BK Precision 4011A Instrucciones de operaciones descargar pdf (Pagina 26)

Laboratory 5: Oscilloscope

201014

a) Measure V

with the oscilloscope for the following values of R: 10kΩ, 100kΩ, and 1MΩ.

b) Calculate the theoretical V

with R

SCOPE

= infinity (ideal).

c) Compare the measured to the calculated results.

d) Calculate the oscilloscope’s DC input resistance. Discuss R

SCOPE

vs. accuracy of V

measured on the oscilloscope.

The next steps use the autotransformer (Variac

) as an AC power supply. When it is time to

apply power, plug the cord into the ISOLATED power outlet on the laboratory bench. Turn off

the power switch when power is not needed, such as when changing the circuit.

3. Peak vs. RMS Voltage:

“RMS” stands for “Root Mean Square” and is a way of expressing an AC voltage or current

in terms functionally equivalent to a DC voltage or current. For example, 10 volts AC RMS

is the AC voltage that would produce the same amount of heat dissipation in a resistor of

given value as would 10 volts DC. The RMS value is also known as the “equivalent” or “DC

equivalent” value of an AC voltage or current. The lab’s digital multimeters (DMM) display

the true RMS values of measured voltage and current, but to see what the actual voltage sig-

nal looks like, we turn to the oscilloscope.

Set up the following circuit:

With the autotransformer turned to zero, turn on its power switch. Gradually increase the

output voltage until the digital AC voltmeter indicates the output is 10 V. Record the exact

value. Observe the waveform on the oscilloscope and compare the DMM reading with the

peak voltage (that is, ½ the peak-to-peak voltage) measured with the oscilloscope. For a sine

wave, the peak voltage, V

as seen on the oscilloscope, should be

times the voltmeter

reading, V

rms

p rms

V V

 and 2 2

p p rms

V V





On the oscilloscope, set up an automatic measurement for the RMS voltage. (See Appendix

E. MEASURE | CH 1 | Cyc RMS.) Compare the values for V

rms

reported by the DMM and the

oscilloscope.

4. Phase Shift through an inductor: Set up the following circuit, using the autotransformer

(Variac

) as an AC power supply. Do not turn on the power until part 4b. The 120 mH induc-

tor is a large, heavy, coaxially wound pair of coils (36 mH and 28 mH), which, because of

their construction, when connected in series yield 120 mH inductance. You will need to con-

nect a jumper from jack 2 to jack 3, then use jacks 1 and 4 for the connections to the 120 mH

coil.

Digital

Voltmeter

10 V

rms

Oscilloscope

CH 1

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 72 73

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BK Precision 4011A Instrucciones de operaciones Pagina 26

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