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How Do You Use a Multimeter? Guide for Beginners

Author: Apogeeweb
Date: 19 Dec 2020
 1726
using a multimeter

Introduction

When it comes to measuring instruments, how to use a multimeter for dummies? Multimeter, also known as a VOM (volt-ohm-milliammeter), is used as an indispensable measuring instrument to measure two or more electrical values—principally voltage (volts), current (amps) and resistance (ohms) in electronic and electrical circuits. In addition, some multimeters can also measure the parameters of transistors and the capacitance of capacitors.

 

Multimeters are divided into two types of analog multimeters and digital multimeters according to the type of circuit being used. This kind of hand-held devices are very useful to detect faults or provide field measurements at a high degree of accuracy. They are one of the preferred tools by electricians to troubleshoot electrical problems on motors, appliances, circuit, power supplies, and wiring systems. This article will introduce how to use a multimeter for beginners. As an beginner, you should know the basic parts of a multimeter, the working principle of multimeters, the function of multimeters, how to read a multimeter, multimeters selection (analog or digital multimeter, famous multimeter brands, etc.) and so on. 

Multimeter for Beginners - How to Measure Voltage, Resistance, Continuity and Amps

Catalog

Introduction

Ⅰ Parts of Multimeter

1.1 Multimeter Head

1.2 Measuring Circuit

1.3 Rotary Switch

Ⅱ Working Principle of Multimeter

Ⅲ Multimeter Operating Procedures

Ⅳ Multimeter Functions

Ⅴ Multimeter Using Tips

Ⅵ How to Find Circuit Faults with Multimeter

6.1 General Ideals

6.2 Multimeter Measuring Tips

Ⅶ How to Measure Current with Digital Multimeter

Ⅷ Which is Better Analog or Digital Multimeter?

Ⅸ Best Multimeter Brands

Ⅹ Frequently Asked Questions about Multimeter Basic and Functions


Ⅰ What are the Parts of Multimeter?

The parts of a multitester are a scale, a needle or pointer, an adjustment screw, a zero-ohm selector, a range selector knob, some ports and test probes. However, there is something different between analog multimeters and digital multimeters (DMM, DVOM). Analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters indicate with numeric display directly, which is easy to read, and even some have voice function. Now digital multimeters have become the mainstream and have replaced analog multimeters. Because DMM have the advantages of high sensitivity, high accuracy, clear display, strong overload capability, easy operation, and so on. The common multimeter is composed of three main parts: the meter head, the measuring circuit and the rotary switch.

1.1 Multimeter Head

The multimeter head is printed with various symbols, scale lines and values. The head of the analog multimeter is a high-sensitivity magnetoelectric DC ammeter. The performance indicators of the multimeter basically depend on the performance of the meter head. The sensitivity of it refers to the value of the DC current flowing through the meter head when the pointer is deflected at full scale. The smaller the value, the higher the sensitivity of the meter head. The greater the internal resistance when measuring voltage, the better its performance. The meter head of DMM is generally composed of an A/D (analog/digital) conversion chip, peripheral components, and liquid crystal display.

1.2 Measuring Circuit

The measuring circuit is used to convert all kinds of measurements to a small DC current suitable for meter measurement. It is composed of resistors, semiconductor components and batteries.

1.3 Rotary Switch

The rotary switch of the multimeter is a multi-position switch, which used to select various measurement lines to meet the measurement different  requirements. The switch is generally a round dial with functions and ranges marked around it.

digital multimeter

Ⅱ Working Principle of Multimeter

DMM converts a DC voltage signal by a conversion circuit, and then using an A/D converter converts the signal into a digital quantity. The digit counted by an electronic counter, and finally displayed on the screen.
The function of multimeter to measure voltage, current and resistance is partially realized through the conversion circuit. Among them, the measurement of current and resistance are all based on the voltage measurement. It means that the DMM is developed on the basis of the digital DC voltmeter.
The A/D converter converts the analog voltage quantity that changes continuously with time into a digital quantity, and then an electronic counter counts the digital quantity to obtain the measurement result, and finally the decoding display circuit displays the measurement result. The logic control circuit controls the coordinated work of the circuit, and completes the entire measurement process in sequence under the action of the clock.

 

Ⅲ Multimeter Operating Procedures

1. Be familiar with the functions of the multimeter before use. Select the proper gear position, range and meter pen jack according to the object to be measured.
2. When the volume of the measured data is unknown, first set the range switch to the maximum value, and then switch it to the small range.
3. A multimeter should be calibrated or adjusted to a known zero-value prior to use for accurate readings.
4. When measuring the resistance of a certain circuit, the power supply of the circuit under test must be cut off.
5. Do not touch the metal part of the test pen with your hands during the test. And it is not allowed to move the position switch with electricity to ensure accurate measurement and avoid accidents such as electric shock and instrument burning.

DMM image

Ⅳ Multimeter Functions

  • Measure Resistance

In the case of power failure, adjust the multimeter to the resistance position and connect the black and red test leads to the two ends of the resistance respectively. Note that if the measurement is directly on the PCB, other resistances may be incorporated, so that the measurement is inaccurate.

  • Measure Current

When the power is on, insert the red test lead into the current test port of the multimeter, and then set the multimeter to the current mode. Connect the black and red test leads of the multimeter to the measured circuit.

  • Measure Voltage

When the power is on, set the multimeter to the voltage range (note that there is a distinction between AC and DC), connect the black pen on the negative or ground terminal of the power supply, and the red pen on the positive power supply to measure the voltage.

  • Detect Short Circuit

In the case of power failure, adjust the multimeter to the buzzer position (if there is no buzzer, use the resistance position), and connect the black and red test leads to the two ends of the circuit to be measured. If the buzzer sounds, it means short circuit (or the resistance is zero or close to zero).

  • Detect Open Circuit

In the case of power failure, adjust the multimeter to the maximum resistance range, and connect the black and red test leads to the two ends of the circuit to under test. If the circuit is open, the resistance is infinite.

  • Test IC

Multimeter can only be used to test the IC dc supply voltage and to use the ohm range to find out if the IC is shorted to ground or not. Generally using an oscilloscope to test an IC is much more accurate because one could see the input and the output signal assuming if the IC did not develop any short circuit and has the right DC SUPPLY input (VCC).

 

Ⅴ Multimeter Using Tips

1. When using the multimeter, you can not touch the metal part of the test pen with your hands. This can ensure the accuracy of the measurement, and personal safety.
2. When measuring a certain amount of electricity, you cannot shift gears, especially at high voltage or high current. Otherwise, the multimeter may be destroyed. If you need to change gears, you should disconnect the meter pen first, and do measure.
3. When using the multimeter, it must be placed horizontally to avoid errors. At the same time, avoid the influence of external magnetic fields on the multimeter.
4. After measurement done, the rotary switch should be set to the maximum range of AC voltage. If it is free for a long time, the battery inside the multimeter should take out to prevent the battery from corroding other components in the meter.

How to Use a Multimeter?

Ⅵ How to Find Circuit Faults with Multimeter

6.1 General Ideals

1. Visual Inspection
You can touch the battery, resistor, transistor, and integrated block to see if the temperature rise is too high. If the newly installed battery becomes hot, the circuit may be short-circuited. In addition, you should also observe whether the circuit has broken parts, desoldering, mechanical damage, etc.

2. Waveform Analysis
Use an electronic oscilloscope to observe the voltage waveform, amplitude, cycle (frequency), etc. of the circuit. For example, if the clock oscillator starts to oscillate, but no output, it means the internal inverter is damaged, or the external component may be open.

3. Measuring Component Parameters
For components within the fault range, perform online or offline measurement, parameter values should analyze. For online resistance measurement, the influence of components connected in parallel should be considered.

4. Hidden Troubleshooting
Hidden failures are more complicated. Common causes include solder joints, loose joints, loose connectors, poor contact of the transfer switch, unstable component performance, and broken leads. It also includes some external factors. For example, the ambient temperature is too high, the humidity is too high, or there are intermittent strong interference signals nearby, etc.

5. Detect Working Voltage
Check the working voltage of each point and compare it with the normal value. First of all, the accuracy of the reference voltage should be ensured. It is best to use a digital multimeter of the same model or similar for measurement and comparison. Detecting whether the external AC voltage of the electrical equipment and the DC voltage of the internal circuit are normal is the basis for analyzing the cause of the failure. Therefore, in the process of repairing electrical equipment and electronic circuits, the relevant voltage should be measured first.

 

6.2 Multimeter Measuring Tips

6.2.1 Voltage Measuring Points
This method is to measure the voltage of each part of the electrical or electronic circuit and compare them with the normal values to find fault. In the process of maintenance, even if the circuit fault has been determined, it is necessary to further measure the voltage of each pin in the relevant circuit such as transistors and integrated circuits or the main nodes in the circuit to see if it is normal. This is helpful for discovering damaged components and analyzing the cause of failure.
For circuits that are inconvenient to measure current, the voltage at both ends of the resistor is often measured. With the help of Ohm's law, have indirect current testing to calculate. Such as the transistor current negative feedback in amplifier circuit and the transistor static operating point ICQ of the emitter follower, it is commonly used. However, there is a certain error between the actual resistance value and the nominal value. The resistance value of the resistor will change after long-term use, especially the carbon film resistor.
In addition, measuring the input or output signal voltage of the detected electrical appliance to check whether the dynamic working status is normal or not. It is also a category of voltage measurement.

 

6.2.2 Measuring Parameters Selection
① Select the appropriate range of AC voltmeter or DC voltmeter (or universal multimeter), and the corresponding power supply voltage.
② Select an electronic voltmeter with an appropriate range and high input impedance when measure the working voltage of the relevant node or device electrode.
③ Choose an electronic voltmeter with an appropriate range and frequency range when measure the input and output signal voltage of the relevant circuit.
④ Find out the faults against the normal value. The place where the voltage deviates greatly from the normal value is often the place where the fault is located.

There are something YOU need to pay attention to 😏

① Pay attention to the polarity of the DC voltmeter to determine the direction of voltage or current.
② Attention should be paid to the relative measurement points of the working voltage: Generally it is to the ground, some are specially selected for zero volts, and some are between the electrodes, which need to be classified and tested carefully.
③ When connecting the electronic voltmeter, pay attention to the sequence of the "high" potential end and the "low" potential. The ground potential terminal (that is, the ground wire) should be connected first, and then the high potential terminal during printing measurement. After the measurement is completed, the high potential terminal should be removed first, and then the low potential terminal.
④ Pay attention to the influence of the input impedance and frequency range of the voltmeter on the test results.

 

Ⅶ How to Measure Current with Digital Multimeter

Measuring AC with a Digital Multimeter

Use a DMM to measure DC current. The red test lead is a positive test lead, inserts into the “mA” jack or “A” jack. The black test lead is a negative test lead, inserts into the “COM” jack. Turn the measuring switch to the DC position “A” to the circuit under test for measurement. When measuring DC below 200mA, the red test lead should be inserted into the “mA” jack; when it is greater than 200mA, the red test lead should be inserted into the “A” jack.
For example, when measuring the working current of a DC relay, disconnect the current loop firstly of the relay as shown in the figure below, then connect the positive test lead to the positive electrode of the battery and the negative test lead to the relay, as shown in the figure below. The number displayed on the screen is the operating current of the relay.

operating current dc relay

Figure 1. Operating Current of DC Relay

 

When the digital multimeter is measuring DC current, if the positive and negative test leads are reversed, the measuring result will be a negative value. During measuring, it is not necessary to consider the direction of the current. Because the magnitude and direction of the current can be measured at the same time.

measure dc

Figure 2. Measure DC

 

Measuring DC with an Analog Multimeter

When measuring DC current, the analog multimeter should be connected in series to the circuit, as shown in the figure below. It can be connected in series between the positive pole and the circuit under test, or between the circuit and the negative pole of the power supply.

measure dc with analog multimeter

Figure 3. Measure DC with Analog Multimeter

 

When measuring 500mA and below DC current, the measurement switch should select the “mA” gear. Measuring the current between 0.5 and 5A, the 500mA gear should be selected, and the positive pen should be inserted into the “5A” jack. When measuring the circuit, the full-scale value (the rightmost side of the scale line) is equal to the number of digits of the selected range scale. The measurement result is converted according to the position indicated by the pointer, as shown in the figure below.

reading of analog multimeter

Figure 4. Reading Numbers of Analog Multimeter

 

Measuring AC with a Digital Multimeter

The measurement of AC current by a digital multimeter is similar to that of DC current. Turn the rotary switch to the required level A, and the multimeter can be connected in series. When measuring current below 200mA, the red test lead should be inserted into the “mA” jack, and when measuring above 200mA, insert it into the “A” jack. The following figure shows the schematic diagram of measuring the working current of the lighting lamp.

measure ac with DMM

Figure 5. Measure AC with DMM

 

Measure AC with an Analog Multimeter

You must use an analog multimeter with an AC current block to measure directly. Similar to measuring DC, you can connect the multimeter to the circuit under test in series.

measure ac with analog multimeter

Figure 6. Measure AC with Analog Multimeter

 

Ⅷ Which is Better Analog or Digital Multimeter?

It's very similar to choose which one to use. The digital is easy to read, gives greater accuracy and reads in tenths, hundreds or less. One important reason to use one is that it has a high internal resistance. That results in drawing less current which would affect the circuit. If you am measuring the output of a small device this kind of meter will not increase the load. This kind of meter is slow to give a reading and when it does the reading may keep changing because the circuitry is unstable. The circuits depend on logic gates that can only handle high and low but not in between.
A digital meter will not move up and down in a smooth way that an analog will. The analog is easier to use in a dynamic situation. There have been times when someone want a meter to draw a load to make the circuit perform as it would under normal conditions, the analog will do this. Here is a comparison of the two. 

Analog Multimeter

Digital Multimeter

It is more sensitive to noise.

Less sensitive to noise , ease of multiplexing.

Analogue multimeter is cheaper.

Digital multimeter is costly than analog.

It gives less accurate results.

It produces more accurate output than analog.


Both meters have their advantages. If you can only afford to have one meter the digital meter is more useful. Now most people prefer to use a digital for measuring resistance those measurements have to be precise. Measuring current should be done with caution because one mistake will burn out the insides.

 

Ⅸ Best Multimeter Brands

A multimeter should be of high quality and accuracy. Be sure to verify that your multimeter conforms to all safety standards. There are various types of digital multimeter based on range of functionality and application. Depending on whether you want it for general purpose or industrial purpose, you need to know some reliable multimeter bands to get a good quality product. The following table can be used for recommendation.

*

Etekcity Digital Multimeter

Mastech Multimeter

INNOVA Multimeters

Klein Tools

Agilent Keysight Multimeter

Brymen Multimeter

Tacklife Multimeter

Kusam Meco

AstroAI Digital Multimeter

Extech Multimeter

Fluke Multimeter


 

Ⅹ Frequently Asked Questions about Multimeter Basic and Functions

1. What are multimeters used for?

A digital multimeter is a test tool used to measure two or more electrical values—principally voltage (volts), current (amps) and resistance (ohms). It is a standard diagnostic tool for technicians in the electrical/electronic industries.

 

2. What are the two types of multimeter?

Multimeters are divided into two types depending on the way the indication is displayed: analog and digital. Analog multimeters are multifunction electrical measuring instruments with indication by means of an arrow (analog) scale.

 

3. What is the principle of multimeter?

Most multimeters inherently measure voltage, and pass a current to be measured through a shunt resistance, measuring the voltage developed across it. The voltage drop is known as the burden voltage, specified in volts per ampere.

 

4. What are the three main function of multimeter?

While standard units measure voltage, resistance, and current, expensive ones measure inductance and capacitance as well. It utilizes three functions in a single instrument – the voltmeter for measuring the voltage between two points, the ohmmeter to determine resistance, and the ammeter to measure the current.

 

5. What are the advantages of digital multimeter?

Advantages of Digital Multimeters
They are more accurate than analog multimeters.
They reduce reading and interpolation errors.
The 'auto-polarity' function can prevent problems from connecting the meter to a test circuit with the wrong polarity.
Parallax errors are eliminated.

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