Oscilloscope
Protocol for measuring the electrical signals using an oscilloscope
Theory of the method:
Oscilloscope
Materials:
- Oscilloscope
- Rectifier: transformer, rectifier (diode), filter capacitor, switch
- Coaxial cable
Procedure:
A. Callibrate the oscilloscope
- turn ON the oscilloscope (on the screen it is visible a bright spot)
- select one channel of the vertical block (ex: channel A)
- adjust the intensity of the spot; adjust the focus
- set the bright spot in the center of the screen ("positioning" knob)
- calibrate the signal on vertical axis - TIME/DIV knob
- calibrate the signal on horizontal axis - VOLTS/DIV knob
- set trigger: AUTOMATE
B. Measure the amplitude A and calculate the voltage V for AC
- select AC option in the vertical block
- obtain a sine wave:
- connect the rectifier to the oscilloscope using the coaxial cable (BNC connector)
- connect the rectifier to the power supply
- settings: the circuit should not include the diode (terminal A and D connected)
- TIME/DIV = 5 ms
- VOLTS/DIV = 5 V
- obtain a sine wave:
- measure the amplitude (number of divisions on the vertical axis)
- calculate the voltage for AC (ex: 5 V/square/5 divisions)
C. Measure the period T and calculate the frequency f for AC
- maintain the same settings
- measure the period (number of divisions on the horizontal axis/one cycle)
- calculate the frequency (ex: 5 ms/square/5 divisions)
D. Measure the amplitude A and calculate the voltage V for DC signal
- start from the previous settings
- transform AC in DC:
- obtain the rectified current: include the diode (terminal B and D) = half-wave signal
- select GND (ground) option in the vertical block; set the signal in the center of the screen
- select DC option in the vertical block
- filter the rectified current: include filter capacitor (same settings + close switch/ C) = filtered signal
- measure the amplitude
- calculate the voltage for DC
Useful links:
AC, DC and electrical signals: http://www.kpsec.freeuk.com/acdc.htm
Oscilloscope: http://www.kpsec.freeuk.com/cro.htm