CRO

Hi friends, this time I am going to tell about one of the most used electronic instruments named CRO. The CRo can be expanded as the Cathode Ray Oscilloscope.

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 a cathode-ray tube. It is an electronic instrument capable of giving a visual indication of a signal waveform. It is widely used for measuring the voltage as a function of time. The CRO depends on the movement of an electron beam, which strikes a screen coated with fluorescent material, to produce a visible spot. If the electron beam is deflected on x-axis and y-axis, a two dimensional display is produced.

A general purpose CRO consists of the following main components:

1.      Cathode Ray Tube (CRT).

2.      Vertical Amplifier.

3.      Triggering Circuit.

4.      Sweep generator.

5.      Horizontal Amplifier.

6.      Delay line.

7.      Power supply.

1. Cathode Ray Tube (CRT): The heart of the CRO is the Cathode Ray Tube which generates the electron beam, accelerates it to a high velocity and deflects it to create the image. The CRT contains the Phosphor screen where the beam becomes visible.To accomplish these tasks, various electrical signals and voltages are required which are generated by the remainder of the blocks. Before striking the screen the electron beam passes between a set of deflection plates. The vertical and horizontal movements are independent of one another so that the spot on the screen can be positioned anywhere on the screen by the simultaneous application of appropriate vertical and horizontal voltage inputs. When a periodic signal is applied to the vertical plates and a sawtooth signal of the same period is applied to the horizontal plates, the spot will trace an image of the periodic signal on the screen.

2. Vertical Amplifier: The signal to be viewed is fed to the vertical amplifier, which is a wideband amplifier used to increase the potential of the input signal to a level that will provide a deflection of the electron beam.

3. Triggering Circuit: To synchronize the horizontal deflection with the vertical input, such that the horizontal deflection starts at the same point of the input vertical signal, a synchronizing or triggering circuit is used. This circuit is the link between the vertical input and the horizontal time base.

4. Time base generator (sweep generator): Time base generator is used to generate the sawtooth voltage required to deflect the beam in the horizontal direction. It controls the rate at which the beam is scanned across the face of the CRT and is adjusted from the front panel.

5. Horizontal Amplifier: The horizontal amplifier is similar to the vertical amplifier and it increases the amplitude of the signals generated in the sweep generator to the level generated by the horizontal deflection plates of the CRT.

6. Delay line: All electronic circuitry in the oscilloscope cause a certain amount of delay in the transmission of signal voltages to the deflection plates. Comparing the vertical and horizontal deflection circuits in the oscilloscope block diagram, we observe that signal processing in the horizontal channel involves trigger circuit, time base generator, and horizontal amplifier whose output is fed to the horizontal deflection plates. This whole process takes time. To allow the operator to observe the leading edge of the wave form, the signal drive for the vertical CRT plates must be delayed by at least the same amount of time. This is the function of the delay line.

7. Power supply: The power supply block provides the voltages required by the CRT to generate and accelerate the electron beam as well as to supply the required operating voltages for the other circuits of the CRO. Relatively high voltages are required by CRTs for acceleration; low voltages are required for the heater of the electron gun, which emits the electrons. Supply voltages for the other circuits are various values, usually not more than a few hundred volts..

There are many applications of CRO, a few of them are:

·         Tracing of an actual waveform of current or voltage.

·         Determination of amplitude of a variable quantity.

·         Comparison of phase and frequency.

·         Measurement of capacitance and inductance.

·         In televisions.

·         In RADAR.

·         For engine pressure analysis.

·         For tracing transistor curves.

 I hope this was useful. Keep visiting the blog for latest posts….