Instruments that can measure different electrical parameters are known as Measuring Instruments. Some common Electrical Instruments are Ammeter, Voltmeter, Ohm Meter, Wattmeter, Energy Meter, etc. While these meters can measure only one electrical quantity (Ammeter – Current, Voltmeter – Voltage, etc.), there is a special meter known as a Multimeter that can measure multiple quantities (Current, Voltage, Resistance, etc.). In a previous guide, we saw the comparison of Ohm Meter vs Multimeter. In this guide, we will do a similar comparison, but this time it is Voltmeter vs Multimeter.
First, we will understand about a Voltmeter and a Multimeter. In the process, we will take a brief look at their types. After that, we will compare Voltmeter vs Multimeter and find out their differences. Finally, we will try to answer an important question “Which one to use, a Voltmeter or a Multimeter?”.
What Is a Voltmeter?
A voltmeter is an electrical instrument that measures electric voltage or the Potential Difference between two points in a circuit. There are different operating principles to measure the voltage.
We can use a Voltmeter to measure the voltage of batteries, different electrical and electronic components in a circuit, electrical appliances, electronic devices, etc. Electricians, Electronic Repair Personnel, Engineering people, etc. often use voltmeters to get accurate voltage readings.
In the past, most volt meters are “mechanical” devices as they require different mechanical interactions between currents, current and magnetic fields, or between conductors.
These mechanical interactions produced a torque that is proportional to the voltage that we are measuring. The torque then causes a pointer on a scale to displace indicating a voltage.
But recent voltmeters are Electronic Voltmeters that use semiconductor devices instead of mechanical devices. As a result, the instruments got smaller, more accurate, and affordable.
Depending on the type of input signal processing involved, Electronic Voltmeters are further divided into Analog Voltmeters and Digital Voltmeters. We will see more about Different Types of Voltmeters in the next section.
How To Use a Voltmeter?
Using a Voltmeter is very simple. Just take the two leads of the voltmeter and place them across the terminal you want to measure.
For example, if you want to measure the voltage of a car battery, then take the red and black wires (positive and negative) of the voltmeter and place them at the positive (red) and negative (black) terminals of the battery.
If the voltage of the battery is more than 12.7V, then you can say that the battery is in a good condition. But if the voltage is less than 12.4V, then the battery is low on charge and you need to recharge it immediately.
In this way, you can use a simple voltmeter to determine whether your car’s battery is in good condition or not.
Similarly, you can use the voltmeter to measure the voltage across any two points in a circuit just by connecting the leads across those two terminals. Remember that we always connect the leads of the voltmeter in parallel to the device or component. But why is this?
Why Do We Connect The Voltmeter In Parallel?
Any measuring instrument must not interfere with the operation of the circuit or device that we are testing. From the basic circuit theory, we know that the voltage across two components in parallel is the same.
As a result, we connect the leads of the voltmeter across or in parallel to the device or component that we want to measure. There is another beautiful thing about the design of the voltmeter.
The internal resistance of the voltmeter is very high. As a result, when we connect this high-resistance voltmeter across the component we are testing, the effective resistance is still equal to the resistance of the component.
In this way, the voltmeter doesn’t affect the operation of the circuit and can get the voltage readings accurately.
Different Types of Voltmeters
Here is a small list of different types of voltmeters from the past as well as the current-gen variants.
- DC Moving Coil Voltmeter
- DC Galvanometer
- AC Moving Coil Voltmeter
- DC Analog Voltmeter
- Rectifier-based AC Analog Voltmeter
- True RMS Analog Voltmeter
- Ramp Type DVM
- Dual Slope DVM
- Successive Approximation DVM
- Delta-Sigma DVM
- Potentiometer Type DVM
- AC Digital Voltmeters
If you are looking to buy a voltmeter today, then chances are, you will come across several Digital Voltmeters. You may find one or two analog voltmeters but a majority of products nowadays are only digital.
A Digital Voltmeter or DVM is a measuring instrument that measures Voltage by converting the analog voltage values into digital values and displaying the numeric readouts.
The main circuitry of a DVM is the ADC, which is responsible to convert the analog voltage into appropriate digital quantities. In its basic form, the DVM can only measure DC Voltages.
But with the addition of AC to DC Conversion circuitry, you can give it the capacity to measure AC Voltages as well. After measuring either AC or DC Voltages, the DVM displays the readings on a seven-segment display or an LCD Screen.
Depending on the type of ADC we use in the DVM, we can further divide the Digital Voltmeters into the following:
- Successive Approximation Type DVM
- Ramp Type DVM (further Linear Ramp or Stair-case Ramp)
- Dual Slope Integrating DVM
- Delta – Sigma Type DVM
Some other types of DVMs
- Voltage to Time Conversion DVM
- Potentiometric DVM
- Voltage to Frequency DVM
- Interpolating Integrating DVM
Important Parameters of Digital Voltmeters
Here is a small list of some important performance parameters of Digital Voltmeters.
- Measurement Range: This indicates the extended range of voltages a DVM can measure. This can be from a few microvolts to several kilovolts. Note that the basic range of any digital voltmeter is either 1V or 10V. Engineers extend this range with the help of attenuators at the input.
- Digits in the Readout: This is the number of digits in the digital readout of the voltmeter. This usually varies from 3 digits to 6 digits or more.
- Resolution: The smallest value the DVM can measure.
- Accuracy: Accuracy of the reading means how close is the value that the DVM displays to the value it measures. The accuracy of the DVM depends on the resolution as well as the number of digits of the readout.
- Speed: In a DVM, there is a lot of signal processing in the form of ADC, digital signal processing, signal transmission, etc. All these conversions and transmissions are a part of the Digitizing circuit. The speed of producing the reading depends on how fast the digitizer circuit works.
Some other parameters that you need to consider are:
- Input Impedance
- Type of Digital Output
- Noise Rejection (Common Mode and Normal Mode)
What Is a Multimeter?
We have seen Voltmeter till now. It is a device that measures the electric voltage at two points in a circuit. Similarly, we have an Ammeter that measures the current flowing in a circuit and an Ohmmeter that measures the resistance.
What if you want to measure all three things? Do you have to carry three different measuring devices? No. This is where the Multimeter comes into play.
A Multimeter, as the name suggests, can measure multiple things using a single instrument. A Typical Multi-functional Meter can measure Voltage, Current, and Resistance. In simple terms, a Multimeter combines the functionalities of a Voltmeter, Ammeter, and Ohmmeter into a single device.
As a result, earlier versions of Multimeters (the analog versions) are known as Volt-Ohm-Milliampere Meters or VOM Meters. But the modern digital versions are known as Digital Multimeters or DMMs.
What Can You Measure With a Multimeter?
So, what can you measure with a basic Multimeter? Even the simplest of Multimeters can measure the following quantities:
- DC Voltage
- AC Voltage
- DC Current
- AC Current
In addition to this, modern multimeters can measure some other parameters such as:
- Mains Frequency
- Duty Cycle
- Non-contact Voltage Detection
- Diode Test
We made a beginner’s guide on “How to Use a Multimeter?”. Check that out if you want more information regarding the basic layout of a typical Digital Multimeter, how to measure some essential electrical quantities and even some safety tips.
Different Types Of Multimeters
In a basic sense, we can divide the multimeters into two types:
- Analog Multimeters
- Digital Multimeters
Analog Multimeters have a permanent magnet moving coil type Galvanometer. This has a needle pointer on a scale to indicate the value of the quantity being measured.
Digital Multimeter on the other hand converts the analog values to digital using special ADC Circuitry. As a result, the readings are available as numbers on the LCD.
Digital Multimeter (DMM)
Just as everything else is going digital, even multimeters are becoming digital (the move from analog to digital multimeters was a long back ago). If you are buying a Multimeter today, chances are you will come across several dozens of manufacturers producing Digital Multimeters.
You can get DMMs for as little as $5 and the price can go upward of $5,000 (for calibrated and certified meters). In fact, it is very hard to find individual voltmeters, ammeters, or ohmmeters nowadays as a Digital Multimeter can do it all and they became very affordable.
Digital Multimeters can measure both AC and DC Voltages and Currents. To measure current, the DMM converts it to a voltage by passing the current through a low resistance shunt.
Coming to AC quantities, it first converts them to DC using rectification and filtering circuits. To measure resistance, the DMM applies a high-precision low current to the resistor under test and then gets the voltage reading (Ohm’s Law to the rescue).
After acquiring all the necessary quantities, which are analog, the DMM converts them to digital using appropriate ADC techniques. It then displays the values on the LCD after some signal processing.
Some advantages of Digital Multimeters over their Analog counterparts are:
- Small and compact
- Clear Digital Display (no chance of parallax error)
- High Accuracy
- Very High Input Impedance (doesn’t have loading effect)
- Affordable (prices will go down, at least in the beginner segment)
Specifications Of a Digital Multimeter (DMM)
Before we proceed, remember that the values of the specifications vary from one multimeter to other. But the list of specifications will remain more or less the same.
Here is a quick look at some essential specifications of a modern multimeter.
- DC Voltage:99mV to 999.9V with a resolution of 0.01mV up to 99.99mV.
- AC Voltage:99mV to 750V with a resolution of 0.01mV up to 99.99mV.
- DC Current:999mA to 9.999A with a resolution of 0.001mA up to 9.999mA.
- AC Current:999mA to 9.999A with a resolution of 0.001mA up to 9.999mA.
- Resistance:99Ω to 99.99 MΩ with a resolution of 0.01Ω up to 99.99Ω.
- Capacitance:999nF to 99.99mF with a resolution of 0.001nF up to 9.999nF.
- Frequency:999Hz to 9.999MHz with a resolution of 0.001Hz up to 9.999Hz.
- Duty Cycle:0% to 99.0% with a resolution of 0.1%.
- Temperature (°C): -40 °C to 0 °C (accuracy of ±5% or ±3 °C), 0 °C to 400 °C (accuracy of ±1% or ±2 °C), 400 °C to 1,000 °C (accuracy of ±2%).
- Temperature (°F): -40 °F to 32 °F (accuracy of ±5% or ±6 °F), 3 °F to 752 °F (accuracy of ±1% or ±4 °F), 752 °F to 1,832 °F (accuracy of ±2%).
Voltmeter vs Multimeter: A Comparison
A Voltmeter is an electrical measuring instrument that can measure electric voltage. A Multimeter is a multi-function device that can measure voltage, current, and resistance.
The main and only function of a voltmeter is to measure the electric voltage. It cannot measure anything else. The multimeter on the other hand is a combination of a Voltmeter (Voltage), Ohmmeter (Resistance), and Ammeter (Current).
Hence, we also call the multimeter a Volt – Ohm – Milliampere Meter or VOM Meter.
How To Connect?
Using a voltmeter is very simple. Just take the leads of the multimeter and connect them across the terminals where you want to measure the voltage or potential difference in a circuit. Essentially, we are connecting the voltmeter in parallel to the electrical component or device.
How we connect the multimeter depends on the quantity that you want to measure. For instance, to measure voltage, set the multimeter to the Voltage (AC or DC) measurement position and place the leads in parallel to the terminals or components.
But if you want to measure current, then we have to connect the multimeter in series with the circuit under test.
Remember, the voltage across two parallel components is the same, and the current through two series components is the same. We are using the same principle to measure voltage and current.
Which One To Buy, The Voltmeter or The Multimeter?
Now that we have seen some basics of both voltmeters and multimeters, the essential question a beginner or novice might have is “Which device to buy, a Voltmeter or a Multimeter?”
Whether you are working with electrical installations, electronic design, and repair, or any other electrical engineering-related jobs, you need a multimeter to measure different electrical quantities.
You can use a Multimeter as a Voltmeter to measure AC and DC Voltages, Ammeter to measure AC and DC Currents, and Ohmmeter to measure resistance. Most modern DMMs can measure additional quantities such as continuity, diode or transistor, capacitance, inductance, temperature, frequency, duty cycle, etc.
As most of the multimeters nowadays are digital, chances are you will be looking at a decent Digital Multimeter (DMM) that suits your need and also fits your budget.
DMMs are available as handheld as well bench-top models. Some come with the traditional rotary dial and alpha-numeric LCD but some fancy ones such as the KAIWEETS KM601 Smart Digital Multimeter come with a large colorful LCD and push button interface.
As we can use a multimeter as a voltmeter, you might be thinking “what’s the need for a separate voltmeter?”. You might need a Voltmeter depending on the purpose or job you are trying to accomplish.
Imagine you want to monitor the AC Mains voltage of an outlet or an inverter. In this case, you can use a tiny digital voltmeter that comes with a direct plug or with leads. All you have to do is insert the voltmeter into the outlet or connect the leads and voila, you have accurate voltage readings on the display.
Another similar application is if you are building a power supply or battery charger or other DC to DC Converter, having a small Digital Voltmeter that can measure DC Voltage is simple as you can always monitor the voltage without using a multimeter.
Electricians, Electronic Design Engineers, Repair and Troubleshooting personnel, HVAC Installers, etc. need different kinds of electrical and electronic measuring equipment.
A Multimeter is a “one-stop solution” kind of device as it can measure voltage, current, and resistance among other things. A voltmeter on the other hand can only measure electric voltage and nothing else.
In this guide, we saw the basics of the Voltmeter and Multimeter. We also saw their types. After that, we compared Voltmeter vs Multimeter using some basic parameters.
Finally, we concluded the discussion with a diplomatic answer to the question “Which one Should You Buy among Voltmeter vs Multimeter?”.
We tried to make this guide as beginner-friendly as possible. If you feel that we missed something or want us to add some extra information, do let us know in the comments section below. We will try to add it.