Question: Learning How To Use Hand Held Oscilloscope

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

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

--
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Real Programmers Do things like this.
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Peter,

For info on sinc function, see

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

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

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

quoted text -

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

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.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

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

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
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Vancouver Power Squadron: http://vancouver.powersquadron.ca

Your silly question has almost completly solved the problem!

Can you give me more information?

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

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 worry about this.

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 channel on your oscilloscope. 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.

Type "oscilloscope tutorial" into Google.

Dave.

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.

(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
Vancouver Power Squadron: http://vancouver.powersquadron.ca

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.

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

Scope, Spectrum, Spectrogram, FREE Signal Generator Science with your sound card!

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.

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).

--
Cats, coffee, chocolate...vices to live by

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.

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 addition, I am able to adjust the amplitude.

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