Voltmeter is a measuring instrument designed to detect the potential difference between two points in an electric or electronic circuit. A voltmeter is commonly used for AC or DC circuits. Specialist voltmeters may also measure Radio Frequency (RF) voltage.
A device’s voltage can be measured using a voltmeter that is connected in parallel to the said device. This arrangement is significant since parallel objects usually tend to have the same potential difference. It is wired in parallel with the circuit, primarily due to similar voltage losses across it. In this article, we will discuss all the topics related to Voltmeter including its diagram, parts, formula, various types, working principle, how to use, etc.
What Is a Voltmeter?
A voltmeter or voltage meter is an appliance used for measuring the voltage of a point to another in any electronic circuit. Normally, volts are used for AC circuits or DC circuit. Alternatively, RF voltage can also be measured using specialised voltmeters.A voltmeter is used to measure voltage usually marked in volts, millivolt (0.001volts) or kilovolts 1(k),ooo Volt).
Voltmeter also has a very high internal resistance. This is done principally since it measures the amount of variation in potential difference between two points across a circuit. As a result, the measuring device’s current remains constant. Basically, a high resistance voltmeter would hinder the flow of current through it. This enables the device to make proper voltage readings.
Voltmeter Symbol
The symbol for the voltmeter is typically V, and it includes a circle that touches two terminals.
A voltmeter has the least count for 0.1 V Voltmeter determines accuracy of voltage measurements The unit used by a scientist or an engineer to measure physical quantities on a continuous scale is called as measurement.
Voltmeter Diagram
The diagram of a voltmeter connected in a circuit as parallel is given as:
Voltmeter Connected as Parallel to Circuit.
Parts of a Voltmeter
Some of the common parts of voltmeter
- Dial/Display: Nowadays, modern voltmeters have digital display that shows the measured voltage in volts directly. And an old analogue voltmeter could have knife and fork.
- Selector switches: Most voltmeters have selector switches to allow their operators to choose the voltage they want to measure.
- Probes/Leads: Voltmeters come with probes or leads that connect to the points in the circuit where voltage is to be measured. These are normally coded by colors, red being positive and black negative.
- Input impedance: In order to minimize the impact of a meter upon the circuit under test, a typical voltmeter has high input impedance. This makes it draw negligible current from the circuit while not changing the measured voltage.
- Intermediate circuitry: Resistance and operational amplifiers constitute internal circuitry of a voltmeter which serves as an amplifier for voltage being measured
- Power source: Also, digital multimeters may employ batteries or external power supply as its power source.
- Housing/enclosure: A protective housing keeps all components of the voltmeter inside it safe from harm and personnel injury.
A multiplier is a resistance connected in series. Its value is determined through the voltage equation. Resistance in a Series Equation is
V = Im × Rse + Vm
Where,
- V = Voltage,
- Im= Full scale current,
- Rse=Resistance in Series, and
- Vm= Full Scale Voltage
Range of Voltmeter
DC Voltmeters have measuring capacities ranging from 10mV to 1000DC. 1V to 1000 V AC is measured by AC voltmeters.
Least Count of Voltmeter (Analog)
The least count of an analog voltmeter depends on its scale and the number of divisions between two consecutive major marks. For example, if there are 100 divisions between 0 and 10 volts, the least count would be 0.1 volts (10 V divided by 100 divisions).
Read more about What is the Least Count of Voltmeter?
Voltmeter Working Principle
It works according to Ohm’s law. As per Ohm’s law, the voltage across a resistance is exactly proportional to the current passing through it. Basic meter shows a potential difference across its terminals with full-scale current running through it.
Voltmeter is always connected in a parallel manner to the element that would be examined for voltage, within a circuit. A DC voltmeter has a polarity symbol on it. In order to construct a meter deflection, link the positive (+) terminal of the voltmeter to one point with higher potential and negative (-) terminal up to another spot that has lower value.
An AC voltmeter consists of no polarity indications and can be connected to any case. In this instance too, the voltmeter is still connected in parallel to the component being observed. As shown in the figure below, a high-voltage range voltmeter is made by connecting series resistance with meter mechanism which has full scale voltage capabilities.
Types of Voltmeter
There are various types of voltmeter, some of these types are:
- Analog Voltmeter
- Digital Voltmeter
- Amplified Voltmeter
- Movable Iron Voltmeter
- Permanent Magnet Moving Coil Voltmeter
- Rectifier Voltmeter
Let’s discuss the types in detail.
Analogue or Analog Voltmeter
Analogue voltmeter is used mainly to measure the AC voltage. The reading is shown using a pointer that is mounted on the calibrated scale. Torque applied to the pointer affects its movement. The strength of the torque that is produced has a direct relationship to voltage measured.
A basic analogue voltmeter consists of a sensitive galvanometer (current meter) which forms part of high resistance series. The meter should have a large internal resistance or it would draw current significantly that might interrupt the operation of the circuit during testing. The meter displays a range of voltage determined by the series resistance value and galvanometer sensitivity.
In contrast, the use of an oscilloscope is quite common to measure low voltages where instantaneous voltage was shown as a vertical shift. The oscilloscopes measure the peak-to-peak and peak voltage of RF or AC applications. High potential differences meters are made using wiring, insulators and heavy-duty probes.
Digital Voltmeter
It shows the voltage as numbers on a digital voltmeter. Many of these meters can calculate voltage measurements to numerous decimal places. Practical laboratory voltmeters have maximum ranges of 100-300 volts. Commercially available voltmeters usually have multiple scales ranging in powers of ten i.they can measure voltage from to 1 Volts, or even up to
Amplified Voltmeter
These fragile sensors sometimes refer to as milli-voltmeters or micro voltmeters can measure pinch of potential drop. These voltmeters essentially have an electronic amplifier in the input line that boosts the amplitude of incoming electricity many times so as to allow for measurement with a basic voltmeter. These are present only in specialized labs and workshops.
Movable Iron Voltmeter
MI is movable iron voltmeter. Because the deflection is proportional to square of voltage assuming constant meter’s impedance, it can be used for AC as well DC measurements. Whatever may be the polarity of that voltage, it has always a directional component. They are further classified in two aspects,
Permanent Magnet Moving Coil Voltmeter
A Permanent Magnet Moving Coil voltmeter, sometimes referred to as a D’Arsonval meter often or simply galvanometer is an instrument that measures electrical current by watching the deviation of its magnetic field. The current is passing the coil and it creates a magnetic field that acts together with the one created by permanent magnet which causes deflection of this coil. The deflection amount is directly proportional to the current flowing through coil. PMMC voltmeters are direct current (DC) voltage measuring devices.
Rectifier Voltmeter
AC circuits are often measured with rectifier voltmeters. This type of voltmeter uses a rectifier for AC signals to DC, which can be further measured with PMMC instrument.
Attributes Defining The Voltmeter
The following are the Attributes of an ideal voltmeter:
- It has unlimited resistance.
- It has extreme sensitivity.
- It has high precision.
- There is no zero error.
- There is no temperature dependence.
- Speedy response.
- It has good resolution.
Why is a Voltmeter Connected in Parallel?
A voltmeter has a function to measure the voltage in an electrical circuit by measuring out potential difference between two points. In the case of an AC circuit, it measures root mean square values at various points in time intervals.
The Voltmeter or the voltage metre is connected in parallel to show that the current which it demonstrates is fed back as a potential difference. This is the common way of connecting parallel circuits whereby it’s arranged so that together with a battery, bulb and voltmeter form one circuit while all other parts are connected in series.
Voltmeter is connected in parallel to prevent it from drawing any current. So that it does not affect the impedance of the circuit and can be fully powered up with full voltage but very high resistance.
In case we use a voltmeter in series as opposed to parallel, it will lead to the reduction of electric current passing through the circuit.
How to Use a Voltmeter?
To set up your voltage measuring device, first choose the appropriate setting based on the type of circuit you’re testing. For AC circuits, use V~, ACV, or VAC, and for DC circuits, select V-, V–, DCV, or VDC and ensure your range setting is higher than the expected voltage to prevent damage.
How to Measure Voltage using Voltmeter?
To measure any voltage using voltmeter we can use the following steps
Step 1: Hold the probes safely. When connecting metal probes to a circuit, do not touch them. If the insulation appears worn or torn, use electrically wrapped gloves – otherwise electrics leads replacement should be made.
Step 2: Place the black test lead on a portion of that circuit. Use leads in parallel to test circuits for voltage. That is, you’ll touch the probes to two points that form a current already-closed circuit.
Step 3: Touch the red test lead to some other point on that circuit. This will close the parallel circuit and make the meter indicate this voltage.
Step 4: If you get an overload reading, raise the range. Immediately raise the range to a higher voltage setting if you get one of the following results, before your device is damaged:
Step 5: Adjust the voltmeter if necessary. If a digital voltmeter displays 0V or nothing at all, of if an analog megohmmeter’s needle hasn’t nearly moved from zero you may need to make adjustments.
Step 6: Read the voltmeter. In turn, a digital voltmeter will show the voltage displayed clearly on its electronic screen. Learning to use an analog voltmeter is slightly more complex, but not very difficult once you get the hang of it. Continue reading for instructions.
How to Check Resistance with a Voltmeter
Resistance checking with a voltmeter is somewhat different compared to measuring; voltage. In this situation, you’ll use the voltmeter together with a known volts source and Ohms Law. Here’s a simple step-by-step guide:
- Turn Off the Circuit: Make sure that the circuit or component which you want to measure its resistance is switched off.
- Select the Resistance Range: Most of voltmeters possess a separate selection for resistivity measurement. Locate the resistance (Ω) sign and choose a suitable range. If you’re not sure of the resistance, begin with a higher range and make adjustments as necessary.
- Disconnect the Component: If you want to measure the resistance of a particular component, separate it from its circuit. This eliminates the interference by other connected elements.
- Connect the Leads: Red lead goes to one side, and black leads is on the other. It does not make any difference in which lead comes to where since resistance is a scalar quantity.
- Read the Display: The voltmeter will indicate the voltage reading. Note this value.
- Use Ohm’s Law: In the formula,, R = V/I; here, Resistance (R) is calculated by using Ohm’s Law. Since you’re measuring resistance, rearrange the formula to find resistance: R = V/I. In this instance, I stands for the current that is passing through the circuit. Knowing the voltage (V) and current (I), one can determine resistance.
- Interpret the Reading: Some sophisticated digital multimeters present resistance value directly. On the other hand, sometimes you may need to calculate an estimated resistance from Ohm’s law before interpreting your reading.
Voltmeter and Ammeter
As we discussed that a voltmeter measures voltage (potential difference) and is connected in parallel to the circuit, whereas an ammeter measures current and is connected in series with the circuit. Both instruments help monitor electrical characteristics.
Difference between Voltmeter and Ammeter
The following table shows the difference between ammeter i.e., ampere meter and voltmeter:
| It can be used to detect currents. |
It may be used to measure the voltage between two points. |
| The resistance is negligible. |
The resistance is High . |
| It is also connected in series with the circuit but offers higher accuracy. |
It is connected in series with the circuit and has low precision. |
| Range cannot be changed. |
It is possible to change the range of possibilities. |
| The resistance of the perfect ammeter device should be zero. |
An ideal voltmeter gear should be resistive approaching infinity. |
| It is symbolized by the letter A. |
It is symbolized by V. |
Uses of Voltmeter
The following are certain applications of voltmeter:
- Voltmeters are used to generate extremely accurate measurements in electric circuits and hardware.
- It also addresses voltage and the reliability and security of the circuit as a whole, including its components.
- They are also useful for fault detection and the verification of correct voltage value.
- They are also used with cathode ray tubes to ascertain the authenticity of findings and readings.
- It is also used in laboratories for testing and analysis.
We believe that now you must have understood what a voltmeter means.
Read More,
Frequently Asked Questions on Voltmeter
What is the Principle of a Voltmeter?
The principle of a voltmeter is to measure the voltage or potential difference between two points in an electrical circuit by using a high-resistance component that allows a small current to flow through it, which is proportional to the voltage being measured.
What is the Difference between Voltmeter and Ammeter?
The main difference between a voltmeter and an ammeter is that a voltmeter measures voltage, while an ammeter measures current.
What is the Use of Voltmeter?
Voltmeters are used to measure voltage levels in electrical circuits, helping to diagnose and troubleshoot problems and ensure proper voltage is applied.
What is the Zero Error of a Voltmeter?
Zero 0 error occurs when a circuit is not connected, that is the pointer of ammeter or voltmeter reads exactly at 0.
How to Convert Galvanometer to Voltmeter?
To convert a galvanometer into a voltmeter, connect a high-value resistor in series with it. Calculate the resistor value using Ohm’s law to suit the desired voltage range.
Why Voltmeter have High Resistance?
Voltmeters have high resistance to minimize their impact on the circuit they’re measuring, ensuring accurate voltage readings without drawing significant current and altering the voltage being measured.
What does the Voltmeter Measure?
A voltmeter measures the electric potential difference, also known as voltage, between two points in an electrical circuit.
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