OK…there it is. It’ll make all EEs scream. But, for goodness sake, what do these silly scopes tell you? So you can produce some waves on your screen. Whoopie! What do these devices really do for a lab technician? …Or, maybe the forgotten TV repair man? - Jinx
You don’t produce the waves on the screen - you view them - it visually displays the shape, wavelength and amplitude of a waveform; this has all manner of uses inclusing analysing sounds and testing response times in electronic circuits
They tell you something about the signal. At a simple level, such as for a sine wave, amplitude, distortion, DC offset, and wavelength. For digital signals, you can look for rise time, pulse width, ringing, glitches, proper levels. It’s one of the most useful pieces of test equipment in the lab. With a dual-trace scope, you can compare two signals. Many modern scopes can do automated measurements, so that you don’t have to count reticle lines and compute the value by hand. Some scopes have a built-in memory for displaying events that only happen once. An oscilloscope displays a signal in the time domain, while a spectrum analyzer displays it in the frequency domain.
Nowadays you don’t see as many 'scopes – a lot of the capabilities are available using Analog-to-Digital samplers that can be put on computer boards, so instead opf having a big bulky Tektronix scope, filled with high voltage sources and ceramic insulayors (or even a cute little compact scope with small profile and itty-bitty screen) , you can directly pipe the output into your computer and analyze it there.
You can see the delay and degradation in signals. By putting your original signal in the first channel, and then the signal after processing in the second, you can compare the two signals and see what has happened in between.
In the world of electronics, things are always changing over time. Like voltages. And currents. As an example, whenever a voltage is used to represent a communication signal, the voltage must be changing over time.
This begs the question, of course: how is an engineer susposed to measure a voltage that is changing over time? One way is to hook up a benchtop voltmeter to the circuit and monitor/record the voltage over time. But this usually doesn’t work too well. Most voltmeters are very “slow.” They can’t measure voltages that change very fast. Even if they could, you wouldn’t be able to write down the values fast enough.
That’s where an oscilloscope comes in. An oscilloscope is an instrument that provides a real-time graphical display of the voltage over time. (The voltage is on the Y-axis, and time is on the X-axis.) A modern oscilloscope is very fast… it can show changes in a voltage with a resolution of a nanosecond.
We could also talk about analog vs. digital scopes, fast ADCs, real-time vs. off-line, time domain vs. frequency domain representations of the signal, etc. But that will only muddy the issue.
Indeed. PC oscilloscopes are a useful kind of “hybrid” - a USB-connected box samples the signal, and PC software displays it.
Let’s say you have a sine wave, and you want to turn it into a square wave. You pass it through a filter, but filters aren’t perfect, and the end result isn’t really a perfect square wave. An oscilloscope lets you see what’s wrong with it, so you can fine tune your filters.
Yeah, they’re nifty cool. One channel is good, but two is way better. IIRC, back when my friend and I did that kind of thing we would most often view the clock signal or the input signal on one, and the output on the other, and figure out just what exactly the thing we built was doing instead of what we wanted it to do.
If you want to get super-cheap, what is your audio card but an A-D sampler? You can buy (or build) a small box to complete the interface between your probes and your card. There’s a bunch of software around to support that kind of thing.
What the others said.
The vertical setting of an analogue 'scope allows you to wave a spot of light up and down on the screen according to the incoming voltage… and the horizontal setting moves that spot left to right at a user-selectable rate. The faster you move it left to right (up to the limits of the instrument), the more spread-apart each change in the incoming voltage is, and the briefer details you can see in its waveform. If your incoming voltage is a repeating waveform, you can repeat the horizontal motion at the same rate, and view the repeating shape of the waveform.
Not only that, but you can apply custom-shaped waveforms to both the horizontal and vertical inputs. Using waveforms of specific shapes, you can create beautiful changing geometrical patterns called Lissajous figures. These work in exactly the way high-school math predicts.
Using waveforms of specifric shapes and frequencies, you can ‘scan’ the spot of light methodically across the entire surface of the screen. You can also vasy the brightness of the spot. If you do it right, you have recreated an analogue monochrome television display from scratch. (Yes, we did this in electronics school. And it is how b&W TV works.)
We did something like that at college, except it was a microprocessor with two D to A outputs - one connected to the X and the other to the Y, by cycling rapidly through a set of coordinate pair values, it was possible to display very rudimentary vector graphics.
Most of my experience has been with digital scopes. The big advantages they give you are:
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The ability to sample a signal at a much higher rate than anything that occurs in the system you are troubleshooting. This is not always true with in-PC cards, as I’ve learned the hard way.
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The ability to visually compare two or more signals within a system.
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The ability to measure frequency and ampitude of anomalies in a signal to give you a clue toward the root cause.
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The ability to snapshot, using a trigger, an anomaly that would otherwise be impossible to capture.
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Most importantly, the ability to generate hard copies of an anomaly to put into powerpoint charts so you can convince manager-types that a problem really exists.
A good 'scope are one of my favorite troubleshooting tools.
I was helping my girlfriend’s 16yr old daughter revise for her GCSE science exam a few months ago. One of the questions concerned the output on the screen of a CRO.
The answer I thought correct was rejected by her teacher because “it looked silly.” All this coming from a science teacher who immediately afterwards had confessed to having never seen one before in her life :smack:
I should point out that an oscilloscope isn’t only useful in the electronics world. We do a lot of data collection of pressures and torques and speeds and temperatures and other physical properties using transducers that produce an electrical signal in response to the property being measured. (In engines, I’m thinking, but the priciple is the same for other machinery.)
A good oscilloscope is often useful to troubleshoot the system in real time: Are things synched up the way they should be? What kind of delays are built into the physical system? Are things changing over time when they’re not supposed to be? What’s the variability from cycle to cycle? That kind of thing.
One picture is worth a thousand words might best describe the value of oscilloscopes.
To be able to actually see the waveform is of value in many cases.
For example you can see time delay, phase shift, distortion of pulses, rise and fall times.
It gives the deisgner/troubleshooter/whatever immediate, visual feedback as to the performance of a device.
Oscilloscopes are cool - but logic analyzers are even cooler.
If you have an oscilloscope, a computer, and a few light pens, you can make your own video game. Behold Spacewar, the coolest thing going in 1962.
Spacewar was not the first video game. That honor apparently goes to Tic-Tac-Toe on the EDSAC a decade earlier. (It’s vaguely possible there were video games earlier.) It was, however, the first action-oriented video game, and it may be the earliest influential video game. (Nolan Bushnell, father of Atari and the video game industry, saw it, tried and failed to bring it to the masses under the name Computer Space, and went on to invent Pong.)
Generally speaking, most of the time you use a scope, you are not making exact measurments, but rather you are trying to find discrepancies in what you expect to see.
Imagine you have a plain old analogue amplifier, you connect it up to some speakers and it sounds fine at lower volumes, but you turn it up and the signal changes, it becomes distorted.
You would probably check that the idle current (ie The amount of current drawn with no signal input present), is within what you would expect.
You can then carry out voltage measurements all around the amplifier, checking that transistors are operating within their correct electrical environment.
This would be a static check, kind of like checking wheel balance by holding it upright and seeing which part of the wheel goes to the lowest point when it is allowed to gently roll free.
Your next step would be an operating test, to use the wheel analogy, you spin the wheel and strobe light it to a particular rate, and what happens is that the wheel appears to be not moving.You can then determine, one way or another, whereabout the wheel is heaviest and so carry out rectification work.
Similar thing applies to our amplifier, we did the static check, we measured the voltages here and there with an ordinary metering device, and things checked out, so now we apply our input signal,and we now need to find a way of representing what is happening.
The easiest way, is to use a two input 'scope, one input is used to show up the signal to the amplifier, the other 'scope input we use to compare it with.
The way a scope works is to display intantaneous voltage, against a baseline of time.
The screen has a certain amount of afterglow, it stays lit for a tiny fraction of time after the plot has passed.
This plot is merely a moving dot, going from left to right, but because of the afterglow (phosphor persistance) it can look like a solid, if rather wavy, line if the dot is set to move fast enough and repeat fast enough.
If there is a differance between our two traces, the original input and the amplified sample, it leads us further toward the front end of the amplifier, if there is not a differance, it leads us toward the output end of the amplifier.
The reality is that when you use 'scopes a lot, you tend to forego the first stage of voltage testing because it can be rather laborious, its just so much faster to stick the 'scope probe on various parts of the amplifer circuit and when something looks wrong, that’s when you start with the voltage checks.
A big part of how scopes help you is due to the power of the human brain for pattern matching. If some electrical circuit is producing incorrect results, you can sample different parts of it and put them up on the screen. In real time, you can fiddle with any input signals and see the resulting changes in your sample paths, and based upon your experience can determine if what you’re seeing is what you expected, or how it differs from what you expected.
A good automotive technician does much of his or her diagnosing with an O-scope. When presented with a problem car, scoping all inputs to the ECM lets you see what is in and out of range.
When I worked for Allen Testproducts, a garage owner showed me a no start car on which he’d replaced the throttle body, fuel filter, and fuel pump, without success. Yes, he was a shotgun repair fellow. I scoped the distributor pickup, expecting a square wave, and saw flat line. Because of the bad pickup, the ECM didn’t see the engine turning, so why supply fuel? 