Instrumentation & Measurement Lab Experiments

Experiment to Study the CRO Operation and Functionality

May 28 2023

AimStudy of CRO.

Introductio:

The CRO forms one of the most useful and versatile test instruments It is essentially a device for Displaying graphs of rapidly changing voltage and current but it is also capable of giving ,information consuming frequency. Phase deterrence and voltage amplitudes.

Diagram of CRO

The principal components of a basic oscilloscope include a cathode ray a sweep oscillator deflection amplifies and suitable controls switches and input terminals. The cathode ray tube Consists of a highly evacuated glass tube containing an electronic gun, two pairs of deflection Plats and a screen coated with fluorescent material so that when the electrons strike the screen they give up energy to it causing light to be emitted at that point of contact. The electron gun produce a beam of electrons witch can be made to focus at the screen, the voltage applied to the deflection plates move the beam either horizontally or vertically. The sweep generator produces A voltage rising linearly with time and then abruptly falling to zero this cycle is repeated and is known as the saw tooth wave form this voltage when applied to the horizontal deflection plate Makes the electron traverse equal.

Deflection in equal intervals of time the unknown voltage is applied to the vertical deflection plate through the vertical amplifier moving the spot on the screen accordingly in addition to its in order to display stationary waveform on the screen, it is essential that the frequency of the saw tooth voltage wave form nave a define relationship to the frequency of the to be displayed. The purpose of the synchronizing circuit is to start the Sweep voltage at a specific instant with respect to the waveform under observation.

Recent advancements in electronics have led to number of features being incorporated in the Oscilloscope which include dual trace (having two display channels) and facilities for adding, subtracting and inverting the waveform on both the channels.

Aplab 37060 30 MHZ Dual Trace Oscilloscope has been provided for experiment various control and their function are enumerated below:-

Intensity:It adjusts for brightness of the pattern a high intensity spot which remains stationary may burn the screen and should me fore be avoided.
Focus:“This control affects the sharpness of the trace. It must be adjusted so that to provide the finest line or the smallest point .
Vertical & horizontal position: Adjustrnom of these controls move the trace up & down o to the left and right of the rube face.
Time Base:It consist of a multi position switch which is used to select various calibrated sweeps.
Level :The level knob is used for selecting trigger point on the displayed waveform.
Volts /Division:This knob, one for each of the channels is used to select the range for vertical deflection of the waveform on the tube face.
Int/ext:These modes are chosen for displaying of trigger signals derived from any other external source is fed through EXT TRIG: BNC. Socket.
Intensity:It adjusts for brightness of the pattern a high intensity spot which remains stationary may burn the screen and should me fore be avoided.
Auto/Norm :In the auto mode type trace is displayed in absence of any input signal . The display is then automatically triggered for signals above 30Hz depending upon correct setting of trigger Level control .
CH1/CH2:This control is used to select the signal trigger in INT mode derived from either CH1/CH2 input of trigger level control.
ALT/CND:This switch select the switching mode for the two channels while in dual position .
Dual/Mono(X-Y):This is to choose between single and dual trace modes of operation It dual is chosen it operates in ALT or CHOP as selected.
Channel Addition:This can be used in dual mode and enable the algebraic addition of both the signals CH1 & CH2 .
Channel subtraction: This can be used in dual mode and the function is realized when ADD and CH2m v switches are pressed CH2 signal is algebraically subtracted from CH1.
CH2 INV: When this switch is pressed the polarity of the signal to CH2 is inverted.

The dual trace oscilloscope differ from the single beam oscilloscope in that it has only one electron beam which generates the two trace In order to generates two independent traces two method exist. ALT & CHOP. In the ALT method, the oscilloscope is deflected to display CH1 & CH2 Vertical input is displayed at different position on the oscilloscope screen. A switching system is used for changing channels. The disadvantage of this system is that the display is not actually a Representation of two simultaneous events, but is of events at two simultaneous events are cyclic.

The other method is to switch from one vertical channel to the other at a rapid rate that the display is created from small segments of the actual waveform .This is called the CHOP mode. This requires that the chopping frequency be much greater than the input waveform in order to prevent. The display form being unrecognizable. The circuitry remains the same for both ALT and CHOP, Modes except that the electronic switch differs. For the ALT the switch is a trigger generator and it is a high frequency clock for CHOP mode.