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Appendix B: Equipment and Instrument Circuits

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Digital Storage Oscilloscope

The digital storage oscilloscope (DSO) is now the preferred type of oscilloscope for most indus-

trial applications, although analog oscilloscopes are still widely used. The DSO uses digital

memory to store data as long as required without degradation. The digital storage allows bring-

ing into play the enormous array of sophisticated digital signal processing tools for the analysis

of complex waveforms in today’s circuitry.

Digital storage oscilloscopes come in a variety of configurations. The units in this laboratory are

dual-beam oscilloscopes with two vertical inputs, as described above.

The vertical input on the oscilloscope, instead of driving the vertical amplifier, is digitized by an

analog-to-digital (A-to-D) converter to create a data set that is stored in the memory of a micro-

processor. The data set is processed and then sent to the display, which today is likely to be an

LCD flat panel. DSOs with color LCD displays are also common. The data set can be written to

a flash drive or sent over a LAN or a WAN for processing or archiving. The screen image can be

directly recorded on paper by means of an attached printer or plotter, without the need for an os-

cilloscope camera. The scope’s own signal analysis software can extract many useful time-

domain features (e.g. rise time, pulse width, amplitude), frequency spectra, histograms and statis-

tics, persistence maps, and a large number of parameters meaningful to engineers in specialized

fields such as telecommunications, disk drive analysis, and power electronics.

Digital oscilloscopes are limited principally by the performance of the analog input circuitry and

the sampling frequency. In general, the sampling frequency should be at least the Nyquist rate,

double the frequency of the highest-frequency component of the observed signal, otherwise

aliasing may occur.

Three-Phase Power Measurements

Wattmeters consist of a voltage coil and current coil that are connected to the circuit as shown in

Figure B.13. Conventional AC wattmeters respond to the product of the rms voltage and rms cur-

rent times the cosine of the phase difference, where

cos

rms rms

P V I





Figure B.13: Wattmeter Connection for Single-Phase Load

Notice in these schematic diagrams that the current coil and the voltage coil of the wattmeter are

connected at one end. This should be done by attaching a jumper wire between the coil connec-

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BK Precision 4011A Instrucciones de operaciones Pagina 56