Tektronix TDS220 user guide: Basic Concepts

Basic Concepts

The oscilloscope shows the time per division in the scale readout. Since all active waveforms use the same time base, the oscilloscope only displays one value for all the active channels, except when you use a Window Zone.

Aliasing. Aliasing occurs when the oscilloscope does not sample the signal fast enough to construct an accurate waveform record. When aliasing happens, you see a waveform with a frequency lower than the actual waveform being input or a waveform that is not stable even though the oscilloscope triggered.

One way to check for aliasing is to slowly change the horizontal scale with the SEC/DIV knob. If the shape of the waveform changes drastically, you may have aliasing.

To represent a signal accurately and avoid aliasing, you must sample the signal more than twice as fast as the highest frequency component. For example, a signal with frequency components of 5 MHz would need to be sampled at 10 Megasamples per second or faster.

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Basic Concepts

The next table lists the time bases that you should use to avoid aliasing at various frequencies and the respective sample rate.

• Bandwidth is not valid for the P2100 probe when the switch is set to 1X.

There are various ways to prevent aliasing: adjust the horizontal scale, push the AUTOSET button, or change the acquisition mode.

NOTE. If aliasing occurs, change to the Peak Detect acquisition mode (described on page 16). This mode samples the highest and lowest values so that the oscilloscope can detect faster signals.

Basic Concepts

Taking Measurements

The oscilloscope displays graphs of voltage versus time and can help you to measure the displayed waveform.

There are several ways to take measurements. You can use the graticule, the cursors, or an automated measurement.

Graticule

This method allows you to make a quick, visual estimate. For example, you might look at a waveform amplitude and determine that it is a little more than 100 mV.

You can take simple measurements by counting the major and minor graticule divisions involved and multiplying by the scale factor.

For example, if you counted five major vertical graticule divisions between the minimum and maximum values of a waveform and knew you had a scale factor of 100 mV/division, then you could easily calculate your peak-to-peak voltage as follows:

5 divisions x 100 mV/division = 500 mV.

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Basic Concepts

Cursors This method allows you to take measurements by moving the cursors, which always appear in pairs, and reading their numeric values from the display readouts. There are two types of cursors: Voltage and Time.

When you use cursors, be sure to set the Source to the waveform that you want to measure.

Voltage Cursors. Voltage cursors appear as horizontal lines on the display and measure the vertical parameters.

Time Cursors. Time cursors appear as vertical lines on the display and measure the horizontal parameters.

Automated When you take automated measurements, the oscilloscope does all the calculating for you. Because these measurements use the waveform record points, they are more accurate than graticule or cursor measurements.

Automated measurements use readouts to show measurement results. These readouts are updated periodically as the oscilloscope acquires new data.

Setting Up the Oscilloscope You should become familiar with three functions that you will use often when operating your oscilloscope: Autoset, saving a setup, and recalling a setup. Included is a description of the default settings for normal operation of the oscilloscope.

Basic Concepts

Using Autoset

The Autoset function obtains a stable waveform display for you. It automatically adjusts the vertical and horizontal scaling, as well as the trigger coupling, type, position, slope, level, and mode settings.

Saving a Setup

By default, the oscilloscope saves the setup each time it is powered off. The oscilloscope automatically recalls this setup the next time it is powered on.

NOTE. You should wait at least five seconds after your last change to the setup before you turn off the power. This ensures that the setup is saved properly.

You can also permanently save up to five setups in the memory of the oscilloscope and overwrite setups as needed.

Recalling a Setup

The oscilloscope can recall any of the saved setups or the factory default setup.

Defaults (Factory Setup)

The oscilloscope is set up for normal operation when it is shipped from the factory. You can recall the factory default setup any time you want to operate the oscilloscope using or starting from the factory default settings.

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Operating Basics

The front panel is divided into easy to use functional areas. This section provides you with a quick overview of the controls and the information displayed on the screen. The next figure shows the front panels for a TDS 210 or TDS 220, and for a TDS 224 oscilloscope.

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Operating Basics

Display Area

In addition to displaying waveforms, the display is filled with many details about the waveform and the instrument control settings.

1. Icon display shows acquisition mode. Sample mode Peak detect mode Average mode

Operating Basics

2. Trigger status indicates the following: ☐ Armed. The instrument is acquiring pretrigger data. All triggers are ignored in this state. [R] Ready. All pretrigger data has been acquired and the instrument is ready to accept a trigger. [T] Trig'd. The instrument has seen a trigger and is acquiring the posttrigger data. [R] Auto. The instrument is in auto mode and is acquiring waveforms in the absence of triggers. ☐ Scan. The instrument is acquiring and displaying waveform data continuously in scan mode. ● Stop. The instrument has stopped acquiring waveform data.

3. Marker shows horizontal trigger position. This is adjusted by the Horizontal Position control.

4. Readout shows the time difference between the center graticule and horizontal trigger position. Center screen equals zero.

5. Marker shows trigger level.

6. Readout shows numeric value of the trigger level.

7. Icon shows selected trigger type as follows: ∫ – Edge trigger for the rising edge. \ – Edge trigger for the falling edge. (video line sync icon) – Video trigger for line sync. (video field sync icon) – Video trigger for field sync.

Operating Basics

8. Readout shows trigger source used for triggering.
9. Readout shows window time base setting if it is in use.
10. Readout shows main time base setting.
11. Readouts show the vertical scale factors of the channels.
12. Display area shows on-line messages momentarily.
13. On-screen markers show the ground reference points of the displayed waveforms. No marker indicates the channel is not displayed.

Using the Menu System

The user interface of the TDS 200-series oscilloscopes was designed for easy access to specialized functions through the menu structure.

When you press a menu button on the front panel, the associated menu title displays at the top right of the screen. There can be up to five menu boxes below the menu title. To the right of each menu box is a bezel button you can use to change the menu setting.

There are four types of menu boxes you can use to change settings: Circular Lists, Action Buttons, Radio Buttons, and Page Selections.

Circular List Menu Boxes

A Circular List menu box appears with a title on top with the selected choice listed below in reverse video. For example, you can push the menu box button to cycle through the vertical coupling choices in the CH1 Menu.

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Operating Basics

Action Button Menu Boxes

An Action Button menu box displays the name of the action. For example, you can use the two lowest menu boxes in the DISPLAY menu to increase or decrease the contrast.

Radio Button Menu Boxes

Radio Button menu boxes are separated by dashed lines. The name of the selected menu box displays in reverse video. For example, you can use the top three menu boxes in the ACQUIRE menu to select an acquisition mode.

Page Selection Menu Boxes

A Page Selection menu box contains two menus for a single button on the front panel with the selected menu displayed in reverse video. Each time you press the top menu box button to toggle between the two menus, the menu boxes below also change.

For example, when you press the SAVE/RECALL front panel button, the top Page Selection menu contains the names of two menus: Setups and Waveforms. When you select the Setups menu, you can use the remaining menu boxes to save or recall setups. When you select the Waveforms menu, you can use the remaining menu boxes to save or recall waveforms.

The SAVE/RECALL, MEASURE, and TRIGGER front panel buttons display Page Selection menu boxes.

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Operating Basics

Waveform Displays

Obtaining a waveform display is dependent on many instrument settings. Once you obtain a waveform, you can take your measurements. But the appearance of these waveforms also provides key information about the waveform.

Depending on the type, waveforms will be displayed in three different styles: black, gray, and broken.

1. A solid black waveform indicates a live waveform display. The waveform remains black when the acquisition is stopped if no controls are changed that make the display accuracy uncertain.

Changing the vertical and horizontal controls is allowed on stopped acquisitions.

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Operating Basics

2. Reference waveforms and waveforms with persistence applied appear gray.
3. A broken line appearance indicates the waveform display accuracy is uncertain. This is the result of stopping the acquisition and then changing a control setting that the instrument cannot modify the displayed waveform to match. For example, changing the trigger controls on a stopped acquisition causes a broken-line waveform.

Vertical Controls

TDS 210 and TDS 220

Operating Basics

MATH MENU

TDS 224

CH 1, 2, 3 & 4 and CURSOR 1 & 2 POSITION. Positions the waveform vertically. When cursors are turned on and the cursor menu is displayed, these knobs position the cursors.

CH 1, CH 2, CH 3 & CH 4 MENU. Displays the channel input menu selections and toggles the channel display on and off.

VOLTS/DIV (CH1, CH 2, CH 3 & CH 4). Selects calibrated scale factors.

MATH MENU. Displays waveform math operations menu and can also be used to toggle the math waveform on and off.

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Operating Basics

Horizontal Controls

TDS 210 and TDS 220

TDS 224

POSITION. Adjusts the horizontal position of all channels and math waveforms. The resolution of this control varies with the time base.

NOTE. To make a large adjustment to the horizontal position, change the SEC/DIV to 50 ms, change the horizontal position, and then change the SEC/DIV back to the previous value.

HORIZONTAL MENU. Displays the horizontal menu.

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Operating Basics

SEC/DIV. Selects the horizontal time/div (scale factor) for the main or the window time base. When Window Zone is enabled, it changes the width of the window zone by changing the window time base. Refer to page 75 for details about creating and using the Window Zone.

Trigger Controls

LEVEL and HOLDOFF. This control has a dual purpose. As an edge trigger level control, it sets the amplitude level the signal must cross to cause an acquisition. As a holdoff control, it sets the amount of time before another trigger event can be accepted. Refer to Holdoff on page 13 for more information.

Operating Basics

TRIGGER MENU. Displays the trigger menu.

SET LEVEL TO 50%. The trigger level is set to the vertical midpoint between the peaks of the trigger signal.

FORCE TRIGGER. Starts an acquisition regardless of an adequate trigger signal. This button has no effect if the acquisition is already stopped.

TRIGGER VIEW. Displays the trigger waveform in place of the channel waveform while the TRIGGER VIEW button is held down. You can use this to see how the trigger settings affect the trigger signal, such as trigger coupling.

Menu and Control Buttons

TDS 210 and TDS 220

SAVE/RCL MEASURE ACQUIRE

HARDCOPY AUTOSET RUN/STOP

UTILITY CURSOR DISPLAY

TDS 224

Operating Basics

SAVE/RECALL. Displays the save/recall menu for setups and waveforms.

MEASURE. Displays the automated measurements menu.

ACQUIRE. Displays the acquisition menu.

DISPLAY. Displays the display menu.

CURSOR. Displays the cursor menu. Vertical Position controls adjust cursor position while displaying the cursor menu and the cursors are turned on. Cursors remain displayed (unless turned off) after leaving the cursor menu but are not adjustable.

UTILITY. Displays the utility menus.

AUTOSET. Automatically sets the instrument controls to produce a usable display of the input signal.

HARDCOPY. Starts print operations. An extension module with a Centronics, RS-232, or GPIB port is required. Refer to Optional Accessories on page 103.

RUN/STOP. Starts and stops waveform acquisition.

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Connectors

PROBE COMP. Voltage probe compensation output and ground. Use this to electrically match the probe to the input circuit. Refer to page 6.

The probe compensation ground and BNC shields are connected to earth ground. Do not connect a voltage source to these ground terminals.

CH 1, CH 2, CH 3 & CH 4. Input connectors for waveform display.

EXT TRIG. Input connector for an external trigger source. Use the trigger menu to select the trigger source.

Operating Basics

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