Electrical Indicating and Recording

Devices

Readout Devices►►VOM (volt VOM (volt -- ohm ohm -- ___________)___________)►►DMM (digital _________)DMM (digital _________)

HandheldHandheldTabletopTabletop

►►OscilloscopesOscilloscopesAnalogAnalogDigitalDigitalNational Instruments National Instruments VirtualScopeVirtualScope

VOM (volt - ohm - milliammeter)►►Typically provide measurement of Typically provide measurement of

________, ________, AC or DC ______, and AC or DC ______, and AC or DC ______ (in milliamps)AC or DC ______ (in milliamps)

►►Good for measuring _____ changing valuesGood for measuring _____ changing values►►Largely replaced by Largely replaced by DMM’sDMM’s (but some “old(but some “old--

timers” still use them regularly!)timers” still use them regularly!)

DMM (digital multimeter)►►Commonly provide measurements of Commonly provide measurements of

_________, _________, AC or DC ______, and AC or DC ______, and AC or DC ______ (amps)AC or DC ______ (amps)

►►Manual and Manual and AutorangingAutoranging scalesscalesmanual set by user manual set by user ►►you should use smallest/largest scale possible!you should use smallest/largest scale possible!

autorangeautorange set by DMMset by DMM

What scale would you choose to measure 1.75 V?

+/- 20 mV+/- 2 V+/- 20 V+/- 200 V

LG #DM-441B Digital Multi-Meter

LG #DM-441B Digital Multi-Meter

What does “positive” or “high” mean?

+

8.432

What if you read it “backwards?”

+

-8.432

Fluke 87 Handheld DMMBlack probe inCom (mon)

Red probe in whatever you’re metering:

Ω: resistanceV: voltageA: current

Note: voltage and current are usually different plugs.

OscilloscopeTwo types:Two types:►►Analog Analog

less expensive ($400 less expensive ($400 -- $1000)$1000)usually cannot store screensusually cannot store screens

►►DigitalDigitalhigher cost ($1000 higher cost ($1000 -- $10,000)$10,000)easy storage of individual screenseasy storage of individual screensusually provides a cursor to read data usually provides a cursor to read data values from onvalues from on--screen tracescreen trace

Leader Analog Oscilloscope

Note on-screen “divisions”

LG Analog Oscilloscope

Note on-screen “divisions”

Oscilloscope - Divisionshorizontal (time) division

verticalamplitudedivision

Oscilloscope

Two primary adjustments:Two primary adjustments:►►horizontal “sweep” rate (____ axis)horizontal “sweep” rate (____ axis)

usually in units of or usually in units of or

►►vertical amplitudevertical amplitude

usually in units of usually in units of or or

Amplitude and Frequency DeterminationVertical Sensitivity: 0.2 volt/divHorizontal Sensitivity: 2 msec/div

“Oscope” settings:

What is the “scope” input?”

Amplitude:

Period:

Frequency =

⇒Vin =

Uncertainty of Amplitude and Frequency Measurement

Leader Model #1021 Analog OscilloscopeVertical Amplifiers (Ch. 1 and Ch. 2)

Accuracy: ± 3% (normal), ± 5% (magnified)

Timebase GeneratorsAccuracy: ± 3% (normal), ± 5% (magnified)

How much uncertainty (tolerance) should you assign to values read from the previous slide?

Determine Amplitude and Frequency

Horizontal Sensitivity Vertical Sensitivity10 µsec/div 50 mV/div

Nat’l. Instruments Virtual Scope

2

1

3 5

6

7 8

4

Function Generator ►►Not a readout, but a common _____ deviceNot a readout, but a common _____ device►►Generate sine, triangle and square wavesGenerate sine, triangle and square waves

adjustable frequency (Hz = _____ /sec)adjustable frequency (Hz = _____ /sec)adjustable amplitudeadjustable amplitude

►►Often has a TTL output alsoOften has a TTL output alsoTTL is a digital output, 0V or +5V onlyTTL is a digital output, 0V or +5V only

Goldstar Function Generator

Normally use the output labeled 50Ω Sine, square, triangle

waveforms

Meter “Impedance”

impedance is a “resistance” that also depends on impedance is a “resistance” that also depends on frequency (capacitors & inductors)frequency (capacitors & inductors)

Does the meter have a Does the meter have a ►►“high” internal resistance / impedance“high” internal resistance / impedance

which draws negligible current ( which draws negligible current ( iimm

Ideal Voltage-Divider

=outVRtop+Vin

- Vout-

+

io = 0 =iiii

Rbot =outV

Voltage-Divider / Potentiometer►►Find VFind Voo for Vfor Vii = 12.05V= 12.05V

220 Ω+Vi

Vo+-

470 Ω-

In-class Exercise – Fall ‘043.3kΩ 4.7kΩ1kΩ 2.2kΩ

+

-+12V

+

-+12V

+

-

12V+

-

12V

In-class Exercise – Fall ‘04

2.2kΩ

+ V3 -

3.3kΩ 4.7kΩ1kΩ

-+

12V+12V

- +BlackBlack

In-class Exercise►► What voltage would you expect to measure across the 2.2 What voltage would you expect to measure across the 2.2

kkΩΩ resistor?resistor? =k2.2V

Just need to know I2.2kCurrent is common to all elements of the circuit:

, but ?I =

=eqR=3V

=K2.2V

In-class Exercise

►►What current would you expect to measure What current would you expect to measure through the through the 2.22.2 kkΩΩ resistor?resistor?

Series circuit Series circuit –– all currents the same, soall currents the same, so

Voltage-Divider / Potentiometer

►► loading error : loading error : iimm > 0 due to > 0 due to RRmm

Vo-

+

im

Rm

Voltage MeasurementDevice

Rtop+Vi

-Rbot

In-class ExerciseCompute Vout (actual) for each of the following cases (assume Vin = 12.05V)

Ideal Vout = 8.208V

Case Rtop Rbot Rm Vout 1 220 Ω 470 Ω 4.7 kΩ 2 220 Ω 470 Ω 47 kΩ 3 220 Ω 470 Ω 470 kΩ 4 220 Ω 470 Ω 4.7MΩ

Electrical Indicating and Recording DevicesReadout DevicesVOM (volt - ohm - milliammeter)DMM (digital multimeter)LG #DM-441B Digital Multi-MeterLG #DM-441B Digital Multi-MeterWhat does “positive” or “high” mean?What if you read it “backwards?”Fluke 87 Handheld DMMOscilloscopeLeader Analog OscilloscopeLG Analog OscilloscopeOscilloscope - DivisionsOscilloscopeAmplitude and Frequency DeterminationUncertainty of Amplitude and Frequency MeasurementDetermine Amplitude and FrequencyFunction GeneratorGoldstar Function GeneratorMeter “Impedance”Ideal Voltage-DividerVoltage-Divider / PotentiometerIn-class Exercise – Fall ‘04In-class Exercise – Fall ‘04In-class ExerciseIn-class ExerciseVoltage-Divider / PotentiometerIn-class Exercise