Download Appendix A: Basic Operation of Tektronix TDS1002 Digital

Appendix A: Basic Operation of Tektronix TDS1002 Digital Oscilloscope
Figure 1 below shows the front panel of the TDS1002. The power button is on the top of the case.
Figure 1. TDS1002 front panel. Note the four major functional areas: Vertical, Horizontal,
Trigger , and Display Settings (on the top), plus the column of five menu buttons.
Vertical controls:
Position 1 and Position 2: Position the waveform vertically. (Position cursors when cursor LED lit.)
Ch1 Menu , Ch2 Menu: Display the vertical function menus and toggles the display of the channel
waveform on/off.
Math Menu: Displays the waveform math operations menu. We will not use this at present.
Volts/Div: Selects calibrated scale factors.
Horizontal controls:
Position: Adjusts the horizontal position of the waveform.
Horiz. menu: Displays the Horizontal menu.
Set to zero: Sets the horizontal position to put the trigger point (see below) at the middle of the screen
Sec/Div: Selects the horizontal time/div scale factor).
Trigger controls:
Level: Used to set up the trigger level.
Trig. menu: Displays the Trigger menu.
Set to 50%: Sets the trigger level to the vertical midpoint between the peaks of the trigger signal
Force Trig.: Complete a waveform acquisition even if a proper trigger signal is not present.
Trig. View: View the waveform seen by the trigger circuit
Menu and Control buttons:
Save/Recall, Measure, Acquire, Cursor, Utility buttons display the corresponding menus.
Auto Set: Automatically sets the oscilloscope controls to produce a usable display of the input signal.
This is your “panic” button. Punch it in anytime something goes wrong and you do not know why…
Default set up: Recalls the factory set up.
Single Seq: Acquires a single waveform and then stops.
Run/Stop: Continuously acquires waveforms.
Print: Starts print operations. You may use this in some of the individual experiments.
1
Basic Setup for 1-Channel Operation
To begin, turn on the oscilloscope by pressing
the POWER button on the top of the
oscilloscope. Because the Tektronix TDS1002 is
a dual input oscilloscope, you can choose to
display a voltage waveform from either of two
inputs (or both simultaneously). The input
“channels” are marked CH1 and CH2,
respectively, on the front panel. Repeatedly
pressing the MENU button for CH 1 will turn
the scope trace for Channel 1 ON and OFF.
Likewise, pressing the MENU button for CH 2
will turn the scope trace for Channel 2 ON and
OFF. Do not have any connections to the scope
input for now.
Fig. 2. Screen shot with scale factor displays.
For now, we are only interested in looking at the voltage on Channel 1, so press the appropriate
MENU buttons to turn CH 1 ON and CH 2 OFF. Press the Trig Menu button to bring up the
TRIGGER MENU. For Mode, select Auto; for Type, select Edge; for Slope, select Rising;, for
Source, CH1, and for Coupling. Next turn the SEC/DIV knob to 10.0 µs (as read out in area C of Fig.
2), and the VOLTS/DIV knob for CH 1 to get 1.00V (as read out on area A of Fig. 2). You should see
a horizontal line on the screen. If not, use the VERTICAL POSITION knob to center the line so that
it is at 0.00 divs (0.00 V). Because we are only looking at CH1, only the left-hand knob for the
VERTICAL POSITION will be useful.
Once the trace has been centered, you can use the DISPLAY option to adjust the brightness of the
trace (if needed) using the Contrast Increase and Contrast Decrease buttons. Next, press the CH 1
MENU button and set the Coupling to Ground. Adjust the VERTICAL POSITION knob so that the
trace is exactly centered at 0.00 div (0.00 V), then return Coupling to the DC setting. Other CH1 menu
settings should be as follows: BW limit: off; Volts/Div: Coarse; Probe: 1X (you will change this later
when using a 10X probe); Invert: Off. You are now ready to connect the BNC cable between the scope
Chan 1 input and the Teachscope output and proceed with the measurement of the signal on
Teachscope Channel 1.
Scale Factor Displays
As we have seen, the horizontal scale factor (time/division) is shown in area C of Fig. 2. Areas A and
B show respectively the CHAN 1 and CHAN 2 scale factors (V/div). Area D shows a high precision
readout of the frequency of the trigger source signal, which will normally be the CHAN or 2 input.
Vertical Coupling Control
From the CH 1 MENU, you can choose what kind of Coupling you wish to have for the oscilloscope
input: Ground, DC, or AC. When the Coupling is set to Ground, the input signal is disconnected
and the input to the oscilloscope is connected to “ground” – the local zero potential reference. While
the Coupling is set to Ground, wherever the beam is positioned vertically on the screen (which can be
done arbitrarily using the VERTICAL POSITION knob) will determine the vertical location that
corresponds to 0 V, or ground. You should always know where ground is referenced to on the display
for both CH1 and CH2 while looking at signals on the scope. Unlike Ground, when the Coupling
button is in the AC position, only the DC (constant) component of the signal will be filtered from the
input, which means that the AC (changing) component of the signal will still be displayed. And finally,
2
it is only when the button is in the DC position that the oscilloscope will display all components of
waveform input into the device— both the DC and AC components of the signal. The advantage of
using AC coupling over DC coupling occurs when you are trying to measure small variations of a
signal that contains a large DC component. As an example, consider the relatively small ”ripple” (5
mV) on the output of a typical DC power supply (say 5 V). With DC coupling, increasing the input
sensitivity in an attempt to see the small variation will send the trace off the top of the screen.
However, with AC coupling, the 5 V level will be suppressed and the sensitivity can be greatly
increased while retaining the trace near the center of the display.
Trigger Controls
The triggering circuitry is the means by which the oscilloscope is able to provide a stable “overlay”
of repeated ”snapshots” of a repetitive signal. By controlling the threshold voltage and slope polarity at
which the waveform plot begins, the user is provided with great flexibility in the appearance of the
display and the use of the scope for capturing elusive signals. The occurrence of the trigger event
determines the start of the waveform plot.
The TRIGGER LEVEL control sets the threshold voltage for the trigger. The current trigger level is
read out in display area D (Fig. 2) and is also indicated by a left-pointing arrow at the righthand edge
of the main display grid. Display area D also shows the trigger source, type (edge, video, or pulse), and
slope, as well as the frequency of the signal from which the trigger is derived.
Fig. 3. Display of a triangle wave with different trigger conditions.
The SLOPE selector chooses whether the trigger event will occur when moving through the
threshold from a high voltage to a low voltage (falling edge/negative slope) or from a low to high
voltage (rising edge/positive slope). Refer to Figure 3 for a pictoral representation of the result of
various trigger level and slope combinations. Setting the trigger level too low or too high (outside the
bounds of the signal amplitude) results in loss of triggering and an unstable “running” waveform.
The trigger source selection EXT allows an external, better-conditioned signal to be used to trigger
the scope while observing a relatively weak signal—one that is too weak for good internal triggering.
External triggering is accomplished by connecting the signal to be used for triggering to the external
trigger input EXT TRIG of the scope and selecting Ext on the trigger Source button.
Cursors and Cursor Controls
Push the CURSOR button to display the measurement cursors and the Cursor Menu. (The oscilloscope
must show a waveform for the cursors and cursor readouts to appear.) The Cursor LEDs near the
Vertical position knobs will light, indicating that those knobs now can be used to position the cursors.
The cursor menu choices are shown on the following page.
3
Automatic Measurement Functions
Push the MEASURE button to access automatic measurements of the waveform. There are eleven
possible measurements available, and you can display up to five at a time. Push the top option button
to display the Measure 1 menu, then choose the channel on which to take a measurement in the Source
option. Choose the type of measurement in the Type option, then push the Back button to return to the
MEASURE menu and display the measurement results.
Measurement Type
Freq
Period
Mean
Pk-Pk
CycRMS
Min
Max
Rise Time
Fall Time
Pos Width
Neg Width
Definition
Calculates frequency of waveform by measuring first cycle
Calculates time of first cycle
Calculates arithmetic mean voltage over the entire record
Calculates the absolute difference between the min & max peaks of entire record
Calculates a true RMS measurement of the first complete cycle of the waveform
Minimum value in entire record (2500 points)
Maximum value in entire record (2500 points)
Measures time between 10% and 90% of the first rising edge of waveform
Measures time between 90% and 10% of the first falling edge of waveform
Measures time between first rising edge and next falling edge at 50% level
Measures time between first falling edge and next rising edge at 50% level
4