Session 2

Multimeters 

Multimeter

The purpose of this session is to teach you how to use a multimeter to measure:

  • Electrical Resistance
  • DC Voltage
  • DC Current

 

For a dc circuit containing 5 resistors. You will compare your measured results with those calculated and simulated during session 1, therefore you will need those results before proceeding. We will meet breadboard, power supplies and multimeters in more detail in later session. 

You will be required to complete a full report to close this session here is the template Report Template Session 1 and 2

Important

  • You should note that we have a range of different test and measurement equipment available in the laboratory. The power supply and multimeter models used for this demonstration may not be available. It is important that you become familiar with the use of all of the different makes of test and measurement equipment.

By the end of this session the learner will be able to:

  • Set up a multimeter to take safe measurement of resistance, dc current and dc voltage
  • Measure the given parameters of a DC network containing a power source and 5 resistors
  • Compare the results of practical measurement with those of simulation and calculation in terms of accuracy
  • Calculate the total power dissipated by the circuit
  • Complete a report evaluating the skills learned during sessions 1 & 2 with reference to the results recorded

BTEC Outcomes Covered

  • Unit 6 Pass 2 

Electrical Safety

Electrical Safety. Before we begin using a multimeter we must know:

  • That the multimeter is safe to use
  • That the multimeter is designed to take the required measurements
  • That we know how to use the multimeter correctly

The multimeter is safe to use, Check:

  • No signs of physical damage
  • The insulation of the probe leads is in good condition
  • The meter has been recently calibrated (within the last year)
  • You have checked the continuity of the test probes
  • You have functionally checked the multimeter on a known supply
  • If you have reason to suspect the accuracy of a reading then check it again using another multimeter

The multimeter is designed to take the measurements required

Check the data sheet for the multimeter if there is any doubt about what the multimeter can or cannot measure. It is highly unlikely that you will encounter currents or voltages in electronic circuits which are too high for the multimeter to measure safely but it never hurts to check.

You know how to use the multimeter correctly

Set up the meter to take the measurement required before connecting the meter to the circuit. Always set the range selector to its highest setting first and move down through the range to improve the accuracy of your reading

Connecting the probes, Probes are always connected ground probe first. Probes are always disconnected ground probe last.

Taking Readings

Resistance measurements are always taken with power switched off and the power supply disconnected. You will never take a resistance reading with power on.

Current is always measured in series so that the electrons must flow through the meter. Multimeters set to measure current must have a low resistance.

Voltage is always measured in parallel. Multimeters set to measure voltage must have a high resistance

Task Procedure

Construct the following circuit on breadboard. You must use exactly the same resistors in the same combination as for the calculations you did in session 1.

Assessed Circuit

 

Here is a plan of the circuit for breadboard. We will deal with breadboard in more detail in a later session.

5 RESISTOR

 

Measure the total resistance of the circuit. The illustration shows the connections required

  • Set the meter to measure resistance
  • Select the highest range
  • Connect as shown in the diagram
  • ‘Range down’ turning the dial anticlockwise until the meter gives a reading of 1
  • Turn the dial one step clockwise and take the reading and record it in your table from session 1

Resistance measurement

Measure the current drawn by the whole circuit. The next illustration shows the connections and equipment required

  • Select the correct voltage from your power supply. Then switch off the supply
  • Select the amps dc range on your multimeter. Once again use the highest setting
  • Connect the multimeter and power supply to the circuit in a chain as shown (in series)
  • Range down the meter to obtain the most accurate reading and record it in your table

Measure current

 

Measure the current flowing through R3

  • Set up your meter to measure amps dc
  • With the power supply switched off. Connect as shown
  • Measure and record the current flowing through R3 using the range down procedure
  • Enter the reading in your table

Current R3

Measure the voltage dropped across R2 as per the illustration below

  • Set the meter to measure voltage dc
  • Connect the circuit as shown. Make sure the power is off
  • Switch on the power and take the reading using the range down method
  • Enter your reading in the table

Measure volts

That is all the readings required for this session. The next video gives a practical demonstration of the connections and settings required.

Your work should be set out correctly as shown here.

RTSD1

RTSD2

Here is the template for this report Report Template Session 1 and 2

When the report is completed the session is finished

 

 

Leave a Reply