Page 52 - Physics - XII

(b) Digital Multimeter: A digital multimeter, also known as DMM, is a modern version of the
multimeter. It utilises semiconductor components and a digital display to show the readings. A
standard digital multimeter can perform all the basic measurements like current, voltage, resistance,

transistor gains, continuity, etc.

Digital Probs
display

Knob
Ports

Fig. 2.2: Digital multimeter
Principle/Theory

To Measure the Resistance

When a resistor of resistance R is connected in a circuit as shown in Fig. 2.3, the potential diff erence across
the two ends of the resistor can be measured by connecting the multimeter (with proper voltage setting) in
parallel with the resistor.
RB R

Multimeter set in resistance
measuring mode

Fig. 2.3: Use of multimeter as ohmmeter

To Measure the Direct Current and Voltage

When a Direct Current (D.C.) is passed through the coil of multimeter, the multimeter shows a defl ection
proportional to D.C. For measuring D.C. current, the multimeter is connected in series with the circuit and
to measure D.C. voltage, it is connected in parallel with the two ends across which the D.C. voltage is to
be measured.

RB
RB

Multimeter set in D.C. current
measuring mode + –

E K
+ – Multimeter set in D.C. voltage

E K measuring mode
Fig. 2.4: Use of multimeter as D.C. ammeter Fig. 2.5: Use of multimeter as D.C. voltmeter

To Measure the A.C. Voltage
To measure the A.C. voltage and A.C. current, the root mean square (rms) values of current and voltage are

measured with proper setting of voltage and current. To measure the A.C. voltage, fi rst the A.C. voltage is

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