Oscilloscope Controls | Cursor, Scaling, Triggering and Advanced Controls

Most aspects of the function of an oscilloscope can be manipulated. Basic controls include waveform scaling, positioning and triggering. Some oscilloscopes offer advanced controls such as mathematics or other waveform measurements.

Horizontal and Vertical Scaling and Positioning

The vertical (y) axis of the graticule represents the voltage being measured. The horizontal (x) axis represents time. Each axis is measured in a grid whose physical spacing is typically 1cm squares but represents units of voltage and time.

These units can be scaled using the dials labeled ‘Scale’. The horizontal and vertical position of a signal can be adjusted using the ‘Position’ dials. The current grid scale and position is displayed over the graticule or beneath it if the context menu is off. The zero position of each channel is indicated by the numbered marker on the left of the graticule.

Note that each channel can have different vertical scale and position but all channels share the same horizontal scale and position. To adjust the waveform it is first selected using the channel select buttons Fig-C) and then changed via the appropriate dial note, some context menu items also require the correct channel to be selected.Parts of an Oscilloscope

Triggering

Signals to be displayed on an oscilloscope must be referenced to a ‘start time’. The setting of this time is called triggering. The trigger is determined by setting the oscilloscope to find the point at which the signal crosses either rising or falling, a particular voltage. If a trigger is not set, the waveform appears to jump around on the display. This is due to the oscilloscope sampling the input at different times and since the signal is time varying displays an animated waveform.

To set the triggers press the Trigger Menu button. On the context menu select the channel that will be the source of the trigger. Also select the edge typically rising to trigger on. Using the Trigger Level dial adjust the trigger level until the waveform is stable. Note the trigger level is indicated by an arrow to the right of the graticule.

Cursors

It is convenient to be able to make measurements of the signal being displayed on the oscilloscope. Although the graticule will give rough values it is more accurate to use the cursors. To activate the cursors press the Cursor button (Fig-F). The cursors which appear as vertical or horizontal lines will be displayed the color of which depends on the current active channel.

The cursors are controlled using the Select button and the dial (Fig-F) at the top of the scope as well as the context menu buttons. The context menu buttons are used to select the horizontal or vertical cursors and turn the cursors off. The dial moves the active cursor solid line position, while the Select button sets the reference cursor the dotted line position as the current active cursor position the cursors actually trade positions.

The horizontal cursers display 2 pieces of information, labeled Δ (delta) and @ asperand or at sign. Δ shows the difference in the voltages between the active cursor and the reference cursor. @ shows the voltage position of the active cursor.

The vertical cursors display 4 pieces of information also labeled Δ and @ but one set in time and the other in voltage. Similar to the horizontal cursors, Δ shows the difference between the active and reference cursor while @ is the position of the active cursor each in time and voltage.

Advanced Controls

The oscilloscope is capable of various advanced functions and features. Two useful features are the Math near the Channel Inputs and the Measure near the Cursor button functions. The Math functions allow combinations of the channels to be manipulated using mathematical functions such as addition, subtraction, multiplication and division.

This can be useful when comparing two signals. The Measure functions provide valuable functions for gauging various aspects of a signal such as rise/fall times, frequency, peak values, offsets and much more. This is very helpful as many of these functions automatically measure specifications that would otherwise have to be done manually although care must be taken as the oscilloscope may not be measuring exactly what you are assuming.