Tutorial on Using a Multimeter

It's important for you to go through this tutorial before doing L11.  You need to know how to use your meter correctly in order to be able to get correct readings as well as to avoid burning out a fuse in the meter.  As you go through the tutorial, record your work.  You'll send it to the instructor as soon as you finish the tutorial.  Open a Word or Open Office document now, put your name and school at the top, and title it as above.  Record your results using the same numbers as in the tutorial.

Equipment for this tutorial:

Multimeter
Set of resistors (These were mailed to your facilitator.)
1.5-V battery
2 alligator clips
Battery holder or tape to hold clips to battery

If you're using a breadboard (optional), these are additional items.

Breadboard
Wire leads to insert into breadboard holes
Wire strippers or knife to strip insulation from wires

Important:  If you think your meter is malfunctioning or if you think you're doing something wrong but don't know what it is, ask the person who loaned you the meter to help out. If the meter was recently purchased, check the instruction manual.

A multimeter is a device for measuring currents and voltages, both AC and DC, and for measuring resistance.  Some also measure capacitance.  They come in both digital and analog varieties.  Either is fine.  Digital meters give you...well...a digital readout.  Analog meters have a needle, and you read the needle's position on a scale.  (An analog meter generally has several scales.  You select the scale to read based on where a dial setting.)  Multimeters all have similar functions, so you should be able to easily adapt the following to your own meter.  If you have an individual ammeter and voltmeter the same basic principles apply about how you hook them up.  However, you won't be able to measure resistance directly with individual meters (unless you happen to have an individual ohmmeter.)  Here's your first question to answer.

1.  Which type of meter do you have:  multimeter or individual meters, digital or analog?

A photo of a typical digital multimeter is shown to the right.  (Click on the photo if you want to see greater detail.)  There are two probes.  The red one is conventionally taken to be positive and the black one negative.  The black probe always connects to the port labeled COM.   On most meters, the red probe can connect to 2 or 3 different ports.  We'll discuss those later. 

The dial has several settings.  A stands for current measurement and V for voltage.  A straight line above the symbol means direct current, and a wavy line means alternating current.  All your measurements will be direct current.  The omega (W) symbol is for resistance.  There's also a symbol, .  This is a continuity checker.  It's used to determine if there's a break in a wire.  You'll try using that setting next.  If you don't have a continuity checker, say so in item 2 and move on.

Part A. Using the continuity checker

Your meter should be turned off.  If it's on, turn it off now.  Always start with the meter off.  Make sure your connections and settings are right before you turn it on.  Another good reason to keep the meter turned off is that you'll conserve the battery energy.

Make sure the black probe is connected to COM.  (This may be designated in other ways, for example, - or ground ).  Check that the red probe is connected to the V, W port or whatever port is designated for measuring voltage.  Turn the dial to the continuity checker setting.  Now touch the metal ends of the probes together.  You should hear a beep or buzz, which indicates that you have electrical continuity.  If you don't have continuity, that signals a problem.  Perhaps a probe isn't connected properly or your meter's battery is dead.  If you don't think the meter is working, check with the person who loaned it to you.

Test one of your alligator clip wires in the same way.  Clip one end of the wire to the positive probe and the other end to the negative probe.  (In the future, we'll call them red and black, assuming that you're using the convention.)  You should have continuity.  If your first continuity check worked but this one doesn't, your clip wire may be broken internally.  If any of your wires give you trouble in the future, you can check them in this way.

2.  Simply indicate on your paper whether you have a continuity checker and whether it worked.

Turn your meter off and read on.

Part B. Measuring resistance

Watch this video tutorial first:  Download

You'll be using resistors in the circuits labs.  Six of them were sent to you.  Take a close look at one of them.  They have several colored bands.  The colors and order of the bands can be read in order to determine the resistance in the ohms.  Here's a link where you can find out how to read the code:  Resistor color code, tutorial.  Here's a calculator you can try. The value that you read from the color code is called a nominal value.  You can't expect it to be closer than about 10% of the value of the resistance.  The actual resistance should be within the tolerance, which is read from one of the colored bands.

3.  Read the color codes of your six resistors now.  Write down the values of the resistances in ohms.

You can also read resistance with the multimeter.  This can give you a value to tenths of ohms of the actual resistance.  (If you don't have an ohmmeter or an ohms scale on your multimeter, say so for item 4 and then go to the next part.)  Don't turn on the multimeter yet!  Read these instructions first.

For measuring resistance, the red and black probes are connected to the same places on the meter as when using the continuity checker.  Turn the dial to the ohms W setting.  Now turn the meter on.  Select one of your resistors.  Touch the red and black probes to opposite ends of the resistor.  It doesn't matter which probe touches which end.  Make sure you have a good contact.  The meter should display the resistance.  If the reading fluctuates, you may not have good contact.  Schematically, what your are doing looks like the diagram to the right.

Note that when measuring resistance, you didn't place a battery in the circuit.  It's important to realize that if you place a battery in the circuit with the resistance, the meter will give the wrong reading.  This is the most common mistake that people make in measuring resistance.

Never have a battery connected to a resistor when you're measuring resistance.

4.  Record the color-coded value of the resistance as well as the value measured with the multimeter.  (If you don't have an ohmmeter function, just say that.)

Turn your meter off and read on.

Pretty simple so far, right?  It's not difficult to use a meter, but you have to know how to use it correctly in order to get good readings and not burn out the meter's fuse or meter movement.

Part C. Measuring voltage differences

Watch this video tutorial first:  Download

When you measure voltage, the reading is the difference between the potential at the red probe and the potential at the black probe.  It's important to realize that any measurement of voltage is actually a difference of potential between two points of a circuit.  When you measure voltage, you simply touch the probes to the two points of the circuit in question.  More about that in a moment.

A diagram of a simple circuit with a battery and a resistor is shown to the right.  Four points are marked for reference.  Recall that the long side of the battery symbol is the positive terminal of the battery.  Conventional (positive) current goes from positive to negative in the circuit.  That is, current goes from A to C to D to B to A.  In the future, when we talk about current, we mean positive current (even though we know that the actual charge carriers are electrons.) 

Note:  If you're using a breadboard instead of alligator clips for making connections, here's information about that.

  1. Using a 1.5-volt battery, the smallest resistor (~470 W),  and a couple of alligator leads, construct the circuit shown to the right.

  2. The probes should be connected to the meter the same as in Parts A and B.  That is, red to the V,W setting and black to COM.

  3. Turn the multimeter dial to read DC voltage.  (If there's a scale for measuring small voltages such as millivolts, don't use that one.)

  4. Turn the meter on.  You're going to measure the voltage difference VAB = VA - VB.  Since A is at the positive end of the battery and B is at the negative end, we expect a measured voltage difference of about 1.5 volts. To actually make the measurement, touch the black probe of the meter to point B and the red probe to point A.  Note that these are simply points where you can obtain a metallic (conducting) contact close to the battery terminals.  You could touch the probes directly to the + and - terminals of the battery.

Schematically, what you've done with the multimeter looks like this:

5. Record the measured battery voltage.

Remember:  In order to measure any voltage difference, V1 - V2, touch the red lead to point 1 and the black lead to point 2. Think "red minus black."

For practice, perform and record the following measurements.  The notation Vij will mean Vi - Vj.  Mentally answer the questions in parentheses.

6.  VCA   (Why is this voltage difference zero?)

7.  VBA  (Why is this voltage difference negative?)

8.  VDC  (Why is this voltage difference negative?)

Turn your meter off and go on to the next part.

Part D. Measuring current

Watch this video tutorial first:  Download

The multimeter is used in a very different way to measure current.  For measuring voltage differences, the multimeter is placed in the circuit in parallel.  When measuring current, the multimeter must be placed in the circuit in series.

Suppose that we want to measure the current at point P shown in Figure 1. To do so, the circuit must be opened at P as shown in Figure 2.

Figure 1 Figure 2

 

Important:  When measuring current, don't touch the meter probes directly to the ends of the battery.  Always have a resistor in the circuit as described below.

Now do the following.

  1. Prepare your meter by moving the red probe to the low current port.  Most multimeters have both a high and low current port.  For the one in the photo above, the low current port is for measuring currents up to 300 mA (milliamperes), and the high current port is for currents up to 10 A.  Assuming you connect your circuits correctly, you won't be measuring high currents.  By the way, for the meter shown, the readout is in units of milliamperes when plugged into the 300 mA port.  Thus, one has to divide by 1000 to get amperes.  For your own meter, you'll need to be sure what the units are.  There may be an indicator on the readout that tells the unit.  If not, you can calculate about what the current should be using I = V/R and compare to the meter reading.  That should tell you if the units are amperes or milliamperes.

  2. Your meter should still be off.  Turn the dial to measure DC current.

  3. Now open your battery-resistor circuit at point P.  You can just unclip the alligator clip attached to the resistor.

  4. Connect the multimeter in series at point P as shown below.  Specifically, connect the red probe to the open circuit connection closest to the battery, and connect the black probe to the open circuit connection closest to the resistor.  You may need to use another wire to make connections.  When you're finished, you'll have a chain that includes the battery, the meter, and the resistor.

9.  Turn on the meter now and read the current.  Record the value with the correct units.  You should have a positive reading if you connected the probes as described above.  The red probe connects to the more positive side of the circuit.  That's the battery in this case.  If you connected the meter backward, you would get a negative reading on a digital multimeter.  That doesn't hurt the meter.  If you're using an analog meter, the needle will try to go backwards.  That's not good for it.  So it's a good idea  to get in the habit of connecting the probes in order to get a positive current.

10.  Remove the meter from the circuit and reconnect the battery directly to the resistor.  Now repeat your measurement technique for point Q.  That is, open the circuit at Q and insert the meter.  This time, where will the red probe connect to?  Record the current reading.  (Is the result what you expected?)

In the future, when you measure current, you only have to open the circuit at one place to take the reading.  We had you do two places (P and Q) this time in order to confirm something that you had already been told about the current in a circuit.

Whenever measuring current, move the red probe to a current port.  Select a port (if you have a choice) for the highest current that you expect to have in your experiment.  Open the circuit at the place where you want to measure current and connect the meter in series.  Be sure the red probe is connected to the positive side of the circuit.

People make more mistakes in measuring current than any other circuit measurement.  That's because they try to use the meter in the same way as for measuring voltage.  Unfortunately, using the meter incorrectly can damage it or at least burn out a fuse.  The person you borrowed the meter from won't be happy if you do that.  So always double check yourself to make sure that you're doing things right.  If you have a partner, double check each other.

Before continuing, did you remember to turn the meter off?  Also disconnect your circuit.

Submitting your work

Save your file with the name meter-WAusername.doc and submit it as instructed.