1-27Q30.What electrical quantity is measured by a voltmeter?Q31.How is a voltmeter connected to the circuit to be measured?Q32.What is the loading effect of a voltmeter?Q33.How is the loading effect of a voltmeter kept to a minimum?MAKING A VOLTMETER FROM A CURRENT SENSITIVE METER MOVEMENTThe meter movements discussed earlier in this chapter have all reacted to current. Various ways havebeen shown in which these movements can be used in ammeters. If the current and resistance are known,the voltage can be calculated by the formula E = IR. A meter movement has a known resistance, so as themovement reacts to the current, the voltage can be indicated on the scale of the meter.In figure 1-27(A), a voltmeter (represented by R_{2}) connected across a 10-ohm resistor with 10 voltsapplied. The current through the voltmeter (R_{2}) is .1 milliamperes. In figure 1-27(B), the voltage isincreased to 100 volts. Now, the current through the voltmeter (R_{2}) is 1 milliampere. The voltage hasincreased by a factor of 10 and so has the current. This illustrates that the current through the meter isproportional to the voltage being measured.Figure 1-27.—Current and voltage in parallel circuit.SENSITIVITY OF VOLTMETERSVoltmeter sensitivity is expressed in ohms per volt (W/V). It is the resistance of the voltmeter at thefull-scale reading in volts. Since the voltmeter’s resistance does not change with the position of thepointer, the total resistance of the meter is the sensitivity multiplied by the full-scale voltage reading. Thehigher the sensitivity of a voltmeter, the higher the voltmeter’s resistance. Since high resistance voltmeters

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