oscilloscope ii

7/28/2019 Oscilloscope II

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Oscilloscope II

PHYS-1008

Winter 2012


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REMINDER

IMPORTANT!

When you record a number in your book,

dont forget the units.

If its a measurement dont forget the error.

Error on your instruments

Analog = Half of the smallest division

Digital = +/- 2 the last stable digit


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Significant Figures(p. 24 in PHYS-1007 lab manual)

Results should have the same number of

decimal places as the error.

Calculations: 2 significant figures for the error.

Final result: 1 significant figure for the error.


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The Oscilloscope

Measure the potential difference (i.e. Voltage)across a component as a function of time.

rence

Trigger

value

Po

tentialdif

f

(units

)

Time (units)

Falling (- slope) Rising (+ slope)


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Function generatorType of signalFrequency Display

& Control

Frequency Range

AttenuatorAttenuator

V(t)

Rg= 50

to

oscilloscopeOutput casings =

common ground


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OscilloscopeTime scale

(sweep time / div)

Trigger

Level (V), slope

(+/-)Intensity / Focus

Channel A and B

V(t)

Rg= 50

RS= 1M

CS= 21pF


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Experiment Outline

Output Resistance of the Function Generator

Measuring the Capacitance of the Coaxial

Cable

e o e an a ower upp y(Converting AC to DC)

YOU WILL ONLY BE EXPECTED TO DO THELAST TWO EXPERIMENTS OF THE LAB.


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Coaxial Cable + BNC connector

External Insulator

Ground

Conductive Mesh

Shield from E-M noise

Insulator

Internal Conductor

Carry the signal


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Indicates how much time a capacitor can take to charge

or discharge.


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2 Measuring the Capacitance of the

Coaxial Cable Assemble Circuit: connect BNC connector + Resistor combination into

the Function Generator.

Make note of colour code of the resistor.

BNC-Alligator coaxial cable: clip one end to resistor, clip other lead to

ground casing, attach BNC to oscilloscope.

Set the frequency on the generator to 800Hz and SQUARE wave. Set oscilloscope trigger to negative slope.

Adjust TIME/DIV control until one complete decay curve fills screen.

Choose a grid line for an arbitrary V=0 and to

= 0.

Measure Vo at to.

Proceed to measure V for four more points of t. Use the large divisions in

t to make things easier.

Plot ln(V) ln(t) vs. t and get RC from slope and thus Cc.


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2 Measuring the Capacitance of the Coaxial Cable

Assemble Circuit: connect BNC connector +

Resistor combination into the Function Generator.

Make note of colour code of the resistor.

BNC-Alligator coaxial cable: clip one end to resistor,

clip other lead to ground casing, attach BNC tooscilloscope.

Set the frequency on the generator to 800Hz and

SQUARE wave.

V(to) = Vo

Set oscilloscope trigger to negative slope.

Adjust TIME/DIV control until one complete decay

curve fills screen.

Choose a grid line for an arbitrary V=0 and to = 0.

Measure Vo at to.

Proceed to measure V for four more points of t.

Use the large divisions in t to make things easier.

Plot ln(V) ln(t) vs. t and get RC from slope and

thus Cc.

V = 0

t = 0


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AC/DCAC from Power

station, along

electrical lines and

substations to

your home...

... From the wall to

your devices AC

adaptor which

converts it to DC.


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The Diode(solid state switch)

V

t

50 F

10 k


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V

t

50 F

10 k


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V

t

50 F

10 k

X


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3 The Diode and a DC Power Supply Assemble the circuit as

shown

Set Function Generator to60Hz, SINE wave.

Set Oscilloscope to +

TO CHANNEL BTO

CHANNEL

s ope, sw c oDUAL, and SOURCE switchto INT.

Disconnect the capacitor.Turn ON oscilloscope butleave FG turned OFF: youshould see 2 horizontallines.

A


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3 Effect of the Diode Turn on Function Generator and increase output voltage

until you have a SINE wave with 8V peak-to-peak.

CH. A SINE WAVE CH. B RECTIFIED SINE WAVE

Draw wave forms.

Superimpose both waves. In your discussion, commenton the relationship between both waves. Why doesnt

the rectified wave reach zero?


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3 Effect of the Diode + Capacitor Connect the Capacitor.

Switch Channel B to ground, GND. Line up horizontal line

near bottom of screen. Switch to DC and measure VDC.

Draw waveforms.

Switch Channel B to AC.

Increase Volts/Div on Channel B to magnify the ripple.

Measure the amplitude of the ripple and calculate the

Quality of the DC supply.

In your Discussion comment on the quality of the signal

and the importance of the Capacitor in use with

everyday appliances (e.g. your laptop).


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You can leave when you have:1) Taken four measurements of V(t).

2) Preliminary graph of ln(V) ln(Vo) vs t.3) Calculated RC and Cc.

5) Measured VDC and Ripple Amplitude, Vripple.

6) Calculated DC Quality, Q.

Dont forget to record the uncertainty of yourmeasurements and units!

oscilloscope ii

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