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Analog Multimeter, MeasuringCurrent

Steps in using your meter to

measure Current flow.

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Basic Steps and Precautions

Remember; Voltage is measured across

a component, but current flowsthrough a component.

You must break the circuit and place

the meter in series with the circuitand/or component.

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This is not a Auto-ranging DigitalMultimeter! Pay attention to the

polarity of the circuit components and

the lead placement.

The Black Lead is the Negative Lead.

The Red Lead is the Positive Lead.

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This is the circuit without the meter

leads in place

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Can you calculate the total resistance?

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Try the following steps to calculate RT

Take R1 or R5 value and divide by 2

This gives you 4.7k /2 = 2350

Now bring R2 in to the mix

2

2

equiv

ParallelEquiv

equiv

R xRR

R R

2350 101902.83

2350 10

x k

k

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Add Equivalent value to R3 and R4

RT = R1,5,2 equiv + R3 + R4

RT

= 1902.83 + 240 + 470k

RT = approximately 472.143k

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IT can now be calculated

You have calculated RT = 472.143K

The total voltage is given as 12VDC.T

T

T

EI

R

1225.416

472.143A

k

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You must break the circuit to place the

meter in series with the component.

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Remember to start at a higher level

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You calculated less than 50A

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You would use the 50 meter range and

this would be the actual range

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This means 20 = 20, 40 = 40 etc

The minor increments = 1.0 A

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What is the meter reading?

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This meter reading is approximately

25.4A. Can you see it?

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Do you know if any other points will have

the same value? If so, where and why?

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Places to measure IT with probes placed

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Calculations for Parallel branches

Calculate voltage drop for parallel

equivalent circuit

Use the calculated equivalent resistance

for the parallel branches multiplied by

the total current.

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254.16 x 1902.83 48.36mV

The next step is to divide the

equivalent voltage by each branchs

resistance to determine thatbranchs current.

The sum of the Branch currents

should equal the Total Currentapplied.

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Here are the component values again

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Remember; the voltage is .04836 V.

.04836 / 10000 = 4.836A

Two resistances of 4.7k

.04836 / 4700 10.29A

IT 25.416A

4.836 + 10.29 + 10.29 = 25.416A

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Where would you open the Parallel

circuits to measure the currents?

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Here is where you open the Parallel

circuits to measure the currents?

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Where would you place your probes to

measure the calculated currents?

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You calculated less than 50A

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You would use the 50 meter range and

this would be the actual range

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This means 20 = 20, 40 = 40 etc

The minor increments = 1.0 A

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What is the meter reading?

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This meter reading is approximately

4.8A. Can you see it?

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You would use the 50 meter range and

this would be the actual range

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What is the meter reading?

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This meter reading is approximately

10.3A. Can you see it?

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Questions?

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The End

Developed and Produced by the

Instructors in the CIE InstructionDepartment. 10/2011