Electronic Measurement using CRO

Download Lissajous pattern.epb

Aim: -

To measure voltage, frequency, time period, phase difference, peak value, peak to peak value and RMS value of an alternating voltage.

Components: -


EDWin Components Used


Number of components required

RES RC05 Resistor 1
VGEN VGEN Voltage Generator 2
GND SPL0 Ground 1

Theory: -

Analogous to the CRO used for measuring the voltage, time period, frequency, peak voltage, peak to peak voltage and RMS voltage, we use Waveform Viewer, for measurement in EDWin.

Time Period: - The time taken by an alternating voltage to complete one cycle is called its Time period, T.

Using CRO: - Measure the number of divisions for a single cycle on the time axis and multiply it by the value indicated by the Times/Div knob on the CRO. This gives the Time Period of the alternating voltage.

Using EDWin: - Waveforms can be observed in the Waveform Viewer which is analogous to the CRO time Period can be directly obtained from the Waveform Viewer.

Frequency: - The number of cycles completed in one second is called the frequency of the alternating voltage. Its unit is Hertz. Frequency is given by the reciprocal of Time period T.


Peak and Peak to Peak Value: - The maximum value, +ve or –ve of the alternating quantity is known as its peak value. It is also called maximum value or amplitude of the alternating quantity.

The total voltage measured from –ve peak to +ve peak is called the Peak to Peak voltage.

Using CRO: - Measure the number of divisions on the voltage axis and multiply it by the value indicated by the Volts/Div knob on the CRO. This gives the peak value.

Using EDWin: - Peak value and Peak to peak value can be directly obtained from waveform viewer.

RMS Value (Root Mean Square Value)

It is given by the steady dc current which when flowing through a given circuit for a given time produces the same heat as produced by the alternating current which when flowing through the same circuit for the same time.

RMS value of alternating voltage is related to its peak value by the relation

Phase: - The phase of an alternating quantity is the fraction of the time period of the alternating voltage which has elapsed since the voltage last passed through the zero position of reference.

Phase difference: - Consider two alternating quantity of same frequency reaching their peak/ zero value at different instants of time. a gives the phase difference between two waves.

The phase difference between two sinusoidal signals of same frequency can be calculated from the amplitudes y1 and y2 of the lissajous pattern. Phase difference is given by

Lissajous Pattern: - A lissajous pattern is produced on the screen when two sine wave voltages are applied simultaneously to both pairs of deflection plates of a CRO.

A known frequency fH is applied to the horizontal input, and an unknown frequency fV is applied to the vertical input. Then a lissajous pattern with loops is obtained. The unknown frequency fV can be measured by the relation;

Figure shows typical case of lissajous pattern for particular frequency and phase difference.

Rise time, Fall time, Duty cycle and Time Period of square pulse.

Rise time: - The time required for a signal to transit from 10% of its maximum value upto 90% of its maximum value.

Fall time: - The time required for a signal to transit from 90% of its maximum value down to 10% of its maximum value.

Duty cycle: - For periodic rectangular waveform, the ratio of the time the signal is high to the time period of the signal.

Time Period: - The time required to complete one cycle is referred to as Time Period, T.

Procedure: -

EDWinXP -> Schematic Editor: The circuit diagram is drawn by loading components from the library. Wiring and proper net assignment has been made. The values are assigned for relevant components.

EDWinXP -> Mixed Mode Simulator: The circuit is preprocessed. The test points and waveform markers are placed at both voltage generators. GND net is set as reference net. The Transient Analysis parameters have been set.

We set one voltage source as fixed and the second is varied with respect to the first. In other words, the second voltage source is set as the unknown voltage source and its frequency and phase is varied in order to obtain standard output waveforms. The Transient Analysis is executed and output waveform is observed in the Waveform Viewer. To obtain lissajous pattern in the Waveform Viewer proceed as follows. Wave form Viewer -> Options -> Waveform -> Axes -> Select X variable and Y variable(in this case V1 and V2 respectively)-> Apply.

Result: -

The output waveform may be observed in the waveform viewer.

Vertical frequency, horizontal frequency and phase difference for each lissajous pattern is shown below.