The use of Multimeter in circuit analysis experiment of Shandong University

experiment 1  Use of multimeter

1.1 The experiment purpose

1. Understand the structure and function of multimeter ;

2. Learn to use a multimeter to measure resistance 、 inductance 、 Methods of capacitors and diodes ;

3. Learn how to use a multimeter to measure DC voltage and DC current ;

4. Understand the influence of internal resistance of multimeter on measurement results ;

1.2 Experimental principle

A multimeter is a voltmeter 、 Ammeter and ohmmeter in one of the multi-purpose common instruments . The measuring line of the multimeter is a multi range DC voltmeter , ammeter , Multi range AC voltmeter, ohmmeter and other circuits are combined . It can be used to measure DC current 、 DC voltage 、 AC voltage 、 After DC resistance and some additional components , It can also measure AC current 、 Capacitance 、 Inductance and diode polarity .

1. Identification of common electronic components

There are generally four methods to mark the specifications of commonly used electronic components ： The direct labeling method 、 Literal notation 、 Digital method and color code method , The resistance value can be read out according to the marking method 、 The nominal value and allowable deviation of inductance value and capacitance value .

2. The basic method of testing common components with Multimeter

（1） Check the resistance with a multimeter , Measure its actual resistance , Compare with the nominal resistance , It can judge whether the resistance is normal .

（2） Check the inductance with a multimeter , Measure its DC resistance , Ohmic gear is often used R×1 or R×10, If the resistance is infinite , Then the inductance is open ; If the resistance is small , The inductance is generally normal .

（3） Check the capacitance with a multimeter , It should be treated differently according to non-polar capacitance, polar capacitance and capacity ：

a、 Non polar fixed capacitors generally have a small capacity , Generally, ohmic gear can be selected for measurement R×10k,0.01μF The following qualitative tests are conducted to check whether there is leakage or short circuit ;0.01μF The above direct tests whether there is charging process and whether there is short circuit or leakage .

b、 The capacity of electrolytic capacitor is large , Its positive value shall be measured 、 Reverse leakage resistance , Usually the capacity is 1～47μF Between the , Ohmic gear can be used R×1k measurement ; The capacity is greater than 47μF Of , Ohmic gear can be used R×100 measurement , Judge whether it can work normally according to the measurement results ; For electrolytic capacitors with unknown polarity identification , It can also be measured by a multimeter 、 The method of reverse leakage resistance .

（4） Check the diode with a multimeter , Select the measuring diode gear . The diode has a single conductivity , Its positive value shall be measured 、 Reverse resistance , Then judge whether its performance is good ; For diodes with unknown polarity identification , It can also be measured with a multimeter 、 Reverse resistance method to distinguish .

1. 3   Experiment content and steps

1. Check the resistance

（1） selection 2 Resistance , Nominal resistance value and allowable deviation of the given resistance ;

（3） Adjust the multimeter to the ohm gear to measure the resistance , Fill the measured data into the column of measured value ;

（4） Compare the nominal value of the resistance with the measured value , And give the corresponding conclusion .

surface 1-1  Check the resistance

electric   Resistance	R1	R2
Nominal value and deviation	300Ω,±5%	600Ω,±5%
Measured value	300Ω	600Ω
junction   On	Within the allowable range of error , The nominal value of the resistance is equal to the measured value .

2. Check the inductance

（1） selection 2 An inductor , Given inductance and allowable deviation , Fill in the table 1-2 Nominal value and deviation column ;

（2） Set the DC resistance in the ideal state , Fill in the ideal value column ;

（3） Turn the multimeter to Ohm , Measure the DC resistance of the inductance , Fill the measured data into the measured value column ;

（4） Simply judge the inductance performance according to the measurement results .

surface 1-2  Check the inductance

element     Pieces of		L1	L2
Nominal value and deviation		10mh, ±5%	15mh,±5%
DC resistance value	Ideal value	0	0
	Measured value	0	0
junction     On		Inductance yes “ Direct current 、 AC resistance ” Characteristics of , When DC current is applied , Its DC resistance is 0

3. Detection diode

（1） Choose one 1N4148 Type diode , According to the table 1-3 The requirements , Use a multimeter to measure the diode block and measure its positive 、 Reverse resistance , Fill in the table 1-3;

（2） Judge the polarity and performance of the diode according to the measurement results .

surface 1-3  Detection diode

Diode model	1N4148
Resistance value	Forward resistance	Reverse resistance
	29.777MΩ	10.03GΩ
Conclusion	The forward resistance of diode is different from the reverse resistance , The reverse resistance is very large , It conforms to the unidirectional conductivity of diode .

4. Measure DC voltage

Select components , The structure is shown in the figure 1-1 The experimental circuit shown .

（1） DC regulated power supply , Adjust the power supply voltage to 3V.

（2） After the circuit is connected , Use a multimeter to measure the resistance in turn R1 and R2 Terminal voltage of U1 and U2, Fill in the measurement data in the table 1-4 in .

surface 1-4  Measurement of DC voltage

	U（V）	U1（V）	U2（V）
Theoretical value	3	2	1
Measured value （ Internal resistance of voltmeter 1G o ）	3	2	1
Measured value （ Internal resistance of voltmeter 1k o ）	3	1.667	0.833
Conclusion	Voltmeter has shunt function , A small internal resistance of the voltmeter will affect the measured data , When the internal resistance of the voltmeter is large , Will make the measured data close to the theoretical value .

5. Measure the DC current

Select components , The structure is shown in the figure 1-2 The experimental circuit shown .

（1） DC regulated power supply set regulated power output 5V;

（2） Adjust the multimeter to DC current , Measure the current of each branch , Fill in the measurement data in the table 2-5 in .

surface 1-5 Measurement of DC current

	U(V)	I1(mA)	I2(mA)	I3(mA)
Theoretical value	5	23.81	14.286	9.524
Measured value （ Internal resistance of ammeter 1n o ）	5	23.81	14.286	9.524
Measured value （ Internal resistance of ammeter 1 o ）	5	23.697	14.205	9.479
Conclusion	Ammeter has the function of partial voltage , When the internal resistance of ammeter is large , Will affect the measured value , When the internal resistance of ammeter is small enough , The impact can be ignored , Will make the measured data close to the theoretical value .

1.4 Experimental requirements and precautions

1． When measuring resistance with a multimeter , Before measurement , According to the nominal value of each measured resistance , Choose the appropriate ohmic gear ratio .

2． When measuring current or voltage , If you don't know the measured size , The maximum range test should be selected , To prevent the clock ; Then switch to the appropriate range , To reduce the measurement error .

3． When measuring DC voltage with a multimeter , Note that the red probe is connected to the high potential , The black probe is connected to the low potential .

4． When measuring DC current with Multimeter , It is necessary to disconnect the tested Branch , Connect the ammeter in series with the measured Branch .

1.5  Experimental report

1． Sort out the experimental data .

2． Analyze the test results of each component , And give the corresponding conclusion .

Beginner circuit analysis , There may be mistakes , Also ask everybody not hesitate to grant instruction .

Due to the text , The relevant experimental projects in this paper cannot be shown , Resources have been uploaded , You can download it yourself .

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