Download Version: QUICK REFERENCE FOR AGILENT 54621A OSCILLOSCOPE PDF

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To use analog channels to view a signal  

To make cursor measurements  

How to make measurements using the grid lines  

To make automatic measurements  

To add/subtract two voltage signals  

To use Fast Fourier Transform (FFT)

1. To set the instrument to the factory-default configuration, press the Save/Recall key, then press the Default Setup softkey.

The default configuration returns the oscilloscope to its default settings. This places the oscilloscope in a known operating condition. This can be useful and save you time when prior user has set oscilloscope to customized settings.  

To use analog channels to view a signal

1. Setup signal generator as described below. 

2. Connect signal generator to channel 1.

3. To configure the oscilloscope quickly, press the Autoscale key to display the connect signal.

To undo the effects of Autoscale, press the Undo Autoscale softkey before pressing any other key. This is useful if you have unintentionally pressed the Autoscale key or do not like the settings Autoscale has selected and want to return to your previous settings.

To capture screen image and/or data to PC: http://www.seattleu.edu/scieng/ece/scopesetup.html 

You can use the cursors to make custom voltage or time measurements on scope signals.

1. Set up signal generator as shown in the previous example.

2. Press the Cursors button.

• X Y softkey selects either the X cursors or the Y cursors for adjustment with the Entry knob.
• X1 and X2 softkey adjust horizontally and normally measure time.
• Y1 and Y2 softkey adjust vertically and normally measure voltage.
• X1 X2 and Y1 Y2 softkey move the cursors together when turning the Entry knob.

3. Press X1 softkey and adjust curser position to the intersection of ground level on the first falling edge of the sine wave, see the following image in section 4.

• Ground level icon: The ground level of the signal is identified by the position of the  icon at the far-left side of the display.

4. Press X2 softkey and adjust curser position to the intersection of ground level on the second falling edge of the sine wave.

5. Measure the period (duration of a cycle) between X1 and X2 = ∆X = 1.0ms = 1/∆X = 1.0kHz

Image and measurments should be similar to above.

6. Press X Y softkey to select Y curser.

7. Press Y1 softkey and adjust curser position to bottom of the waveform.

8. Press Y2 softkey and adjust curser position to the top of the waveform. 

9. Measured voltage between Y1 and Y2 = ∆1 = 4.0V

Image and measurments should be similar to above.

To capture screen image and/or data to PC: http://www.seattleu.edu/scieng/ece/scopesetup.html  

How to make measurements using the grid lines  

The vertical scale is often referred to as the vertical sensitivity or input sensitivity and the horizontal scale as the horizontal sweep speed.  The signal voltage levels are measured against the vertical scale and the duration of each cycle is measured on the horizontal scale. The rectangular grid on the scope’s display is the graticule. The graticule is a grid of squares that serve as reference marks for measuring the displayed trace. In this case the vertical scale is set to 1V per division and the horizontal scale is 200us per division.

Vertical Scale Measurement:

Horizontal Scale Measurement:

To make automatic measurements

The following automatic measurements can be made in the Quick Meas menu. 

            Time Measurements

                        • Counter   • Duty Cycle   • Frequency   • Period   • R i se Time   • Fall Time   • +Width   
                        • -Width   • X at Max   • X at Min

            Phase and Delay

                        • Phase   • Delay

            Voltage Measurements

                        • Average   • Amplitude   • Base   • Maximum   • Minimum   • Peak-to-Peak   • R MS   
                        • Top   Preshoot and Overshoot   • Preshoot   • Overshoot

1. Continue with the previous setup.

2. Press the Quick Meas key to display the automatic measurement menu. The default measurements shown will be Frequency and Peak-Peak as shown below..

3. Press the Clear Meas softkey to stop making measurements and to erase the measurement results from the measurement line.

4. Press the Quick Meas again; the default measurements are shown.

5. Press the Square wave button on the signal generator.

6. Press the Select softkey then turn the Entry knob quickly before the popup list closes to select Duty Cycle (see image below)

7. Press Measure Duty softkey to display the square wave’s duty cycle (http://en.wikipedia.org/wiki/Duty_cycle).

8. Press the Measure softkey to make the selected measurement.

Image and measurments should be similar to above.

9. Option: On the signal generator select the Duty Cycle softkey and change to 70.0%. Note the changes to the oscilloscope display.

10. To turn off Quick Meas, press the Quick Meas key again until it is not illuminated.

To capture screen image and/or data to PC: http://www.seattleu.edu/scieng/ece/scopesetup.html

When you select the math function 1 – 2, channel 2 voltage values are subtracted from channel 1 voltage values point by point, and the result is displayed. You can use 1 – 2 to make a differential measurement or to compare two waveforms.

To perform the addition of channel 1 and channel 2, select Invert in the Channel 2 menu and perform the 1 – 2 math function.

Subtract

1. Setup the following circuit on a breadboard and connect the instruments.

 2. Setup the signal generator as followed:

3. Press the Save/Recall key, then press the Default Setup softkey.

4. Press the Autoscale key.

5. Option:

• When examining the circuit built in step 1; What value for Vpp would you expect to see on Channel 1?
• When examining the circuit built in step 1; What value for Vpp would you expect to see on Channel 2?

6. Press the Math key, press the 1 – 2 softkey,

You should now have the following image displayed.

7. Press the Settings softkey.

8. Set the Scale and Offset softkeys as shown below.

9. Press the vertical channel adjustment knobs and set both vertical channels to 1.00V as shown below.

10. Options: Activate the Automatic measurements for channel 1, 2, and Math 1-2 as shown above.

• Once the function is displayed, the analog channel(s) may be turned off for better viewing.
• If the analog channel or math function is clipped (not fully displayed on screen,) the resulting displayed math function will also be clipped.
• The vertical scaling and offset of each math function can be adjusted for ease of viewing and measurement considerations.   

To use Fast Fourier Transform (FFT)

FFT Units: 0 dBV is the amplitude of a 1 Vrms sinusoid.

FFT: Use the FFT function to find crosstalk problems, to find distortion problems in analog waveforms caused by amplifier non-linearity, or for adjusting analog filters.

FFT is used to compute the fast Fourier transform on the analog input channels. FFT takes the digitized time record of the specified source and transforms it to the frequency domain. When the FFT function is selected, the FFT spectrum is plotted on the oscilloscope display as magnitude in dBV versus frequency. The readout for the horizontal axis changes from time to frequency (Hertz) and the vertical readout changes from volts to dB.

1. Setup the signal generator as followed:

2. Connect signal generator to Channel 1.

3. Press the Save/Recall key, press the Default Setup softkey. press the Autoscale key.

4. Set horizontal sweep speed to 50us.

5. Press the Math key, press the FFT softkey, press the Settings softkey to display the FFT menu.

6. Press the lighted channel 1 button    twice to turn off  display of channel 1.

7. Set Source, Span, and Center softkeys as shown below.

8. Press the More FFT softkey to display additional FFT settings.

9. Set Scale, Offset, and Window softkey as shown below.

10. To make cursors measurements, press the Cursors key.

• Use the X1 and X2 cursors to measure frequency values and difference between two frequency values (∆X).

Cursors Frequency Measurements ∆X = 20.0kHz

• Use the Y1 and Y2 cursors to measure amplitude in dB and difference in amplitude (∆Y).

Cursors Amplitude Measurements ∆Y = -9.69dBV

FFT Measurement Hints

It is easiest to view FFTs with Vectors set to On. The Vector display mode is set in the Display menu. The number of points acquired for the FFT record 2048 and when frequency span is at maximum, all points are displayed. Once the FFT spectrum is displayed, the frequency span and center frequency controls are used much like the controls of a spectrum analyzer to examine the frequency of interest in greater detail. Place the desired part of the waveform at the center of the screen and decrease frequency span to increase the display resolution. As frequency span is decreased, the number of points shown is reduced, and the display is magnified.

While the FFT spectrum is displayed, use the Math and Cursors keys to switch between measurement functions and frequency domain controls in FFT menu. Decreasing the effective sampling rate by selecting a slower sweep speed will increase the low frequency resolution of the FFT display and also increase the chance that an alias will be displayed. The resolution of the FFT is one-half of the effective sample rate divided by the number of points in the FFT. The actual resolution of the display will not be this fine as the shape of the window will be the actual limiting factor in the FFTs ability to resolve two closely space frequencies. A good way to test the ability of the FFT to resolve two closely spaced frequencies is to examine the sidebands of an amplitude modulated sine wave. For example, at 2 MSa/s effective sampling rate, a 1 MHz AM signal can be resolved to 2 kHz. Increasing the effective sampling rate to 4 MSa/s increases the resolution to 5 kHz for a set 2048 point FFT.

For the best vertical accuracy on peak measurements:

• Set the source sensitivity so that the input signal is near full screen, but not clipped.

• Use the Flat Top window.

• Set the FFT sensitivity to a sensitive range, such as 2 dB/division.

For best frequency accuracy on peaks:

• Use the Hanning window.

• Use Cursors to place an X cursor on the frequency of interest.

• Adjust frequency span for better cursor placement.

• Return to the Cursors menu to fine tune the X cursor.

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