BK Precision 4011A Instrucciones de operaciones descargar pdf (Pagina 54)

Appendix B: Equipment and Instrument Circuits

201042

to measure voltage or current. When measuring voltage, the input resistance is relatively large

(10 MΩ for DC, 10 MΩ in parallel with 100pF for AC). For current measurements, the input re-

sistance is small (1 Ω for 0.2 A DC; 0.1 Ω for 2.0 A DC). Figure B.11 (b) shows an equivalent

circuit for the DMM in the resistance measuring mode. The test current, I

test

, varies with the re-

sistance range.

(a) (b)

Figure B.11 (a) Equivalent circuit for voltage and current measurement with the DMM.

(b) Equivalent circuit for resistance measurement with the DMM.

LCR Meter

The LCR meter is a solid-state instrument used to measure resistance, inductance, and capaci-

tance. It replaces the impedance bridge that was used before this type of direct measuring tool

became available. When first turned on, the LCR meter enters an autoranging mode, so that the

appropriate scales are used in displaying the measurements. Tests can be performed using a test

frequency of either 1 kHz or 120 Hz by pressing the appropriate button.

By pressing the L/C/R button until the letter L is shown in the upper-left-hand corner of the dis-

play, the user can measure inductance. The meter assumes that resistance is in series with this

inductance, and the amount of this series resistance can be found from the quality factor Q dis-

played in the secondary display in the upper-right-hand corner. The relationship between the in-

ductance, resistance, Q, and a dissipation factor D is given by:

2 1

frequency L

R D



 

 

Note that the dissipation factor is simply the inverse of the quality factor.

Pressing the L/C/R button until the letter C is shown in the upper-left-hand corner of the display

allows one to measure capacitance. This time the meter assumes that the capacitance is in paral-

lel with a resistance. The amount of resistance is related to the quality factor Q and dissipation

factor D by:

1 1

frequency C R Q



 

  

Resistance by itself can be measured by pressing the L/C/R button until the letter R is shown in

the upper-left-hand portion of the display.

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BK Precision 4011A Instrucciones de operaciones Pagina 54