The Oscilloscope Training Package
MAIN MENU
Please select one of the options below:
A Brief
Introduction
Operating
Principles
Controls &
Indicators
Basic
Operating
Instructions
Applications
of the
Oscilloscope
Glossary
Copyright © 1997-8 Jigar C Shah
The Oscilloscope
A Brief Introduction…
What’s Inside?
As you can see in the diagram above, an analog scope has two major signal
paths. The first is the vertical signal path, which ultimately is responsible
for deflecting the CRT beam vertically in response to the input signal. The
second path is the horizontal. It triggers the scope and moves the beam from
left to right across the screen. In a typical display, time is represented
horizontally and voltage is represented by the vertical axis.
The Vertical Channels
When a signal comes into an analog scope, the first thing it sees are the
attenuators. Attenuators match the high impedance of the scope probes
(typically 1 M or 10 M ) to the low impedance of the vertical preamplifiers.
The attenuators also scale the input signals to a level the vertical preamps
can handle. The amount of attenuation and preamp gain is set by the front
panel vertical sensitivity knob.
Triggering
The triggering portion plays a very important part in the operation of a
scope-it determines where (in time) the trace starts. In essence, the
triggering circuits tell the horizontal section when to start moving the beam
from the left side of the CRT to the right. If the trace starts too early, the
part of interest on the signal won't be seen. The same is true if it starts too
late. The figure below gives you an idea of what happens.
How does the trigger circuit know when to trigger? It gets a replica of the
signal, called the sync pickoff, from the selected trigger source. This sync
pickoff is compared to a pre-set trigger voltage that is set with the front
panel trigger level knob. Most analog scopes let you specify a slope as well
as a trigger voltage. This allows you to trigger at a specific point on a rising
or falling transition.
When the trigger circuit finds a voltage and transition from the source that
matches those set with the trigger controls, it tells the horizontal sweep
circuits to start moving the beam from left to right. The speed of the beam
is determined by the seconds/division knob on the front panel. As the beam
is moved horizontally across the screen, the vertical amplifiers move the
beam up and down, relative to the input voltage.
Both the horizontal sweep and vertical deflection information have to arrive
at the CRT at the same time. If they don't, the scope won't be able to display
the voltage information properly.
Look at the block diagram at the top of this section. Since the delays in the
horizontal path are longer, vertical information will reach the CRT before
the horizontal information. The solution to the problem is to put a calibrated
delay into the vertical path so both horizontal and vertical signals will get to
the CRT at the same time. When properly adjusted, an analog scope does
not display the signal fluctuations before the trigger event.
The Horizontal Section
For external triggering, the horizontal path of an analog scope has an
attenuator like the vertical channels. This attenuator serves the same
purpose as those in the vertical channels, i.e., impedance matching and
scaling the external trigger signal. However, the horizontal attenuator is
followed by trigger comparison circuits, instead of a preamp, as in the
vertical channels.
The horizontal portion of the scope, which is responsible for moving the
trace along the time or horizontal axis, directly affects the time accuracy of
an analog scope. The horizontal beam movement is controlled by a voltage
ramp (called the sweep ramp); the time interval accuracy of the scope
depends heavily on this ramp.
Once the trigger comparator has found a valid trigger, it tells the horizontal
sweep ramp generator to start. As the ramp rises, it causes the beam to
move from left to right across the CRT. Since the left to right movement
represents time on the CRT, the ramp must be very linear. If the ramp has
non-linearities, the beam moves at different rates across the screen.
Typically, ramp linearity controls time interval accuracy of an analog scope
within ±3%.
The CRT
The last major portion of an analog scope is the display or CRT. Analog
CRTs are vector displays that can move the beam to any point directly. A
signal from the vertical amplifier moves the beam in the vertical direction.
This may seem obvious, but it brings up a very important point. The CRT
and its drivers must be able to deflect the beam vertically as fast as the
signal rises. What this means is that the CRT bandwidth must be the same
as the input bandwidth of the scope! High bandwidth CRTs pose several
problems. As CRT bandwidth goes up, the following happens:
●
Cost of the CRT goes up;
●
Accuracy of the CRT goes down;
●
Reliability of the CRT goes down.
To keep the cost of the CRT down while keeping the accuracy and
reliability up, the scope must use as low a bandwidth CRT as possible.
However, since the CRT must have the same bandwidth as the scope, high
bandwidth analog scopes demand high bandwidth CRTs. The only real
solution is to move to a new architecture.
Summary
In this first section we have talked about how an analog scope works. We
also pointed out some of the shortcomings of current analog scope
architecture. Here are some of the key points to remember about analog
scopes:
●
There are two major signal paths-horizontal and vertical;
●
Everything (including the CRT) must work at the same speed as the
input signal;
●
All input channels are usually multiplexed through a single vertical
path to the CRT;
●
The horizontal path is responsible for triggering;
●
The scope triggers on a voltage level and rising or falling slope;
●
As input bandwidth goes up, cost of the CRT also goes up, while
reliability and accuracy of the CRT go down.
BACK TO MAIN MENU
Oscilloscope Training Package Programmed by Jigar C. Shah NTU Final
Year Project.
Copyright © 1997-8 Jigar C Shah
The Oscilloscope
Operating Principles : The Cathode Ray Tube
The Cathode Ray Tube Many logic analysers and some DSOs use
magnetically deflected c.r.t.s either as monochrome or colour. This is the
type of display technology used in TV sets.
In the c.r.t. storage oscilloscope, the cathode ray tube is basically similar to
the electrostatistically deflected type of tube described below; but with the
addition of one or more storage meshes.
The cathode ray tube is the main component of an oscilloscope. A cathode
ray tube consists basically of an electrode assembly mounted in an
evacuated glass vessel. The electrodes perform the following functions:
●
A triode assembly generates the electron beam, originally called the
'cathode ray'. It consists of a cathode K heated by a filament F, a
control grid G and the first beam-acceleration electrode (1).
●
An electrode (2) focuses the beam.
●
The beam is then further accelerated before reaching the deflection
plates.
●
The vertical deflection plates change the direction of the beam in
proportion to the potential difference between them. When this is zero,
i.e. the two plates are at the same potential, the beam passes through
undeflected. The vertical deflection plates are so called because they
can deflect the bean in the vertical direction, so that it hits the screen at
a higher or lower point; they are actually mounted horizontally above
and below the beam. Similarly the horizontal deflection plates permit
the beam to be deflected to left or to right.
●
The deflected beam then hits the fluorescent coating on the inner
surface of the glass screen of the c.r.t. The coating consists of t thin
layer of phosphor, a preparation of very fine crystals of metallic salts
deposited on the glass. The 'spot' or point of impact of the beam glows,
emitting light in all directions including forwards. Modern c.r.t.s are
aluminized, i.e. a think layer of aluminum is evaporated on to the rear
of the coated screen. The electrons pass through this with little
retardation., causing the phosphor to glow as before, but not the light
emitted rearwards is reflected forwards, almost doubling the useful
light output.
The potential at the focus electrode is adjusted to obtain a very small round
spot on the end of the tube. Unfortunately, if no other control were
provided, it would often be found that the focus control setting for
minimum spot width was different from that for minimum spot height. This
is avoided by providing an astigmatism control. In the case of a simple
cathode ray tube this consists of a potentiometer that adjusts the voltage on
the final anode and screen relative to the deflection plate voltages. Alternate
adjustments of the focus and astigmatism controls then permit the smallest
possible spot size to be achieved. With more complicated tubes using a high
post deflection acceleration ratio another electrode is often needed. This is a
'geometry' electrode and is connected to another preset potentiometer,
which is adjusted for minimum 'pincushion' or 'barrel' distortion of the
display. When an electron beam passes between two horizontal plates that
have a potential difference of V volts between them it is deflected vertically
by an amount:
where
L = Length of the plates
D = distance between the plates and the point on the axis where the
deflection is measured
d = distance between the plates
Va = acceleration voltage applied to the beams at the level of the plates
K = a constant relating the charge of an electron to its mass
Brilliance or intensity modulation (also called Z modulation) is obtained by
the action of a potential applied to the cathode or grid hat controls the
intensity of the beam. Generally, a change of 5V will produce a noticeable
change of brightness, while a swing of about 50V will extinguish a
maximum intensity trace. The beam is normally extinguished during
'flyback' or retrace; by means of an auxiliary 'blanking' electrode, which can
deflect the beam so that it no longer passes through the deflection plates
and hence does not reach the screen.
TUBE SENSITIVITY
The deflection plates of a c.r.t. are connected to amplifiers, which can be
relatively simple design when the required output amplitude is low; it is
therefore desirable for the tube sensitivity to be as high as possible. To
enable the amplifier to have a wide bandwidth, the capacity between the
plates must be kept low, so they must be small and well seperated. On the
other handm in order to obtain a suitably clear trace of a signal with low
repitition frequency (or single shot) the energy of the beam must be high.
But the ideal tube must be:
Short (not cumbersome) : D small
Bright (high acceleration voltage) : Va large
And with low acceleration deflection-plate capacity: L small, d large.
This gives the tubes with very low sensitivity, considering the formulae:
The requirements for high sensitivity contradicts the terms of the equation.
Practical cathode ray tubes are therefore the result of a compromise.
However, techniques have been developed to improve a selected parameter
without prejudice to the others.
Post deflection acceleration (p.d.a) is one of these; To improve the trace
brightness while retaining good sensitivity, it is arranged that the beam
passes through the deflection system in a low energy condition; post
deflection acceleration is then applied to the electrons. This is achieved by
applying a voltage of several kilovolts to the screen of c.r.t.
Spiral p.d.a is a development of the basic p.d.a technique, and consists of
the application of the p.d.a. voltage to a resistive spiral (500M Ohms)
deposited on the inner tube surface between the screen and the deflection
system. The unformity of the electric field is improved, which reduces
distortion. In addition to the effect of the p.d.a. field between the deflection
plates is weaker, so the loss in sensitivity caused by this field is reduced.
The use of a field grid, avoids any reduction in sensitivity caused by the
effect of the post deflection acceleration field. A screen is interposed
between the deflection system and the p.d.a; this makes the tube sensitivity
independent of the p.d.a, a significant benefit. The screen must, of course,
be transparent to the electrons and is formed from a very fine metallic grid.
With this system we reach the domain of modern cathode ray tubes.
The next development is the electrostatic expansion lens. By modifying the
shape of the field gird it is possible to create, with respect to the other
electrodes, an electric field that acts on the beam in the same way as a lens
acts on a light beam. It is therefore possible to increase the beam deflection
angle, for example by a factor of 2 which improves the sensitivity by the
same amount.
The field can also be formed by quadripolar lenses.
For example, if the sensitivity of a spiral tube is 30 V/cm in the X-axis and
10 V/cm in the Y axis, then the sensitivity of a lens fitted tube, for the same
trace brightness, may be 8V/cm in X and 2V/cm in Y or even better.
To improve the sensitivity by modifying the deflection system it is
necessary to do one of two things:
Reduce the distance between the plates, increasing the capacity between
them; in addition it must be possible to deflect the beam without it striking
them.
Lengthen the plates, again increasing the capacity, however, the transit time
involved limits the application of this idea.
The transmit time is the time taken for an electron to pass through the
deflection system
BACK TO MAIN MENU
Oscilloscope Training Package Programmed by Jigar C. Shah NTU Final
Year Project.
Copyright © 1997-8 Jigar C Shah
The Oscilloscope
First Looks : Controls & Indicators
Please click on the various parts of the Oscilloscope for a
description of the part.
1. CH1 Position Control
Rotation of this knob will adjust the vertical position of the Channel 1 waveform on the
screen. In the X-Y operation, rotation adjusts vertical position of display.
Back to Oscilloscope Diagram
2. CH1 Volts/Div Control & Variable Control
For the Volts/Div Control, it is a vertical attenuator for channel 1. Provides step adjustment
of verticaal sensitivity in 1-2-5 sequence. VARIABLE control is turned to the CAL
position, the calibrated vertical sensitivity is obtained. In X-Y operation, this control serves
as the attenuator for Y-axis.
Rotation of the variable control provides fine control of channel 1 vertical sensitivity. In
the fully clockwise (CAL) position, the vertical attenuator is calibrated. In X-Y operation,
this control serves as the Y-axis attenuation fine adjustment.
Back to Oscilloscope Diagram
3. CH1 AC-GND-DC Switch
This switch is the Channel 1 vertical axis coupling mode selector, for X-Y operation, the
Y-Axis coupling mode control.
AC:
AC Input coupling with blocking of any DC signal
component.
GND: Vertical amplifier is disconnected from the input signal
and connected to ground. This mode is useful in
determining the zero reference.
DC:
DC Coupling, with both the DC and AC components of
the input signal displayed on the CRT.
Back to Oscilloscope Diagram
4. CH1 INPUT Jack
Vertical input for channel 1 trace in normal sweep operation. Y-axis input for X-Y
operation.
Back to Oscilloscope Diagram
5. CH2 Position / PULL INVert Control
CH2 Position:
Rotation adjusts vertical position of channel 2 trace.
INV:
Push-pull swtich selects channel 2 signal inverted when pulled out.
Back to Oscilloscope Diagram
6. CH2 Volts/Div Control & Variable Control
Volts/Div Knob:
For the Volts/Div Control, it is a vertical attenuator for channel 1. Provides step adjustment
of verticaal sensitivity in 1-2-5 sequence. VARIABLE control is turned to the CAL
position, the calibrated vertical sensitivity is obtained. In X-Y operation, this control serves
as the attenuator for X-axis.
Variable Control:
Rotation of the variable control provides fine control of channel 1 vertical sensitivity. In
the fully clockwise (CAL) position, the vertical attenuator is calibrated. In X-Y operation,
this control serves as the X-axis attenuation fine adjustment.
Back to Oscilloscope Diagram
7. CH2 AC-GND-DC Switch
Three position lever switch which operates as follows :
AC:
Blocks DC Component of channel 2 input signal.
Opens singnal path and grounds input to vertical amplifier.
This provides a zero-signal base line, the position of which
GND:
can be used as a reference when performing DC
measurements.
Direct input of AC and DC component of channel 2 input
DC:
signal.
Back to Oscilloscope Diagram
8. CH2 INPUT Jack
Vertical input for channel 2 trace in normal sweep operation. X-axis input in X-Y
operation.
Back to Oscilloscope Diagram
9. MODE Switch
Selects the basic operating mode of the oscilloscope.
CH1:
Only the input signal to channel 1 is displayed as a single trace.
CH2:
Only the input signal to channel 2 is displayed as a single trace.
ALT:
Alternate sweep is selected regardless of sweep time.
CHOP:
Chop sweep is selected regardless of sweep time at approximately 300 KHz.
ADD:
The waveforms from channel 1 and channel 2 inputs are added and the sum is displayed as
a single trace. When the CH2 INV Button is engaged, the waveform from channel 2 is
subtracted from the channel 1 waveform and the difference is displayed as a single trace.
Back to Oscilloscope Diagram
10. GND Terminal
Earth and chassis ground reference.
Back to Oscilloscope Diagram
11. CAL Terminal
Provides 1 kHz, 1 V peak-to-peak square wave signal. This is useful for probe
compensation adjustment.
Back to Oscilloscope Diagram
12. EXT Trigger Input Jack
Input terminal for external sync signal.
When SOURCE switch is selected in EXT position, the input signal at the EXT TRIG
input jack becomes the trigger.
Back to Oscilloscope Diagram
13. Power Switch
A press of this switch turns the power ON.
Back to Oscilloscope Diagram
14. Power Indicator
Lights when the POWER swtich is pressed.
Back to Oscilloscope Diagram
15. Intensity (REAL) Control
Controller for adjusting the brightnesss of the real-time waveform.
Back to Oscilloscope Diagram
16. Focus / PULL Astig Control
FOCUS: Focus adjustment
ASTIG: Used to bring the waveform into the best condition with the FOCUS adjustment
by adjusting trace and spot aberration. Pull the knob to make a spot circular.
Back to Oscilloscope Diagram
17. Scale Illum / PULL Trace Rota Control
SCALE ILLUM:
Brightness adjustment of the scale of the CRT. For photographing, rotate the knob to adjust
bright to prevent halation caused by too bright illumination.
TRACE ROTA:
Tilt adjustment of the horizontal bright line in the case where goemagnetism influences the
bright line to tilt.
Back to Oscilloscope Diagram
18. Variable SWEEP TIME/DIV Control
A SWEEP Time / Div Control
Range select dial of 19 ranges from 0.2us/div to 0.5s/div.
To calibrate the set value, rotate the SWEEP VARIABLE controlle clockwise up to the
CAL position.
B SWEEP Time / Div Control
Range select dial of 17 ranges from 50ms/div to 0.2us/div. Set this dial to a value same as
the A SWEEP Time/Div Control or higher than it.
A SWEEP Variable Control
Fine sweep time adjustment. In the fully clockwise (CAL) position, the sweep time is
calibrated.
Back to Oscilloscope Diagram
19. Horizontal Position / PULL 10X Magnification Control
Horizontal position controller, which provides horizontalal shift of waveform. By pulling
the knob, the sweep time is quickened ten times.
In the X-Y operation, rotation adjusts horizontal posistion of display.
Back to Oscilloscope Diagram
20. Level / PULL Slope (-) Control
LEVEL:
Trigger level adjustment determines point on triggering waveform where A sweep
triggered.
Back to Oscilloscope Diagram
21. Hold Off Control
HOLD OFF:
Adjusts holdoff (trigger inhibit period beyond sweep duration). Clockwise rotation from
the NORM position increases holdoff time, up to 10 times at the MAX position (fully
clockwise).
Trace Seperation Control
Adjusts vertical seperation between A sweep and B sweep (control has effect only in the
ALT of HORIZ. MODE).
Clockwise rotation increases seperation; B sweep moves down with respect to A sweep up
to 4 divisions.
Back to Oscilloscope Diagram
22. Coupling Switch
Selects coupling for sync trigger signal.
AC:
Trigger is AC coupled. Blocks DC component of input signal; mostly commonly used
position.
HFrej:
Sync signal is DC coupled through a low-pass filter to eliminate high frequency
components for stable triggering of low frequency signals.
DC:
The sync signal is DC coupled for sync which includes the effect of DC components.
TV FRAME:
Vertical sync pulses of a composite video signal are selectec for triggering.
TV LINE:
Horizontal sync pulses of a composite video signal are selected for triggering.
Back to Oscilloscope Diagram
23. Source Switch
Sweep trigger source select switch.
VERT MODE:
The sweep trigger source is selected with the MODE selector for the vertical operation.
When the vertical MODE selectoris set to CH1, the channel-1 signal is used as a trigger
source. When is is ser to CH2, the channel 2 signal is used as a trigger source. When ser to
ALT both the channel 1 and channel 2 signals are used alternatively. When set to CHOP or
ADD, the channel 1 signal is used as a trigger source.
CH1:
Channel 1 signal is used as a trigger source.
CH2:
Channel 2 signal is used as a trigger source.
LINE:
Sweep is triggered by line voltage.
Back to Oscilloscope Diagram
24. Triggering Mode Control
Selects triggering mode.
AUTO:
Triggered sweep operation when trigger signal is present, automatically generates sweep in
absence of trigger signal.
NORM:
Normal triggered sweep operation. No trace is presented when a proper trigger signal is not
applied.
X-Y:
X-Y operation. Channel 1 input signal produces vertical deflection (Y-axis). Channel 2
input signal produces horizontal deflection (X-axis).
This operates regardless vertical MODE selection.
SINGLE:
Single sweep mode
RESET:
Reset mode of single sweep operation. when reset, the switch returns to the SINGLE
position, with the READY LED lighting until completion of the sweep.
Back to Oscilloscope Diagram
Ready Indicator
When the reset is single-sweep operation, this lamp lights and remains lit until the sweep
operation is completed.
Back to Oscilloscope Diagram
Horizontal Mode Switch
Used to select the horizontal display mode.
A:
Only A sweep is operative, with the B sweep dormant.
ALT:
A sweep alternates with the B sweep. For this mode of operation, the B sweep appears as
an intensified section of the A sweep.
B:
Only delayed B sweep is operative.
X-Y:
Channel 1 becomes the Y-axis and channel 2 becomes the X-axis for the X-Y operation.
The setting of the vertical MODE and TRIG MODE switches have no effect.
Back to Oscilloscope Diagram
Delay Time Postion Control
Used to set delay time of the B sweep start point from the A sweep start point, if the
HORIZ MODE selector is set to ALT or B position. (Delay time position) It controls delay
time continuously between 0,2 and 10 times of a set value with the A sweep time/div
controller.
Back to Oscilloscope Diagram
CRT Screen
This is where all the output signals will be displayed.
Back to Oscilloscope Diagram
BACK TO MAIN MENU
Oscilloscope Training Package Programmed by Jigar C. Shah NTU Final Year Project.
Copyright © 1997-8 Jigar C Shah
The Oscilloscope
Getting Started : Basic Operating Instructions
OPERATION AS A GENERAL-USE OSCILLOSCOPE
The 5 basic operations of the scope
NORMAL SWEEP DISPLAY OPERATION
MAGNIFIED SWEEP OPERATION
ALTERNATE SWEEP OPERATION
X-Y OPERATION
SINGLE SWEEP OPERATION
BACK TO MAIN MENU
Oscilloscope Training Package Programmed by Jigar C. Shah NTU Final Year Project.
Copyright © 1997-8 Jigar C Shah
The Oscilloscope
Put it to Work : Applications of the Scope
The Oscilloscope KENWOOD TMI's CS -5135
PROBE COMPENSATION
For an accurate measurement, perform appropriate probe correction prior to measurement.
1. Connect a probe to the INPUT terminal, and set each switch so that normal sweep is
displayed.
2. Connect the probe to the CAL terminal on the front panel, and adjust the SWEEP
TIME/DIV switch so that several cycles of this signal are displayed.
3. Adjust compensation trimmer on probe for optimum square wave waveshape (minimum
overshoot, rounding offm and tilt).
TRACE ROTATION COMPENSATION
Rotation from a horizontal trace position can be the cause of measurement errors.
Adjust the controls for a single display. Set the AC-GND-DC switch to GND and TRIG
MODE to AUTO. Adjust the CH1 position control such that the trace is over the centre
horizontal graticule line. If the trace appears to be rotated from horizontal, align it with the
centre graticule line using the TRACE ROTATION control located on the front panel.
Please click on the topics below to learn that application :
1. DC VOLTAGE MEASUREMENT
2. MEASUREMENT OF THE VOLTAGE BETWEEN TWO POINTS ON THE
WAVEFORM
3. ELIMINATION OF UNDESIRED SIGNAL COMPONENTS
4. TIME MEASUREMENTS
5. TIME DIFFERENCE MEASUREMENTS
6. PULSE WIDTH MEASUREMENTS
7. PULSE RISETIME AND FALLTIME MEASUREMENTS
8. PHASE DIFFERENCE MEASUREMENTS
9. FREQUENCY MEASUREMENTS
10. RELATIVE MEASUREMENTS
11. SWEEP MULTIPLICATION (MAGNIFICATION)
12. APPLICATION OF X-Y OPERATION
BACK TO MAIN MENU
Oscilloscope Training Package Programmed by Jigar C. Shah NTU Final Year Project.
Copyright © 1997-8 Jigar C Shah
The Oscilloscope
A - Z : Glossary of terms
AC
(Alternating Current) A signal in which the current and voltage vary in
a repeating pattern over time.
ADC
(Analog-to-Digital Converter) A digital electronic component that
converts an electrical signal into discrete binary values.
Alternate Mode
A display mode of operation in which the oscilloscope completes
tracing one channel before beginning to trace another channel.
Amplitude
The magnitude of a quantity or strength of a signal. In electronics,
amplitude usually refers to either voltage or power.
Attenuation
A decrease in signal voltage during its transmission from one point to
another.
Averaging
A processing technique used by digital oscilloscopes to eliminate noise
in a signal.
Bandwidth
A frequency range.
CRT
(Cathode-Ray Tube) An electron-beam tube in which the beam can be
focused on a luminescent screen and varied in both position and
intensity to produce a visible pattern. A television picture tube is a
CRT.
Chop Mode
A display mode of operation in which small parts of each channel are
traced so that more than one waveform can appear on the screen
simultaneously.
Circuit Loading
The unintentional interaction of the probe and oscilloscope with the
circuit being tested, distorting the signal.
Compensation
A probe adjustment for 10X probes that balances the capacitance of
the probe with the capacitance of the oscilloscope.
Coupling
The method of connecting two circuits together. Circuits connected
with a wire are directly coupled; circuits connected through a capacitor
or a transformer are indirectly (or AC) coupled.
Cursor
An on-screen marker that you can align with a waveform to take
accurate measurements.
DC (Direct Current)
A signal with a constant voltage and current.
Division
Measurement markings on the CRT graticule of the oscilloscope.
Earth Ground
A conductor that will dissipate large electrical currents into the Earth.
Envelope
The outline of a signal's highest and lowest points acquired over many
repetitions.
Equivalent-time Sampling
A sampling mode in which the oscilloscope constructs a picture of a
repetitive signal by capturing a little bit of information from each
repetition.
Focus
The oscilloscope control that adjusts the CRT electron beams to
control the sharpness of the display.
Frequency
The number of times a signal repeats in one second, measured in Hertz
(cycles per second). The frequency equals 1/period.
Gigahertz (GHz)
1,000,000,000 Hertz; a unit of frequency.
Glitch
An intermittent error in a circuit.
Graticule
The grid lines on a screen for measuring oscilloscope traces.
Ground
1. A conducting connection by which an electric circuit or equipment is
connected to the earth to establish and maintain a reference voltage
level.
2. The voltage reference point in a circuit.
Hertz (Hz)
One cycle per second; the unit of frequency.
Kilohertz (kHz)
1000 Hertz; a unit of frequency.
Interpolation
A "connect-the-dots" processing technique to estimate what a fast
waveform looks like based on only a few sampled points.
Megahertz (MHz)
1,000,000 Hertz; a unit of frequency.
Megasamples per second (MS/s)
A sample rate unit equal to one million samples per second.
Microsecond
A unit of time equivalent to 0.000001 seconds.
Millisecond (ms)
A unit of time equivalent to 0.001 seconds.
Nanosecond (ns)
A unit of time equivalent to 0.000000001 seconds.
Noise
An unwanted voltage or current in an electrical circuit.
Oscilloscope
An instrument used to make voltage changes visible over time. The
word oscilloscope comes from "oscillate," since oscilloscopes are
often used to measure oscillating voltages.
Peak - V[p]
The maximum voltage level measured from a zero reference point.
Peak-to-peak - V[p-p]
The voltage measured from the maximum point of a signal to its
minimum point, usually twice the V[p] level.
Peak Detection
An acquisition mode for digital oscilloscopes that lets you see the
extremes of a signal.
Period
The amount of time it takes a wave to complete one cycle. The period
equals 1/frequency.
Phase
The amount of time that passes from the beginning of a cycle to the
beginning of the next cycle, measured in degrees.
Probe
An oscilloscope input device, usually having a pointed metal tip for
making electrical contact with a circuit element and a flexible cable for
transmitting the signal to the oscilloscope.
Pulse
A common waveform shape that has a fast rising edge, a width, and a
fast falling edge.
RMS
Root mean square.
Real-time Sampling
A sampling mode in which the oscilloscope collects as many samples
as it can as the signal occurs.
Record Length
The number of waveform points used to create a record of a signal.
Rise Time
The time taken for the leading edge of a pulse to rise from its
minimum to its maximum values (typically measured from 10% to
90% of these values).
Sample Point
The raw data from an ADC used to calculate waveform points.
Screen
The surface of the CRT upon which the visible pattern is produced the display area.
Signal Generator
A test device for injecting a signal into a circuit input; the circuit's
output is then read by an oscilloscope.
Sine Wave
A common curved wave shape that is mathematically defined.
Single Shot
A signal measured by an oscilloscope that only occurs once (also
called a transient event).
Single Sweep
A trigger mode for displaying one screenful of a signal and then
stopping.
Slope
On a graph or an oscilloscope screen, the ratio of a vertical distance to
a horizontal distance. A positive slope increases from left to right,
while a negative slope decreases from left to right.
Square Wave
A common wave shape consisting of repeating square pulses.
Sweep
One horizontal pass of an oscilloscope's electron beam from left to
right across the CRT screen.
Sweep Speed
Same as the time base.
Time Base
Oscilloscope circuitry that controls the timing of the sweep. The time
base is set by the seconds/division control.
Trace
The visible shapes drawn on a CRT by the movement of the electron
beam.
Transducer
A device that converts a specific physical quantity such as sound,
pressure, strain, or light intensity into an electrical signal.
Transient
A signal measured by an oscilloscope that only occurs once (also
called a single-shot event).
Trigger
The circuit that initiates a horizontal sweep on an oscilloscope and
determines the beginning point of the waveform.
Trigger Holdoff
A control that inhibits the trigger circuit from looking for a trigger
level for some specified time after the end of the waveform.
Trigger Level
The voltage level that a trigger source signal must reach before the
trigger circuit initiates a sweep.
Volt
The unit of electric potential difference.
Voltage
The difference in electric potential, expressed in volts, between two
points.
Waveform
A graphic representation of a voltage varying over time.
Waveform Point
A digital value that represents the voltage of a signal at a specific point
in time. Waveform points are calculated from sample points and stored
in memory.
Z-axis
The signal in an oscilloscope that controls electron-beam brightness as
the trace is formed.
BACK TO MAIN MENU
Oscilloscope Training Package Programmed by Jigar C. Shah NTU Final
Year Project.
Copyright © 1997-8 Jigar C Shah
NORMAL SWEEP DISPLAY OPERATION
a. Press the POWER switch to supply power, and the POWER LED lights
up.
b. A bright line appears in the CRT Centre. If it is not in the centre, adjust
its position to the centre with the CH 1 POSITION controller. Then adjust
the brightness with the INTENSITY controller, and the focus with the
FOCUS controller as required for easy observation.
c. Supply input signal into the CH1 INPUT jack. Rotate the VOLTS/DIV
control to adjust waveform to appropriate dimensions.
Set the MODE select switch to CH2. Then supply the inpu signal to the
CH2 INPUT jack. Its waveform is displayed on the CRT in the same
precedures with channel 1.
When the MODE select switch is set to ADD, the composite waveforms of
CH1 and CH2 (the algebric sum of CH1 + CH2) is displayed on the CRT.
In this status, if CH2 INV is engaged by pulling out the CH2 POSITION,
the algebriac difference between CH1 and CH2 (CH1-CH2) will be
displayed.
The sensitivity of the ADDed waveform becomes the sames as the value
inficated by VOLT/DIV provided that the same as VOLTS/DIV value has
been set for the waveforms of the two channels.
When the MODE select swtich is set to ALT, the channel 1 and channel 2
waveforms are displayed alternatively in every sweep. Waveforms of each
channel is triggered independently. If the MODE select switch is set to
CHOP, channel 1 and channel 2 waveforms through chopped triggering are
displayed. If the SOURCE select switch is set to V.MODE, the channel 1
signal only is triggered. To made the channel 2 signal triggered, set the
SOURCE select switch to CH2.
The display on the screen will probably be unsynchronized. Refer to
TRIGGERING procedure below for adjusting synchronization and sweep
speed to obtain a stable display showing the desired number of waveform.
TRIGGERING
The input signal must be properly triggered for stable waveform
observation. TRIGGERING is possible the input signal INTernally to create
a trigger or with an EXTernally provided signal of timimng relationship to
the observed signal, applying such a signal to the EXT. TRIG INPUT jack.
1. The selection of a signal that serves as a trigger signal is made using the
SOURCE switch.
Internal Sync
When the SOURCE selector is set to V.MODE, CH1, CH2, or LINE, the
input signal is connected to the internal trigger circuit. In this position, a
part of the input signal is fed to the INPUT jack or is applied from the
vertical amplifier to the trigger circuit to cause the trigger signal
synchronously with the input signal to drive the sweep circuit. If the
SOURCE select switch is set to V.MODE, the trigger signal is selected in
compliance with the vertical MODE selector setting. Setting the vertical
MODE selector to ALT causes independent trigger to the channel 1 and
channel 2 signals respectively, enabling two signals with no time
relationship to be observed.
If the SOURCE select swtich is set to CH1 or CH2, triggering is made by
the channel 1 and channel 2 signals respectively, regardless of MODE
setting. Setting the SOURCE select switch to LINE causes synchronisation
with commercial power frequency.
External Sync
When the SOURCE selection is in EXT, th input signal at the EXT TRIG
INPUT jack becomes the trigger. This signal must have a time or frequency
relationship to the signal being observed to synchronise the display.
External sync is preferred for waveform observation in many applications.
For example, the figure below
shows that the sweep circuit is driven bt the gate signal when the gate signal
in the burst signal is applied to the EXT. TRIG INPUT jack.
Shows the input/output signals, where the burst signal generated from the
signal is applied to the instrument under test. Thus, accurate triggering can
be achieved without regard to the input signal fed to the INPUT or jack so
that no further triggering is required even when the input signal is varied.
2. After the SOURCE has been set, the trigger point can be set by rotating
LEVEL/SLOPE control.
AC:
The trigger signal is capacitatively coupled, so its DC component is cut,
giving a stable trigger which is not affected by the DC component. With
this advantage, this position of the coupling switch is conveniently selected
for ordinary applications. However, id the trigger signal is lower than 10Hz,
the trigger signal level becomes attenuated, resulting in difficulty in
triggering.
HFrej:
The trigger signal is supplied through a low pass filter to eliminate the high
frequency component (higher than 10 kHz), giving a stable triggering with
low frequency component. When high-frequency noise is superimposed
over te trigger signal as shown in Fig 9, the high frequency noise is cut to
provide a stable trigger.
DC:
Permits triggering from DC to over 60MHz. Couples DC component of
sync trigger signal. Useful for triggering from very low frequency signals
(below 10 Hz) ot ramp waveforms with slow repeating DC.
3. Setting of coupling switch.
Triggering Level
Trigger point on waveform is adjusted bt the LEVEL/PULL control. Figure
10 shows the relationship between the SLOPE and LEVEL of the trigger
point. Triggering level can be adjusted as necessary.
Auto Trigger
When the TRIG MODE selection is in AUTO, the sweep circuit becomes
free-running s long as there is no trigger signal, permitting a check of GND
level. When a trigger signal is present, the trigger point can be determined
bt the LEVEL control for observation as in the nornal trigger signal. When
the trigger level exceeds the trigger signal, the trigger circuit also becomes
free running where the waveform starts running. When the TRIG MODE is
set to NORM and/or, when the trigger signal is absent or the triggering
level exceeds the signal there is no sweep.
Fix
When the TRIG MODE is set to FIX, triggering is always effected in the
center of the waveform, eliminating the need for adjusting the triggering
level. As shown in Fig 11 (a) or (b), when the TRIG MODE is set to
NORM and the triggering level is adjusted to either side of the signal, the
trigger point is deviated as the input signal becomes small which, in turn,
stops the sweep operation. By setting the TRIG MODE to FIX, the
triggering level is automatically adjusted to the approximate centre of the
waveform and the signal is synchronised regardless of the poistion of
LEVEL control as shown in fig 11(c). When the input signal is suddenly
changed from a square waveform to a pulse waveform, the trigger point is
shifted extremely towards the "-" side of the waveform unless the triggering
level is readjusted as shown in Fig 12(a).
See Fig 12(a)-(2). Also, if the trigger point has been set to the "-" of
squarewave (Fig 12(b)-(1)) and the input signal is changed to a pulse signal,
the trigger point is deviated and the sweep stops. When this happens, set the
TRIG MODE to FIX and the triggerring is effected in the approximate
centre of the waveform, making it possible to observe a stabilised
waveform.
5. Adjust the A SWEEP/TIME DIV control to obtain an appropriate
display. Now a normal sweep display is obtained.
BACK TO MENU
MAGNIFIED SWEEP OPERATION
Since merely shortening the sweep time to magnify a portion of an
observed waveform can result in the desired position disappearing off the
screen, such magnified display should be performed using the
MAGNIFIED SWEEP.
Using the Horizontal POSITION control, adjust the desired portion of
waveform to the CRT. Pull the PULL X 10 MAG control to magnify the
display 10 times. For this type of display the sweep time is the SWEEP
TIME/DIV setting divided by 10.
BACK TO MENU
ALTERNATE SWEEP OPERATION
A sweep and B delayed sweep are usable in an alternating fashion making it
possible to observe both the normal and magnified waveform
silmultaneously.
Procedure:
1. Set the HORIZ MODE to A and adjust for a normal waveform display.
2. Depress the HOLD OFF control and set the HORIZ MODE to ALT.
Adjust TRACE SEPERATION for easy observation of both the A and B
traces. The upper trace is the non-magnified portion of the waveform with
the magnified portion super-imposed as an intensified section. The love
waveform is the intensified portion displayed magnified.
3. The DELAY TIME POSITION control can be used to continuously slide
the magnified portion of the waveform across the A sweep period to allow
magnification or precisely the desired portion of waveform.
4. Set the HORIZ MODE to B to display the INT intensified portion as a
magnified B sweep.
5. For starts AFTER DELAY operation, apparent jitter increases as
magnification increases. To obtaina jitter free display pull the HOLD OFF
control out. In this "Triggerable After Delay" moe the A trigger signal
selected by the SOURCE switch becomes the B trigger source.
FIG11
FIG12
FIG 13
Note that for this type operation both the DELAY TIME POSITION and
TRIG LEVEl affect the start of the B sweep so that the delay time is used as
a reference point.
BACK TO MENU
X-Y OPERATION
For some measurements, an external horizontal deflection is required. This
is also referred to as an X-Y measurement, where the Y input provides
vertical deflection and X input provides horizontal deflection.
X-Y operation permist the oscilloscope to perform many types of
measurements not possible with conventional swep operation. The CRT
display becomes an electronic graph of two instantaneous voltages. The
display may be a direct comparision of two voltages such as during phase
measurement, or frequency measurement with Lissajous waveforms.
To use an external horizontal input, use the following procedure:
1. Set the HORIZ MODE switch to X-Y the position.
2. Use the channel 1 probe for the vertical input and the channel 2 probe for
the horizontal input.
3. Adjust the amouiunt of horizontal deflection with the CH2 VOLTS/DIV
and VARIABLE controls.
4. The CH2 POSITION control now serves as the horizontal position
control and the horizontal POSITION control is disabled.
5. All sync controls are disconnected and have no effect.
BACK TO MENU
SINGLE SWEEP OPERATION
This mode of display is useful for looking at non-synchronous or one time
events.
Procedure:
1. Set the TRIF MODE to either AUTO or NORM. Apply a signal of
approximately the same amplitude and frequency as the disnal thais is to be
obeserved as he tridder signal and set the trigger level.
2. Set TEIG MODE to RESET - observe that the READY indicator LED
lights to indicate the reset condition. This LED goes out when the sweep
period is completed.
3. After the above set up is completed the scope is ready to operate in the
SINGLE sweep ,ode of operation after resetting the instrument using the
RESET switch. Input of the trigger signal results in one and only one sweep
and ready indicator LED goes out.
BACK TO MENU
DC VOLTAGE MEASUREMENT
To measure waveform DC level, carry out the following operations:
1. Connect the signal to be measured to the INPUT jack. For the channel
which is selected by the vertical MODE switch, set the AC-GND-DC
switch to DC and adjust the controls for normal sweep. Then adjust the
VOLTS/DIV and SWEEP TIME/DIV controls to the optimum settings for
measurement of the waveform.
2. Set the TRIG MODE switch to AUTO and AC-GND-DC switch to
GND. The trace displayed at this time is the GND level (reference line).
Using the CH1 POSITION control, adjust the trace position to the desired
reference level position, making sure not to disturb this setting once made.
3. Set the AC-GND-DC switch to the DC position to observe the input
waveform, including its DC component. If an appropriate reference level or
VOLTS/DIV setting was not made, the waveform may not be visible on the
CRT screen at this point. If so, reset VOLTS/DIV and/or the CH1
POSITION control.
4. Use the horizontal POSITION control to bring the portion of the
waveform to be measured to the center vertical graduation line of the CRT
screen.
5. Measure the vertical distance from the reference level to the point to be
measured, (the reference level can be rechecked by setting the
AC-GND-DC switch again to GND).
To obtain the real voltage, multiply the vertical distance value by the
VOLTS/DIV infication value. When a 10:1 probe is used, further multiply
the value by 10. Voltages above and below the reference level are positive
and negative values respectively.
When a 10:1 probe is used:
DC level = Vertical Distance (div) X VOLTS/DIV setting X 10
With direct measurement
DC level = Vertical distance in divisions X VOLTS/DIV setting X (probe
attenuation ratio)
Example
For the example, the point being measured is 3.8 divisions from the
reference level (ground potential).
If the VOLTS/DIV was set to 0.2 V and 10:1 probe was used.
Substituting the given values:
DC level = 3.8 (div) X 0.2 (V) X 10 = 7.6 V
Back to Menu
MEASUREMENT OF THE VOLTAGE BETWEEN
TWO POINTS ON THE WAVEFORM.
This technique can be used to measure peak to peak voltages.
1. Apply the signal to be measured to the INPUT jack. Set the vertical
MODE to the channel to be used. Set the veritical MODE to the channel to
be used. Set the AC-GND-DC to AC, adjusting VOLTS/DIV and SWEEP
TIME/DIV for a normal display. Set the VARIABLE control to CAL
position.
2. Using the CH POSITION control, adjust the waveform position such that
one of the two points falls on a CRT graduation line and that the other is
visible on the display screen.
3. Using the horizontal POSITION control, adjust the second point to
conincide with the centre vertical graduation line.
4. Measure the vertical distance between the two points and multiply this by
the setting of the VOLT/DIV control. When a 10:1 probe is used, further
multiply the value by 10.
When a 10:1 probe is used.
Volts peak-to-peak = Vertical distance (div) X (VOLTS/DIV setting) X 10
With direct measurement
Voltage between 2 points = Vertical distance (div) x 2 points.
Example
For the example, the 2 points are seperated by 4.5 divisions vertically. Set
the VOLTS/DIV setting be 0.2 V/div and the probe attenuation be 10:1.
Substituting the given values:
Voltage between two points = 4.5 (div) X 0.2 (V/div) X 10 = 9.0 V
Back to Menu
ELIMINATION OF UNDESIRED SIGNAL
COMPONENTS
The ADD feature can be conveniently used to cancel out the effect of an
undesired signal component which superimposed on the signal you wish to
observe.
Procedure:
1. Apply the signal containing an undesired component to CH1 INPUT jack
and the undesired signal itself alnoe to the CH2 INPUT jack.
2. Set the vertical MODE switch to CHOP and SOURCE switch to CH2.
Verify that CH2 represents the unwanted signal in reverse polarity. Reverse
the polarity by setting CH2 INV as required.
3. Set the vertical MODE to ADD, SOURCE to V.MODE and CH2
VOLTS/DIV and VARIABLE so that the undesired signal component is
cancelled as much as possible. The remaining signal you wish to observe
alone and free of the unwanted signal.
Back to Menu
TIME MEASUREMENTS
Time between two points on a wave can be measured fromthe SWEEP
TIME/DIV value and horizontal distance between two points.
Procedure:
1. Apply the signal to be measured to the INPUT jack. Set the vertical
MODE to the channel to be used. Set the AC-GND-DC to DC, adjusting
VOLTS/DIV and SWEEP TIME/DIV for a normal display. Set the
VARIABLE control to CAL position.
2. Horizontal position control set to this point at the intersection of any
vertical graduation line. Using the CH POSITION control, set one of the
points to be used as a reference to conincide with the horizontal centerline.
3. Measure the horizontal distance between the two points. Multiply this by
the setting of the SWEEP TIME/DIV control to obtain the time between the
two points. If horizontal "X 10 MAG" is used, multiply this further by 1/10.
Using the formula :
Time = horizontal distance (div) X (SWEEP TIM/DIV setting) / "X 10"
value
Example
For the example, the horizontal distance between the 2 points is 5.4 sweep
divisions. If the SWEEP TIME/DIV is 0.2ms/div we calculate.
Substituting the given value:
Time = 5.4 div X 0.2 ms/div = 1.08ms
Back to Menu
TIME DIFFERENCE MEASUREMENTS
Time difference between two synchronised signals can be measured as
follows:
Procedure:
1. Apply the 2 signals to CH1 and CH2 INPUT jacks. Setting the vertical
MODE to either ALT or CHOP mode. Generally for low frequency signals
CHOP is chosen with ALT used for high frrequency signals.
2. Select the faster of the two signals as the SOURCE and use the
VOLTS/DIV and SWEEP TIME/DIV to obtain an easily observed display.
Set the VARIABLE control to CAL position.
3. Using the vertical POSITION control set the waveform to the center of
the CRT display and use the horizontal POSITION control to set the
reference signal to be coincident with a vertical graduation line.
4. Measure the horizontal distance between the two signals and multiply
this distance in division by the SWEEP TIME/DIV setting.
If "X 10 MAG" is being used multiply this again by 1/10.
Using the formula:
Time = Horizontal distance X (SWEEP TIME/DIV setting) / "X10 MAG"
value
Example
For the example, when the horizontal distance between two signals is 4.4
divisions. The SWEEP TIME/DIV is 0.2 (ms/div)
Substituting the given value:
Time = 4.4 (div) X 0.2 (ms/div) = 0.88ms
Back to Menu
PULSE WIDTH MEASUREMENTS
Pulse width can be measured as follows:
Procedure:
1. Apply the pulse signal to the INPUT jack. Set the vertical MODE switch
to the channel to be used.
2. Use the VOLTS/DIV, VARIABLE and vertical POSITION to adjust the
waveform such that the pulse is easily observed and such that the center
pulse width conincides with the center horizontal line on the CRT screen.
3. Set the SWEEP VARIABLE switch to CAL. Measurement the horizontal
distance between the intersections of the pulse waveform and CRT center
horizontal line in divisions, and multiply the measured distance by the value
indicatedby SWEEP TIME/DIV. If the "X10 MAG" mode is being used,
also multiply the product by 1/10.
Using the formula:
Pulse width = Horizontal distance (div) X (SWEEP TIME/DIV setting) /
"X10 MAG" value.
Example
For the example, the distance at the center horizontal line is 4.6 divisions
and the SWEEP TIME/DIV is 0.2 (ms/div)
Substituting the given value:
Pulse width = 4.6 (div) X 0.2 (ms/div) = 0.92 ms
Back to Menu
PULSE RISETIME AND FALLTIME
MEASUREMENTS
For risetime and falltime measurements, the 10% and 90% amplitude points
are used as starting and ending reference points.
Procedure:
1. Apply a signal to the INPUT jack. Set the vertical MODE to the channel
to be used.
Use the VOLTS/DIV and VARIABLE to adjust the waveform peak-to-peak
height to five divisions.
2. Using the vertical POSITION control and the other controls, adjust the
display sich that the wavedoem is centered vertically in the display. Set the
SWEEP TIME/DIV to as fast a setting as possible consistent with
observation of both the 10% and 90% points. Set the SWEEP VARIABLE
control to CAL position.
3. Use the horizontal POSITION control to adjust the 10% point to coincide
with a vertical graduation line and measure the distance in divisions
between the 10% and 90% points on the waveform. Multiply this by the
SWEEP TIME/DIV and also by 1/10 if "X10MAG" mode was used.
NOTE:
The graticule on the CRT includes the 0, 10, 90, and 100 % lines assuming
that 5 divisions correspond to 100 %. Use them as a reference for accurate
measurements.
Using the formula:
Risetime = Horizontal distance (div) X (SWEEP TIME/DIV setting) / "X10
MAG" value.
Example
For the example, the horizontal distance is 3.3 divisions. The SWEEP
TIME/DIV is 2 (us/div)
Substituting the given value:
Risetime = 3.3 (div) X 2 (us/div) = 6.6 us
Risetime and falltime can be measured by making use of the alternate step 3
as described below as well.
4. Use the Horizontal POSITION control to set the 10% point to coincide
with the center vertical graduation line and measure the horizontal distance
to the point of the intersection of the waveform with the center horizontal
line. Let this distance be D1. Next adjust the waveform position such that
the 90% point coincides with the vertical centerline and measure the
distance from that line to the intersection of the waveform with the
horizontal centerline. This distance is D2 and the total horizontal distance is
then D1 plus D2 for use in the above relationship in calculating the risetime
or falltime.
Using the formula:
Risetime = (D1 + D2) (div) X (SWEEP TIME/DIV setting) / "X10 MAG"
value.
Example
For the example, the measured D1 is 1.6 divisions while D2 is 1.4
divisions. If SWEEP TIME/DIV is 2 us/div we use the following
relationship.
Substituting the given value:
Risetime = (1.6 + 1.4) (div) X 2 (us/div) = 6 us
Back to Menu
PHASE DIFFERENCE MEASUREMENTS
Phase difference between two sine waves of the same frequency can be
measured as follows:
Procedure:
1. Apply the 2 signals to the CH1 and CH2 INPUT jacks, setting the
vertical MODE to either CHOP or ALT mode.
2. Set the controls to obtain normal sweep. Set the SOURCE switch to
select the signal which is leading in phase, and adjust the VOLTS/DIV and
vertical VARIABLE controls such that the two signals are equal in
amplitude.
3. Use the SWEEP TIME/DIV and SWEEP VARIABLE to adjust the
display such that one cycle of the signals occupies 8 divisions of horizontal
display.
Operate the vertical POSITION to shift the two signals on the center of the
scale.
Having set up the display as above, one division now represents 45 degrees
in phase.
4. Measure the horizontal distance between corresponding points on the two
waveforms.
Using the formula:
Phase difference = Horizontal distance (div) X 45 degrees/div
Example
For the example, the horizontal distance is 1.7 divisions.
Substituting the given value:
The phase difference = 1.7 (div) X 45 degrees/div = 76.5 degrees.
The above setup allows 45 degrees per division but if more accuracy is
required the SWEEP TIME/DIV may be changed and magnified without
touching the VARIABLE control and if necessat the trigger level can be
readjusted.
In this case, the phase difference can be obtained from the SWEEP
TIME/DIV setting for 8 divisions.cycle and the new SWEEP TIME/DIV
setting changed for higher accuracym by using the following formula:
Phase difference = Horizontal distance of new sweep range X 45
degrees/div
X New SWEEP TIME/DIV setting
Original SWEEP TIME/DIV setting
Another simple method of obtaining more accuracy quickly is to simply use
X 10 MAG for a scale of 4.5 degrees/division.
One cycle adjusted to occupy 8 div
Expanded sweep waveform display.
Back to Menu
FREQUENCY MEASUREMENTS
Frequency measurement are made by measuring the period of one cycle of
waveform and taking the reciprocal of this time value as the frequency.
Procedure
1. Following the procedure described in section 5 "Time Measurement",
measure the time of each cycle. The figure obtained in the signal period.
2. Frequency is the the reciprocal of the period measured.
Using the formula:
Frequency = 1/period.
Example
A period of 40us is observed and measured.
Assuming that SWEEP TIME/DIV indicated 5 us/div, sustituting the given
value:
Frequency = 1/(40us) = 25 kHz
While the above method relies on the measurement directly of the period of
one cycle, the frequency may also be measured by counting the number of
cycles present in a given time period.
1. Apply the signal to the INPUT jack. Set the vertical MODE to the
channel to be used and adjusting the various controls for a normal display.
Set the VARIABLE control to CAL position.
2. Count the number of cycles of waveform between a chosen set of
graticules in the vertical axis direction. Using the horizontal distance
between the vertical lines used above and the SWEEP TIME/DIV, the time
span may be calculated. Multiply the reciprocal of this value by the number
of cycles present in the given time span. If "X10 MAG" is used multiply
this by a further 10.
Note that errors will only occur for displays having only a few cycles.
Using the formula :
Frequency =
Example
For the example, within 7 divisions, there are 10 cycles. The SWEEP
TIME/DIV is 5us/div.
Substituting the given value:
Freq =
Back to Menu
RELATIVE MEASUREMENTS
If the frequency and amplitude of some reference signals are known, an
unknown signal may be measured for level and frequency without use of
the VOLTS/DIV or SWEEP TIME/DIV for calibration.
The measurement is made in units relative tothe reference signal.
Vertical sensitivity
Setting the relative vertical sensitivity using a reference signal.
Procedure:
1. Apply the reference signal to the INPUT jack and adjust the display for a
normal waveform display.
Adjust the VOLTS/DIV and VARIABLE so that the signal conincides with
the CRT face's graduation lines. After adjusting, be sure not to disturb the
setting of the VARIABLE control.
2. The vertical calibration coefficient is now the reference signal's
amplitude (in volts) divided by the product of the vertical amplitude set in
step 1 and the VOLTS/DIV setting.
Using the formula:
Vertical coefficient= Voltage of the ref signal/vertical amplitude
3. Remove the reference signal and apply the unknown signal to the INPUT
jack, using the VOLTS/DIV control to adjust the display for easy
observation. Measure the amplitude of the displayed waveform and use the
following relationship to calculate the actual amplitude of the unknown
waveform.
Using the formula
Amplitude of the unknown signal =
Example
For the example, the VOLTS/DIV is 1V/div.
The reference signal is 2 Vrms. Using the VARIABLE, adjust so that the
amplitude of the reference signal is 4 divisions.
Substituting the given value:
Vertical coefficient =
Then measure the unknown signal and VOLTS/DIV is 5V and vertical
amplitude is 3 divisions.
Substituting the given value:
Effective value of unknown signal = 3 (div) X 0.5 X 5
Period
Setting the relative sweep coefficient with respect to a reference frequency
signal.
Procedure:
1. Appy the reference signal to the INPUT jack, using the VOLTS/DIV and
VARIABLE to obtain an easily observed waveform display.
Using the SWEEP TIME/DIV and VARIABLE adjust one cycle of the
reference signal to occupy a fixed number of scale divisions accurately.
After this is done be sure not to disturb the setting of the VARIABLE
control.
2. The sweep (horizontal) calibration coefficient is then the period of the
reference signal divided bt the product of the number of divisions used in
step 1 for setup of the reference and seting of the SWEEP TIME/DIV
control.
Using the formula:
Sweep coefficient =
3. Remove the reference signal and input the unknown signal, adjusting the
SWEEP TIME/DIV conrtol for easy observation.
Measure the width of one cycle in divisions and use the following
relationship to calculate the actual period.
Using the formula:
Period of unknown signal =
Example
SWEEP TIME/DIV is 0.1 ms and apply 1.75 kHz reference signal. Adjust
the VARIABLE so the the distance of one cycle is 5 divisions.
Substituting the given values.
Horizontal coefficient =
Then, SWEEP TIME/DIV is 0.2 and horizontal amplitude is 7 div
Substituting the given value:
Pulse width = 7 (div) X 1.143 X 0.2 = 1.6 ms
Back to Menu
SWEEP MULTIPLICATION (MAGNIFICATION)
The apparent magnification of the delayed sweep is determined by the
values set by the A and B SWEEP TIME/DIV controls.
1. Apply a signal to the INPUT jack and set the vertical MODE tothe
channel to be used, adjusting the VOLTS/DIV for an easily observed
display of the waveform and the other controls if necessary.
2 Set the A SWEEP TIME/DIV so that several cycles of the waveform are
displayed. Depress the HOLD OFF control to (AFTER DELAY).
When the HORIZ MODE is set to INT, the magnified portion of the
waveform will appear intensified o the CRT display.
3. Use the DELAY TIME MULT to shift the internsified porttion of the
waveform to correspond with the section to be magnified for observation.
Use the B SWEEP TIME/DIV to adjust the intesified portion to cover the
entire portion to be magnified.
4. Set the HORIZ MODE to either ALT or B and use the POSITION and
TRACE SEPERATION controls to adjust the display for easy viewing.
5. Time measuements are performed in the same manner from the B sweep
as was described above for A sweep time measurements.
The apparent magnification of the intensified waveform section is tha A
SWEEP TIME/DIV divided by the B SWEEP TIME/DIV.
Using the formula:
The apparent Magnification
of the Intensified Waveform
Example:
In the example, the A SWEEP TIME is 2us and the B SWEEP TIME is 0.2
us.
Substituting the given value:
Apparent magnification ratio:
With the above magnification, if the magnification ratio is increased, delay
jitter will occur.
To achieve a stable display, set the B MODE to TRIG and used the
triggered mode of operation.
1. Perform the above steps 1 through 3.
2. Pull the HOLD OFF control to activate B TRIG'D function.
3. Set the HORIZ MODE to either ALT or B. The apparent magnification
will be the same as described above.
Back to Menu
APPLICATION OF X-Y OPERATION
Phase shift measurement
A method of phase measurement requires calculations based on the
Lissajous patterns obtained using X-Y operations. Distortions due to a
non-linear amplification also can be displayed.
A sine wave input is applied to the audio circuit being tested. The same sine
wave input is applied to the vertical input of the oscilloscope, and the
output of the tested circuit is applied to the horizontal input of the
oscilloscope. The amount of phase difference between the two signals can
be calculated from the resulting waveform.
To make phase measurements, use the following procedure.
1. Using an audio signal generator witha a pure sinosoidal signal, apply a
sine wave test signal at the desired test frequency to the audio network
being tested.
2. Set the signal generator output for the normal operating level of the
circuit being tested. If desired, the circuit's output may be observed on the
oscilloscope. If the test circuit is overdriven, the sine wave display on the
oscilloscope is clipped and the signal level must be reduced.
3. Connect the channel 2 probe to the output of the test circuit.
4. Select X-Y operation by placing the TRIG MODE switch in the X-Y
position.
5. Connect the channel 1 probe to the input of the test circuit.
(The input and output test connections to the vertical and horizontal
oscilloscope inputs may be reserved).
6. Adjust the channel 1 and 2 gain controls for a suitable viewing size.
7. Some typical results are shown in Fig 4.7.
If the two signals are in phase, the oscilloscope trace is straight diagonal
line. If the vertical and horizontal gain are properly adjusted, this like is at a
45 degree angle. A 90degree phase shift produces a circular oscilloscope
pattern.
Phase shift of less that 90 degrees produces an elliptical oscilloscope
pattern. the amoint of phase shift can be calculated from the oscilloscope
trace as shown in Fig below.
Frequency measurement
1. Connect the sine wave of known frequency to the channel 2 input jack of
the oscilloscope and select X-Y operation. This provides external horizontal
input.
2. Connect the vertical input probe (CH1 INPUT) to the unknown
frequency.
3. Adjust the channel 1 and 2 size controls for convenient, easy to read size
of display.
4. The resulting pattern, called a Lissajous pattern, shows the ratio between
the two frequncies.
Back to Menu