Is Voltmeter the Best Meter? How to Use it?
What are your criteria for choosing an electrical or electronic meter? Aside from the most obvious one, the purpose or the circuit quantity that you’re going to measure, have you ever thought is you are biased towards using a particular meter? For me, it’s the voltmeter. But is voltmeter the best meter? Here’s why I love it and how to use it.
During this post, I will be using some terms that you will need to know – Here they are
- Voltmeter: Meter used for measuring voltage
- Ammeter: Meter used for measuring current
- Ohmmeter: Meter used for measuring resistance
- Ratings: The maximum measurement value. For example, if a meter has a rating of 600V, using it in a situation with higher voltages will most likely damage it.
- Readings: Another term used for measurements
- Portable appliance: Any appliance or equipment that has a plug, e.g. toaster, electric kettle, etc.
- Fixed appliance: Any appliance or equipment that is permanently wired to the circuit and does not have a plug, e.g. Air conditioner, ceiling lights, etc.
Voltmeter is perhaps the Most Robust Meter
So long as you don’t exceed the ratings, you cannot damage a voltmeter, doesn’t matter how you connect it – correctly or incorrectly. It doesn’t even matter what type of circuit it is; it’s hard to damage a voltmeter.
If you misconnect an ammeter, you will damage it or at least blow a fuse. If you connect an ohmmeter to a live circuit, you can damage it. If you incorrectly connect any other meter, even if you happen to be within the ratings, there’s a high chance you will damage it.
But not a voltmeter. Now, why is that? It’s the internal resistance of a voltmeter. The beauty of having this is that high resistance means low current. Usually, it’s the current that damages the meters, so if the current is less, there is less chance of damage.
A Voltmeter Can Save Your Life
Let’s say that you are planning to work on a portable appliance that operates on 230V. Please remember that you need to be a licensed Electrician, at least in Australia, to work on fixed appliances that exceed 50V AC and 120V DC.
Although anyone can work on a portable appliance if it is disconnected from the 230V, to disconnect the equipment, you may have to touch it or may accidentally touch it. At this stage, you may not know what the problem might be, and one of the issues could be that there is a voltage on the surface.
In this situation, you will use a voltmeter to measure every possible point that you will be touching or may accidentally touch. If you get a voltage reading other than 0V, you may have to disconnect the supply from another point.
You see, a voltmeter can save your life if you know there is a voltage present and exactly where.
Understand Abnormal Conditions with a Voltmeter
Fault finding is probably the trickiest and perhaps the most satisfying and profitable part of anyone’s work in electrotechnology. You may have a situation in your hands where equipment or components are not working as expected.
I’ll give you an example of something that happened to me recently. There was a 24V DC shunt motor that we usually use for training our learners which wasn’t working as expected. The problem was, that when we turned it on, the motor drew massive current but wouldn’t turn. It’s a typical indicator of a locked rotor. But it wasn’t that.
I used a voltmeter to see if we were getting correct voltages on all points and found out that shunt field winding had no voltage, which means that the rotor or the armature was drawing all the current. Since the field winding wasn’t getting any voltage, it couldn’t generate a magnetic field to turn the motor.
The measurement gave me an indication that perhaps one of the connections was loose, but that wasn’t the case either. So, I started measuring voltages across the cable and found that one wire was showing the voltage drop of 24V, and intact wires should show 0V.
At this stage, I turned off the supply and tested that wire’s continuity and found that it was broken at the connection point. So, the connection to the motor was solid, but the wire had come loose at the termination.
I was able to understand the problem by using the voltmeter.
How to Use a Voltmeter
Here are the basic steps of using a voltmeter:
- Turn on the meter
- Set the appropriate type of voltage – AC or DC
- Set the appropriate voltage range if its non-autoranging. If the voltage is unknown, set the meter to the highest range.
- Connect the probes of the meter to the points where you wish to measure the voltage.
- Record the reading
In the video below, Ill show you how to measure voltage with various meters in our Electromag pracbox
Voltmeter connects in parallel
A voltmeter should connect in parallel to the component or equipment that you are measuring. For example, if you want to measure the voltage of your car battery, you will connect one of the meter leads to the negative terminal of the battery and the other to the positive. This is called a parallel connection.
What happens if you connect the voltmeter in series?
Short answer, the load or equipment won’t work because of the high internal resistance of the meter. But we should first understand what a series connection is. In the circuit below, if the switch was replaced with a voltmeter, then it’s in series. Now the circuit has a massive resistance in series with the load, and the overall current will become very small.
Dangers when using a voltmeter
Voltmeter itself is not at all dangerous, but the circumstances that you will be using it in can be. Any meter that requires the power to be available or the supply is suspected of being available, is exposing you to the danger. For example, voltmeter or ammeter is not very useful if there is no voltage supply.
When using a voltmeter, you must consider the ratings of the meter. If you exceed these ratings, there’s a high chance that you will damage the meter.
I hope that I was able to explain to you why I like voltmeter so much – it’s the most robust meter, keeps me safe and very useful in fault finding situations.
I also hope that you now understand how to use a voltmeter and what you should consider before using it.
Thanks for dropping by.