%.

2. Take battery out for long time storagebecause battery may leak to make interiorcomponents deteriorated.

3. Severe stroke @ drop should be avoided.

4. Do not get close to any circumstance there isa powerful magnetic field.

5. Usually user facing problem needle meter

cannot adjust to 0 always check battery.1.5V x1 /x10 and 9V x1k /x10k

6 M t t f ti


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6. Meter not function :-

- range mode wrong selection

- protection fuse open open andcheck

the continuity of the fuse.

7. Always check the continuity of thetester

probe.


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Prevention Maintenance & Troubleshooting

Oscilloscope

1. Equipment composed of high precision

components/ high internal pressure care is requiredin handling & storing.

2. Occasionally, clean the graticule scale/ controlbutton with a clean, soft cloth.

3. Ideal ambient temp for storing -10 C - 60 C

4. To maintain the effeciency of the equipment -

Service osc. Every 1000 hours operating time

@ 1 year.

ch -8 equipment maintenance

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