precautions while using cathode ray oscilloscope

Precautions while using Cathode Ray Oscilloscope

The cathode-ray oscilloscope (CRO) is a common laboratory instrument that provides accurate time.
11. Cathode ray tube
Power and Scale Illumination Turns instrument on and controls illumination of the graticule.Focus Focus the spot or trace on the screen.Intensity Regulates the brightness of the spot or trace.
12. Vertical amplifier section
Position Controls vertical positioning of oscilloscope display.
Sensitivity Selects the sensitivity of the vertical amplifier in calibrated steps.
Variable Sensitivity Provides a continuous range of sensitivities between the calibrated steps. Normally the sensitivity is calibrated only when the variable knob is in the fully clockwise position.
AC DC GND Selects desired coupling ac or dc for incoming signal applied to vertical amplifier, or grounds the amplifier input. Selecting dc couples the input directly to the amplifier; selecting ac send the signal through a capacitor before going to the amplifier thus blocking any constant component.
13. Horizontal sweep section
Sweep time cm Selects desired sweep rate from calibrated steps or admits external signal to horizontal amplifier.
Sweep time cm Variable Provides continuously variable sweep rates. Calibrated position is fully clockwise.
Position Controls horizontal position of trace on screen.
Horizontal Variable Controls the attenuation reduction of signal applied to horizontal aplifier through Ext. Horiz. connector.
14. Trigger
The trigger selects the timing of the beginning of the horizontal sweep.Slope Selects whether triggering occurs on an increasing + or decreasing portion of trigger signal.Coupling Selects whether triggering occurs at a specific dc or ac level.
15. Operating instructions
Before plugging the oscilloscope into a wall receptacle, set the controls as follows
a Power switch at off
b Intensity fully counter clockwise
c Vertical centering in the center of range
d Horizontal centering in the center of range
e Vertical at 0.2
f Sweep times 1
16. Warning
Never advance the Intensity Control so far that an excessively bright spot appears. Bright spots imply burning of the screen. A sharp focused spot of high intensity great brightness should never be allowed to remain fixed in one position on the screen for any length of time as damage to the screen may occur.
17. Procedure
I. Set the signal generator to a frequency of 1000 cycles per second. Connect the output from the gererator to the vertical input of the oscilloscope. Establish a steady trace of this input signal on the scope. Adjust play with all of the scope and signal generator controls until you become familiar with the functionof each. The purpose fo such playing is to allow the student to become so familiar with the oscilloscope that it becomes an aid tool in making measurements in other experiments and not as a formidable obstacle. Note If the vertical gain is set too low, it may not be possible to obtain a steady trace.
18. Measurements of voltage
Consider the circuit in Fig. 4 a . The signal generator is used to produce a 1000 hertz sine wave. The AC voltmeter and the leads to the verticle input of the oscilloscope are connected across the generators output. By adjusting the Horizontal Sweep time cm and trigger, a steady trace of the sine wave may be displayed on the screen. The trace represents a plot of voltage vs. time, where the vertical deflection of the trace about the line of symmetry CD is proportional to the magnitude of the voltage at any instant of time.
19. Multimeter
A multimeter is used to make various electrical measurements, such as AC and DC voltage, AC and DC current, and resistance. It is called a multimeter because it combines the functions of a voltmeter, ammeter, and ohmmeter. Multimeters may also have other functions, such as diode andcontinuity tests. The descriptions and pictures that follow are specific to the Fluke 73 Series III Multimeter, but other multimeters are similar.
20. Function generator
A function generator is a device that can produce various patterns of voltage at a variety of frequencies and amplitudes.It is used to test the response of circuits to common input signals. The electrical leads from the device are attached to the ground and signal input terminals of the device under test.