What's a Digital Voltmeter

What's a Digital Voltmeter

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Sravan

And why should you know how to use one ?

Digital voltmeters (or) Multi-meters, are a essential tool that belongs in every electronic, or electrical engineer's arsenal of tools.

But almost everyone should know how to use one, as their implications have a wide variety of utilities that helps solve basic electrical issues without needing the assistance of a dedicated electrical or electronic engineer on site.

Standard basic multi-meter/voltmeter.

These days multi-meters can do things like measure current, voltage, resistance, continuity, etc.

Let's take a look at what those things are, and how we can use a multi-meter in real world applications.


Index:

  • Multi-meter parts
  • Different operational modes
  • Using a multi-meter in real life
  • Wrap up

Multi-meter parts

Multi-meter anatomy

A multi-meter has a couple simple parts,

  • An LCD display to show decimal values of the quantity to be measured
  • A function dial to select what operation to do
  • Contact probes to make electrical connections between the contact points for measuring

Every Multi-meter has a voltage and current rating according to how much it can withstand when measuring.

Polarity is the direction in which electric current flows, from positive to the negative end. The Red color probe is for positive terminal (+), and the Black color probe is for the negative terminal (-).

Probe polarity does not matter for AC current.


Different operational modes

Before we can see how to use the multi-meter we need to know how electric current works in a very simple fashion, let's take a sample analogy:

in a very simple way, to measure the voltage you have to measure the points across the appliance to see how much voltage is being applied to it.

To measure the current, you have to measure in-between the point where current exits the appliance and goes to the ground (-)


Measuring voltage with a multi-meter

Rotate the function dial to choose the appropriate setting, with the probes in the right points:

Voltage measuring mode

turn the function dial to the option shown above according to the appropriate icon,
The icon with the wavy line for AC current, the dotted line for DC current.

Once you have chosen the appropriate function, probe across the appliance you want to measure voltage across like a battery:

measure the battery voltage with the appropriate DC current mode

Measuring current with a multi-meter:

Rotate the function dial to choose the appropriate setting, with the probes in the right points:

Current measuring mode

turn the function dial to the option shown above according to the appropriate icon,
The icon with the wavy line for AC current, the dotted line for DC current.

Once you have chosen the appropriate function, probe in line with the appliance you want to measure current with like in-between a light bulb and a battery.

measure current usage with the appropriate DC current mode

The current measurement is made by letting electricity pass from one probe through the other, technically creating a short, and it's advisable not to directly connect your multi-meter directly to the power supply or inline without any appliance.

This will inevitably cause the multi-meter to short the current from the positive to the negative, blowing the multi-meter fuse, and causing damage to the instrument itself!

Do not probe power supplies directly in current mode, it will short circuit and cause damage

Testing continuity with a multi-meter

Rotate the function dial to choose the appropriate setting, with the probes in the right points:

Continuity testing mode

with this mode selected, you can check if there is a path of conductivity between two points, and if it is conductive, you will hear a shrill sound made by the multi-meter indicating it.

To self-test if this mode is working properly, you can touch the probes together and make sure the sound is made.

Use this to check if wiring in houses have breaks in them for example or if you are testing if connections exist on electronics circuit boards.


Measuring Resistance with a multi-meter

Rotate the function dial to choose the appropriate setting, with the probes in the right points:

Resistance testing mode

With this mode selected, you can measure the resistance across two points in a circuit. This is very important when working with electronics and design testing. But it can also help if you are trying to do wiring jobs with signals like speakers where combined speaker resistance is important.

pretty much anywhere resistance is important, and needs to be measured, this function can be used.


Using a multi-meter in real life

As seen with the different modes, a lot of functionality is available in a single multimeter, but how does one make use of these functions in day-to-day work?

Most likely you will make more use of Voltage, Resistance, and Continuity settings, and only ever use the Current measuring setting.

Some places you might use these functions are:

Voltage measurement:

  • Testing the voltage of your car battery, in good condition a battery should show the following voltage characteristics:
    - 12.6 - 13v when charged
    - 13.6v when being float charged
    - 14.6v when being rapid charged

Resistance measurement:

  • Checking Resistance/impedance of speakers in speaker setups, sometimes the speaker amplifier can only handle a certain threshold of combined speaker resistances, so in multi-speaker setups, you need to make sure you are above that threshold or you risk blowing your amplifier. for example:
    - Say you have some 8-ohm speakers and there are 3 speakers on the same amplifier channel, measuring with your multi-meter you should see about 2.67 ohms of resistance. make sure your amplifier can handle that much lower resistance of speakers combined.
  • Sometimes, an electronic appliance might fail and not power on (maybe due to an accidental short). The resistance measuring mode can be used to measure points of 0 resistance, or low resistance which can cause high current through pass through and cause failure. The continuity function can also be used, but sometimes it doesn't detect some lower resistance paths.

Continuity testing:

  • With household wiring jobs, in the case of faulty wiring, you need to know which particular wire has a line break, the continuity mode can help measure a conductive path and make sure that such a path exists.

Wrap up

In summary, digital multi-meters are super versatile, offer a lot of useful functionality for electronics problem solving. It shows why it's a staple part of every electronics or electrical engineer's toolkit.

There are a lot more features in some multi-meters, and only the common features have been discussed here.

To learn more about using a multi-meter, check out the manual guide presented by the manufacturer of your multi-meter.

If you are looking to get a new multi-meter, here are some recommendation links for some simple multi-meters.

Fluke multi-meters, very accurate, good quality, should last a lifetime
Basic Multi-meter, good enough if you are a beginner with electronic instruments.

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