Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

6.2.3 Tutorial 6a - Data Collection with an Oscilloscope and LabVIEW

 

· Objectives:

  1. 1. To collect a single sweep of Tektronix 2230 oscilloscope data.
  2. 2. To plot single sweep data on the HC100 digital plotter.
  3. 3. To control a Tektronix PS5010 programmable power supply.
  4. 4. To control GPIB instruments with LabVIEW.

 

· Theory:

  1. We need to observe how system behavior changes over time. To do this we can take successive readings and then plot them as a function of time. If we look at the screen of an oscilloscope, the horizontal axis represents time and the vertical axis voltage. One significant problem with any time based sampling device is when to start recording. We use certain settings to trigger the beginning of the beam scan. Each type of signal will require a different type of trigger, and so oscilloscopes have multiple settings to make them adaptable.
  2. We will connect the lab oscilloscope to the computer with an interface card and cable. The interface between the computer and oscilloscope is called GPIB (General Purpose Instrument Bus) and is also known as IEEE-488. It is a networking scheme that will allow more than one device to be connected to the computer by using chains of cables. To interface to GPIB devices, we need a special interface card in the computer and interface software. We will use LabVIEW to communicate with the oscilloscope.
  3. In general, an oscilloscope can sample voltages at rates from 0Hz up to about 1GHz. A typical inexpensive oscilloscope will sample data up to 10MHz. The DAQ card in the computer have the potential to sample up to 100KHz.

 

Materials/Equipment:

  1. Tektronix 2230 Oscilloscope
  2. Tektronix PS5010 Power Supply
  3. Scope probes
  4. Tektronix HC100 Plotter
  5. Red and Black Banana Jack Plugs (with alligator clips)
  6. PC with GPIB Interface and LabVIEW

 

Procedure:

  1. 1. Before turning on the power to the oscilloscope, you must give it an address as a GPIB device. The address is a number XX set with dip switches. These are found on the side of the oscilloscope and switches 1, 6 and 8 should be set to "1". All others should be set to "0".
  2. 2. The oscilloscope is a very flexible device that can be reconfigured for various measurements. To set various parameters, we use the switches on the front panel, near the display. Set the switches on the front to match the descriptions below:
    1. POSITION CURS-SELECT WAVEFORM (in) -
    2. 1K-4K (in) - this sets the speed of the data collection
    3. ROLL SCAN (out) - keep the display steady
    4. PRETRIG-POST TRIG (out) -
    5. SAVE-CONTINUE (out) - scan repeatedly
    6. STORE-NON STORE (out) - don't store the screen
    7. SLOPE (out) - deselects the input slope as a trigger
    8. A&B INT (CH 1) - selects channel 1 to trigger channel A
    9. A SOURCE (INT) - uses an internal clock for the sweep time
    10. A EXT COUPLING (DC) - sets the input signal as DC
    11. HORIZONTAL MODE (A) - sets channel A for the sweep axis
    12. VERTICAL MODE (CH1) - uses the magnitude of channel 1 for height
    13. X-Y (out) - do a normal time sweep
    14. BW LIMIT (out) -
    15. A AND B SEC/DIV (1 ms) - sets the scan divisions on the scope
  3. 3. Now set up the power supply and connect it to the oscilloscope so that it will supply a signal. To do this, you need to connect the probe to the oscilloscope (CH1) and then to the positive and common terminals of the power supply.
  4. 4. You can now set up a signal to be measured. Turn on the power supply and then program it for 10V on the POS, and 0V on NEG supplies. The OUTPUT should be OFF. Finally, lock the program by pressing LOCK. You may now set up the scan trigger on the oscilloscope. Start the scope scanning continuously in the A TRIGGER mode by pressing P-P AUTO (on). Next you need to 'zero' CH1. To do this, set the input to GND and use CH1 POSITION to center the trace. Once centered, change the input from GND to DC. The trace on the screen should now reflect the actual input. Set the scale to 2 VOLTS/DIV.
  5. 5. Scope is in analog mode.
  6. 6. Put scope in store mode by pressing the STORE button.
  7. 7. Move cursor and observe values.
  8. 8. Connect scope to plotter with GPIB cable and plot waveform.
  9. 9. Turn off scope, disconnect from plotter, connect to computer. Set the address dip switches on side so that only switch 1 is set to "1", all others set to "0". Turn on the scope.
  10. 10. Run LabVIEW and load GPIB vi. This is found under XXXXXXX. Verify GPIB setting, scope should be device 1.
  11. 11. Load the LabVIEW vi for the scope "XXXXXXXXX.
  12. 12. Capture a scan of data into LabVIEW.