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E i i P j t (1)Engineering Project (1)

T t d M tLecture_3

Tests and Measurements

Instructor: Eng. IBRAHIM ABU-ISBEIH

Introduction

Tests and measurements are important in designing, maintaining, troublshooting, and servicing all types of electrical and electronic

d dproducts and circuit systems. Wile it is possible to detect some circuit

actions and defects by visual inspection, in electronics and electronics we are concerened with operational characteristics that are not always visible.

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Measuring instruments

1. Multimeters This is an electrical instrument designed to measure

voltage, current, resistance, and often other variables as ell M ltimete s a e man fact ed in both digitalas well. Multimeters are manufactured in both digitaland analog form. A digital multimeter is preferred for precision work but analog meters are also useful forprecision work, but analog meters are also useful for gaining an intuitive understanding of instrument sensitivity and range.

2. Oscilloscopes

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1. Multimeters

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Digital Multimeter

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2. Oscilloscope

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How to measure resistanceHow to measure resistance with a multimeter Connect the meter's

test probes across thetest probes across the resistor as such, and note its indication on ote ts d cat o othe resistance scale.

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Photocell Connect your meter to the terminals of a photocell

and measure the change in resistance created by differences in light exposure.

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How to measure current with a multimeter

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How to measure voltage gwith a multimeter

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Meter check of a diode

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Typical diode packages

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Typical LEDs

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Meter check of a BJT transistor

Bipolar transistors are constructed of a three-layer semiconductor "sandwich " either PNP or NPN Assemiconductor sandwich, either PNP or NPN. As such, they register as two diodes connected back-to-back when tested with a multimeter's "resistance" or "di d h k" f i"diode check" functions.

Some multimeters are equipped with two separate continuity check functions: resistance and "diodecontinuity check functions: resistance and diode check", each with its own purpose. If your meter has a designated "diode check" function, use that rather than h " i " d h ill di l hthe "resistance" range, and the meter will display the

actual forward voltage of the PN junction and not just whether or not it conducts current.

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whether or not it conducts current.

PNP transistor (step one)

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PNP transistor (step two)

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NPN transistor Meter readings will be exactly opposite for an NPN

transistor with both PN junctions facing the other waytransistor, with both PN junctions facing the other way. If a multimeter with a "diode check" function is used

in this test, it will be found that the emitter-base ,junction possesses a slightly greater forward voltage drop than the collector-base junction. This forward voltage difference is due to the disparity in dopingvoltage difference is due to the disparity in doping concentration between the emitter and collector regions of the transistor: the emitter is a much more h il d d i f i d i l h hheavily doped piece of semiconductor material than the collector, causing its junction with the base to produce a higher forward voltage drop.

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a higher forward voltage drop.

NPN transistor

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Transistor packages and p gterminal identification

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Meter check of a JFET transistor

Testing a JFET with a multimeter might seem to be a relatively easy task, seeing as how it has only one PN junction to test: either

d b dmeasured between gate and source, or between gate and drain.

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N-Channel JFET

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N-Channel JFET

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Operational Amplifier

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Operational Amplifier

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Operational Amplifier

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REFERENCES Buban and Schmitt, “Technical Electricity & Electronics”,

McGraw HillMcGraw Hill. Floyd, “Electric Circuits Fundamentals”,4th edition,

Prentice Hall 1998Prentice Hall, 1998. Floyd, “Electronic Devices”,5th edition, Prentice Hall,

19991999.

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