New users are invariably challenged by the large number of front-panel controls and extensive menu trees found on modern scopes. Many menu items have single-word designations, which only begin to describe their extensive functions. In on-screen menus, specific display modes are not always where you expect to find them. Learning the layout of this architecture is a necessary first step in becoming adept with this complex instrument.
Advanced digital storage oscilloscopes are often categorized as either mixed domain oscilloscopes (MDOs) or mixed-signal oscilloscopes (MSOs). An MDO is capable of displaying a single signal simultaneously in real-time in both time and frequency domains. An MSO is capable of displaying two separate signals again simultaneously in real-time. Both modes, which are completely different and available only in distinctly different instruments, are immensely useful in creating prototypes of new electronic equipment, troubleshooting existing units and in research, development, and education. It is interesting to note that in the Tektronix models, digital channels are labeled “MSO Capable.” This means you can view digital waveforms as analog inputs and simultaneously in split-screen format as digital inputs with high and low states.
Consider the case of diagnosing a system having an intermittent output. One channel in an MSO oscilloscope can be connected to the problematic signal, and the other connected to the dc power supply. When the intermittent output arises, the power supply can be observed to see if irregularities in both channels coincide. That way, the common internal power supply or external facility source can be identified or ruled out as the problem.
The MDO boots into a home screen displaying a reassuring message that the Power-On Self-Test passed. To proceed, it is always good to press Default Setup to remove any scope parameters that have survived power-off cycles. Now we see the default time-domain screen with a yellow horizontal line representing the default Channel One triggering level. Pressing the Channel One On button, the horizontal analog input menu appears below the display. Menu items are:
• Coupling – The associated soft key toggles dc and ac.
• Termination – The soft key toggles one Megohm and 50 ohm.
• Invert – The soft key toggles it On and Off.
• Bandwidth – The soft key brings up the vertical submenu with soft keys selecting Full, 250 MHz and 20 MHz.
• Label – This brings up an on-screen keyboard wherein the user can choose or clear letters, numbers and characters. A vertical submenu includes Preset Labels. Soft keys permit the user to choose, insert and display the labels.
Returning to the horizontal menu, fine scales, vertical offset and position can be adjusted by turning Multipurpose Knob a. Probe Setup permits the user to select voltage or current probe type, adjust probe attenuation and measure current. Probe model can be selected with Deskew Value and Propagation Delay.
Obviously, there are numerous menus, submenus and user choices available in the channel menus, which can be set simultaneously for each of the oscilloscope channels.
Pressing Measure in the Wave Inspector section brings up the horizontal Measure menu. To see how it works, it is best to apply a waveform to the analog input. The source can be the oscilloscope’s internal arbitrary function generator or an external AFG. The horizontal Measure menu, starting at the left, has menu items designated Add Measurement and Remove Measurements. They are accessed by pressing the associated soft keys. Pressing Add Measurement brings up the vertical Add Measurement menu at the right side of the display. The top menu item, activated by pressing the soft key, permits the user to select the source, Channel One or Channel Two, by turning Multipurpose Knob a, and Measurement Type by turning Multipurpose Knob b. Measurement Type consists of 31 waveform parameters, such as frequency, phase, pulse width, duty cycle, etc. Each of these is illustrated by a diagram at the left side of the screen, plus a precise definition and the statement that all measurements use the portion of the acquisition selected in the Gating menu. The bottom menu item is OK Add Measurement. Pressing the soft key places the measurement in tabular form in the analog display. Measurements can be removed by pressing Default Setup.
In the horizontal Measurements menu, the third menu item is DVM. Pressing the associated soft key, the vertical Digital Voltmeter menu appears. Available DVM Modes, selected by turning Multipurpose Knob a, are DC + AC RMS, DC, AC RMS and Frequency. In each of these modes, the selected metric is displayed in large, clear characters above the display. Multipurpose Knob a selects the source. The signal in each channel is measured individually.
The next menu item in the horizontal Measure menu is Waveform Histograms. Pressing the associated soft key, the vertical Histogram menu appears. The top soft key selects Off, Vertical or Horizontal Histogram. The histogram provides statistical measurement data for a section of a waveform along one axis. The sources for a histogram can be any of the four analog channels, a Math waveform or one of the four Reference waveforms. Horizontal and vertical limits can be imposed by pressing the appropriate soft keys and turning Multipurpose Knobs a and b. Horizontal histograms are suitable for measuring signal jitter and vertical histograms are suitable for measuring signal noise.
Statistics that appears in the vertical menu when the soft key associated with More is pressed can be toggled On and Off. The number of Mean and Standard Deviation Samples, set by turning Multipurpose Knob a, ranges between two and 1,000. The bottom menu item permits the user to reset Statistics by pressing the soft key.
Gating constrains a portion of the full record between limits and cursors. Reference limits can be set at high reference, mid reference and low reference levels.
Pressing the Acquire button in the horizontal section, the horizontal Acquisition menu appears below the display. (It is a good idea to first press Default Setup to clear the processor.) Then, to illustrate, apply a sine wave at the analog channel input.
The first menu item is Mode, with the default Sample Mode activated. This is by far the most common mode that the oscilloscope uses to acquire, digitize, process and display waveforms. The other acquisition modes are Peak Detect, High Resolution, Envelope and Average.
Sample Mode simply retains the first sampled point from each acquisition interval. Then, using one of the interpolation methods, the samples are connected to create a readable waveform in the display.
Peak Detect Mode uses the highest and lowest of all the samples contained in two consecutive acquisition intervals. This mode works only with real-time, noninterpolated sampling, and is useful for catching high-frequency glitches.
High-Resolution Mode calculates the average of all the samples for each acquisition interval. This mode also works only with real-time, noninterpolated sampling. High Resolution provides a more detailed waveform at the cost of lower bandwidth.
Envelope Mode finds the highest and lowest record points over all acquisitions. Envelope Mode uses Peak Detect for each individual acquisition.
Average Mode calculates the average value for each record point over a user-specified number of waveforms. The number of waveforms averaged, ranging from two to 512, is set by turning Multipurpose Knob a, and as the number rises, random noise diminishes and the waveform becomes sharper.
To adjust Record Length, press the associated soft key. Multipurpose Knob a permits the user to set the record length at 1,000, 10 thousand, 100 thousand, 1 million, 5 million or 10 million points.
FastAcq can be toggled On and Off. When it is On, Waveform Palettes can be selected. Then, multipurpose Knob a determines how it is displayed. The purpose is to enhance the visibility of events. Intensity grading indicates how often rare transients occur relative to a normal signal. The choices are Temperature, Spectral, Normal and Inverted.
Similarly, a contextual soft key permits the user to toggle Delay On and Off. In normal operation, the default Off setting is used. Toggling Delay On, the Horizontal Position knob turned counterclockwise increases the delay. This moves the trigger point to the left, earlier in time, and ultimately it goes outside the acquired waveform. Then, the user can adjust the Horizontal Scale knob to acquire more detail around the area of interest at the center of the screen.
Pressing the soft key associated with waveform Display brings up the vertical Waveform Display menu, permitting the user to disable interpolation so the waveform is shown as Dots Only, and to set the amount of Persistence, which enhances readability.
XY Display, when toggled On, shows the waveform as a Lissajous figure, which can be displayed by itself or in split-screen format along with the conventional time-domain mode. Pressing the Test button in the Wave Inspector Section, the Horizontal Application menu appears at the bottom of the screen. The first menu item lists applications, such as Limit/Mask Test, Video Picture, Power Analysis and Act on Event.
Limit/Mask, shown in the horizontal menu, includes Set Up Mask, Select Mask, Create Limit Mask, Set Up Test, Run Test and Show Results.
Video Picture enables the oscilloscope to receive and display actual TV broadcasts. This mode can be configured for either of the two TV formats – National Television Standards Committee (NTSC) or Phase Alternating Line (PAL), with even or odd interlacing.
Power Analysis Modes appear in a vertical menu, consisting of Power Quality, Switching Loss, Harmonics, Ripple, Modulation and Deskew. Act On Event brings up a horizontal menu, in which None, Trigger or Acquisitions can be chosen.
Other extensive menus are available in the Tektronix MDO3000 oscilloscope, including AFG, Reference, Search, RF, Frequency/Span, Amplitude, Bandwidth, Markers, Utility and Save/Recall. They will require individual consideration.