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# H A B O T

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Student Name: ___________________________

# O L L E G E

C I S C O N E T W O R K I N G

## 3B- Multimeter Lab

A C A D E M Y I

Instructions:

Use curriculum pages 4.1.5 and 4.1.8 for reference - review these pages before you begin. Students will work in teams of two, and each team will use one Fluke 12B digital multimeter. The instructor will check out a multimeter to your team; return it as soon as you finish. Answer all questions shown in

italic!

Background:

A multimeter is a powerful electrical testing tool that can measure  resistance levels  open/closed circuits (continuity)  voltage levels (both AC & DC) The Fluke 12B is an "autoranging" meter. In most circumstances, it will automatically select the appropriate units or "range" of measurement. However, for the measurement to be meaningful, the user must always note the units of measurement displayed on the screen. The manual for the Fluke 12B is available on the Semester 1 class website. It describes advanced features not used in this lab.

Part A - Resistance Measurements Notes:

 Resistance is measured in Ohms (indicated by the Greek letter Omega: Ω ).  Copper wires (conductors) such as those commonly used in network cabling (UTP and coax) normally have very low resistance if you check them from end to end. This low resistance is also termed "good continuity" (the wire is continuous).  If there is a break in the wire it is called an "open" circuit which creates very high resistance. An open circuit has "no continuity".  The multimeter has a battery in it which it uses to test the resistance of a conductor (wire) or insulator (wire sheathing). When the probes are applied to the ends of a conductor, the battery current flows through the conductor and the meter measures the resistance it encounters.

Step 1 - Move the multimeter's rotary selector to the Omega symbol for Ohms (red

Ω

) in order to measure resistance. Examine the screen.

The meter will default to the continuity test mode. To change between continuity tests and resistance measurements, press the button that has the Ohms symbol (red Ω ) on it: 

Continuity Measurements:

The screen will show a diode symbol (a small black triangle pointing to a vertical bar). A diode is an electronic device that either passes or blocks electrical current. You may see a small sound symbol next to it which means that when there is good continuity (less than 25 ohms resistance) the beep will sound. The continuity setting is used when you just want to know whether there is a good path for electricity and don't care about the exact amount of resistance. 

Resistance Measurements:

The screen will show Ω (ohms), K Ω (kilohms = thousands of Ohms) or M Ω (megohms = Millions of Ohms). Because the meter defaults to "auto-ranging", the units of measurement may change depending on the item tested. Always record both the displayed number and the type of units ( Ω , K Ω , or M Ω ) If the resistance reading is infinite or greater than the meter's limit, the

O.L

(Over Limit) indicator will be displayed on the screen. 1

Student Name: ___________________________

Step 2 - Select the resistance measurement mode by pressing the button that has the Ohms symbol (red

Ω

) on it. Step 3 - Measure the following resistances.

Include units ( Ω , K Ω , or M Ω) Touch red and black probe contacts together Your own body (touch the tips of the probes with you fingers)

Step 4 - Go to a "Resistance Measurement Station" in our lab and measure the following resistances. You may find the alligator clips useful for connecting the probes to small parts or wires.

Include units ( Ω , K Ω , or M Ω) Yellow-Purple-Orange-Gold Resistor Brown-Black-Brown-Gold Resistor Orange wire from 1' section of Cat 5 UTP solid cable Orange wire from 30' section of Cat 5 UTP solid cable Metal screw on chassis of hub to safety ground pin on power cord 6v light bulb leads on circuit "breadboard" Normally Open (N.O.) switch leads on circuit "breadboard" N.O. switch leads on circuit "breadboard" with button pressed.

Step 5 - Switch the multimeter to the continuity testing mode and retest the N.O switch on the breadboard.

Be sure to press the switch button while you test continuity.

What happens? _____________________________________________________________________

____________________________________________________________________ Step 6 - Find a short circuit in a Cat 5 cable.

At the "Resistance Measurement Station", you will find a special cable labeled "SHORTED". One end of this cable has stripped wires you can test, and the other is hidden. Use the continuity testing mode of the multimeter to identify the two wires in this cable that are touching each other unintentionally (shorted).

Which are the two shorted wires? Wire 1 Color: _____________________________ Wire 2 Color: _____________________________

Step 7 - Find an open circuit in a Cat 5 cable.

At the "Resistance Measurement Station", you will find a special cable labeled "OPEN". Both ends of this cable have stripped wires you can test. Use the continuity testing mode of the multimeter to identify the wire that has a break between its ends.

What color is the open wire? __________________________

2

Student Name: ___________________________

Part B - Voltage Measurements Step 1 – Move the multimeter's rotary selector to the V symbol for voltage (black V) in order to be able to measure. Examine the screen.

The meter will default to the Direct Current (DC) voltage measurement mode. To change between Direct Current (DC) and Alternating Current (AC) measurements , press the button that has the

VDC

and

VAC

symbol on it: 

Direct Current Measurements:

The screen will show a V (voltage) with a series of dots and a line over the top. 

Alternating Current Measurements:

after it. The screen will show a V (voltage) with a tilde or (

~

)

Step 2 – Go to the "Voltage Measurement Station" and measure the following voltages: Be sure to select DC or AC voltage current as needed by pressing the VDC/VAC button. Item to Measure: Current Voltage reading:

Include units

Lantern battery. Measure from terminal to terminal. Power supply A Measure between center & outer conductor of plug. Power supply B Measure between center & outer conductor of plug. DC AC AC Power supply C Measure between center & outer conductor of plug. AC

Immediately return the multimeter to your instructor for use by another student team. (Be sure to turn the meter off when finished.) Reflection Question

:

How might a multimeter be used in maintaining and troubleshooting a computer network? (Describe several examples.)

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