Measuring Waveform Voltage and Frequency with a CRO
Experiment 1: Waveform Measurement
Aim: To measure the voltages and frequency of different waveforms using a Cathode Ray Oscilloscope (CRO).
Apparatus: Cathode Ray Oscilloscope (CRO), function generator, BNC connector, and connecting wires.
Theoretical Background
Cathode Ray Oscilloscope (CRO)
The Cathode Ray Oscilloscope (CRO) is a common laboratory instrument that provides accurate time and amplitude measurements of voltage signals over a wide range of frequencies. Its reliability, stability, and ease of operation make it suitable as a general-purpose laboratory instrument. The heart of the CRO is the Cathode Ray Tube (CRT).
Cathode Ray Tube (CRT) Components
The following are the primary components of a CRT:
- Electron Gun: This consists of a series of elements, primarily a heating filament (heater) and a cathode. The electron gun creates a source of electrons which are focused into a narrow beam directed at the face of the CRT.
- Control Electrode: This is used to turn the electron beam on and off.
- Focusing System: This is used to create a clear picture by focusing the electrons into a narrow beam.
- Deflection Plates: These are used to control the direction of the electron beam. They create an electric or magnetic field which bends the electron beam as it passes through the area.
- Phosphor-coated Screen: The inside front surface of every CRT is coated with phosphor. Phosphor glows when a high-energy electron beam hits it. Phosphorescence is the term used to characterize the light given off by a phosphor after it has been exposed to an electron beam.
Function Generator
A function generator is a piece of electronic test equipment used to generate different types of electrical waveforms over a wide range of frequencies. Some of the most common waveforms produced by the function generator are the sine, square, triangular, and sawtooth shapes.
Experimental Procedure
- Observe the controls on the front panel of the CRO.
- Observe the front panel of the signal generator.
- Connect the CRO to the signal generator using a BNC connector.
- Turn on the signal generator and set it to produce sine, square, and triangular signals.
- If using CH1, keep the operating keys of the CRO on CH1. Switch to GND mode for CH1.
- Switch to AC mode on CH1, observe the sine wave on the screen, and measure its voltage and frequency.
- Repeat the process for other waveforms (square and triangular).
- Note the frequency of the signal generator. The voltage measured on the CRO should equal the voltage of the signal generator.
Observations and Data
| Name of Waveform | Freq. of Signal Generator (Hz) | No. of Divisions on X-axis (A) | Time Period on T/DIV Knob (B) | Time Period of Waveform (T = A × B) |
|---|---|---|---|---|
| Sine | 100 | 2.6 | 2 | 5.2 × 10-3 s |
| Sine | 1000 | 1 | 1 | 1.0 × 10-3 s |
| Sine | 10000 | 1 | 0.1 | 0.1 × 10-3 s |
| Triangular | 100 | 2.8 | 2 | 5.6 × 10-3 s |
| Triangular | 1000 | 1 | 1 | 1.0 × 10-3 s |
| Triangular | 10000 | 1 | 0.1 | 0.1 × 10-3 s |
| Frequency of CRO (Hz) F = 1/T | Vp-p = No. of Vertical Divisions × V/DIV (V) |
|---|---|
| 192 Hz | 2V |
| 1000 Hz | 2V |
| 10000 Hz | 2V |
| 178.5 Hz | 2V |
| 1000 Hz | 2V |
| 10000 Hz | 2V |
Conclusion
In this experiment, we observed different types of waveforms produced by a function generator and successfully measured their amplitude in volts and their frequency in Hz.