BK Precision 4011A Instrucciones de operaciones descargar pdf (Pagina 51)

Appendix B: Equipment and Instrument Circuits

201039

One might be tempted to “float” the oscilloscope instead of the circuit being tested. This could

be accomplished by removing the ground prong on the scope’s power plug. However, doing this

would create a safety hazard, since the oscilloscope’s case would be at the same potential as

whatever is connected to the scope probe’s ground. It would then be possible for an individual

simultaneously touching the scope and an earth connection to be electrocuted.

The 3-phase 208 V, 60 Hz, non-isolated supply

Figure B.9 shows the equivalent circuit for the 3-phase, 208 V (rms), 60 Hz, non-isolated supply,

which is also available at terminals on your workbench. This supply is grounded at the source so

that the potential of each of the 3 phases, the “A”, “B”, and “C” phase is 120 V with respect to

ground, but the phase-to-phase voltage (A to B, B to C, C to A) is 208 Volts due to the 120° dif-

ference between each of the phases.

Figure B.9 Equivalent circuit for non-isolated 208 V (rms), 60 Hz 3-phase power supply.

Autotransformer

One electrical source that you will often use for experiments will be a variable transformer (auto-

transformer) plugged into the ISOLATED 120 V (rms), 60 Hz, electrical outlet on the workbench.

This combination is represented by the equivalent circuit shown in Figure B.4. The isolation

transformer itself is a transformer with a turns ratio of one. It is mounted behind the lab bench.

The autotransformer, also referred to by the brand name Variac, enables one to select a portion of

the input voltage to use in a particular experiment. The autotransformer has a single winding that

is connected to a voltage source. By adjusting a slider mechanism (called a wiper), one can vary

the number of turns on the load side of the circuit, hence giving the user control over the magni-

tude of the load-side voltage, from 0 V up to 140 V.

1 2 ... 46 47 48 49 50 51 52 53 54 55 56 ... 72 73

Sin comentarios

BK Precision 4011A Instrucciones de operaciones Pagina 51