• SkillCat Team

Multimeter Basics

Updated: Apr 7

Using a Multimeter: Chapter 1


Multimeter Basics


In this module, we will introduce you to the different types of multimeters and how multimeters are rated. Skip to quiz!


What Is A Multimeter?


A multimeter is a handheld device used for diagnosing problems in electrical components. Multimeters are one of the most common tools you will use in the HVAC trade.


A multimeter can be used to measure:

  • AC and DC voltage,

  • AC and DC current,

  • Resistance,

  • Continuity,

  • Capacitance, and

  • Temperature

Types Of Multimeters


There are two types of multimeters that we will cover in the next section.

  • Digital multimeters, and

  • Clamp multimeters


Before digital multimeters, you had to carry a tool for every measurement. There would be a tool for measuring voltage, another for current, another for resistance, etc. Digital multimeters combined all of these tools into one instrument.


Digital multimeters have:

  • A dial that determines what you are measuring

  • A display that shows your measurement results

  • Ports for connecting accessories

We will go into more detail on these items in the multimeter components topic.


A clamp multimeter is a digital multimeter with an additional current sensor. The current sensor sits in a red claw at the top of the multimeter. See the picture above for an example. A clamp meter can perform all of the same measurements as a digital multimeter.


Clamp meters have several advantages over digital multimeters when you are measuring current. Clamp multimeters are much safer to use and can measure higher amounts of current than digital meters. Some clamp meters can measure up to 2500A of current! Most digital meters can only measure 10A.


Fuses


What happens if you are measuring more current than your multimeter can handle? Normally, measuring too high a level of current would destroy your multimeter and shock you. Fortunately, we have a device in a multimeter called a fuse. The fuse protects us.

A fuse is found in almost every electronic you interact with. A fuse is a device designed to protect electrical equipment from surges in current or voltage. Most multimeters come with a fuse built into the multimeter.


When the multimeter experiences too much current or voltage, a wire in the fuse melts. When the wire melts, the circuit within the multimeter is broken. The broken circuit prevents more current or voltage from flowing into the meter.


A fuse with a melted wire is called a “blown fuse”. Fuses can only be used once. After the wire melts, your multimeter will not function properly. You must replace the fuse before using your multimeter again.


When you buy a multimeter, check that it comes with a fuse built in. Fused multimeters are critical to protecting you from electric shock or fatal injury.


Multimeter Ratings


Every multimeter has three ratings that differentiate the quality of the meter.

The three ratings are:

  • Range

  • Resolution

  • Accuracy


The range rating tells you the maximum and minimum values that the multimeter can measure. You must buy a multimeter that can measure the range of the equipment you are working on. Your meter will display “OL” if you measure a component above the range.


For example, you have a meter with a range of 1A-10A. If you measure equipment with 15A of current, you will blow the fuse on your meter and can be injured. If you measure equipment with 0.5A of current, your meter will not be able to read it. The value is below the range.


A multimeter’s resolution tells you how many decimal points the meter can display. The more decimal points, the more accurate the measurement will be. If you need very precise measurements, then a multimeter with a high resolution will be important.

For example, imagine you have two rulers. One ruler only has inches marked. The other ruler has inches and fraction of inches marked. The ruler with only inches could tell you an object was between 1-2 inches. The ruler with fractions of inches could tell you if an object was 1.25 inches.


Resolution is measured in “counts”. The count specifies the number of decimal places the meter can display and at what point the meter will become less precise. Once the measurement goes over the count limit, the measurement will lose a decimal place and become less precise.


Let’s go over a few examples. A meter with a 2000 count could display a maximum value on 1.999 on the display. Once the measurement goes over 1.999, the measurement will lose a decimal place. The meter would then display 2.00.


A meter with a 3200 count could display a maximum value on 3.199 on the display. Once the measurement goes over 3.199, the measurement will lose a decimal place. The meter would then display 3.20.


A meter with a 20,000 count could display a maximum value on 1.9999 on the display. Once the measurement goes over 1.9999, the measurement will lose a decimal place. The meter would then display 2.000.


A multimeter’s accuracy determines how close to the real value the meter can measure. Accuracy is usually described in terms of plus or minus sign (+/-) and a percentage sign (%). Based on the accuracy rating, the meter will be over or under the real value by the accuracy percentage.


For example, you have a multimeter rated with a +/- 5% accuracy. You want to measure the voltage of a 100V wire. 5% of 100V would be 5V. Your meter can display any value between 100 + 5 and 100 - 5. When measuring the 100V wire, your meter will display a number between 95-105V.



Ports & Leads On A Multimeter


In this module, we will introduce you to the ports and leads on your multimeter. This includes an explanation of each port, what a lead is, and how to properly use a lead. Skip to quiz!


COM Port


Ports are small holes found at the bottom of your multimeter. Multimeter accessories get plugged into the ports on your multimeter. Multimeters can have 2-4 ports.


The COM port on your multimeter will have a black label. It will also have COM written next to it. In the field, this port will be referred to as the “COM” port or the “common” port. The COM port is used for most multimeter measurements.


Current Ports


The “A” port is used for measuring current. The “A” port usually has a red color around the port. The port will also be labeled with a large “A”. Recall that “A” stands for amps, the unit of measurement for current.

The “A” port will have a number next to the port label. This could look like “10A”. The number in front of the “A” is the maximum current that your multimeter can handle. For example, your multimeter says “10A”. You can safely measure current under 10A.


The “mA” port allows your meter to more accurately measure small amounts of current. The “mA” port is not present on all meters. Some meters do not have the range to measure milliamps. Recall that mA stands for milliamp. There are 1000mA in an amp.


Some “mA” ports will also be used for measuring µA. The label on the port will look like this “mA/µA.” Recall that µA stands for microamp. There are 1,000,000 microamps in an amp. Using mA/µA gives you a more accurate measurement. For example, 0.30A is not has accurate as 300.2mA.


Similar to the “A” port, the “mA” port will have a number in front of mA. This number is the maximum amount of mA you can safely measure while using the “mA” port. For example, you have a meter that says 600mA. You can safely measure current under 600mA or 0.6A.


Other Ports


The VΩ port is used when you are measuring voltage or resistance. The port will have a red border and the label VΩ. It is common for the VΩ port to be used for other measurements. You may see the symbol for capacitance, continuity, and temperature.


So what do we connect into the ports? Leads! We will get into details on leads over the next few slides.


Leads


Leads are long wires with two different heads at each end of the wire. One end of the lead connects into your multimeter ports. The other end of the lead is used to touch the component you are measuring.


The end of the lead which connects into your multimeter ports will have a circular plug at the end. The plug looks similar to a power cord for a desktop computer. We refer to the end of the lead that plugs into ports as the plug end.


The other end of the lead is called the probe end. The probe is used to take measurements with your multimeter. The probe has a rubber handle and a sharp metal point extending from the handle.

You will hold the probe end of the lead by the rubber handle. Keeping your hands as far from the metal tips reduces the chance of you getting shocked. You will press the metal tips of the leads onto the component you are measuring.


Your multimeter will come with two test leads - a black one and a red one. The black lead represents the negative lead. The red lead represents the positive lead. You will use the color of the lead to determine which port to plug the lead into.


To connect a lead to your multimeter, hold the lead by the plug end. Press the plug end into the correct port on the multimeter. Be sure to hold the plug by the rubber grip. This makes it easier and safer to insert the lead.


The leads we have covered up until now are called test leads. There are other types of leads which can be helpful in specific situations. Another common type of leads are alligator clips.


Alligator clips are used just like a standard lead. Unlike standard leads which have a metal point on the probe end, alligator clips have metal jaws. The metal jaw can be used to grip and hook the lead onto what you are measuring.


The main benefit of alligator clips is that you can attach them to what you are measuring. Conventional multimeter leads require you to hold the lead against the component.


There are two types of alligator clips: push on and standard clips. Push on alligator clips attach to your normal multimeter leads. They are the most common alligator clips. Standard alligator clips replace your multimeter leads entirely.


So how do we connect alligator clips to our multimeter? For push on clips, press the tip of your probe into the hole on the opposite side of the jaws. You should see the probe fully insert into the push on alligator clips.


To connect standard alligator clips to your multimeter, follow the same process you used for standard multimeter leads. Press the port end of the alligator leads into the correct port on the multimeter.


Conclusion


In this section, you learned about all the ports on your multimeter. You also learned about common types of leads and how to connect them to your multimeter.




Question #1: A clamp multimeter is a digital multimeter with an additional current sensor.

  1. True

  2. False

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Answer: True

True, a clamp multimeter is a digital multimeter with a current sensor in a clamp.


Question #2: Clamp multimeters can measure higher current than a digital multimeter.

  1. True

  2. False

Scroll down for the answer...

















Answer: True

True, a clamp multimeter can measure higher current than a digital multimeter.


Question #3: A fuse is not important to have in a multimeter.

  1. True

  2. False

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Answer: True

False, fuses are critical to safely using a multimeter.


Question #4: A fuse can be used how many times?

  1. 2

  2. 5

  3. 1

  4. Unlimited

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Answer: 1

A fuse can only be used once. After the fuse is blown, the fuse cannot be used again.


Question #5: A multimeter’s range describes the minimum and maximum values the multimeter can safely measure.

  1. True

  2. False

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Answer: True

True, a multimeter’s range describes the range of values the multimeter can safely measure.


Question #6: What number below would the multimeter display with a 20,000 count resolution?

  1. 1.9

  2. 1.99

  3. 1.999

  4. 1.9999

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Answer: 1.9999

A meter with a 20,000 count resolution could display four numbers after the decimal. Once the measurement exceeds 1.9999V, the measurement will lose a decimal point.


Question #7: The wire you are measuring has 50V flowing through it. Your meter has an accuracy of +/-5%. What is the range of values your meter would display?

  1. 30V-60V

  2. 47.5V-52.5V

  3. 40V-80V

  4. 10V-20V

Scroll down for the answer...

















Answer: 47.5V-52.5V

The multimeter will display a value within plus or minus 5% of the real voltage. In this case, that would be values between 47.5 - 52.5V.


Question #8: What is a multimeter port?

  1. A screen that displays measurements

  2. A hole where multimeter accessories are plugged in

  3. A device used to measure temperature

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Answer: A hole where multimeter accessories are plugged in

Multimeter accessories connect into the ports.


Question #9: When should you use the “A” port?

  1. To measure temperature

  2. When the current will be larger than the limit on your “mA” port.

  3. To get the average measurement

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Answer: When the current will be larger than the limit on your “mA” port

The “A” port should be used to measure any current that is larger than the “mA” limit. If you are not sure what the current is, start with the “A” port.


Question #10: What does the number next to the “A” port mean?

  1. How many times you can measure current before changing the fuse.

  2. The maximum current that the meter can safely handle while using the A port.

  3. The accuracy of the A port.

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Answer: The maximum current that the meter can safely handle while using the A port

It is the maximum amount of current that the multimeter can handle without being damaged.


Question #11: How many “mA” are in an amp?

  1. 10

  2. 200

  3. 1000

  4. 5000

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Answer: 1000

There are 1000 milliamps in an amp.


Question #12: What is the VΩ port used to measure?

  1. Voltage or resistance

  2. Current

  3. Pounds

  4. All of the above

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Answer: Voltage or resistance

The VΩ is used to measure voltage and resistance unless it has any additional symbols.


Question #13: What connects into the ports on your multimeter?

  1. Leads

  2. Thermometers

  3. Your fingers

  4. Resistors

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Answer: Leads

Leads connect into your multimeter ports.


Question #14: Which end of the lead do you press onto what you are measuring?

  1. The probe end

  2. The plug end

  3. Neither

  4. Both A and B

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Answer: The probe end

You press the probe end of your lead onto what you are measuring. The plug end of the lead will connect into ports.


Question #15: The black lead represents the negative lead.

  1. True

  2. False

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Answer: True

True, the black lead represents the negative lead.


Question #16: What is the main benefit of using alligator clips?

  1. They look cooler

  2. They can be attached to what you are measuring

  3. They are the same color

  4. They require you to hold them when taking a measurement

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Answer: They can be attached to what you are measuring

Alligator clips attach onto what you are measuring. This frees your hands and keeps you farther from the live component.


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