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Intermediate Analog Discovery, Module 2

Measuring DC Voltage

Project 1: Digital Multimeter

Introduces the use of digital multimeters for voltage measurement.
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Measuring DC Current

Project 2: Digital Multimeter

Introduces the use of digital multimeters for current measurement.
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Measuring Resistance

Project 3: Digital Multimeter

Introduces the use of a digital multimeter for resistance measurement.
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Measuring Resistance

Project 3: Digital Multimeter

Measuring Resistance

Project 3: Digital Multimeter

Introduction

Related Material:
Introduction to Resistance
Practical Resistors
Ohmmeters
Digital Multimeter

This experiment introduces the use of a digital multimeter for resistance measurement. It is also designed to increase understanding of resistance. Resistance is theopposition to current flow between two points. This value has only magnitude, there is no direction or polarity associated with resistance—it is always a positive value.

Although resistors are created with color bands that indicate their values, the total resistance of an object can be more accurately measured with an Ohmmeter. In this experiment, we will use a Digital Multimeter (DMM) as an Ohmmeter to measure the resistance of resistors. We will also examine a few ways that measurements can be done improperly to produce incorrect results.

Before you begin, you should:
  • Be able to identify fixed resistors by their color bands.
After you're done, you should:
  • Be able to use a digital multimeter to measure resistance.

Inventory:

Qty Description Typical Image Schematic Symbol Breadboard Image
1 Digital multimeter (DMM)
1 Any resistor
1 A different resistor
2 Analog Discovery™ pins

Procedures

Step 1: Measure the Resistance of an Individual Resistor

A. Create the circuit

  1. Place the two resistors on the breadboard so that none of their terminals are connected to one another.

  2. Once on the breadboard, place the mode selector on your DMM to the Ω symbol. Ensure that your leads are plugged into the V-Ω and COM ports.

  3. Place one probe on each side of a resistor to obtain its resistance value.

B. Measure Resistances

  1. Measure and record the individual resistance values of the resistors.

  2. Use the color codes on the resistors to determine an expected resistance value. Does the expected value agree with the measured value?

Step 2: Measure Resistance of a Resistor in a Circuit

A. Create the circuit

  1. Connect the resistors to one another as shown.

  2. Connect the AWG lead (W1), to the first resistor.

  3. Connect the second resistor to the ground () terminal.

  4. Do NOT turn on the AWG!

B. Re-measure Resistances

  1. Re-measure the individual resistance values of the resistors.

  2. The values you have now should be different than those you first measured. What caused the resistance measurement to change?
    • Because these resistors are now in a circuit, the Ohmmeter measures how much resistance there is to current flow through EVERY available path. This includes the path through the Analog Discovery and the other resistor.
  3. The moral of this experiment: always remove components from circuits before measuring their resistance values.

Test Your Knowledge!

  1. We can use our Ohmmeter not only to tell the value of resistance, but we can also check continuity. (To see if current can flow between two points)
    • Place several Analog Discovery pins in the same numbered row on your breadboard and measure the resistance between them. All pins on the same side of the channel (the divider through the middle) should read 0 Ohms. This means that pins in the same row are all electrically connected.
    • Place several Analog Discovery pins in the same lettered column on your breadboard and measure the resistance between them. They should all read OL, or infinity. This means that pins in different rows, even if in the same column, are not electrically connected.

  2. Everything has a resistance. Grab some components out of your parts kit and measure the resistance between their leads.
    • It is important to realize that although everything has some resistance, the resistance value is not always constant. Transistors and diodes, for example, change their resistance depending on the voltage applied to them. This is how they received the name semi-conductor.
    • There is a component in your kit that has only 2 leads and changes its resistance as it warms. Can you find it? (Hint: Temperature effects are called thermal effects. Check the parts kit list on the Digilent web site for a part with something like “thermal” in its name. Beware: there are similar components listed on the web site that have more than two leads!)
    • There is a component in your kit that has only 2 leads and changes its resistance as it is exposed to light. Can you find it? (Hint: Light is caused by photons. Check the parts kit list on the Digilent web site for a part with something like “photon” or “photo” in its name.)
  • Other product and company names mentioned herein are trademarks or trade names of their respective companies. © 2014 Digilent Inc. All rights reserved.
  • Circuit and breadboard images were created using Fritzing.
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