Oscilloscope how does it work

Modern digital instruments may calculate and display these properties directly. A basic oscilloscope has a bandwidth of up to MHz and is found in almost every design laboratory, education lab, service center and manufacturing environment. An oscilloscope works in pretty much the same way as a CRT television. For instance, the electron beams in a tv scan back and forth across a screen coated on the back with phosphors.

These phosphors light up whenever the beam hits the screen. So when the electron beams fall on the whole screen, they brighten up the phosphors thus forming an image on the screen. This happens time and again and rather quickly - within the blink of an eye, in fact. Thus we end up seeing moving pictures as opposed to a series of still images. In an oscilloscope, the electron beams work in the same fashion except that they brighten up the phosphors to form a graph.

So when a line is displayed on the screen of an oscilloscope, it is being caused by an electron beam going up and down. How does an oscilloscope draw a trace? This can be explained with the help of an example. Now your hand is strapped to two electric motors, both of which are in turn connected to electronic circuits that can test signals of different kinds.

Moreover, one of the motors can move your hand in a vertical y direction, even as the other moves the hand in the horizontal x direction.

Now say, we connect the x-circuit to an electronic quartz clock. So when the clock ticks, it sends a signal to the x motor thus moving your hand to the right, thereby making you draw a horizontal line. With the x and y circuits connected at the same time, your hand will move across the page, but it will jump up vertically each time the heart beats.

This, in effect, is what happens in an oscilloscope too; except the pencil is the electronic beam and the graph paper is the screen. Oscilloscopes are used in several fields today - be it sciences, medicine, engineering, automotive or the telecommunications industry. General-purpose oscilloscopes are used for maintenance of electronic equipment and laboratory work. For instance, within radio frequency RF design, general electronics circuit design, electronics manufacturing, service, repair or an area where electronic circuits and the waveforms on them have to be observed.

In fact, troubleshooting with an oscilloscope is a common and rather reliable method for analyzing modern electronic circuitry. Special-purpose oscilloscopes, as the name suggests, are used with a specific aim in mind, say, displaying the waveform of the heartbeat as an electrocardiogram or analyzing an automotive ignition system. Oscilloscopes can be bought from Tektronix, a leading manufacturer of test and measurement devices including oscilloscopes, logic analyzers, and video and mobile test equipment.

Tektronix also provides oscilloscope calibration services. Engineering : Electronic, sound and computer design engineering rely heavily on oscilloscopes -be it carrying out complicated measurements or tracking sound and engine vibrations. Electronics : Electronic technicians, including those who service and repair household and business electronics such as televisions, computers, and audio video systems, use oscilloscopes for testing equipment, parts and assemblies in these devices.

Healthcare : Oscilloscopes are used as medical measuring instruments; especially to check for heart irregularities. Sciences Physics : Oscilloscopes are extensively used for diagnosis in the scientific community, and enjoy greater demand from physicists who tend to regularly use them for several applications.

Vehicle Repair : Mechanics use oscilloscopes to test fuel injectors or to examine and repair a car in a no-start condition. This is the earliest and simplest type of oscilloscope that was made up of a cathode ray tube, a vertical amplifier, a timebase, a horizontal amplifier and a power supply. Now referred to as analog oscilloscopes to distinguish them from the digital ones that shot to popularity in the s, these CROs do not always include a calibrated reference grid for size measurement of waves, and they may not show waves in the conventional sense of a line segment sweeping from left to right.

But they could be used for signal analysis by putting a reference signal into one axis and the signal to measure into the other axis. The dual-beam analog oscilloscope can send out two signals at the same time. A special dual-beam CRT produces and deflects the two different beams. A dual-trace analog oscilloscope can simulate a dual-beam display with chop and alternate sweeps, but simultaneous displays are still lacking here.

This is where a dual-beam oscilloscope fares better: unlike the dual trace oscilloscope, it can switch quickly between traces, and capture two fast transient events. Analog oscilloscopes work somewhat differently than digital oscilloscopes.

However, several of the internal systems are similar. Analog oscilloscopes are somewhat simpler in concept and are described first, followed by a description of digital oscilloscopes. Analog Oscilloscopes. When you connect an oscilloscope probe to a circuit, the voltage signal travels through the probe to the vertical system of the oscilloscope. Following Figure is a simple block diagram that shows how an analog oscilloscope displays a measured signal.

Next, the signal travels directly to the vertical deflection plates of the cathode ray tube CRT. Voltage applied to these deflection plates causes a glowing dot to move. An electron beam hitting phosphor inside the CRT creates the glowing dot. A positive voltage causes the dot to move up while a negative voltage causes the dot to move down. The signal also travels to the trigger system to start or trigger a "horizontal sweep.

Triggering the horizontal system causes the horizontal time base to move the glowing dot across the screen from left to right within a specific time interval. Many sweeps in rapid sequence cause the movement of the glowing dot to blend into a solid line. At higher speeds, the dot may sweep across the screen up to , times each second. Together, the horizontal sweeping action and the vertical deflection action traces a graph of the signal on the screen.

The trigger is necessary to stabilize a repeating signal. It ensures that the sweep begins at the same point of a repeating signal, resulting in a clear picture as shown in following figure. In conclusion, to use an analog oscilloscope, you need to adjust three basic settings to accommodate an incoming signal:. Digital Oscilloscopes. Some of the systems that make up digital oscilloscopes are the same as those in analog oscilloscopes; however, digital oscilloscopes contain additional data processing systems.

With the added systems, the digital oscilloscope collects data for the entire waveform and then displays it. When you attach a digital oscilloscope probe to a circuit, the vertical system adjusts the amplitude of the signal, just as in the analog oscilloscope.

Next, the analog-to-digital converter ADC in the acquisition system samples the signal at discrete points in time and converts the signal's voltage at these points to digital values called sample points. The horizontal system's sample clock determines how often the ADC takes a sample. The rate at which the clock "ticks" is called the sample rate and is measured in samples per second. These probes are commonly called 10X attenuated probes.

Many probes include a switch to select between 10X and 1X no attenuation. Attenuated probes are great for improving accuracy at high frequencies, but they will also reduce the amplitude of your signal.

Beyond the passive attenuated probe, there are a variety of other probes out there. Active probes are powered probes they require a separate power source , which can amplify your signal or even pre-process it before it get to your scope. While most probes are designed to measure voltage, there are probes designed to measure AC or DC current. Current probes are unique because they often clamp around a wire, never actually making contact with the circuit. The infinite variety of signals out there means you'll never operate an oscilloscope the same way twice.

But there are some steps you can count on performing just about every time you test a circuit. On this page we'll show an example signal, and the steps required to measure it. First off, you'll need to select a probe. For most signals, the simple passive probe included with your scope will work perfectly fine. Next, before connecting it to your scope, set the attenuation on your probe. If you're trying to measure a very low-voltage signal though, you may need to use 1X.

Connect your probe to the first channel on your scope, and turn it on. Have some patience here, some scopes take as long to boot up as an old PC. When the scope boots up you should see the divisions, scale, and a noisy, flat line of a waveform. The screen should also show previously set values for time and volts per div. Ignoring those scales for now, make these adjustments to put your scope into a standard setup :.

For help making these adjustments, consult your scope's user's manual as an example, here's the GACAL manual. Let's connect that channel up to a meaningful signal. Most scopes will have a built-in frequency generator that emits a reliable, set-frequency wave -- on the GACAL there is a 1kHz square wave output at the bottom-right of the front panel.

The frequency generator output has two separate conductors -- one for the signal and one for ground. Connect your probe's ground clip to the ground, and the probe tip to the signal output. As soon as you connect both parts of the probe, you should see a signal begin to dance around your screen. Try fiddling with the horizontal and vertical system knobs to maneuver the waveform around the screen. Rotating the scale knobs clockwise will "zoom into" your waveform, and counter-clockwise zooms out.

You can also use the position knob to further locate your waveform. If your wave is still unstable, try rotating the trigger position knob. Make sure the trigger isn't higher than the tallest peak of your waveform. By default, the trigger type should be set to edge, which is usually a good choice for square waves like this. If your probe is set to 10X, and you don't have a perfectly square waveform as shown above, you may need to compensate your probe.

Most probes have a recessed screw head, which you can rotate to adjust the shunt capacitance of the probe. Try using a small screwdriver to rotate this trimmer, and look at what happens to the waveform. Adjust the trimming cap on the probe handle until you have a straight-edged square wave.

Compensation is only necessary if your probe is attenuated e. Once you've compensated your probe, it's time to measure a real signal! Go find a signal source frequency generator? The first key to probing a signal is finding a solid, reliable grounding point. Clasp your ground clip to a known ground, sometimes you may have to use a small wire to intermediate between the ground clip and your circuit's ground point. Then connect your probe tip to the signal under test.

Probe tips exist in a variety of form factors -- the spring-loaded clip, fine point, hooks, etc. Once your signal is on the screen, you may want to begin by adjusting the horizontal and vertical scales into at least the "ballpark" of your signal.

If part of your wave is rising or falling of the screen, you can adjust the vertical position to move it up or down. If your signal is purely DC, you may want to adjust the 0V level near the bottom of your display. Once you have the scales ballparked, your waveform may need some triggering. Edge triggering -- where the scope tries to begin its scan when it sees voltage rise or fall past a set point -- is the easiest type to use.

Using an edge trigger, try to set the trigger level to a point on your waveform that only sees a rising edge once per period. Now just scale, position, trigger and repeat until you're looking at exactly what you need.

With a signal scoped, triggered, and scaled, it comes time to measure transients, periods, and other waveform properties. Some scopes have more measurement tools than others, but they'll all at least have divisions, from which you should be able to at least estimate the amplitude and frequency. Many scopes support a variety of automatic measurement tools, they may even constantly display the most relevant information, like frequency.

To get the most out of your scope, you'll want to explore all of the measure functions it supports. Most scopes will calculate frequency, amplitude, duty cycle, mean voltage, and a variety of other wave characteristics for you automatically.

A third measuring tool many scopes provide is cursors. Cursors are on-screen, movable markers which can be placed on either the time or voltage axis.

Cursors usually come in pairs, so you can measure the difference between one and the other. Measuring the ringing of a square wave with cursors.

Once you've measured the quantity you were looking for, you can begin to make adjustments to your circuit and measure some more! Some scopes also support saving , printing , or storing a waveform, so you can recall it and remember those good ol' times when you scoped that signal. Now that you've learned all about this handy tool's features and benefits, it's time to put an oscilloscope on your workbench.

See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering. Take me there! With the tools discussed in this tutorial, you should be prepared to start scoping signals of your own.

If you're still unsure of what certain parts of your scope are for, first consult your user's manual. Here are some additional resources we recommend checking out as well:. Now that you're a practiced oscilloscop-er, what circuit are you going to be debugging? Need some inspiration? Here are some related tutorials we'd recommend checking out next! Need Help? Mountain Time: Shopping Cart 0 items. Product Menu. Today's Deals Forum Desktop Site.