Measure and set frequency by using an oscilloscope, Electrical Engineering

1. Introduction:

Theory: Frequency is the number of occurrences of a repeating event per unit time. It can also be defined as the number of repetitions (cycles) of a waveform that appear in a one second. It is very important to measure the frequency of a waveform passed through a circuit used in various electronic gadgets. The frequency can be measured using the oscilloscope using the formula,

F= 1 / T

Hence, if the Time period (T) gets measured, the frequency also can be calculated. Time period is defined as the duration between two adjacent repeating events.

Material Required: Oscilloscope, frequency generator, connecting wires.

Description and Aim: To measure and set frequency by using an oscilloscope.

The frequency is fed into the oscilloscope by using a generator. Hence, oscilloscope will show the frequency signal on a visual display. The oscilloscope display is adjusted so that a clear wave form is seen on the display. The time period is calculated from this waveform.

F = 1/T

2. Method:

Step 1) Use terminal ports to connect generator to DC/AC waveforms circuit block. Now, use two port connector to connect generator source to R1.

Step2) From the generator, set frequency = 1Hz roughly, and select the sine wave. To calibrate the frequency, use dial setting properly. Now, connect channel 1 probe of oscilloscope across the resistor R1. Adjust generator amplitude so that

V(R1) = Vpk-pk = 6 V

Step 3) Set time base control = 0.1 ms/div. Adjust the frequency of generator for a waveform cycle that is seven divisions wide on the horizontal axis (time axis). Measure the no of divisions on the oscilloscope display.

3. Results: (check the readings.. it shud be close to 1 hz as you have set a rough reading of 1 HZ in generator...for that you can change the no of measured time divisions to 8....also note down the unit of signals...was it mHz or Hz)

Vpk-pk = 6 V

No of time divisions for one waveform = 7

One time division = 0.1ms/div

Total time period  = 7 * 0.1 = 0.7 ms

Frequency = F = 1 / T = 1 / 0.7  = 1.42 Hz.

4. Discussion:

The frequency measured using the oscilloscope is 1.42Hz.  This frequency is close to the frequency signal from the generator as the dial was set to 1 Hz roughly. There is a difference between the two frequencies due to reasons like attenuation in the circuit components, degree of accuracy to measure width of waveform on oscilloscope (i.e. divisions in waveform), fluctuations in the generator etc. To precisely read the circuit we can set the signal more accurately in the generator using dial up knob and then measure the time period at oscilloscope.

Posted Date: 3/2/2013 12:56:11 AM | Location : United States

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