Page 94 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Fig 2

Checking oscillator frequency: The frequency of an oscillator can be computed if the values of L (L = L1 + L2)
and C are known using the formula,
f =

where, f is in hertz, L in henry, and C in farad.
The frequency of an oscillator may be measured in two ways,
• Using a direct read-out frequency meter also known as frequency counter which is most accurate, popular and
easy to use.
• Using an oscilloscope with a calibrated time base to measure the period of the wave-form. From the measured
period, ‘T’ frequency is calculated using the formula
f =
where, f is the frequency in Hz and ‘T’ the time period in seconds.
A practical hartley oscillator circuit using medium-wave oscillator coil as L is shown in Fig 3.
The advantage of using a medium wave oscillator coil for L is that the output can be taken out of the secondary
winding (4 and 5) of the coil.

Fig 3

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