13 Jul 2026

Measurement of Voltage and Time Period of a Periodic Waveform Using CRO

practical ug-iv electronics cro waveform

Aim

To measure the peak-to-peak voltage, time period, and frequency of a periodic waveform using a cathode-ray oscilloscope.

Apparatus

CRO, function generator, connecting leads, and a calibrated probe.

Apparatus image

CRO and function generator used for waveform measurements.

Theory

A CRO displays the input voltage as a vertical deflection against time along the horizontal axis. If the waveform occupies $n_v$ vertical divisions and the vertical sensitivity is $S_v$ volts per division,

\[V_{pp}=n_vS_v.\]

If one complete cycle occupies $n_t$ horizontal divisions and the time-base setting is $S_t$ seconds per division,

\[T=n_tS_t,\qquad f=\frac{1}{T}.\]

Procedure

1. Connect the function generator to the CRO input.
2. Select a sinusoidal waveform and obtain a steady trace.
3. Adjust intensity, focus, and vertical position.
4. Count the vertical divisions between the positive and negative peaks.
5. Count the horizontal divisions for one complete cycle.
6. Substitute the readings in the formulae.

Observations

Vertical sensitivity: $S_v=2\,\text{V div}^{-1}$; time-base setting: $S_t=0.5\,\text{ms div}^{-1}$.

Trial	Vertical divisions $n_v$	$V_{pp}$ (V)	Horizontal divisions $n_t$	$T$ (ms)	$f$ (Hz)
1	3.0	6.0	4.0	2.0	500
2	3.1	6.2	4.0	2.0	500
3	3.0	6.0	4.0	2.0	500

Calculation

For the second observation,

\[V_{pp}=3.1\times2=6.2\,\text{V},\] \[T=4.0\times0.5=2.0\,\text{ms},\qquad f=\frac{1}{2.0\times10^{-3}}=500\,\text{Hz}.\]

The peak voltage is $V_p=V_{pp}/2=3.1\,\text{V}$.

Result

The measured peak-to-peak voltage is

\[\boxed{V_{pp}=6.1\,\text{V}},\]

and the frequency of the waveform is

\[\boxed{f=500\,\text{Hz}}.\]

Precautions

1. Do not exceed the maximum input voltage of the CRO.
2. Obtain a stationary trace before counting divisions.
3. Use the correct probe attenuation setting.
4. Keep the time-base and sensitivity controls unchanged during a trial.

Viva Questions

1. What does the vertical axis represent? It represents the instantaneous input voltage.
2. What does the horizontal axis represent? It represents time through the sweep circuit.
3. Why must the trace be stationary? A stationary trace permits accurate division counting.
4. What is triggering used for? It synchronises the sweep with the waveform and stabilises the display.

Maxima Code

Download the Maxima calculation file.