BK Precision 4011A Instrucciones de operaciones descargar pdf (Pagina 64)

Appendix D: Operating Instructions for a Typical Oscilloscope

201052

ground to the common ground of the circuit. Exercise great care when making measurements

with both terminals above ground potential, as there may be a difference in potential between

two instrument cases, causing ground loop currents, faulty readings, and damaged equipment.

Voltage Measurement (AC & DC)

The oscilloscope has advantages as a voltmeter: a very high input impedance compared to an

analog voltmeter;, the ability to measure voltages over a very wide frequency range; and the abil-

ity to indicate magnitude regardless of waveform. Also, scopes measure peak-to-peak values of

AC voltages, whereas standard AC voltmeters measure rms values of sine wave voltages. How-

ever, the oscilloscope only has an accuracy of 2% to 5%, while the AC voltmeter’s accuracy will

be from 0.25% to 2%.

To use the oscilloscope as an AC voltmeter, apply the signal to the vertical input terminals, and

adjust the calibrated VERTICAL SENSITIVITY (or VOLTS/DIV) so the amplitude is of suitable magni-

tude on the graticule. The

peak-to-peak value is then the

distance indicated multiplied

by the vertical calibration. For

example, assume that a sine

wave generator is set to 1000

Hz and adjusted for maximum

output voltage. A peak-to-peak

value of 60V is observed on

the oscilloscope. The output of

the generator at 1000 Hz,

therefore, is approximately

60V peak-to-peak, and 21.2

rms

Note:

2 2

rms p p

V V





For DC measurements, apply the voltage to the vertical input terminals, again suitably adjusting

the VERTICAL SENSITIVITY. A straight line is produced with the horizontal sweep functioning.

With no horizontal voltage applied, a spot will appear on the screen. In measuring DC voltages,

it is necessary to remember where the trace was with 0V applied to the vertical input.

Frequency Measurement

The frequency of an unknown signal may be calculated

from the oscilloscope very easily. The period of the

waveform is the product of the distance along the x-axis

covered by one cycle and the horizontal sweep setting.

As an example, a sine-wave generator is set to 1000 Hz

with the voltage applied to the oscilloscope vertical.

One cycle covers 9.95 cm, with a sweep speed of

100 µsec/cm. The period is T = (9.95)·(10010

-6

)sec.

The measured frequency is f = 1/T = 1005 Hz.

rms value

= 21.2 V

T = 9.95x10

sec

f = 1005 Hz

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