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Lab Equipment

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Topic Slides

DC Power Supply 3-4

Digital Multimeter 5-8

Function Generator 9-12

Scope – basic controls 13-20

Scope – cursors 21-24

Scope – triggering 25-32

Scope – exploring the waveform 33-34

Scope – trace rotation and probe compensation 35-40

Scope – rise/fall time measurements 41-47

Scope – computer communication problems 48

Contents

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DC Power Supply

All three supplies share a common terminal, which is NOT connected to the power supply “ground”. This terminal should normally be connected to your circuit “ground”.

The negative 0 to 20 volt supply is proportional (by an adjustable ratio of up to -1) to the positive supply

Vneg = (0 to –1) times Vpos

Don’t use; connects to chassis and power line gndDC = 0 to Vpos

DC = 0 to 6 DC = 0 to 20

+

++

Vpos

4

DC Power Supply

DC = 0 to Vpos

DC = 0 to 6 DC = 0 to 20

+

++

CBA D

Since the COM terminal is isolated from the power supply ground, you are not limited to using point B for your circuit ground. If you use point A, C, or D as your circuit ground you can use series combinations of the three internal voltage sources to obtain voltages higher than +20V and lower than –20V.

Vpos

5

Digital Multimeter (DMM)

Power switchDC voltage

AC voltage

DC current

AC currentResistance

AC = RMS value of AC part of waveform only

DC = value of DC part of waveform only

To measure TRUE RMS value of the complete waveform, press both DC and AC

Range is set automatically

6

Diode test (passes small current through diode and measures the resulting voltage drop)

Connect the RED lead to the diode anode and the black lead to the cathode.

7

Use the RATE switch to set the speed of measurement and the resolution of the displayed values:

F = fast speed = low resolution

M = medium speed = medium resolution

S = slow speed = high resolution

8

10 AMP current input has low internal resistance and introduces the lowest error; use this input whenever possible

100 milliamp current input has considerable internal resistance and may introduce considerable error; use the 10 A input whenever possible.

For current measurements, move the RED lead to a current input

9

Function Generator

outputSelect waveform

Set frequency, amplitude, and DC offset

10

To enter values, press “Enter Number”, then the number keys, then “Enter”

Observe decimal point; ignore the commas

11

When entering values, use these keys to define the

units. Notice that voltage values can be defined as

either RMS or peak-to-peak.

12

If the amplitude of the waveform measured by the scope or digital multimeter does not agree with the amplitude shown on the function generator display, reset the output termination to “HIGH Z”

“SYS Menu”>

“OUT TERM”

EnterShift >

“50 OHM ” “HIGH Z ”

> >

>

>

Enter

13

OscilloscopeAlways adjust the scope to obtain as large of a waveform as possible (to maximize accuracy)

Adjust the FOCUS and INTENSITY to obtain a clear, readable display.

When not actively observing waveforms, turn down the intensity to extend the life of the scope screen

Function buttons

14The AUTO SET button helps the scope find the waveform, but it also sets the waveform signal coupling to AC (undesirable)

After using the AUTO SET button, reset the waveform signal coupling to DC using the AC/DC buttons

General Rule: ALWAYS use DC coupling on the vertical channels so that you can observe the complete (AC & DC) waveform

15

The VAR controls must be in the CAL position for the display values to be valid

16

Use the X POS control to start the scope trace at the left edge of the grid

17

Set the zero volt positions for ch A and ch B to known positions on the grid, usually the center horizontal line, by first selecting GND and then adjusting the Y POS controls

18

Zero voltage reference line set to known point (usually center line, but may anywhere you desire)

Once positioned, be careful not to change it.

Trace starts at first vertical grid line

Example of Setting Zero Volt Reference

19

vertical and horizontal values per division (cm) are shown on the display

Use these to set the vertical (voltage) values

per division

Use this control to set the horizontal (time) value per division

20

DIGITAL MEMORY mode must be selected to be able to use cursors and transfer waveforms to the computer

21

Use function buttons to control cursors

Scope Cursors

22

Cursor Positioning Buttons

Controls lower cursor

Controls upper cursor

Controls left

cursor

Controls right

cursor

RETURN key takes you back to the previous higher level

23

Setting the Cursor Mode and Reference Channel

Use to turn cursors on/off and to select what they display (vertical measurement = voltage or ratio;

horizontal measurement = time, phase angle, or ratio)

Voltage cursor will use either channel A or B “voltage per division” setting, as selected.

RETURN key takes you back to the previous higher level

cursor reference channel

Reference channel selection available only when both channels A and B are displayed

24

Value of differences between horizontal

(voltage) cursors

Value of difference between vertical (time) cursors

Frequency computed from inverse of time interval (valid only if interval is one cycle)

25

Scope Triggering

The waveform on the scope display is drawn from left to right (repetitively), beginning at a point when one of the signals being displayed meets a specified criteria. This criteria is defined by the settings of the horizontal (time base) trigger controls:

Mode - the standard mode is AUTO

Source - which signal is being used to trigger the scope

Coupling - normally P-P (AC), but sometimes DC gives more control

Slope - the scope trace begins on the upward or downward slope of the wave

Level - the voltage level of the wave at which the trace begins

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Sets the trigger mode (normally set to AUTO)Displays the trigger mode

Displays trigger slope Sets the trigger slope

Displays trigger source and coupling

Sets trigger coupling

Sets trigger source

Adjusts the trigger level

Horizontal (time base) trigger controls

27

To capture a non-repetitive waveform, set the desired trigger conditions, select the SINGLE TRACE trigger mode, then press RESET to “arm” the scope.

After the scope has been “armed”, a single trace will be drawn when the signal level matches the trigger conditions (slope and level) you have selected. The trace will remain displayed until you press RESET or transfer the waveform to the computer.

Single Trace Operation

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Trigger level set to zero volts and a positive (upward) slope

Example Waveform

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Trigger level set to +1 volt, with a positive slope

Zero volt reference line

Example Waveform

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Trigger level set to –1 volts, with a

positive slope

Zero volt reference line

Example Waveform

31

Trigger level set to zero volts, with a

negative (downward) slope

Example Waveform

32

The trigger delay can be used to shift where the trigger point appears on the screen; this allows you to observe the waveform up to 10 divisions prior to the trigger point on repetitive waveforms.

Delayed Trigger

33

Use the X-magnification button to zoom in on part of the waveform; the magnification factor is changed each time you press the button.

Waveform Zoom

34

Use the Display Part rocker switch to move the display window across the waveform image stored in the scope. (The scope stores two screen widths of data at X1 magnification)

Move the display window

35

Adjust to make trace parallel

with horizontal grid

Trace Rotation

36

Scope Probe Compensation Adjustment

Connect probe to calibration

signal

Make sure channel A and B signal coupling are set to DC

37

Scope Probe Compensation Adjustment

Each probe has an adjustment screw

that changes the compensating

capacitor

38

Scope Probe Compensation Adjustment

Adjustment capacitor value needs to be increased until waveform is rectangular

39

Scope Probe Compensation Adjustment

Adjustment capacitor value needs to be decreased until waveform is rectangular

40

Scope Probe Compensation Adjustment

Rectangular waveform with correct probe adjustment

41

0%10%

90%100%

For rise or fall time measurements, use the 0%, 10%, 90%, and 100% lines on the scope grid

Making Rise and Fall Time Measurements on Pulse Waveforms

42

Using the vertical scale control to set your waveform amplitude so that it is greater than the range of 0% to 100%

Then use the var and the Ypos controls to line up your waveform with the 0% and 100% grid lines.

43

100%90%

10%0%

The adjusted waveform display

44

Expand the waveform horizontally using the time base (TB) control

Set the trigger slope to positive (upward) for rise

time measurements

Set trigger coupling to

DC

Adjust trigger level to the 10% point or below

For rise time measurements

45

Adjust the vertical cursors so that they pass the 10% and 90% points on the waveform, and read off the rise time.

10%

90%

46

Expand the waveform horizontally using the time base (TB) control

Set the trigger slope to negative (downward) for rise time measurements

Set trigger coupling to

DC

Adjust trigger level to the 90% point or above

For fall time measurements

47

Adjust the vertical cursors so that they pass the 10% and 90% points on the waveform, and read off the fall time.

10%

90%

48

Use OPTION function button to check or correct communications settings

If scope fails to communicate with the computer:

OPTION

IEEE

IEEE-ADDR: 8 MODE: talker/listener

If you have to correct the communications settings, cycle the scope power to reset the communications interface.