# Question: Learning How To Use Hand Held Oscilloscope

Discussion in 'Electronic Basics' started by Chris L, Nov 11, 2007.

1. ### Chris LGuest

Hello, I've been trying to learn how to use my new Protek 800 series
hand held Digital Oscilloscope.

So, I connected the single oscilloscope probe to the output of a used
function generator that I bought on EBay.

On oscilloscope auto, what I see is a waveform that I can only
describe as a repeating sinc function. When I increase the frequency
of the sine wave on the generator, I see more and more tiny waves
appear in this sinc-like function. If I increase the amplitude on the
generator I see these tiny waveforms in the sinc-like waves increase
in amplitude.

This seems strange to me because I set the function generator for a
repeating sine wave, but what I see is this repeating sinc-like
waveform. The sinc waveform becomes more and more detailed.

How do I get a repeating sine wave without the sinc?

I set the oscilloscope to auto and the resulting setting are:

20V/div, 200mV/time div
coupling is AC
probe set to 1X
Trigger set to edge and slope set to rising

If I try fooling around with the various setting I cannot improve
things.

Setting trigger to pulse, pattern, or video did not help.

Setting coupling to DC or ground did not help.

If I set the time division very low (micro divisions) to zoom in on my
tiny
sine waves they still seem to want to float around.

What do I do?

Thank you,
Christopher Lusardi

2. ### Michael BlackGuest

Most function generators approximate a sinewave. They are great
at generating triangle waves, and the square waves that are a byproduct,
but the sinewave is created by "smoothing" the triangle wave, usually
by a circuit of diodes and resistors.

Function generators are general purpose devices, and their sinewave
out put is good enough for what they are intended for.

If you need a perfect sinewave, then you choose a generator that
starts with a sinewave, or at the very least uses frequency filtering
to get the sinewave. But, those are usually cumbersome to switch
bands, and add a lot of overhead to the timing so rapidly sweeping
the generator is not in the picture.

If you are seeing the sinewave become smoother the higher the
frequency, likely you are seeing the frequency response of the scope
kick in. Once you start hitting its limits, its frequency response
will affect the waveform. Use a high enough frequency, or a scope
with a low enough response, and the scope loses much of its purpose,
since you can't tell whether that sinewave is really a sinewave, or
the frequency response of the scope is turning a signal into a sinewave.

Michael

3. ### Peter BennettGuest

What exactly do you mean by a "sinc function"? My first thought was
that "sinc" was a typo for "sine", but it apparently isn't.

Can you describe the display more clearly, or better, put a picture of
it on a web site somewhere - then we'll have a better idea of what you
are seeing.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

4. ### JamieGuest

I think he has the unit set up incorrectly. It's generating 10% or duty
cycle pulses for example.

5. ### Richard SerianiGuest

Peter,

For info on sinc function, see
http://mathworld.wolfram.com/SincFunction.html

Chris L,
I'm not familiar with your particular o'scope (and I haven't time to look up
the user's manual), but check to see if it has an FFT function and that it
is turned off.

Good luck,
Richard

6. ### Bob MastaGuest

You can use the FREE signal generator that comes in my Daqarta
software package. That will give you known-good waveforms to test,
and it also displays the waveforms (or spectra) with advanced
triggering options so you can compare with the hand-held. The only
downside is that since it uses your computer's sound card, you will be
limited to audio-range signals (few Hz to 22 kHz, typically).

There is no need to purchase Daqarta for this. The signal generator
and all the display functions (and most everything else except signal
inputs) will continue to work after Daqarta's trial period expires.
You are welcome to use it this way as long as you like.

Best regards,

Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator

7. ### Chris LGuest

Hello, I went to Frys Electronics and bought a \$350 function
generator, hooked it up, and got the exact same plot on the
oscilloscope.

What the plot looks like is this: consider a repeating sine wave. It
has 2 large side lobes which are smaller than the middle lobe. This
repeats the same way a sine wave repeats. If I then increase the
frequency on the function generator these repeating waves become more
developed/detailed.

It may be because the oscilloscope triggering is wrong!
/\
/ \
/\ / \ /\
/ \/ \/ \ ...

If increase frequency I get :
./\.
./ \.
../\. / \../\.
/ \/ \/ \ ...
/\
Consider the dots to be / \. I.E.: Little sine waves

What should I do?

Chris Lusardi

8. ### Bob MastaGuest

What is the test frequency, and what is the sample rate of the scope?
What you describe sounds like what you see when the sample rate is
too slow for the test frequency. Adjacent samples on the display
don't come from the same waveform cycle, but from subsequent cycles
whenever the A/D gets back to fetch them. Since there is no sync
between the sample rate and the input signal, they don't form a single
complete waveform.

You can try reducing the signal way down (say, a few 100 Hz) and see
if that gives a clean trace, then slowly bring up the frequency.

Digital scopes typically have a way to avoid this problem by sampling
only every Nth sample on the first trigger, then on the next trigger
they add a one-sample delay and again grab every Nth sample, etc.
So if N = 4, the first trigger will get samples 0, 4, 8, 12 ... Then
the second trigger will get 1, 5, 9, 13..., the third will get 2, 6,
10, 14..., the fourth will get 3, 7, 11, 15... and the display will
put them all in the correct order.

I couldn't find any on-line info about the Protek 800, so I don't know
what its intrinsic sample rate is, or what they label the controls
that activate the above mechanism. But I bet it's covered in the
manual. <g>

Best regards,

Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator

9. ### Chris LGuest

Can the below information solve the problem?

Christopher Lusardi

The Operator's Manual says:
Product Standards and Specifications

Model 840
Bandwidth/
Sample Rate 400MHZ
Real Sampling 100MS/s per Channel, 200 MS/s Single
Channel with 2.5 GS/s Repetive Sampling

2 Input channels
input coupling: DC, AC, GND
input impedance IM +/- 1%, 20pF +/- 2pF
Probe attenuation x1 or x10
Max Input 300V direct input, 600V through 10:1 probe

Vertical
vertical resolution 8 bit
Volts/div range 5mV/div ~100V/div(1,2,5 step)
offset position +/- 5 div from center
vertical accuracy +/- 3%

Horizontal
Sec/Div Range 10ns/div ~ 50s/div
time base accuracy +/- 0.01%
Position Range pre-Trigger:20 div max. Post-Trigger: 1000div
Delay Resolution 1/250 of screen diameter
delay accuracy 0.04 divisins
delta time measurement accuracy +/- 3%
Modes Main, XY
XY Yes
Horizontal Pan and Zoom Yes

Trigger
Sources Channel A and B
Modes Normal, single, roll, auto trigger
Advanced selections edge, pulsewidth, pattern video
edge : trigger on a rising or falling edge of any source
pulsewidth: trigger on a positive or negative pulsewidth of any source
larger than, less than, equal to or not equal the duration
width 200nS ~ 10S
TV: NTSC, PAL, SECAM, Normal Video, Even field, Odd field, Line
#select
TV Sensitivity: 0.7 div trigger level
auto scale : yes
range: +/- 10 div from center of screen
Level Accuracy +/- 0.4 divisions
Level resolutions: 500 pixels
sensitivity: DC 5MHz - 0.5 div 1.5 divisions
noise rejections : yes
Coupling Modes: DC: DC Coupled trigger
AC: AC Coupled trigger cutoff frequency < 1HZ
HF-Refject: > 50KHz
LF-Reject: > 30KHz
Noise Reject: 3 times the DC coupled limits

Acquistion
Real-Time: 200MS/s single channel
Sample Rate : 100MS/s per channel
Waveform Interpolation : Dot, Linear, Sine, Pulse
Record Length: 125 Kbytes/channel
Acquisition Mode: Sample, Peak detect, envelope, average
peak detection: 10ns
Average: 2-256
Vertical resolution: 8 bit
same rate accuracy: 100ppm
Minimum sample rate: 100MS/s (250 ns to 50S/div)

Measurement
Automatic Measurement: Peak-to-peak, Maximum, amplitude, top,
base, positive/negative overshoot, preshoot,
RMS mean, one cycle mean, frequency
period, + width, - width, + - duty cycle, rise
time, fall time, delay, phase shift
Waveform math: Ch A + Ch B, Ch A - Ch B, Ch B - Ch A
Cursors : delta V voltage
Delta V : voltage diff between cursors
Delta T: Time difference between cursors
FFT : Model 840
Windows : Rectangular, Hamming, Hanning, Blackman-Harris
Amplitude Display: Variable dB (1/2/5/10 dB)
Maximum Frequency: 1.25 GHz

10. ### Peter BennettGuest

<further specs snipped...>

Not really - of more importance is the frequency and voltage of the
signal you are measuring, and the sweep rate, vertical gain and
trigger settings of the scope when you are doing these measurements.

A silly question: do you have the scope ground connected to the signal
generator? You can get very strange displays if you only connect the
signal lead (tip of the test probe) without any ground connections.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

11. ### Chris LGuest

Your silly question has almost completly solved the problem!

My function generator has 3 connections for oscillocope probes plus 2
connections for a multi-meter. The oscilloscope connections are
labelled,

Input VCF
Output TTL/CMOS
Output 50 Ohms with a ground symbol

The oscilloscope has 2 connections. One for channel A and one for
channel B.

Via buttons, if I set the oscillocope channels A and B both on. And,
connect channel A to either Input VCF or Output TTL/CMOS with channel
B connected to the Output 50 Ohms I get the correct sine, square, and
trianular waves.

Five questions:

1. Is this the correct way to measure the signals?
2. Why can I connect channel A to both Input VCV and Output TTL/CMOS?
3. Does it matter what I connect channel A to?
4. How do I keep my oscilloscope operating correctly?
5. Is there anything else that I have to explicitly be reminded about?

Many thank yous,
Christopher Lusardi

12. ### David L. JonesGuest

That is not a "connection for an oscilloscope", it is an input signal
which can be used to modulate the output signal. You don't need to
That is a 5V square wave output. You won't get a sine or triangle wave
out of this.
This is the "normal" sine/square/triangle output.
Yes. With the exception of connecting to the VCF input which is
incorrect.
You can connect either the TTL output or the "50 ohm" output to either
Connecting the VCF input will do nothing.
You connect Channel A to whatever signal you want to measure with
Channel A.
Ensure you know how to use it correctly. An oscilloscope is a complex
measurement tool that can operate in many different ways, you need to
read some tutorials that explain how they work and how to use them.

Dave.

13. ### David L. JonesGuest

What you have here is a "digital storage" oscilloscope, not exactly
the best tool for a beginner.
You should be starting out with a basic "analog" oscilloscope.
Digital storage oscilloscopes have many ways in which they can play
tricks on you if you don't know how to use them correctly.

Dave.

14. ### Peter BennettGuest

(I assume you mean function generator connections)
That would be an input to the function generator - from the "VCF" I
might guess that applying a varying voltage to that connector would
vary the output frequency of the generator.
Probably a signal intended to be used to trigger the sweep on an
oscilliscope.
That would be the actual signal output.
You also need to look at the scope trigger settings. If you connect
the 'scope's "A" input tor the signal generator main output, you
should set the 'scope trigger input to "A", and other trigger settings
to "AC" and "Auto", as well as setting the time base to something
suitable for the signal you are measuring.

Sometimes it is useful to trigger the scope directly from the signal
generator, rather than from the signal you are measuring - for that
use, you could set the trigger source to "B", and connect the "B"
probe to the TTL/CMOS output of the signal generator. Many scopes
have a separate trigger input for this sort of application.

It depends a lot on what you are trying to measure, and why.
Carefully study the manuals for both your signal generator and
oscilliscope, and try playing around (sorry - experimenting with) the
various controls on both the signal generator and scope to see what
happens. You are unlikely to damage anything (unless you try
measuring 120VAC). As others have said, search the web for
oscilliscope tutorials. (You may find some useful tutorials on
Tektronix and other scope manufacturers' web sites.)
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter

15. ### Chris LGuest

Well my current investigation has hit a roadblock where I have to try
and alternate route.

I was successful at using channel A for input and channel B for ground
a few days ago with sinewave, triangle wave, and square wave. I
connect channel B to the function generator with a banana clip, but I
just touched the channel probe A to the function generator output.

I cannot, now, reproduce what I did earlier in the week! With the
manual on my lap, I tried and tried. The only thing I get is a square
wave which I can change the frequency but not the amplitude.

I was thinking the reason it initially worked was I worked a long time
with one probe and channel A. And, the scope requires the probe to be
tested (calibrated) before use. Maybe after the scope was shut off I
calibrate the probe(s) incorrectly!

Chris L.

16. ### Bob MastaGuest

Hmm, this all sounds really strange. What sort of connectors do you
have on your scope inputs? Typically, scopes use BNC connectors,
where the outer shell is ground and the inner pin/socket is the
signal. If your signal is going into channel A input, you would
connect its ground via the channel A connector. The scope probe
should have a point or a clip for the signal, and probably a little
collar for the ground lead. The ground lead will usually have an
alligator clip on the end, and a "U"-type clip to attach to the probe
collar.

Channel B is for the purpose of seeing a second signal trace on the
screen at the same time as A. It is not for grounding A.

Best regards,

Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator

17. ### Chris LGuest

I went home and tried it because it was on my mind.

If I hook only one probe up to the function generator (by touching the
point of the probe for channel A to the f.g. output, and clip the
banana clip from the metal base of the probe to the function generator
ground) I get square waves.

If I switch the f.g. function from square waves to sinwaves or to
triangle waves the oscilloscope still displays square waves.

I am able to increase or decrease the frequency, but tweeking the f.g.
amplitude knob does nothing.

(I also, later, tried substituting a channel B probe [after
calibrating the channel A probe] for the banana clip to the f.g.
ground but without success.)

Happy Thanksgiving,
Chris Lusardi

PS: I do own copies of the following books but they have not helped,
yet: The XYZ's of Oscilloscopes by Tektronix , How to Use
Oscilloscopes and Other Test Equipment by R. A. Penfold, and 101 Ways
to use your... Oscilloscope by Robert Middleton.

18. ### EcnerwalGuest

Sounds like you are on the "sync" output of the function generator, not
the actual normal output - behaves exactly as described - constant
amplitude (generally TTL logic levels) and variable frequency, but
always square waves. Used to synchronize a scope or some other thing
(nice sharp trigger signal) to the normal output (different waveforms
and amplitudes).

19. ### David L. JonesGuest

Sounds like you are using the TTL output of the generator. That output
will *always* give you a square wave at the *same* voltage, onyl the
frequency will change. The "50 ohm" output is the one that produces
sine/square/triangle with varying amplitude.
You only need *one* connection between your function generator and
oscilloscope.
That connection should be a BNC cable, with a BNC connector on both
ends. If your function generator is an older style one then it may
have banana plugs, in which case you simply connect your CRO probe to
the two banana terminals, ground clip on the black plug, tip of the
probe on the red plug.

Then it's simply a matter of operating both your oscilloscope and
function generator to get the correct waveform. Forget channel 2, it
is obviously confusing the situation.

For the purposes of getting a waveform on the screen your probe does
not need to be calibrated.

Post a photo so everyone is clear what is happening here.
And get yourself an analog oscilloscope.

Dave.

20. ### Chris LGuest

I think I've got it, and I helped a little!

If I use one probe with an attached wire/clip at the base of the probe
I am able to to see sine waves, triangular waves, and square waves. In

The function generator has an output labelled output 50 Ohms with a
ground symbol. This output is a connection for a BNC probe.

When I touch the pointer of the probe into the hole of this function
generator output with the clip attached to the raised portion of the
connection for the BNC probe, it works.

Question: What is so great about an analog oscillocope? Can't I just
live with what I have.

FYI, I can, now, attempt to use the function generator and digital
oscilloscope with my expensive Lab-Volt system (I got it on EBay at a
great discount). This system comes with a computer, program lessons,
and 16 circuit boards. The circuit boards look exactly like regular
circuits with transistors, resitors, voltage source, function
generator connections, etc, etc, etc.

There are many holes in the circuit boards where I can connect the
oscilloscope, and function generator probes. The system has a few
small 2 post connectors to connect different portions of the circuit.
The Lab-Volt system comes with its own power source +/- 15 Volts.

For example, the generator symbol on one of the boards has holes where
you can hook-up the function generator outputs. Question: What is the
best way to do this? I'm going to try to connect the function
generator probe with a clip wire on the metal base of the probe to
opposite holes of the function generator symbol on the boards. The Lab-
Volt system has a few metal posts that I can stick into the holes for
the probe clips.

The power source symbol on the same board has an arrow through it, and
two holes on either side of it. The positive side is the one closest
the arrow head. Question: What is the best way to hook-up the
oscilloscope to the board? I'm going to experiment with this.

Thanks and I hope I did not bore everyone,
Christopher Lusardi