Page 57 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

The trigger will produce a pulse or impulse for triggering the time-base. Every time the time-base is triggered, one
saw-tooth wave-form is produced.

There are three forms of triggering in an oscilloscope.
Internal triggering : The signal which is supplied to the trigger is the internal signal of the CRO produced by
using the signal from the vertical input signal. The sequence of signal processing is shown in Fig 6.

External triggering : The signal which is supplied to the trigger is the external signal, produced by using the
signal from the external, sync.
Line triggering : The signal which is supplied to the trigger is the signal from the power supply of CRO. (Not
shown in the block diagram)
Switches are provided to select the form of triggers as required. In a CRO, suitable timing can be selected that
causes the image on the screen to be stationary.

CRO (The Cathode ray tube): The constructional features are explained later in this text.
Power supply: Low voltage and high voltage DC supplies which are required for the oscilloscope function are
produced by rectifier filters and switch mode power supply circuits.

Controls and their functions in a cro: The operating controls on the front panel of a general purpose oscilloscope
is shown in Fig 7. The names of the controls and their functions are listed below.

Fig 6 Fig 7

General

Power-on (1): It is toggle switch meant for switching on power. In the ON position, power is supplied to the
instrument and the neon lamp (3) glows.
Intensity (2): It controls the trace intensity from zero to maximum.

It controls the sharpness of the trace. A slight readjustment of this control may be necessary after changing the
intensity of the trace.
X-Magnification (5): It expands length of the time-based from 1 to 5 times continuously, and makes the maximum
time-base to 40ns/cm.
Square wave (6): This provides a square wave of 2 V (p-p) amplitude to enable the user of the scope to check
the Y-calibration of the scope.

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CITS : Power - Electrician & Wireman - Lesson 60-69