Transcript Lab Equipment

1
Lab Equipment
2
Contents
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
3
DC Power Supply
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
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”.
Vpos
+
+
DC = 0 to 20
DC = 0 to 6
+
DC = 0 to Vpos
Don’t use;
connects to
chassis and
power line
gnd
4
DC Power Supply
A
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.
B
Vpos C
+
+
DC = 0 to 20
DC = 0 to 6
+
DC = 0 to Vpos
D
5
Digital Multimeter (DMM)
Range is set
automatically
DC voltage
AC voltage
DC current
Resistance
Power switch
AC current
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
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
For current measurements, move the RED lead to a current input
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.
9
Function Generator
Select waveform
output
Set frequency, amplitude, and DC offset
10
Observe
decimal
point;
ignore the
commas
To enter values, press “Enter Number”, then the number keys, then “Enter”
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”
Shift
Enter
>
>
> “SYS Menu”
>
“OUT TERM”
>
“50 OHM ” > “HIGH Z ” Enter
13
Oscilloscope
Always adjust the scope to obtain as large of a
waveform as possible (to maximize accuracy)
Function buttons
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
14
The 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
Example of Setting Zero Volt Reference
Trace starts at first vertical
grid line
Zero voltage
reference line set to
known point
(usually center line,
but may anywhere
you desire)
Once positioned, be
careful not to
change it.
19
Use these to set the
vertical (voltage) values
per division
vertical
and
horizontal
values per
division (cm)
are shown on
the display
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
Scope Cursors
Use function buttons to control 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
Reference channel selection
available only when both channels
A and B are displayed
cursor 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)
RETURN key takes you back to
the previous higher level
Voltage cursor will use either channel A or B
“voltage per division” setting, as selected.
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
26
Sets the trigger mode (normally set to AUTO)
Displays the trigger mode
Sets the trigger slope
Displays trigger slope
Horizontal
(time base)
trigger
controls
Sets trigger
coupling
Adjusts the
trigger level
Displays trigger source and coupling
Sets trigger source
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.
Single Trace
Operation
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.
28
Example Waveform
Trigger level set to
zero volts and a
positive (upward)
slope
29
Example Waveform
Trigger level set to
+1 volt, with a
positive slope
Zero volt reference line
30
Example Waveform
Trigger level set to
–1 volts, with a
positive slope
Zero volt reference line
31
Example Waveform
Trigger level set to
zero volts, with a
negative (downward)
slope
32
Delayed
Trigger
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.
33
Waveform
Zoom
Use the X-magnification button to zoom in on part of the
waveform; the magnification factor is changed each time
you press the button.
34
Move the
display
window
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)
35
Trace Rotation
Adjust to make
trace parallel
with horizontal
grid
36
Scope Probe Compensation Adjustment
Make sure channel A and B signal coupling are set to DC
Connect probe
to calibration
signal
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
Making Rise and Fall Time Measurements on
Pulse Waveforms
100%
90%
10%
0%
For rise or fall time measurements, use the 0%,
10%, 90%, and 100% lines on the scope grid
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
The adjusted waveform display
100%
90%
10%
0%
44
For rise time measurements
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
45
Adjust the vertical cursors so that they pass the 10% and 90%
points on the waveform, and read off the rise time.
90%
10%
46
For fall time measurements
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
47
Adjust the vertical cursors so that they pass the 10% and 90%
points on the waveform, and read off the fall time.
90%
10%
48
If scope fails to communicate with the computer:
Use OPTION function button to check or
correct communications settings
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.