The vertical system

The vertical axis shows voltage as a function of time. It is used to scale and position the waveform vertically. For displaying and scaling the waveforms, the volts/div control is used, which controls the amplification or attenuation of the input signal.

The most important thing to keep in mind when configuring the vertical system is to use the volts/div control to maximize the waveform on the screen. In other words, to have the positive and negative peaks as close to the top and bottom as possible without clipping the waveform.

This ensures that all bits of the scopes analog to digital converter (ADC) and the full advantages of the ADC are used. It is also easier to see small details or features in a waveform when maximizing the vertical scale.

The horizontal system

When it comes to the horizontal system, there are two separate topics or aspects that need to be covered: waveform display and sample rate.

Waveform display

Waveform display controls in the horizontal system are related to the horizontal axis, which corresponds to time. These controls can be used to scale the waveform and/or to change its horizontal position. Similar to volts/div in the vertical system, sec/div changes the duration of each division, meaning how many cycles can be seen on the oscilloscope screen. Use the position control to move waveform right and left on the screen.

Sample rate

The more important aspect to the horizontal system is called sampling.
The horizontal system digitizes the input signal at a given sample rate in samples per second or at every sampling interval. These samples are stored in memory and together they make up a so-called waveform record.

The higher the sample rate:

• the greater the resolution / detail of the displayed waveform
• the greater the probability of catching infrequent events
• the greater the storage requirements (larger memory depth)

What sample rate should be chosen?
If the input signal is sampled too slowly, there is the risk of getting an alias signal that will not be an accurate representation of the sample signal.

Trigger system and trigger modes

The trigger system is extremely important, because triggering is needed for almost all oscilloscope operations. Essentially, a trigger defines the conditions that have to be met before the oscilloscope begins an acquisition or begins taking samples.
Triggering can do two different things:

It is important, to set the trigger properly. Incorrect trigger configuration is a very common problem when using oscilloscopes. There are many different types of triggers. Modern scopes can trigger on things like pulse widths, runts or glitches. The most common trigger type is the edge triggering.

In edge triggering, the trigger occurs when the threshold of the defined voltage is crossed, either on the rising edge or on the falling edge on a waveform.

Besides the different trigger types there also exist various trigger modes. The trigger mode determines the behavior of the instrument if no trigger occurs. Here we distinguish between Auto and Norm mode.

At the Auto mode the oscilloscope triggers repeatedly after a time interval if the trigger conditions are not fulfilled. If a real trigger occurs, it takes precedence. This mode helps to see the waveform even before the trigger is set. The waveform on the screen is not synchronized and successive waveforms are not triggered at the same point of the waveform.

In the Norm mode the instrument acquires a normal waveform only if a trigger occurs, that is if all trigger conditions are fulfilled. If no trigger occurs, no waveform is acquired and the last acquired waveform is displayed. If no waveform was captured before, nothing is displayed.

The display system

In analog oscilloscopes the display system was little more than a cathode rate tube showing a glowing green trace. Analyzing or measuring signals often met counting divisions on the display.

Modern digital oscilloscopes have many display and measurement functions, such as zooming in and out of a signal and using cursors or markers to make manual measurements. There is also a large number of automated functions, like peak or peak-to-peak voltage, frequency, rise and fall times, slew rate, crest factor and pulse counts.
Many of these values can also be made on a statistical basis (statistical measurements).