NE344 Lab1 Laboratory Instruments

7/31/2019 NE344 Lab1 Laboratory Instruments

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University of Waterloo

Electrical and Computer Engineering Department

Electronic Circuits and Integration

NE-344 Lab manual

Lab 1: Laboratory Instruments for Electronic Circuits

Spring 2012

Nanotechnology Engineering

University of Waterloo

Waterloo, Ontario N2L 3G1, Canada


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1.ObjectiveThe objectives of this instrumentation laboratory are:

- To review the operation of instruments in the lab- Gain practical experience in using

o DC Power Supplyo Digital Multi-Meter (DMM)o Function Generatoro Oscilloscope

Various voltages and currents are measured for DC and AC circuits. Different AC signals are analyzed with an oscilloscope.

Error in measurements and accuracy of equipment are reviewed.

2.BackgroundLet us quickly review the basic operation of different instruments in the lab. This is simply a repetition of what

you learned in NE-241 NE-242 labs.

2.1 Voltage MeasurementVoltage is analogous to pressure in a water pipe. And like pressure, it has to be measured relative to a reference

A voltage is measured across a circuit component, to indicate the voltage difference or voltage drop.

Figure 1. Measuring Voltage

The dashed lines in figure 1 indicate that all parts are contained within one physical unit. In this case, the

resistance is a part of the meter and there is no way to separate it from the meter. An ideal meter has a

resistance of 0 or depending upon the type of meter (current or voltage) and the meter model (series or

parallel).

To measure voltage electronically, a voltmeter uses a known, stable, resistor. All voltage meters draw current,

because of that resistor. A typical digital volt meter (DVM) has a resistance of 10 M while some older analog

meters may be as low as 3.2 k.


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2.2 Current MeasurementCurrent is the rate change of charge and is, therefore, a measure of the number of electrons per second moving

through a circuit. Since the current into and the current out of a lumped component are equal, you cannot

measure a current drop across a component. To measure current you have to measure the actual charge flow

through the wire.

This measurement is done by inserting relatively small resistor in series with the circuit and measuring the

voltage drop across the resistor. This is normally shown transformed into a series resistor and an ideal current

meter. Both the series and parallel models are shown in figure 2. In the typical digital multi-meter (DMM), on a

2A range, the resistance is 100 m.

Figure 2. Measuring Current

Because a current meter has resistance it will cause a voltage drop and may affect the operation of the circuit.

The actual amount of resistance depends upon the sensitivity of the meter. For example, the Tektronix 4020

digital multi-meter has a resistance of 2 on the 20 mA range when it is used as an ammeter.

2.3 Meter LoadingEvery meter affects the circuit it is connected to by drawing current (voltage meter) or having a voltage drop

(current meter). In later years you will learn more about other ways in which a meter affects a circuit

(capacitance, inductance, adding noise, ...).

Analog Meters

An analog voltmeters resistance is usually specified as a sensitivity in ohms/volt. The resistance for a particular

voltage range is determined by multiplying the sensitivity by the full scale voltage on that range. Some meters

may give the total resistance while others give the current required for full scale deflection. As long as the mete

draws much less current than the component across which it is connected, you can say that its effect will be

small.

Ammeters are more complex. The standard current shunt (precision resistor in the meter) has a fixed voltage

drop at the maximum current rating. Since this voltage is usually small, an ammeter should not affect the circuit


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too much. Remember that every time you change the range, the shunt resistance changes. Since the shunt

resistance, in a normal meter, can vary from milliohms to kilo-ohms, using the wrong current range can easily

affect your circuit. In comparison, a voltmeters resistance will typically only vary from 100 K to 10 M.

Digital Meters

For all ac and dc voltage ranges, the DMM has a fixed input resistance which is typically 10M. On the current

range, the meter will usually have a 200 mV drop at the maximum current, but the resistance is different for eac

range.

Digital meters are usually more accurate, since they remove parallax and other mechanical errors. However, if

you do not know how to select the range properly, it is very easy to obtain errors as large as any analog meter.

This happens quite often on the current ranges.

2.4 Measurement Errors and AccuracyThe method of calculating meter error depends whether you use an analog meter or digital meter. Though we dnot have any analog meter in our lab, for your knowledge we review both analog and digital meters.

Analog Meters

Since we will be using Digital Multi-Meters in the lab, the error for analog meters is explained briefly and more

attention will be given to DMMs. Most of the error in analog meters is due to the mechanical meter movement

This error is constant, across a given meter range, regardless of the magnitude of the variable being measured.

An analog meter stamped as being accurate to 2%, is accurate to 2% of the Full Scale Deflection (FSD).

For example, suppose a reading of 35.0 V (dc) was obtained on the 50 V range of a dc voltmeter, that is accurate

to 2%.

The error is: 2% * 50 VFSD = 1 V

Therefore V = 35.0 1 V (dc) or expressed as a percent V = 35.0 V (dc) 2.9%

Since the absolute error of 1 V is constant for the range, the smaller the measured voltage is in relation to full

scale, the larger the percent error becomes. If this meter range was used to measure a 9V battery the error

would be 11%. For analog meters, it is more accurate to measure values with the needle close to full scale.

Digital Multi-Meters

The DMM is the most common instrument you will encounter. The precision of a DMM is usually expressed in

digits. The most common model has 3 digits. That means that you have three full digits that are capable of

indicating from 0 to 9 and one digit. The digit means that a +1, blank i.e. 0, or -1 can be displayed. There ar

also 4 , 5 and 6 digit meters as well as 3/4 digit meters. A 3/4 digit meter can display +2, +1, blank (0), -1 o

2 as the leading digit.


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A DMM has two sources of systematic error. One part of the error is due to tolerances in resistors. It is expresse

as a percentage of the input and therefore varies with the magnitude of the voltage being measured. The secon

part of the error is due to the digital conversion process for monitoring. It is fixed for a given meter range and is

expressed as a percentage of that range.

For example, consider a Tektronix 4020 with a reading of 1.34545V on a 2 V DC range. The meter displays a

maximum of 1.99999 V on this range. The smallest change on the meter display is 0.00001 V.

Then the errors are (based on specifications from Appendix A),

percent error of reading: 0.015% * 1.34545 V = 201.82 V

percent error of range: 0.003% * 2 V = 60 V

Therefore, V = 1.34545 V 0.26182 mV or V = 1.34545 V 0.019%.

Now consider the same measurement on the 200 V range. The reading would have been 1.345V and,

percent error of reading: 0.015% * 1.345 V = 201.75 V

Percent error of range: 0.003% * 200V = 6 mV.

Therefore, V = 1.345 V 6.20175 mV or V = 1.345 V 0.461%.

This shows that the most accurate measurements are made on the lowest meter range that will accommodate

the measured value.

If the meter were to read 16.3245 Vrms while measuring an 8 kHz triangle wave on a 20.00 Vrms scale; how larg

is the error? The meter measures True RMS and we can trust a reading done on a triangular wave. On the 45Hz 20kHz AC range the error is 0.2% of reading + 0.05% of range. Then the errors are,

percent of reading error: 0.2% * 16.3245 V = 32.65 mV (rms)

percent of range error: 0.05% * 20V = 10 mV (rms)

Therefore V = 16.3245 VRMS 42.65 mVRMS or V = 16.3245 VRMS 0.261%.

Table 1 shows the accuracy for various measurements made with the Tecktronix 4020 model. Important note:

Use the values under the 1 year column as the default accuracy values. The complete accuracy tables can be

found in the Appendix.


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Table 1. Accuracy of Tektronix 4020 in DC voltage mode

2.5 Considerations For Measuring AC Signals by DMMThe more common meters measure the rectified average voltage, while better ones measure the root mean

square (RMS). Unless you know what the shape of the waveform is, and understand how the meter measures a

voltage, the number that you read will be useless. Each of the different methods gives the same voltage for a

sine-wave in a certain frequency range. However, they will all be different if given another wave-shape.

AC meters are calibrated at one sinusoidal frequency to read the RMS voltage or current. However, most

measure the rectified average of the AC component of a signal. The rectifier circuit acts like an absolute

mathematical function. The AC component is what you have left when you remove the average or DC voltage

from a signal. In real life, when you set a meter to read an AC signal you not only remove the DC signal but you

also remove some of the low frequencies of a waveform (i.e. the meter acts like a high pass filter).

Meter bandwidth is the frequency range over which measurements are accurate. It more generally refers to the

frequency range over which a circuit or instrument functions properly. For example, a Tektronix 4020 digital

meter should not be used below 20 Hz or above 100 kHz. Look over the AC sections for the appendix to see how

the accuracy varies with frequency. Oscilloscopes and all other instruments also suffer from similar effects.

Before you can use a meter, you must consider the Crest Factor of the waveform being measured. It is the ratio

of the peak voltage to the RMS voltage. Mechanical meters are slow to respond because the needle, as a physic

system with mass, takes time to accelerate. Electronic meters also have similar problems and this is responsible

for the use of the Crest Factor. Some examples are given in table 2.


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Table 2. Crest factor for different waveforms

Waveform Crest Factor

Square wave

Sine wave

Triangular wave

White noise

1.0

1.414

1.732

3.0 to 4.0

The Tektronix 4020 meters only measure the correct rms value if the Crest Factor is under 3.0. So if, for a sine-

wave, you measure the RMS voltage and measure the peak voltage on an oscilloscope (that can handle the

waveform without introducing more errors), you can see if the meter is reading the RMS value properly. The

Crest Factor is more difficult to calculate for rectangular waveforms. A good instrumentation book or instrumen

manual will explain this.

An rms reading meter measures the root of the mean of the square of the signal (proportional to the power) or:

T

RMS dttvT

V0

2)(

1(= peaktopeak

peaktopeakV

V

2

707.0

22For sine wave)

The purpose of an rms equivalent value of a waveform, is to simplify power calculations by providing an

equivalent DC voltage, that would develop the same average power in a resistive load. If a voltage waveform is

not described, but you know that it is equivalent to 10 Vrms, then you will have 100W of average power

dissipated in a 1 load (i.e. PAVERAGE = VRMS *VRMS /R). If you did not know the rms voltage, the only way to

calculate the power would be to do an integration, from an approximation of the wave-shape as seen on an

oscilloscope. This only works for resistive loads because rms value is a magnitude and does not consider phase

information. A meter that reads an average rectified value for a waveform of period T, indicates a value

T

AVE dttvT

V0

)(1

( peaktopeakV 637.0 For sine wave)

Therefore meter scales are calibrated to read 1.11 * Vaverage, and since 1.11 * 0.637 = 0.707, the reading is the rm

value for a sine-wave and a sine-wave only.

Notes:

1) As 0.637 VPK is the average value of full-wave rectified sinusoids only, a rectifying averaging meter is

only accurate for sinusoidal waveforms. The multiplier 1.11, known as the form factor, is specific to a pure

sinusoidal waveform. Averaging AC meters are therefore, only accurate for sinusoidal waveforms.

2) The above discussion assumes that the meter uses a full-wave rectifier. A second type, called a half-

wave rectifier, exists and would read a different voltage because it only responds to the positive parts of a

waveform. Because of this, a half-wave rectifier can give very strange measurements if the waveform is not

symmetrical about 0V.


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Table 3 shows how some meters would respond to common signals of 1 V (peak) or 2 V (peak-to-peak). The DC

average value will usually be 0V for a sine-wave since sine-wave generators usually have no DC voltage while

square or triangular wave usually start from 0V and go to some positive or negative voltage (single ended signal

generator).

2.6 DC Power SupplyThere are two types of DC power supplies. There are those with fixed voltages, and those which are adjustable.

Adjustable supplies have a control which allows one to change the DC voltage. Both types have two output lead

where one is indicated as being positive (with respect to the other lead).

Many supplies also have current limiting. This feature decreases the voltage when the current goes beyond a

certain limit. Because of this, the power supply will act like a voltage source until the current limit is exceeded.

Then it acts like a current source which is fixed at the current limit. For some power supplies, the current limit ca

be set by the user using a control on the front panel. For the Agilent E3620A power supply, figure 3, the current

limit threshold is fixed at one ampere and cannot be changed by user. This feature also protects the device

against short circuit at output.

Figure 3. DC power supply

Power Supply Connections: Most power supplies are floating. This means that neither the positive, nor

negative outputs are connected to ground or any common point. This means that you can connect the power

supply in any way, even several hundred volts above ground. A non-floating power supply has one lead grounde

or connected to a common point. This means that there is only one lead which can be connected anywhere in a

Table 3. Comparing the reading of different meters for a 2 VP-P signal

Waveform

1 VPK(2 Vpeak-to-peak)

DC average

voltage

AC rectified average

voltage * 1.11 (A)

RMS

Volts (B)

% difference

(A), (B)Square

Sine

Triangular

1 or 0

0

0.5 or 0

1.11

0.707

0.555

1.00

0.707

0.577

+11.0%

+0%

-3.8%


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circuit since the common or grounded one cannot be moved. These power supplies may be referred to as single

ended. The word single means that you can only have a positive or negative voltage from the supply. If the supp

is double ended, you can obtain either a positive or negative voltage from it.

For the Agilent E3620A power supply, the two outputs are floated and therefore can be connected to each othe

to build a power supply with positive and negative output voltages. Here is a simplified block diagram of the

power supplies in the lab:

2.7 Function GeneratorA signal generator provides a time-varying voltage signal at its output. This can be anything from a simple sine,

square or triangular wave up to a TV station signal with different types of noise added. As a signal generator

provides output voltage of different functions (sine, square and triangle), it sometimes is referred to as function

generator. Its symbol and basic circuit model for a non-ideal signal generator are shown in figure 4.

Routis the output resistance of the signal generator and may sometimes be called R intor internal resistance.

Every electronic circuit has a certain amount of resistance. Signal generators are usually 600, 75, 50 or some

other value due to varying industry standards. For the Agilent 33120A signal generator, Rout= 50. You have to

keep the output resistance in mind. Whenever you draw current from a signal generator, the voltage at the

output terminals will be decreased due to the voltage drop across the internal resistance.

Figure 4. Function generator model

Signal generators, like DC power supplies, can have different properties. They may have one of the outputs

connected to ground or have a circuit common point. This is a single-ended generator as opposed to a floating

one, where neither of the outputs is connected to a common or ground. The generator may be unipolar, where

the voltage is always of one polarity, or it may be bipolar, where the voltage is both positive and negative at

different times.

Generally, sine-wave generators are bipolar and square-wave generators are unipolar. Unipolar generators are

further broken down into positive and negative. A positive, unipolar, square-wave generator produces square-

waves that start at 0 V, go up to some positive peak, and then return to 0 V in each cycle.


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Signal generators have imperfections. The waveforms are not pure. There can be noise or distortion in the

output. Noise is a random signal and distortion is a change in or distortion of a pure signal. An ideal sine-wave

generator should produce v(t) = sin(t), while a distorted signal could be v(t) = sin(t) + 0.1 * sin(3t) .

The frequency or amplitude of a generator output voltage will be stable. The user is expected to keep this in

mind. Each generator has an amplitude and frequency control. The controls generally work in ranges so you will

usually see a range control that limits the minimum and maximum frequency or amplitude. With time, and as th

instrument warms up, the frequency and amplitude of the signal generator may drift slightly from starting point

2.8 OscilloscopeOscilloscope Operation (Y vs. X mode): The main function of an oscilloscope is to measure time

varying voltages. The measured voltage is amplified and used to dynamically graph the time-varying

electrical signal which is shown as a trace on the oscilloscope display. This trace can be measured wit

the aid of calibrated lines on the display. There are three main controls for this process: horizontal,

vertical, and trigger.

The vertical position of the trace is proportional to the voltage measured at the input, and its exact

position is determined by the vertical controls which determine the amplitude per division setting.

There are typically 8 vertical divisions on a display. The amplitude per division setting determines the

maximum voltage swing that can be displayed as well as the volts per division seen.

The input signal can be AC or DC coupled. AC coupling involves adding a series capacitor. This has th

effect of blocking (removing) the dc bias and low frequency components of a signal. DC coupling does

not have this capacitor and therefore allows measurements down to 0 Hz. AC coupling is useful when

you are trying to measure a small AC voltage that is on-top of a large dc voltage. A typical exampleis trying to measure the noise of a DC power supply.

The horizontal position of the trace is controlled by the trigger and horizontal controls. When

activated the trigger circuitry causes the trace to sweep from the left of the screen to the right. When

the trace reaches the right of the display it will automatically reset so the trace will start rendering at

the left side of the display the next time its triggered. The time it takes to traverse the display is

controlled by the horizontal controls. Here the user can change the time per division settings. There

are typically 10 horizontal divisions on the display. The time per division setting determines the total

time shown on the display was well as the time per division.

The trigger controls determines when the trace will start its sweep across the display. This is

controlled by a reference voltage level (trigger level) which is set by the user. Once in input voltage

reaches this trigger level the trigger circuitry is activated and the trace will start to sweep across the

display. Note: Once the trigger is activated it cannot be retriggered until the trace has finished its

sweep, even if the input voltage crosses the trigger level during the sweep. At any time the position o

the trace is determined by the combination of the voltage (vertical) and time (horizontal) conditions.


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To avoid a lengthy document, no more info is given on oscilloscope here. If you need more detailed

review on oscilloscope, please go to your lab resources for NE-241.

3.Pre LabQuestion 1. For the dual-trace oscilloscope display as shown in the figure 9, calculate:

a) The RMS value of the sinusoidal waveforms displayed.

b) The frequency of the waveforms.

c) The phase angle between the two waveforms.

Figure 9. A sample oscilloscope screen display


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Question 2. Match the graphs in figure 10 (numbered with alphabet ones).

Figure 10. Voltage and Current sources

Question 3. What would the accuracy of the 5 digit DMM be if it measured 1.3454V (DC) on the 20V range?


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4.In Lab ProcedureSince DMM and oscilloscope are the main measurement devices in the lab, we will review these items in detail i

following sections.

Oscilloscope

The front panel of Agilent DSO-X 2012A oscilloscope is shown in figure 11.

Figure 11. Front panel of the Agilent DSO-X 2012A oscilloscope

To review the operation of each section, we will examine each button/knob individually for each section. Put the

Agilent function generator to 1 kHz sine wave, 4 V peak-to-peak with no offset and connect it to a 50 load (use

the decade box) and to channel-1, see Figure 11.5.


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Signal generator

output

Oscilloscope

channel-150

Figure 11.5 Circuit for 1kHz sine wave, 4 Vpp connected to 50 load

Press the Autoscale button. You should have gotten a screen similar to figure 12.

Figure 12 Display after the Autoscale button pressed

Please note that you are NOT allowed to use this Autoscale button during all sessions of the NE-344 lab! This on

time use is only to have consistent result at the beginning.

In the following sections, examine the function of each button or knob on the graph you see on youroscilloscopes display. Make sure to undo any changes you apply before going to next sub-section.


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Vertical inputs/controlsMeasure the peak-to-peak amplitude of the signal using the oscilloscope. Change the Volts/div button and read

the value on the display. Fill out the table 4.

Table 4. Changing Volt/div knob

Volts/div

# of vertical divisions

(peak-to-peak)

Volts/div x # of vertical divisions

(peak-to-peak amplitude of the signal)1 V 4 1 x 4 = 4

2 V

0.5 V

So, as you see, changing the Volts/div does only change the amplifier/attenuator ratio, and in any case we read 4

V peak-to-peak for the incoming signal.

Rotate the vertical position knob. As you see it moves the signal up or down, and the amount you move is writte

on display during the move.

Press the button 1 several times. As you see, it toggles between on and off state for the channel-1 signal. Once

you press this button, you also get the menu for channel-1. In this menu, you have these controls:

- Coupling (AC, DC, or Ground). AC eliminates the DC component of the incoming signal. In other words,shows only AC part of the signal. DC shows both AC and DC parts. Ground shows a ground signal (as if the

input is grounded).

- BW Limit. Limits the band-width of the oscilloscope to 20 or 25 MHz. Signals with higher frequenciescannot be shown on the display.

- Vernier. Allows having smaller steps between different Volts/div values.- Invert. Show the signal as if it was inverted.- Probe. Allows using probes with different attenuation ratios. Make sure it is set to 1:1.

To understand the function of Coupling, give some positive or negative (like +1 V or -1 V) offset to the signal usin

the function generator, and at the same time look at the oscilloscope while using DC coupling and AC coupling

separately. Are you able to measure the offset added to the signal?

Put the Volts/div back to 1 V, and bring back the vertical position to zero.

Horizontal controlsMeasure the period of the signal using the oscilloscope. Change the Time/div knob and fill out the table 5.

Table 5. Changing Time/div knob

Time/div# of horizontal divisions

for one period

Time/div x # of horizontal divisions

(period of the signal)

200 S 5 200 S x 5 = 1000 S = 1 ms

100 S

500 S


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Horizontal position knob controls the position of time-reference for the signal. Once you rotate this knob, pay

attention to the small triangle at the top of screen display.

Once you press the Main button, you get the Horizontal menu. In this menu, you have these controls:

- Main. This is the main mode of operation for an oscilloscope. It is the mode in which oscilloscope isshowing the voltage versus time for both channels.

- Delayed. Not covered in this lab exercise.- X-Y. In this mode, the time dependence of incoming signals will not be shown! Instead, channel-2 signal

(Y) will be shown versus channel-1 (X) signal. So, both axes will have voltage scales. This mode is used for

example when you want to see the I-V characteristic of a diode.

- Roll. Used for low frequency inputs. It shows the changes to input in real time. Put the frequency offunction generator to 2 Hz to see the effect of this button.

- Vernier. Allows having smaller steps between different Time/div values.- TimeReference (Left, Centre, and Right). Changes the reference point for time axis.

To examine the Rollfunction, put the oscilloscope to this mode and change the frequency of the function

generator to 1 Hz. Your signal should be rolling on the display.

To have a better understanding of the Roll/Main/X-Y modes, wire the circuit in figure 13 with a 10 k resistor an

a 10 nF capacitor. Put the function generator on 1 kHz sine wave, 1 VP-P with no offset. Without going through

circuit theory to justify circuits behavior, briefly describe what you see on oscilloscopes display in Main and X-Y

mode. Put the frequency to 1 Hz, and compare the three modes of Roll, Main, and X-Y. In 1 Hz, the capacitor

works as an open circuit (like if there is no capacitor in the circuit at all), and therefore the output is the same as

input.

Figure 13. An RC circuit

Put the Time/div back to 200 S, and bring back the horizontal position to centre.


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Run controlsThere are only two buttons in this section.

- Run/Stop. You can freeze the oscilloscopes operation and bring it to a stopped mode, once this button ispressed and illuminated red. If you press the button again, it goes back to run mode again.

- Single. Not covered in this lab exercise.One application for this Stop button is when you have a continuously changing signal, and you want to study one

pattern for example.

Once the oscilloscope is in Stop mode, change something on the function generator (like frequency or amplitude

of the signal). Do you see it on the oscilloscopes display?

Trigger controlsThis is the most important section in an oscilloscope in order to capture a signal effectively on the screen display

- Level. This knob is simply controlling the trigger level. If this level is within the range of maximum tominimum of the incoming signal, the oscilloscope is able to trigger and capture the incoming signal.Otherwise, a stationary signal cannot be achieved on display.

- Edge (Rising and Falling). It determines whether the rising edge or falling edge of the signal should beshown right at the reference point of time. In the Edge Trigger Menu, you can also select the source of

trigger signal to be channel-1, channel-2, or the External trigger input.

- Mode/Coupling. By pressing this button, you get the Trigger Mode and Coupling Menu using the softkeyHere is the function of button: (no description is required for your report regarding the Mode/Coupling

section)

o Mode (Auto, Auto-Level, and Normal). For simplicity, use the Auto or Auto-level modes in this labo Coupling (DC, AC, LF-Reject). Similar to Coupling in Vertical control section, determines the

coupling applied for the signal used for trigger. If the incoming signal has a large DC componentwith a weak AC part mounted on it, it may be helpful if AC coupling is used. In most cases, DC

coupling is fine for us. LF-Reject (low frequency reject) is used when strong low-frequency, like 60

Hz, signals present in the incoming signal, and make it difficult for the trigger system to do its

function.

o Noise-Reject. Is used when the incoming signal is noisy.o HF-Reject. Is used when the incoming signal has unwanted high-frequency signals added to it.o Holdoff. Not covered in this lab exercise.o External.Used for the external trigger input only.

- Pulse-Width.Not covered in this lab exercise.- Pattern.Not covered in this lab exercise.- More.Not covered in this lab exercise.

Try Level knob and Rising/Falling edges to see how they affect the signal on display.

To try the source of trigger in the Edge Trigger Menu, we need to have another signal source to oscilloscope.

Connect the BK Precision function generator to channel-2. Using the Coarse/Fine frequency control knobs try to

keep the frequency to 1000 2 Hz. Put the amplitude to minimum and waveform to triangular. Make sure only

three buttons are pushed in: Power (red), 1k for frequency, and triangular waveform (all other buttons should no

be pushed in).


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Put the channel-2 to 1 V/div. Now if you toggle the source of trigger between channel-1 and channel-2, you will

see only the signal used for trigger stationary, and the other one rolling slowly because its frequency is slightly o

compared to the other function generator.

WaveformThere are two buttons in this section.

- Acquire. Controls the way signal is acquired to the oscilloscope. It has the following options usingsoftkeys:

oNormal. This is the mode usually used for most applications.

o Peak Detect. Not covered in this lab exercise.o Averaging. Used to reduce random noise associated with the signal to create a smoother

waveform on the display. The depth of the averaging function can be controlled by the control

knob.

o Realtime. Not covered in this lab exercise.- Display. Controls the way signal is displayed. It has the following options:

o Persistent. Gives memory to the screen display pixels. In other words, keeps a faint track of thepreviously shown signals. Change the frequency/amplitude of the function generator to see the

effect of this button.

o Clear Display.Clears patterns created by the persistence mode.o Grid. Controls the intensity of the grid shown on the display.o Vectors. Not covered in this lab exercise.

Try the Averaging, Persistence, and Clear Display modes on the oscilloscope.

MeasureThis section has two buttons.

- Cursors. Creates horizontal and vertical cursors used for measurement. Here are the options using thesoftkeys:

o Mode (Normal, Binary, and Hex). For analog measurements, we only use Normal mode.o Source (1, 2, and Math). Selects the channel to work on.o X & Y. Gives the option to move/select X1, X2, Y1, and Y2 axes.

- Quick measurement. Using this tool one can do many different automated measurements using theinternal functions of the oscilloscope. Here are the options available using softkeys:

o Source (1, 2, and Math). Selects the channel to work on.o Clear measurement. Deletes posted numbers on the display.o Functions. Such as Frequency, Period, Peak-to-peak, Maximum, Minimum, Rise time, Fall time,

Duty cycle, RMS, + Width, - Width, Average, Amplitude, Top, Base, Overshoot, Pre-shoot, X at ma

It should be noted that the Quick Measurement function performs the task for that part of the signal which is

seen on the oscilloscopes screen display.

Measure the frequency and peak-to-peak amplitude of the voltage signal provided by the function generator. Do

these values match with each other and also with what you read on function generator?


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Digital-Multi-Meter (DMM)

A DMM can be used to measure resistance (), DC voltage, DC current, AC voltage, and AC current. Let us review

DC measurement separate from AC measurement.

DC measurement

Wire the circuit shown in figure 14 on the breadboard. Put the DC power supply on 10 V.

Figure 14. Resistive circuit

Fill out the table 6. Use 20 V range for voltmeter and 20 mA range for ammeter. Remember, Voltmeter across

the component, and Ammeter in series with the component under measurement!

Table 6. DC measurement errors

Item Calculated value (A) Measured value (B) Error =

V1

V2I1

I2

I3

AC measurement

Replace the DC power supply in the above circuit with the Agilent function generator. But to keep the AC circuit

identical with DC circuit, put another 100 resistor parallel with the 100 resistor! Why? (Remember the

function generator has an internal resistor of 50 )

Put the function generator to sine wave, 100 Hz, 10 Vp-p with no offset. Fill out the table 7. Use 20 V range for

voltmeter and 20 mA range for ammeter. Remember, the Tektronix DMMs in the lab are true RMS measuring

equipment! Note that the voltage you measure across the 50 resistor is

in this case, and voltage across the

function generator is


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Table 7. AC measurement errors

Item Calculated value (A) Measured value (B) Error =

V1

V2

I1

I2

I3


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Appendix

Accuracy of the Tektronix Digital Multimeter 4020

(DMM 4020)

Important note:Use the values under the 1 year column as the default accuracy values.

1- DC voltageTable A.1

2- AC voltageTable A.2


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3- DC currentTable A.3

4- AC currentTable A.4

5- ResistanceTable A.5

Documents

NE344 Lab1 Laboratory Instruments