BK Precision 4011A Instrucciones de operaciones descargar pdf (Pagina 55)

Appendix B: Equipment and Instrument Circuits

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The LCR meter has many other useful features, which are described in the manual. If CAL is dis-

played in the center area, check the secondary display to see if OPn or Srt is displayed. These

indicate that the leads should be either opened or shorted followed by pressing the CAL key, for

an automatic calibration.

Dual-Beam Oscilloscope

The oscilloscope is a tool to allow engineers to look at the shape of an electrical voltage versus

time or versus a second signal. Until relatively recently, oscilloscopes used a cathode ray tube

(CRT) to draw the waveforms onto a screen, just like an image on a television. In fact, televi-

sions and computer monitors also used cathode ray tubes until the advent of the new flat screens.

Because of this fact, some people have referred to the laboratory oscilloscope as a CRO, short for

“cathode ray oscilloscope”. The oscilloscopes in this lab now use LCD screens, so the CRO ref-

erence is no longer valid. Most engineers refer to the instrument as a “scope”.

The Dual-Beam Oscilloscope, which we use in this lab, has two vertical (“y”) input channels and

one horizontal (“x”) channel. The horizontal channel can be connected either to an external AC

voltage signal or to an internal time-base generator (x = time). You should become familiar with

the scale options on the y input channels, the x input channel, and the time base, since you will

be using these to obtain values for voltage and time. The y inputs can be either direct (1X) or

through a 10X probe. Figure B.12 (a) shows the equivalent input circuit for a direct input and

Figure B.12 (b) shows an equivalent circuit for the 10X probe input. Note that in both configura-

tions one side of the input is grounded, which means that care must be used in connecting the

ground clip of the probe or connector used to assure that these are not connected to a “hot” (|V| >

0) part of the circuit. (See the section “Oscilloscope Grounding Errors”.) The calibrated time

base is useful when measuring the phase difference between two waveforms (on the y

and y

inputs) by carefully lining up the zero levels for both y inputs and then using in the ac-couple

mode to observe the time difference between zero crossings of the two waveforms.

20 pF

Figure B.12: (a) Equivalent circuit for oscilloscope input with 1X probe (direct input).

(b) Equivalent circuit for oscilloscope input with 10X probe.

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BK Precision 4011A Instrucciones de operaciones Pagina 55